Merge remote-tracking branch 'upstream/master' into config-isolation

130 files changed, 6575 insertions, 306 deletions

diff --git a/src/core/ext/filters/client_channel/OWNERS b/src/core/ext/filters/client_channel/OWNERS
index c8760d947b..d38970e0fa 100644
--- a/src/core/ext/filters/client_channel/OWNERS
+++ b/src/core/ext/filters/client_channel/OWNERS
@@ -1,4 +1,4 @@
 set noparent
 @markdroth
-@dgquintas
+@apolcyn
 @AspirinSJL
diff --git a/src/core/ext/filters/client_channel/client_channel.cc b/src/core/ext/filters/client_channel/client_channel.cc
index 388736b60a..23da11363b 100644
--- a/src/core/ext/filters/client_channel/client_channel.cc
+++ b/src/core/ext/filters/client_channel/client_channel.cc
@@ -129,6 +129,8 @@ typedef struct client_channel_channel_data {
   grpc_core::UniquePtr<char> info_lb_policy_name;
   /** service config in JSON form */
   grpc_core::UniquePtr<char> info_service_config_json;
+  /* backpointer to grpc_channel's channelz node */
+  grpc_core::channelz::ClientChannelNode* channelz_channel;
 } channel_data;
 
 typedef struct {
@@ -153,6 +155,23 @@ static void watch_lb_policy_locked(channel_data* chand,
                                    grpc_core::LoadBalancingPolicy* lb_policy,
                                    grpc_connectivity_state current_state);
 
+static const char* channel_connectivity_state_change_string(
+    grpc_connectivity_state state) {
+  switch (state) {
+    case GRPC_CHANNEL_IDLE:
+      return "Channel state change to IDLE";
+    case GRPC_CHANNEL_CONNECTING:
+      return "Channel state change to CONNECTING";
+    case GRPC_CHANNEL_READY:
+      return "Channel state change to READY";
+    case GRPC_CHANNEL_TRANSIENT_FAILURE:
+      return "Channel state change to TRANSIENT_FAILURE";
+    case GRPC_CHANNEL_SHUTDOWN:
+      return "Channel state change to SHUTDOWN";
+  }
+  GPR_UNREACHABLE_CODE(return "UNKNOWN");
+}
+
 static void set_channel_connectivity_state_locked(channel_data* chand,
                                                   grpc_connectivity_state state,
                                                   grpc_error* error,
@@ -177,6 +196,12 @@ static void set_channel_connectivity_state_locked(channel_data* chand,
     gpr_log(GPR_INFO, "chand=%p: setting connectivity state to %s", chand,
             grpc_connectivity_state_name(state));
   }
+  if (chand->channelz_channel != nullptr) {
+    chand->channelz_channel->AddTraceEvent(
+        grpc_core::channelz::ChannelTrace::Severity::Info,
+        grpc_slice_from_static_string(
+            channel_connectivity_state_change_string(state)));
+  }
   grpc_connectivity_state_set(&chand->state_tracker, state, error, reason);
 }
 
@@ -699,6 +724,7 @@ static grpc_error* cc_init_channel_elem(grpc_channel_element* elem,
   // Record enable_retries.
   arg = grpc_channel_args_find(args->channel_args, GRPC_ARG_ENABLE_RETRIES);
   chand->enable_retries = grpc_channel_arg_get_bool(arg, true);
+  chand->channelz_channel = nullptr;
   // Record client channel factory.
   arg = grpc_channel_args_find(args->channel_args,
                                GRPC_ARG_CLIENT_CHANNEL_FACTORY);
@@ -933,11 +959,6 @@ typedef struct client_channel_call_data {
   grpc_closure pick_closure;
   grpc_closure pick_cancel_closure;
 
-  // state needed to support channelz interception of recv trailing metadata.
-  grpc_closure recv_trailing_metadata_ready_channelz;
-  grpc_closure* original_recv_trailing_metadata;
-  grpc_metadata_batch* recv_trailing_metadata;
-
   grpc_polling_entity* pollent;
   bool pollent_added_to_interested_parties;
 
@@ -999,8 +1020,6 @@ static void start_internal_recv_trailing_metadata(grpc_call_element* elem);
 static void on_complete(void* arg, grpc_error* error);
 static void start_retriable_subchannel_batches(void* arg, grpc_error* ignored);
 static void start_pick_locked(void* arg, grpc_error* ignored);
-static void maybe_intercept_recv_trailing_metadata_for_channelz(
-    grpc_call_element* elem, grpc_transport_stream_op_batch* batch);
 
 //
 // send op data caching
@@ -1299,7 +1318,6 @@ static void pending_batches_resume(grpc_call_element* elem) {
     pending_batch* pending = &calld->pending_batches[i];
     grpc_transport_stream_op_batch* batch = pending->batch;
     if (batch != nullptr) {
-      maybe_intercept_recv_trailing_metadata_for_channelz(elem, batch);
       batch->handler_private.extra_arg = calld->subchannel_call;
       GRPC_CLOSURE_INIT(&batch->handler_private.closure,
                         resume_pending_batch_in_call_combiner, batch,
@@ -1977,15 +1995,6 @@ static void recv_trailing_metadata_ready(void* arg, grpc_error* error) {
       batch_data->batch.payload->recv_trailing_metadata.recv_trailing_metadata;
   get_call_status(elem, md_batch, GRPC_ERROR_REF(error), &status,
                   &server_pushback_md);
-  grpc_core::channelz::SubchannelNode* channelz_subchannel =
-      calld->pick.connected_subchannel->channelz_subchannel();
-  if (channelz_subchannel != nullptr) {
-    if (status == GRPC_STATUS_OK) {
-      channelz_subchannel->RecordCallSucceeded();
-    } else {
-      channelz_subchannel->RecordCallFailed();
-    }
-  }
   if (grpc_client_channel_trace.enabled()) {
     gpr_log(GPR_INFO, "chand=%p calld=%p: call finished, status=%s", chand,
             calld, grpc_status_code_to_string(status));
@@ -2211,9 +2220,9 @@ static void add_retriable_send_initial_metadata_op(
                                    .grpc_previous_rpc_attempts);
   }
   if (GPR_UNLIKELY(calld->num_attempts_completed > 0)) {
-    grpc_mdelem retry_md = grpc_mdelem_from_slices(
+    grpc_mdelem retry_md = grpc_mdelem_create(
         GRPC_MDSTR_GRPC_PREVIOUS_RPC_ATTEMPTS,
-        *retry_count_strings[calld->num_attempts_completed - 1]);
+        *retry_count_strings[calld->num_attempts_completed - 1], nullptr);
     grpc_error* error = grpc_metadata_batch_add_tail(
         &retry_state->send_initial_metadata,
         &retry_state->send_initial_metadata_storage[calld->send_initial_metadata
@@ -2590,69 +2599,6 @@ static void start_retriable_subchannel_batches(void* arg, grpc_error* ignored) {
 }
 
 //
-// Channelz
-//
-
-static void recv_trailing_metadata_ready_channelz(void* arg,
-                                                  grpc_error* error) {
-  grpc_call_element* elem = static_cast<grpc_call_element*>(arg);
-  channel_data* chand = static_cast<channel_data*>(elem->channel_data);
-  call_data* calld = static_cast<call_data*>(elem->call_data);
-  if (grpc_client_channel_trace.enabled()) {
-    gpr_log(GPR_INFO,
-            "chand=%p calld=%p: got recv_trailing_metadata_ready_channelz, "
-            "error=%s",
-            chand, calld, grpc_error_string(error));
-  }
-  GPR_ASSERT(calld->recv_trailing_metadata != nullptr);
-  grpc_status_code status = GRPC_STATUS_OK;
-  grpc_metadata_batch* md_batch = calld->recv_trailing_metadata;
-  get_call_status(elem, md_batch, GRPC_ERROR_REF(error), &status, nullptr);
-  grpc_core::channelz::SubchannelNode* channelz_subchannel =
-      calld->pick.connected_subchannel->channelz_subchannel();
-  GPR_ASSERT(channelz_subchannel != nullptr);
-  if (status == GRPC_STATUS_OK) {
-    channelz_subchannel->RecordCallSucceeded();
-  } else {
-    channelz_subchannel->RecordCallFailed();
-  }
-  calld->recv_trailing_metadata = nullptr;
-  GRPC_CLOSURE_RUN(calld->original_recv_trailing_metadata, error);
-}
-
-// If channelz is enabled, intercept recv_trailing so that we may check the
-// status and associate it to a subchannel.
-// Returns true if callback was intercepted, false otherwise.
-static void maybe_intercept_recv_trailing_metadata_for_channelz(
-    grpc_call_element* elem, grpc_transport_stream_op_batch* batch) {
-  call_data* calld = static_cast<call_data*>(elem->call_data);
-  // only intercept payloads with recv trailing.
-  if (!batch->recv_trailing_metadata) {
-    return;
-  }
-  // only add interceptor is channelz is enabled.
-  if (calld->pick.connected_subchannel->channelz_subchannel() == nullptr) {
-    return;
-  }
-  if (grpc_client_channel_trace.enabled()) {
-    gpr_log(GPR_INFO,
-            "calld=%p batch=%p: intercepting recv trailing for channelz", calld,
-            batch);
-  }
-  GRPC_CLOSURE_INIT(&calld->recv_trailing_metadata_ready_channelz,
-                    recv_trailing_metadata_ready_channelz, elem,
-                    grpc_schedule_on_exec_ctx);
-  // save some state needed for the interception callback.
-  GPR_ASSERT(calld->recv_trailing_metadata == nullptr);
-  calld->recv_trailing_metadata =
-      batch->payload->recv_trailing_metadata.recv_trailing_metadata;
-  calld->original_recv_trailing_metadata =
-      batch->payload->recv_trailing_metadata.recv_trailing_metadata_ready;
-  batch->payload->recv_trailing_metadata.recv_trailing_metadata_ready =
-      &calld->recv_trailing_metadata_ready_channelz;
-}
-
-//
 // LB pick
 //
 
@@ -3288,9 +3234,16 @@ static void try_to_connect_locked(void* arg, grpc_error* error_ignored) {
   GRPC_CHANNEL_STACK_UNREF(chand->owning_stack, "try_to_connect");
 }
 
+void grpc_client_channel_set_channelz_node(
+    grpc_channel_element* elem, grpc_core::channelz::ClientChannelNode* node) {
+  channel_data* chand = static_cast<channel_data*>(elem->channel_data);
+  chand->channelz_channel = node;
+}
+
 void grpc_client_channel_populate_child_refs(
-    grpc_channel_element* elem, grpc_core::ChildRefsList* child_subchannels,
-    grpc_core::ChildRefsList* child_channels) {
+    grpc_channel_element* elem,
+    grpc_core::channelz::ChildRefsList* child_subchannels,
+    grpc_core::channelz::ChildRefsList* child_channels) {
   channel_data* chand = static_cast<channel_data*>(elem->channel_data);
   if (chand->lb_policy != nullptr) {
     chand->lb_policy->FillChildRefsForChannelz(child_subchannels,
diff --git a/src/core/ext/filters/client_channel/client_channel.h b/src/core/ext/filters/client_channel/client_channel.h
index 0b44a17562..4935fd24d8 100644
--- a/src/core/ext/filters/client_channel/client_channel.h
+++ b/src/core/ext/filters/client_channel/client_channel.h
@@ -40,9 +40,13 @@ extern grpc_core::TraceFlag grpc_client_channel_trace;
 
 extern const grpc_channel_filter grpc_client_channel_filter;
 
+void grpc_client_channel_set_channelz_node(
+    grpc_channel_element* elem, grpc_core::channelz::ClientChannelNode* node);
+
 void grpc_client_channel_populate_child_refs(
-    grpc_channel_element* elem, grpc_core::ChildRefsList* child_subchannels,
-    grpc_core::ChildRefsList* child_channels);
+    grpc_channel_element* elem,
+    grpc_core::channelz::ChildRefsList* child_subchannels,
+    grpc_core::channelz::ChildRefsList* child_channels);
 
 grpc_connectivity_state grpc_client_channel_check_connectivity_state(
     grpc_channel_element* elem, int try_to_connect);
diff --git a/src/core/ext/filters/client_channel/client_channel_channelz.cc b/src/core/ext/filters/client_channel/client_channel_channelz.cc
index b66c920b90..bad1ef668c 100644
--- a/src/core/ext/filters/client_channel/client_channel_channelz.cc
+++ b/src/core/ext/filters/client_channel/client_channel_channelz.cc
@@ -49,6 +49,7 @@ ClientChannelNode::ClientChannelNode(grpc_channel* channel,
     : ChannelNode(channel, channel_tracer_max_nodes, is_top_level_channel) {
   client_channel_ =
       grpc_channel_stack_last_element(grpc_channel_get_channel_stack(channel));
+  grpc_client_channel_set_channelz_node(client_channel_, this);
   GPR_ASSERT(client_channel_->filter == &grpc_client_channel_filter);
 }
 
diff --git a/src/core/ext/filters/client_channel/client_channel_channelz.h b/src/core/ext/filters/client_channel/client_channel_channelz.h
index 8ce331e529..8a5c3e7e5e 100644
--- a/src/core/ext/filters/client_channel/client_channel_channelz.h
+++ b/src/core/ext/filters/client_channel/client_channel_channelz.h
@@ -25,17 +25,10 @@
 #include "src/core/lib/channel/channel_stack.h"
 #include "src/core/lib/channel/channel_trace.h"
 #include "src/core/lib/channel/channelz.h"
-#include "src/core/lib/gprpp/inlined_vector.h"
 
 typedef struct grpc_subchannel grpc_subchannel;
 
 namespace grpc_core {
-
-// TODO(ncteisen), this only contains the uuids of the children for now,
-// since that is all that is strictly needed. In a future enhancement we will
-// add human readable names as in the channelz.proto
-typedef InlinedVector<intptr_t, 10> ChildRefsList;
-
 namespace channelz {
 
 // Subtype of ChannelNode that overrides and provides client_channel specific
diff --git a/src/core/ext/filters/client_channel/http_connect_handshaker.cc b/src/core/ext/filters/client_channel/http_connect_handshaker.cc
index 7ce8da8c00..bfabc68c66 100644
--- a/src/core/ext/filters/client_channel/http_connect_handshaker.cc
+++ b/src/core/ext/filters/client_channel/http_connect_handshaker.cc
@@ -351,6 +351,7 @@ static grpc_handshaker* grpc_http_connect_handshaker_create() {
 
 static void handshaker_factory_add_handshakers(
     grpc_handshaker_factory* factory, const grpc_channel_args* args,
+    grpc_pollset_set* interested_parties,
     grpc_handshake_manager* handshake_mgr) {
   grpc_handshake_manager_add(handshake_mgr,
                              grpc_http_connect_handshaker_create());
diff --git a/src/core/ext/filters/client_channel/lb_policy.h b/src/core/ext/filters/client_channel/lb_policy.h
index 3c0a9c1118..21f80b7b94 100644
--- a/src/core/ext/filters/client_channel/lb_policy.h
+++ b/src/core/ext/filters/client_channel/lb_policy.h
@@ -151,9 +151,9 @@ class LoadBalancingPolicy
   /// LB policy's referenced children. This is not invoked from the
   /// client_channel's combiner. The implementation is responsible for
   /// providing its own synchronization.
-  virtual void FillChildRefsForChannelz(ChildRefsList* child_subchannels,
-                                        ChildRefsList* child_channels)
-      GRPC_ABSTRACT;
+  virtual void FillChildRefsForChannelz(
+      channelz::ChildRefsList* child_subchannels,
+      channelz::ChildRefsList* child_channels) GRPC_ABSTRACT;
 
   void Orphan() override {
     // Invoke ShutdownAndUnrefLocked() inside of the combiner.
@@ -212,8 +212,8 @@ class LoadBalancingPolicy
   // Dummy classes needed for alignment issues.
   // See https://github.com/grpc/grpc/issues/16032 for context.
   // TODO(ncteisen): remove this as soon as the issue is resolved.
-  ChildRefsList dummy_list_foo;
-  ChildRefsList dummy_list_bar;
+  channelz::ChildRefsList dummy_list_foo;
+  channelz::ChildRefsList dummy_list_bar;
 };
 
 }  // namespace grpc_core
diff --git a/src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb.cc b/src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb.cc
index 0061190016..5511df7a27 100644
--- a/src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb.cc
+++ b/src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb.cc
@@ -136,8 +136,9 @@ class GrpcLb : public LoadBalancingPolicy {
   void HandOffPendingPicksLocked(LoadBalancingPolicy* new_policy) override;
   void ExitIdleLocked() override;
   void ResetBackoffLocked() override;
-  void FillChildRefsForChannelz(ChildRefsList* child_subchannels,
-                                ChildRefsList* child_channels) override;
+  void FillChildRefsForChannelz(
+      channelz::ChildRefsList* child_subchannels,
+      channelz::ChildRefsList* child_channels) override;
 
  private:
   /// Linked list of pending pick requests. It stores all information needed to
@@ -1258,8 +1259,9 @@ bool GrpcLb::PickLocked(PickState* pick, grpc_error** error) {
   return pick_done;
 }
 
-void GrpcLb::FillChildRefsForChannelz(ChildRefsList* child_subchannels,
-                                      ChildRefsList* child_channels) {
+void GrpcLb::FillChildRefsForChannelz(
+    channelz::ChildRefsList* child_subchannels,
+    channelz::ChildRefsList* child_channels) {
   // delegate to the RoundRobin to fill the children subchannels.
   rr_policy_->FillChildRefsForChannelz(child_subchannels, child_channels);
   MutexLock lock(&lb_channel_mu_);
@@ -1489,7 +1491,7 @@ void GrpcLb::OnBalancerChannelConnectivityChangedLocked(void* arg,
         grpclb_policy->lb_call_backoff_.Reset();
         grpclb_policy->StartBalancerCallLocked();
       }
-      // Fall through.
+      // fallthrough
     case GRPC_CHANNEL_SHUTDOWN:
     done:
       grpclb_policy->watching_lb_channel_ = false;
diff --git a/src/core/ext/filters/client_channel/lb_policy/pick_first/pick_first.cc b/src/core/ext/filters/client_channel/lb_policy/pick_first/pick_first.cc
index ed8cc60ea1..f4dca146f7 100644
--- a/src/core/ext/filters/client_channel/lb_policy/pick_first/pick_first.cc
+++ b/src/core/ext/filters/client_channel/lb_policy/pick_first/pick_first.cc
@@ -59,8 +59,8 @@ class PickFirst : public LoadBalancingPolicy {
   void HandOffPendingPicksLocked(LoadBalancingPolicy* new_policy) override;
   void ExitIdleLocked() override;
   void ResetBackoffLocked() override;
-  void FillChildRefsForChannelz(ChildRefsList* child_subchannels,
-                                ChildRefsList* ignored) override;
+  void FillChildRefsForChannelz(channelz::ChildRefsList* child_subchannels,
+                                channelz::ChildRefsList* ignored) override;
 
  private:
   ~PickFirst();
@@ -147,8 +147,8 @@ class PickFirst : public LoadBalancingPolicy {
   /// Lock and data used to capture snapshots of this channels child
   /// channels and subchannels. This data is consumed by channelz.
   gpr_mu child_refs_mu_;
-  ChildRefsList child_subchannels_;
-  ChildRefsList child_channels_;
+  channelz::ChildRefsList child_subchannels_;
+  channelz::ChildRefsList child_channels_;
 };
 
 PickFirst::PickFirst(const Args& args) : LoadBalancingPolicy(args) {
@@ -300,7 +300,8 @@ void PickFirst::NotifyOnStateChangeLocked(grpc_connectivity_state* current,
 }
 
 void PickFirst::FillChildRefsForChannelz(
-    ChildRefsList* child_subchannels_to_fill, ChildRefsList* ignored) {
+    channelz::ChildRefsList* child_subchannels_to_fill,
+    channelz::ChildRefsList* ignored) {
   MutexLock lock(&child_refs_mu_);
   for (size_t i = 0; i < child_subchannels_.size(); ++i) {
     // TODO(ncteisen): implement a de dup loop that is not O(n^2). Might
@@ -320,7 +321,7 @@ void PickFirst::FillChildRefsForChannelz(
 }
 
 void PickFirst::UpdateChildRefsLocked() {
-  ChildRefsList cs;
+  channelz::ChildRefsList cs;
   if (subchannel_list_ != nullptr) {
     subchannel_list_->PopulateChildRefsList(&cs);
   }
diff --git a/src/core/ext/filters/client_channel/lb_policy/round_robin/round_robin.cc b/src/core/ext/filters/client_channel/lb_policy/round_robin/round_robin.cc
index 8dd5820bae..e9ed85cf66 100644
--- a/src/core/ext/filters/client_channel/lb_policy/round_robin/round_robin.cc
+++ b/src/core/ext/filters/client_channel/lb_policy/round_robin/round_robin.cc
@@ -70,8 +70,8 @@ class RoundRobin : public LoadBalancingPolicy {
   void HandOffPendingPicksLocked(LoadBalancingPolicy* new_policy) override;
   void ExitIdleLocked() override;
   void ResetBackoffLocked() override;
-  void FillChildRefsForChannelz(ChildRefsList* child_subchannels,
-                                ChildRefsList* ignored) override;
+  void FillChildRefsForChannelz(channelz::ChildRefsList* child_subchannels,
+                                channelz::ChildRefsList* ignored) override;
 
  private:
   ~RoundRobin();
@@ -223,8 +223,8 @@ class RoundRobin : public LoadBalancingPolicy {
   /// Lock and data used to capture snapshots of this channel's child
   /// channels and subchannels. This data is consumed by channelz.
   gpr_mu child_refs_mu_;
-  ChildRefsList child_subchannels_;
-  ChildRefsList child_channels_;
+  channelz::ChildRefsList child_subchannels_;
+  channelz::ChildRefsList child_channels_;
 };
 
 RoundRobin::RoundRobin(const Args& args) : LoadBalancingPolicy(args) {
@@ -402,7 +402,8 @@ bool RoundRobin::PickLocked(PickState* pick, grpc_error** error) {
 }
 
 void RoundRobin::FillChildRefsForChannelz(
-    ChildRefsList* child_subchannels_to_fill, ChildRefsList* ignored) {
+    channelz::ChildRefsList* child_subchannels_to_fill,
+    channelz::ChildRefsList* ignored) {
   MutexLock lock(&child_refs_mu_);
   for (size_t i = 0; i < child_subchannels_.size(); ++i) {
     // TODO(ncteisen): implement a de dup loop that is not O(n^2). Might
@@ -422,7 +423,7 @@ void RoundRobin::FillChildRefsForChannelz(
 }
 
 void RoundRobin::UpdateChildRefsLocked() {
-  ChildRefsList cs;
+  channelz::ChildRefsList cs;
   if (subchannel_list_ != nullptr) {
     subchannel_list_->PopulateChildRefsList(&cs);
   }
diff --git a/src/core/ext/filters/client_channel/lb_policy/subchannel_list.h b/src/core/ext/filters/client_channel/lb_policy/subchannel_list.h
index 5e8682e056..e0e0e1e638 100644
--- a/src/core/ext/filters/client_channel/lb_policy/subchannel_list.h
+++ b/src/core/ext/filters/client_channel/lb_policy/subchannel_list.h
@@ -201,7 +201,7 @@ class SubchannelList
   bool shutting_down() const { return shutting_down_; }
 
   // Populates refs_list with the uuids of this SubchannelLists's subchannels.
-  void PopulateChildRefsList(ChildRefsList* refs_list) {
+  void PopulateChildRefsList(channelz::ChildRefsList* refs_list) {
     for (size_t i = 0; i < subchannels_.size(); ++i) {
       if (subchannels_[i].subchannel() != nullptr) {
         grpc_core::channelz::SubchannelNode* subchannel_node =
diff --git a/src/core/ext/filters/client_channel/lb_policy/xds/client_load_reporting_filter.cc b/src/core/ext/filters/client_channel/lb_policy/xds/client_load_reporting_filter.cc
new file mode 100644
index 0000000000..d79453d008
--- /dev/null
+++ b/src/core/ext/filters/client_channel/lb_policy/xds/client_load_reporting_filter.cc
@@ -0,0 +1,140 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#include <grpc/support/port_platform.h>
+
+#include "src/core/ext/filters/client_channel/lb_policy/xds/client_load_reporting_filter.h"
+
+#include <grpc/support/atm.h>
+#include <grpc/support/log.h>
+
+#include "src/core/ext/filters/client_channel/lb_policy/xds/xds_client_stats.h"
+#include "src/core/lib/iomgr/error.h"
+#include "src/core/lib/profiling/timers.h"
+
+static grpc_error* init_channel_elem(grpc_channel_element* elem,
+                                     grpc_channel_element_args* args) {
+  return GRPC_ERROR_NONE;
+}
+
+static void destroy_channel_elem(grpc_channel_element* elem) {}
+
+namespace {
+
+struct call_data {
+  // Stats object to update.
+  grpc_core::RefCountedPtr<grpc_core::XdsLbClientStats> client_stats;
+  // State for intercepting send_initial_metadata.
+  grpc_closure on_complete_for_send;
+  grpc_closure* original_on_complete_for_send;
+  bool send_initial_metadata_succeeded;
+  // State for intercepting recv_initial_metadata.
+  grpc_closure recv_initial_metadata_ready;
+  grpc_closure* original_recv_initial_metadata_ready;
+  bool recv_initial_metadata_succeeded;
+};
+
+}  // namespace
+
+static void on_complete_for_send(void* arg, grpc_error* error) {
+  call_data* calld = static_cast<call_data*>(arg);
+  if (error == GRPC_ERROR_NONE) {
+    calld->send_initial_metadata_succeeded = true;
+  }
+  GRPC_CLOSURE_RUN(calld->original_on_complete_for_send, GRPC_ERROR_REF(error));
+}
+
+static void recv_initial_metadata_ready(void* arg, grpc_error* error) {
+  call_data* calld = static_cast<call_data*>(arg);
+  if (error == GRPC_ERROR_NONE) {
+    calld->recv_initial_metadata_succeeded = true;
+  }
+  GRPC_CLOSURE_RUN(calld->original_recv_initial_metadata_ready,
+                   GRPC_ERROR_REF(error));
+}
+
+static grpc_error* init_call_elem(grpc_call_element* elem,
+                                  const grpc_call_element_args* args) {
+  call_data* calld = static_cast<call_data*>(elem->call_data);
+  // Get stats object from context and take a ref.
+  GPR_ASSERT(args->context != nullptr);
+  if (args->context[GRPC_GRPCLB_CLIENT_STATS].value != nullptr) {
+    calld->client_stats = static_cast<grpc_core::XdsLbClientStats*>(
+                              args->context[GRPC_GRPCLB_CLIENT_STATS].value)
+                              ->Ref();
+    // Record call started.
+    calld->client_stats->AddCallStarted();
+  }
+  return GRPC_ERROR_NONE;
+}
+
+static void destroy_call_elem(grpc_call_element* elem,
+                              const grpc_call_final_info* final_info,
+                              grpc_closure* ignored) {
+  call_data* calld = static_cast<call_data*>(elem->call_data);
+  if (calld->client_stats != nullptr) {
+    // Record call finished, optionally setting client_failed_to_send and
+    // received.
+    calld->client_stats->AddCallFinished(
+        !calld->send_initial_metadata_succeeded /* client_failed_to_send */,
+        calld->recv_initial_metadata_succeeded /* known_received */);
+    // All done, so unref the stats object.
+    // TODO(roth): Eliminate this once filter stack is converted to C++.
+    calld->client_stats.reset();
+  }
+}
+
+static void start_transport_stream_op_batch(
+    grpc_call_element* elem, grpc_transport_stream_op_batch* batch) {
+  call_data* calld = static_cast<call_data*>(elem->call_data);
+  GPR_TIMER_SCOPE("clr_start_transport_stream_op_batch", 0);
+  if (calld->client_stats != nullptr) {
+    // Intercept send_initial_metadata.
+    if (batch->send_initial_metadata) {
+      calld->original_on_complete_for_send = batch->on_complete;
+      GRPC_CLOSURE_INIT(&calld->on_complete_for_send, on_complete_for_send,
+                        calld, grpc_schedule_on_exec_ctx);
+      batch->on_complete = &calld->on_complete_for_send;
+    }
+    // Intercept recv_initial_metadata.
+    if (batch->recv_initial_metadata) {
+      calld->original_recv_initial_metadata_ready =
+          batch->payload->recv_initial_metadata.recv_initial_metadata_ready;
+      GRPC_CLOSURE_INIT(&calld->recv_initial_metadata_ready,
+                        recv_initial_metadata_ready, calld,
+                        grpc_schedule_on_exec_ctx);
+      batch->payload->recv_initial_metadata.recv_initial_metadata_ready =
+          &calld->recv_initial_metadata_ready;
+    }
+  }
+  // Chain to next filter.
+  grpc_call_next_op(elem, batch);
+}
+
+const grpc_channel_filter xds_client_load_reporting_filter = {
+    start_transport_stream_op_batch,
+    grpc_channel_next_op,
+    sizeof(call_data),
+    init_call_elem,
+    grpc_call_stack_ignore_set_pollset_or_pollset_set,
+    destroy_call_elem,
+    0,  // sizeof(channel_data)
+    init_channel_elem,
+    destroy_channel_elem,
+    grpc_channel_next_get_info,
+    "client_load_reporting"};
diff --git a/src/core/ext/filters/client_channel/lb_policy/xds/client_load_reporting_filter.h b/src/core/ext/filters/client_channel/lb_policy/xds/client_load_reporting_filter.h
new file mode 100644
index 0000000000..31a799154c
--- /dev/null
+++ b/src/core/ext/filters/client_channel/lb_policy/xds/client_load_reporting_filter.h
@@ -0,0 +1,29 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#ifndef GRPC_CORE_EXT_FILTERS_CLIENT_CHANNEL_LB_POLICY_XDS_CLIENT_LOAD_REPORTING_FILTER_H
+#define GRPC_CORE_EXT_FILTERS_CLIENT_CHANNEL_LB_POLICY_XDS_CLIENT_LOAD_REPORTING_FILTER_H
+
+#include <grpc/support/port_platform.h>
+
+#include "src/core/lib/channel/channel_stack.h"
+
+extern const grpc_channel_filter xds_client_load_reporting_filter;
+
+#endif /* GRPC_CORE_EXT_FILTERS_CLIENT_CHANNEL_LB_POLICY_XDS_CLIENT_LOAD_REPORTING_FILTER_H \
+        */
diff --git a/src/core/ext/filters/client_channel/lb_policy/xds/load_balancer_api.cc b/src/core/ext/filters/client_channel/lb_policy/xds/load_balancer_api.cc
new file mode 100644
index 0000000000..3bd2653635
--- /dev/null
+++ b/src/core/ext/filters/client_channel/lb_policy/xds/load_balancer_api.cc
@@ -0,0 +1,307 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#include <grpc/support/port_platform.h>
+
+#include "pb_decode.h"
+#include "pb_encode.h"
+#include "src/core/ext/filters/client_channel/lb_policy/xds/load_balancer_api.h"
+
+#include <grpc/support/alloc.h>
+
+/* invoked once for every Server in ServerList */
+static bool count_serverlist(pb_istream_t* stream, const pb_field_t* field,
+                             void** arg) {
+  xds_grpclb_serverlist* sl = static_cast<xds_grpclb_serverlist*>(*arg);
+  xds_grpclb_server server;
+  if (GPR_UNLIKELY(!pb_decode(stream, grpc_lb_v1_Server_fields, &server))) {
+    gpr_log(GPR_ERROR, "nanopb error: %s", PB_GET_ERROR(stream));
+    return false;
+  }
+  ++sl->num_servers;
+  return true;
+}
+
+typedef struct decode_serverlist_arg {
+  /* The decoding callback is invoked once per server in serverlist. Remember
+   * which index of the serverlist are we currently decoding */
+  size_t decoding_idx;
+  /* The decoded serverlist */
+  xds_grpclb_serverlist* serverlist;
+} decode_serverlist_arg;
+
+/* invoked once for every Server in ServerList */
+static bool decode_serverlist(pb_istream_t* stream, const pb_field_t* field,
+                              void** arg) {
+  decode_serverlist_arg* dec_arg = static_cast<decode_serverlist_arg*>(*arg);
+  GPR_ASSERT(dec_arg->serverlist->num_servers >= dec_arg->decoding_idx);
+  xds_grpclb_server* server =
+      static_cast<xds_grpclb_server*>(gpr_zalloc(sizeof(xds_grpclb_server)));
+  if (GPR_UNLIKELY(!pb_decode(stream, grpc_lb_v1_Server_fields, server))) {
+    gpr_free(server);
+    gpr_log(GPR_ERROR, "nanopb error: %s", PB_GET_ERROR(stream));
+    return false;
+  }
+  dec_arg->serverlist->servers[dec_arg->decoding_idx++] = server;
+  return true;
+}
+
+xds_grpclb_request* xds_grpclb_request_create(const char* lb_service_name) {
+  xds_grpclb_request* req =
+      static_cast<xds_grpclb_request*>(gpr_malloc(sizeof(xds_grpclb_request)));
+  req->has_client_stats = false;
+  req->has_initial_request = true;
+  req->initial_request.has_name = true;
+  strncpy(req->initial_request.name, lb_service_name,
+          XDS_SERVICE_NAME_MAX_LENGTH);
+  return req;
+}
+
+static void populate_timestamp(gpr_timespec timestamp,
+                               xds_grpclb_timestamp* timestamp_pb) {
+  timestamp_pb->has_seconds = true;
+  timestamp_pb->seconds = timestamp.tv_sec;
+  timestamp_pb->has_nanos = true;
+  timestamp_pb->nanos = timestamp.tv_nsec;
+}
+
+static bool encode_string(pb_ostream_t* stream, const pb_field_t* field,
+                          void* const* arg) {
+  char* str = static_cast<char*>(*arg);
+  if (!pb_encode_tag_for_field(stream, field)) return false;
+  return pb_encode_string(stream, reinterpret_cast<uint8_t*>(str), strlen(str));
+}
+
+static bool encode_drops(pb_ostream_t* stream, const pb_field_t* field,
+                         void* const* arg) {
+  grpc_core::XdsLbClientStats::DroppedCallCounts* drop_entries =
+      static_cast<grpc_core::XdsLbClientStats::DroppedCallCounts*>(*arg);
+  if (drop_entries == nullptr) return true;
+  for (size_t i = 0; i < drop_entries->size(); ++i) {
+    if (!pb_encode_tag_for_field(stream, field)) return false;
+    grpc_lb_v1_ClientStatsPerToken drop_message;
+    drop_message.load_balance_token.funcs.encode = encode_string;
+    drop_message.load_balance_token.arg = (*drop_entries)[i].token.get();
+    drop_message.has_num_calls = true;
+    drop_message.num_calls = (*drop_entries)[i].count;
+    if (!pb_encode_submessage(stream, grpc_lb_v1_ClientStatsPerToken_fields,
+                              &drop_message)) {
+      return false;
+    }
+  }
+  return true;
+}
+
+xds_grpclb_request* xds_grpclb_load_report_request_create_locked(
+    grpc_core::XdsLbClientStats* client_stats) {
+  xds_grpclb_request* req =
+      static_cast<xds_grpclb_request*>(gpr_zalloc(sizeof(xds_grpclb_request)));
+  req->has_client_stats = true;
+  req->client_stats.has_timestamp = true;
+  populate_timestamp(gpr_now(GPR_CLOCK_REALTIME), &req->client_stats.timestamp);
+  req->client_stats.has_num_calls_started = true;
+  req->client_stats.has_num_calls_finished = true;
+  req->client_stats.has_num_calls_finished_with_client_failed_to_send = true;
+  req->client_stats.has_num_calls_finished_with_client_failed_to_send = true;
+  req->client_stats.has_num_calls_finished_known_received = true;
+  req->client_stats.calls_finished_with_drop.funcs.encode = encode_drops;
+  grpc_core::UniquePtr<grpc_core::XdsLbClientStats::DroppedCallCounts>
+      drop_counts;
+  client_stats->GetLocked(
+      &req->client_stats.num_calls_started,
+      &req->client_stats.num_calls_finished,
+      &req->client_stats.num_calls_finished_with_client_failed_to_send,
+      &req->client_stats.num_calls_finished_known_received, &drop_counts);
+  // Will be deleted in xds_grpclb_request_destroy().
+  req->client_stats.calls_finished_with_drop.arg = drop_counts.release();
+  return req;
+}
+
+grpc_slice xds_grpclb_request_encode(const xds_grpclb_request* request) {
+  size_t encoded_length;
+  pb_ostream_t sizestream;
+  pb_ostream_t outputstream;
+  grpc_slice slice;
+  memset(&sizestream, 0, sizeof(pb_ostream_t));
+  pb_encode(&sizestream, grpc_lb_v1_LoadBalanceRequest_fields, request);
+  encoded_length = sizestream.bytes_written;
+
+  slice = GRPC_SLICE_MALLOC(encoded_length);
+  outputstream =
+      pb_ostream_from_buffer(GRPC_SLICE_START_PTR(slice), encoded_length);
+  GPR_ASSERT(pb_encode(&outputstream, grpc_lb_v1_LoadBalanceRequest_fields,
+                       request) != 0);
+  return slice;
+}
+
+void xds_grpclb_request_destroy(xds_grpclb_request* request) {
+  if (request->has_client_stats) {
+    grpc_core::XdsLbClientStats::DroppedCallCounts* drop_entries =
+        static_cast<grpc_core::XdsLbClientStats::DroppedCallCounts*>(
+            request->client_stats.calls_finished_with_drop.arg);
+    grpc_core::Delete(drop_entries);
+  }
+  gpr_free(request);
+}
+
+typedef grpc_lb_v1_LoadBalanceResponse xds_grpclb_response;
+xds_grpclb_initial_response* xds_grpclb_initial_response_parse(
+    grpc_slice encoded_xds_grpclb_response) {
+  pb_istream_t stream =
+      pb_istream_from_buffer(GRPC_SLICE_START_PTR(encoded_xds_grpclb_response),
+                             GRPC_SLICE_LENGTH(encoded_xds_grpclb_response));
+  xds_grpclb_response res;
+  memset(&res, 0, sizeof(xds_grpclb_response));
+  if (GPR_UNLIKELY(
+          !pb_decode(&stream, grpc_lb_v1_LoadBalanceResponse_fields, &res))) {
+    gpr_log(GPR_ERROR, "nanopb error: %s", PB_GET_ERROR(&stream));
+    return nullptr;
+  }
+
+  if (!res.has_initial_response) return nullptr;
+
+  xds_grpclb_initial_response* initial_res =
+      static_cast<xds_grpclb_initial_response*>(
+          gpr_malloc(sizeof(xds_grpclb_initial_response)));
+  memcpy(initial_res, &res.initial_response,
+         sizeof(xds_grpclb_initial_response));
+
+  return initial_res;
+}
+
+xds_grpclb_serverlist* xds_grpclb_response_parse_serverlist(
+    grpc_slice encoded_xds_grpclb_response) {
+  pb_istream_t stream =
+      pb_istream_from_buffer(GRPC_SLICE_START_PTR(encoded_xds_grpclb_response),
+                             GRPC_SLICE_LENGTH(encoded_xds_grpclb_response));
+  pb_istream_t stream_at_start = stream;
+  xds_grpclb_serverlist* sl = static_cast<xds_grpclb_serverlist*>(
+      gpr_zalloc(sizeof(xds_grpclb_serverlist)));
+  xds_grpclb_response res;
+  memset(&res, 0, sizeof(xds_grpclb_response));
+  // First pass: count number of servers.
+  res.server_list.servers.funcs.decode = count_serverlist;
+  res.server_list.servers.arg = sl;
+  bool status = pb_decode(&stream, grpc_lb_v1_LoadBalanceResponse_fields, &res);
+  if (GPR_UNLIKELY(!status)) {
+    gpr_free(sl);
+    gpr_log(GPR_ERROR, "nanopb error: %s", PB_GET_ERROR(&stream));
+    return nullptr;
+  }
+  // Second pass: populate servers.
+  if (sl->num_servers > 0) {
+    sl->servers = static_cast<xds_grpclb_server**>(
+        gpr_zalloc(sizeof(xds_grpclb_server*) * sl->num_servers));
+    decode_serverlist_arg decode_arg;
+    memset(&decode_arg, 0, sizeof(decode_arg));
+    decode_arg.serverlist = sl;
+    res.server_list.servers.funcs.decode = decode_serverlist;
+    res.server_list.servers.arg = &decode_arg;
+    status = pb_decode(&stream_at_start, grpc_lb_v1_LoadBalanceResponse_fields,
+                       &res);
+    if (GPR_UNLIKELY(!status)) {
+      xds_grpclb_destroy_serverlist(sl);
+      gpr_log(GPR_ERROR, "nanopb error: %s", PB_GET_ERROR(&stream));
+      return nullptr;
+    }
+  }
+  return sl;
+}
+
+void xds_grpclb_destroy_serverlist(xds_grpclb_serverlist* serverlist) {
+  if (serverlist == nullptr) {
+    return;
+  }
+  for (size_t i = 0; i < serverlist->num_servers; i++) {
+    gpr_free(serverlist->servers[i]);
+  }
+  gpr_free(serverlist->servers);
+  gpr_free(serverlist);
+}
+
+xds_grpclb_serverlist* xds_grpclb_serverlist_copy(
+    const xds_grpclb_serverlist* sl) {
+  xds_grpclb_serverlist* copy = static_cast<xds_grpclb_serverlist*>(
+      gpr_zalloc(sizeof(xds_grpclb_serverlist)));
+  copy->num_servers = sl->num_servers;
+  copy->servers = static_cast<xds_grpclb_server**>(
+      gpr_malloc(sizeof(xds_grpclb_server*) * sl->num_servers));
+  for (size_t i = 0; i < sl->num_servers; i++) {
+    copy->servers[i] =
+        static_cast<xds_grpclb_server*>(gpr_malloc(sizeof(xds_grpclb_server)));
+    memcpy(copy->servers[i], sl->servers[i], sizeof(xds_grpclb_server));
+  }
+  return copy;
+}
+
+bool xds_grpclb_serverlist_equals(const xds_grpclb_serverlist* lhs,
+                                  const xds_grpclb_serverlist* rhs) {
+  if (lhs == nullptr || rhs == nullptr) {
+    return false;
+  }
+  if (lhs->num_servers != rhs->num_servers) {
+    return false;
+  }
+  for (size_t i = 0; i < lhs->num_servers; i++) {
+    if (!xds_grpclb_server_equals(lhs->servers[i], rhs->servers[i])) {
+      return false;
+    }
+  }
+  return true;
+}
+
+bool xds_grpclb_server_equals(const xds_grpclb_server* lhs,
+                              const xds_grpclb_server* rhs) {
+  return memcmp(lhs, rhs, sizeof(xds_grpclb_server)) == 0;
+}
+
+int xds_grpclb_duration_compare(const xds_grpclb_duration* lhs,
+                                const xds_grpclb_duration* rhs) {
+  GPR_ASSERT(lhs && rhs);
+  if (lhs->has_seconds && rhs->has_seconds) {
+    if (lhs->seconds < rhs->seconds) return -1;
+    if (lhs->seconds > rhs->seconds) return 1;
+  } else if (lhs->has_seconds) {
+    return 1;
+  } else if (rhs->has_seconds) {
+    return -1;
+  }
+
+  GPR_ASSERT(lhs->seconds == rhs->seconds);
+  if (lhs->has_nanos && rhs->has_nanos) {
+    if (lhs->nanos < rhs->nanos) return -1;
+    if (lhs->nanos > rhs->nanos) return 1;
+  } else if (lhs->has_nanos) {
+    return 1;
+  } else if (rhs->has_nanos) {
+    return -1;
+  }
+
+  return 0;
+}
+
+grpc_millis xds_grpclb_duration_to_millis(xds_grpclb_duration* duration_pb) {
+  return static_cast<grpc_millis>(
+      (duration_pb->has_seconds ? duration_pb->seconds : 0) * GPR_MS_PER_SEC +
+      (duration_pb->has_nanos ? duration_pb->nanos : 0) / GPR_NS_PER_MS);
+}
+
+void xds_grpclb_initial_response_destroy(
+    xds_grpclb_initial_response* response) {
+  gpr_free(response);
+}
diff --git a/src/core/ext/filters/client_channel/lb_policy/xds/load_balancer_api.h b/src/core/ext/filters/client_channel/lb_policy/xds/load_balancer_api.h
new file mode 100644
index 0000000000..3f096af6d6
--- /dev/null
+++ b/src/core/ext/filters/client_channel/lb_policy/xds/load_balancer_api.h
@@ -0,0 +1,89 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#ifndef GRPC_CORE_EXT_FILTERS_CLIENT_CHANNEL_LB_POLICY_XDS_LOAD_BALANCER_API_H
+#define GRPC_CORE_EXT_FILTERS_CLIENT_CHANNEL_LB_POLICY_XDS_LOAD_BALANCER_API_H
+
+#include <grpc/support/port_platform.h>
+
+#include <grpc/slice_buffer.h>
+
+#include "src/core/ext/filters/client_channel/lb_policy/grpclb/proto/grpc/lb/v1/load_balancer.pb.h"
+#include "src/core/ext/filters/client_channel/lb_policy/xds/xds_client_stats.h"
+#include "src/core/ext/filters/client_channel/lb_policy_factory.h"
+
+#define XDS_SERVICE_NAME_MAX_LENGTH 128
+
+typedef grpc_lb_v1_Server_ip_address_t xds_grpclb_ip_address;
+typedef grpc_lb_v1_LoadBalanceRequest xds_grpclb_request;
+typedef grpc_lb_v1_InitialLoadBalanceResponse xds_grpclb_initial_response;
+typedef grpc_lb_v1_Server xds_grpclb_server;
+typedef google_protobuf_Duration xds_grpclb_duration;
+typedef google_protobuf_Timestamp xds_grpclb_timestamp;
+
+typedef struct {
+  xds_grpclb_server** servers;
+  size_t num_servers;
+} xds_grpclb_serverlist;
+
+/** Create a request for a gRPC LB service under \a lb_service_name */
+xds_grpclb_request* xds_grpclb_request_create(const char* lb_service_name);
+xds_grpclb_request* xds_grpclb_load_report_request_create_locked(
+    grpc_core::XdsLbClientStats* client_stats);
+
+/** Protocol Buffers v3-encode \a request */
+grpc_slice xds_grpclb_request_encode(const xds_grpclb_request* request);
+
+/** Destroy \a request */
+void xds_grpclb_request_destroy(xds_grpclb_request* request);
+
+/** Parse (ie, decode) the bytes in \a encoded_xds_grpclb_response as a \a
+ * xds_grpclb_initial_response */
+xds_grpclb_initial_response* xds_grpclb_initial_response_parse(
+    grpc_slice encoded_xds_grpclb_response);
+
+/** Parse the list of servers from an encoded \a xds_grpclb_response */
+xds_grpclb_serverlist* xds_grpclb_response_parse_serverlist(
+    grpc_slice encoded_xds_grpclb_response);
+
+/** Return a copy of \a sl. The caller is responsible for calling \a
+ * xds_grpclb_destroy_serverlist on the returned copy. */
+xds_grpclb_serverlist* xds_grpclb_serverlist_copy(
+    const xds_grpclb_serverlist* sl);
+
+bool xds_grpclb_serverlist_equals(const xds_grpclb_serverlist* lhs,
+                                  const xds_grpclb_serverlist* rhs);
+
+bool xds_grpclb_server_equals(const xds_grpclb_server* lhs,
+                              const xds_grpclb_server* rhs);
+
+/** Destroy \a serverlist */
+void xds_grpclb_destroy_serverlist(xds_grpclb_serverlist* serverlist);
+
+/** Compare \a lhs against \a rhs and return 0 if \a lhs and \a rhs are equal,
+ * < 0 if \a lhs represents a duration shorter than \a rhs and > 0 otherwise */
+int xds_grpclb_duration_compare(const xds_grpclb_duration* lhs,
+                                const xds_grpclb_duration* rhs);
+
+grpc_millis xds_grpclb_duration_to_millis(xds_grpclb_duration* duration_pb);
+
+/** Destroy \a initial_response */
+void xds_grpclb_initial_response_destroy(xds_grpclb_initial_response* response);
+
+#endif /* GRPC_CORE_EXT_FILTERS_CLIENT_CHANNEL_LB_POLICY_XDS_LOAD_BALANCER_API_H \
+        */
diff --git a/src/core/ext/filters/client_channel/lb_policy/xds/xds.cc b/src/core/ext/filters/client_channel/lb_policy/xds/xds.cc
new file mode 100644
index 0000000000..16e910b2d9
--- /dev/null
+++ b/src/core/ext/filters/client_channel/lb_policy/xds/xds.cc
@@ -0,0 +1,1894 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+/// Implementation of the gRPC LB policy.
+///
+/// This policy takes as input a list of resolved addresses, which must
+/// include at least one balancer address.
+///
+/// An internal channel (\a lb_channel_) is created for the addresses
+/// from that are balancers.  This channel behaves just like a regular
+/// channel that uses pick_first to select from the list of balancer
+/// addresses.
+///
+/// The first time the policy gets a request for a pick, a ping, or to exit
+/// the idle state, \a StartPickingLocked() is called. This method is
+/// responsible for instantiating the internal *streaming* call to the LB
+/// server (whichever address pick_first chose).  The call will be complete
+/// when either the balancer sends status or when we cancel the call (e.g.,
+/// because we are shutting down).  In needed, we retry the call.  If we
+/// received at least one valid message from the server, a new call attempt
+/// will be made immediately; otherwise, we apply back-off delays between
+/// attempts.
+///
+/// We maintain an internal round_robin policy instance for distributing
+/// requests across backends.  Whenever we receive a new serverlist from
+/// the balancer, we update the round_robin policy with the new list of
+/// addresses.  If we cannot communicate with the balancer on startup,
+/// however, we may enter fallback mode, in which case we will populate
+/// the RR policy's addresses from the backend addresses returned by the
+/// resolver.
+///
+/// Once an RR policy instance is in place (and getting updated as described),
+/// calls for a pick, a ping, or a cancellation will be serviced right
+/// away by forwarding them to the RR instance.  Any time there's no RR
+/// policy available (i.e., right after the creation of the gRPCLB policy),
+/// pick and ping requests are added to a list of pending picks and pings
+/// to be flushed and serviced when the RR policy instance becomes available.
+///
+/// \see https://github.com/grpc/grpc/blob/master/doc/load-balancing.md for the
+/// high level design and details.
+
+// With the addition of a libuv endpoint, sockaddr.h now includes uv.h when
+// using that endpoint. Because of various transitive includes in uv.h,
+// including windows.h on Windows, uv.h must be included before other system
+// headers. Therefore, sockaddr.h must always be included first.
+#include <grpc/support/port_platform.h>
+
+#include "src/core/lib/iomgr/sockaddr.h"
+#include "src/core/lib/iomgr/socket_utils.h"
+
+#include <inttypes.h>
+#include <limits.h>
+#include <string.h>
+
+#include <grpc/byte_buffer_reader.h>
+#include <grpc/grpc.h>
+#include <grpc/support/alloc.h>
+#include <grpc/support/string_util.h>
+#include <grpc/support/time.h>
+
+#include "src/core/ext/filters/client_channel/client_channel.h"
+#include "src/core/ext/filters/client_channel/client_channel_factory.h"
+#include "src/core/ext/filters/client_channel/lb_policy/xds/client_load_reporting_filter.h"
+#include "src/core/ext/filters/client_channel/lb_policy/xds/load_balancer_api.h"
+#include "src/core/ext/filters/client_channel/lb_policy/xds/xds.h"
+#include "src/core/ext/filters/client_channel/lb_policy/xds/xds_channel.h"
+#include "src/core/ext/filters/client_channel/lb_policy/xds/xds_client_stats.h"
+#include "src/core/ext/filters/client_channel/lb_policy_factory.h"
+#include "src/core/ext/filters/client_channel/lb_policy_registry.h"
+#include "src/core/ext/filters/client_channel/parse_address.h"
+#include "src/core/ext/filters/client_channel/resolver/fake/fake_resolver.h"
+#include "src/core/ext/filters/client_channel/subchannel_index.h"
+#include "src/core/lib/backoff/backoff.h"
+#include "src/core/lib/channel/channel_args.h"
+#include "src/core/lib/channel/channel_stack.h"
+#include "src/core/lib/gpr/host_port.h"
+#include "src/core/lib/gpr/string.h"
+#include "src/core/lib/gprpp/manual_constructor.h"
+#include "src/core/lib/gprpp/memory.h"
+#include "src/core/lib/gprpp/mutex_lock.h"
+#include "src/core/lib/gprpp/orphanable.h"
+#include "src/core/lib/gprpp/ref_counted_ptr.h"
+#include "src/core/lib/iomgr/combiner.h"
+#include "src/core/lib/iomgr/sockaddr.h"
+#include "src/core/lib/iomgr/sockaddr_utils.h"
+#include "src/core/lib/iomgr/timer.h"
+#include "src/core/lib/slice/slice_hash_table.h"
+#include "src/core/lib/slice/slice_internal.h"
+#include "src/core/lib/slice/slice_string_helpers.h"
+#include "src/core/lib/surface/call.h"
+#include "src/core/lib/surface/channel.h"
+#include "src/core/lib/surface/channel_init.h"
+#include "src/core/lib/transport/static_metadata.h"
+
+#define GRPC_XDS_INITIAL_CONNECT_BACKOFF_SECONDS 1
+#define GRPC_XDS_RECONNECT_BACKOFF_MULTIPLIER 1.6
+#define GRPC_XDS_RECONNECT_MAX_BACKOFF_SECONDS 120
+#define GRPC_XDS_RECONNECT_JITTER 0.2
+#define GRPC_XDS_DEFAULT_FALLBACK_TIMEOUT_MS 10000
+
+namespace grpc_core {
+
+TraceFlag grpc_lb_xds_trace(false, "xds");
+
+namespace {
+
+class XdsLb : public LoadBalancingPolicy {
+ public:
+  XdsLb(const grpc_lb_addresses* addresses, const Args& args);
+
+  void UpdateLocked(const grpc_channel_args& args) override;
+  bool PickLocked(PickState* pick, grpc_error** error) override;
+  void CancelPickLocked(PickState* pick, grpc_error* error) override;
+  void CancelMatchingPicksLocked(uint32_t initial_metadata_flags_mask,
+                                 uint32_t initial_metadata_flags_eq,
+                                 grpc_error* error) override;
+  void NotifyOnStateChangeLocked(grpc_connectivity_state* state,
+                                 grpc_closure* closure) override;
+  grpc_connectivity_state CheckConnectivityLocked(
+      grpc_error** connectivity_error) override;
+  void HandOffPendingPicksLocked(LoadBalancingPolicy* new_policy) override;
+  void ExitIdleLocked() override;
+  void ResetBackoffLocked() override;
+  void FillChildRefsForChannelz(
+      channelz::ChildRefsList* child_subchannels,
+      channelz::ChildRefsList* child_channels) override;
+
+ private:
+  /// Linked list of pending pick requests. It stores all information needed to
+  /// eventually call (Round Robin's) pick() on them. They mainly stay pending
+  /// waiting for the RR policy to be created.
+  ///
+  /// Note that when a pick is sent to the RR policy, we inject our own
+  /// on_complete callback, so that we can intercept the result before
+  /// invoking the original on_complete callback.  This allows us to set the
+  /// LB token metadata and add client_stats to the call context.
+  /// See \a pending_pick_complete() for details.
+  struct PendingPick {
+    // The xds lb instance that created the wrapping. This instance is not
+    // owned; reference counts are untouched. It's used only for logging
+    // purposes.
+    XdsLb* xdslb_policy;
+    // The original pick.
+    PickState* pick;
+    // Our on_complete closure and the original one.
+    grpc_closure on_complete;
+    grpc_closure* original_on_complete;
+    // The LB token associated with the pick.  This is set via user_data in
+    // the pick.
+    grpc_mdelem lb_token;
+    // Stats for client-side load reporting.
+    RefCountedPtr<XdsLbClientStats> client_stats;
+    // Next pending pick.
+    PendingPick* next = nullptr;
+  };
+
+  /// Contains a call to the LB server and all the data related to the call.
+  class BalancerCallState
+      : public InternallyRefCountedWithTracing<BalancerCallState> {
+   public:
+    explicit BalancerCallState(
+        RefCountedPtr<LoadBalancingPolicy> parent_xdslb_policy);
+
+    // It's the caller's responsibility to ensure that Orphan() is called from
+    // inside the combiner.
+    void Orphan() override;
+
+    void StartQuery();
+
+    XdsLbClientStats* client_stats() const { return client_stats_.get(); }
+
+    bool seen_initial_response() const { return seen_initial_response_; }
+
+   private:
+    // So Delete() can access our private dtor.
+    template <typename T>
+    friend void grpc_core::Delete(T*);
+
+    ~BalancerCallState();
+
+    XdsLb* xdslb_policy() const {
+      return static_cast<XdsLb*>(xdslb_policy_.get());
+    }
+
+    void ScheduleNextClientLoadReportLocked();
+    void SendClientLoadReportLocked();
+
+    static bool LoadReportCountersAreZero(xds_grpclb_request* request);
+
+    static void MaybeSendClientLoadReportLocked(void* arg, grpc_error* error);
+    static void ClientLoadReportDoneLocked(void* arg, grpc_error* error);
+    static void OnInitialRequestSentLocked(void* arg, grpc_error* error);
+    static void OnBalancerMessageReceivedLocked(void* arg, grpc_error* error);
+    static void OnBalancerStatusReceivedLocked(void* arg, grpc_error* error);
+
+    // The owning LB policy.
+    RefCountedPtr<LoadBalancingPolicy> xdslb_policy_;
+
+    // The streaming call to the LB server. Always non-NULL.
+    grpc_call* lb_call_ = nullptr;
+
+    // recv_initial_metadata
+    grpc_metadata_array lb_initial_metadata_recv_;
+
+    // send_message
+    grpc_byte_buffer* send_message_payload_ = nullptr;
+    grpc_closure lb_on_initial_request_sent_;
+
+    // recv_message
+    grpc_byte_buffer* recv_message_payload_ = nullptr;
+    grpc_closure lb_on_balancer_message_received_;
+    bool seen_initial_response_ = false;
+
+    // recv_trailing_metadata
+    grpc_closure lb_on_balancer_status_received_;
+    grpc_metadata_array lb_trailing_metadata_recv_;
+    grpc_status_code lb_call_status_;
+    grpc_slice lb_call_status_details_;
+
+    // The stats for client-side load reporting associated with this LB call.
+    // Created after the first serverlist is received.
+    RefCountedPtr<XdsLbClientStats> client_stats_;
+    grpc_millis client_stats_report_interval_ = 0;
+    grpc_timer client_load_report_timer_;
+    bool client_load_report_timer_callback_pending_ = false;
+    bool last_client_load_report_counters_were_zero_ = false;
+    bool client_load_report_is_due_ = false;
+    // The closure used for either the load report timer or the callback for
+    // completion of sending the load report.
+    grpc_closure client_load_report_closure_;
+  };
+
+  ~XdsLb();
+
+  void ShutdownLocked() override;
+
+  // Helper function used in ctor and UpdateLocked().
+  void ProcessChannelArgsLocked(const grpc_channel_args& args);
+
+  // Methods for dealing with the balancer channel and call.
+  void StartPickingLocked();
+  void StartBalancerCallLocked();
+  static void OnFallbackTimerLocked(void* arg, grpc_error* error);
+  void StartBalancerCallRetryTimerLocked();
+  static void OnBalancerCallRetryTimerLocked(void* arg, grpc_error* error);
+  static void OnBalancerChannelConnectivityChangedLocked(void* arg,
+                                                         grpc_error* error);
+
+  // Pending pick methods.
+  static void PendingPickSetMetadataAndContext(PendingPick* pp);
+  PendingPick* PendingPickCreate(PickState* pick);
+  void AddPendingPick(PendingPick* pp);
+  static void OnPendingPickComplete(void* arg, grpc_error* error);
+
+  // Methods for dealing with the RR policy.
+  void CreateOrUpdateRoundRobinPolicyLocked();
+  grpc_channel_args* CreateRoundRobinPolicyArgsLocked();
+  void CreateRoundRobinPolicyLocked(const Args& args);
+  bool PickFromRoundRobinPolicyLocked(bool force_async, PendingPick* pp,
+                                      grpc_error** error);
+  void UpdateConnectivityStateFromRoundRobinPolicyLocked(
+      grpc_error* rr_state_error);
+  static void OnRoundRobinConnectivityChangedLocked(void* arg,
+                                                    grpc_error* error);
+  static void OnRoundRobinRequestReresolutionLocked(void* arg,
+                                                    grpc_error* error);
+
+  // Who the client is trying to communicate with.
+  const char* server_name_ = nullptr;
+
+  // Current channel args from the resolver.
+  grpc_channel_args* args_ = nullptr;
+
+  // Internal state.
+  bool started_picking_ = false;
+  bool shutting_down_ = false;
+  grpc_connectivity_state_tracker state_tracker_;
+
+  // The channel for communicating with the LB server.
+  grpc_channel* lb_channel_ = nullptr;
+  // Mutex to protect the channel to the LB server. This is used when
+  // processing a channelz request.
+  gpr_mu lb_channel_mu_;
+  grpc_connectivity_state lb_channel_connectivity_;
+  grpc_closure lb_channel_on_connectivity_changed_;
+  // Are we already watching the LB channel's connectivity?
+  bool watching_lb_channel_ = false;
+  // Response generator to inject address updates into lb_channel_.
+  RefCountedPtr<FakeResolverResponseGenerator> response_generator_;
+
+  // The data associated with the current LB call. It holds a ref to this LB
+  // policy. It's initialized every time we query for backends. It's reset to
+  // NULL whenever the current LB call is no longer needed (e.g., the LB policy
+  // is shutting down, or the LB call has ended). A non-NULL lb_calld_ always
+  // contains a non-NULL lb_call_.
+  OrphanablePtr<BalancerCallState> lb_calld_;
+  // Timeout in milliseconds for the LB call. 0 means no deadline.
+  int lb_call_timeout_ms_ = 0;
+  // Balancer call retry state.
+  BackOff lb_call_backoff_;
+  bool retry_timer_callback_pending_ = false;
+  grpc_timer lb_call_retry_timer_;
+  grpc_closure lb_on_call_retry_;
+
+  // The deserialized response from the balancer. May be nullptr until one
+  // such response has arrived.
+  xds_grpclb_serverlist* serverlist_ = nullptr;
+  // Index into serverlist for next pick.
+  // If the server at this index is a drop, we return a drop.
+  // Otherwise, we delegate to the RR policy.
+  size_t serverlist_index_ = 0;
+
+  // Timeout in milliseconds for before using fallback backend addresses.
+  // 0 means not using fallback.
+  int lb_fallback_timeout_ms_ = 0;
+  // The backend addresses from the resolver.
+  grpc_lb_addresses* fallback_backend_addresses_ = nullptr;
+  // Fallback timer.
+  bool fallback_timer_callback_pending_ = false;
+  grpc_timer lb_fallback_timer_;
+  grpc_closure lb_on_fallback_;
+
+  // Pending picks that are waiting on the RR policy's connectivity.
+  PendingPick* pending_picks_ = nullptr;
+
+  // The RR policy to use for the backends.
+  OrphanablePtr<LoadBalancingPolicy> rr_policy_;
+  grpc_connectivity_state rr_connectivity_state_;
+  grpc_closure on_rr_connectivity_changed_;
+  grpc_closure on_rr_request_reresolution_;
+};
+
+//
+// serverlist parsing code
+//
+
+// vtable for LB tokens in grpc_lb_addresses
+void* lb_token_copy(void* token) {
+  return token == nullptr
+             ? nullptr
+             : (void*)GRPC_MDELEM_REF(grpc_mdelem{(uintptr_t)token}).payload;
+}
+void lb_token_destroy(void* token) {
+  if (token != nullptr) {
+    GRPC_MDELEM_UNREF(grpc_mdelem{(uintptr_t)token});
+  }
+}
+int lb_token_cmp(void* token1, void* token2) {
+  if (token1 > token2) return 1;
+  if (token1 < token2) return -1;
+  return 0;
+}
+const grpc_lb_user_data_vtable lb_token_vtable = {
+    lb_token_copy, lb_token_destroy, lb_token_cmp};
+
+// Returns the backend addresses extracted from the given addresses.
+grpc_lb_addresses* ExtractBackendAddresses(const grpc_lb_addresses* addresses) {
+  // First pass: count the number of backend addresses.
+  size_t num_backends = 0;
+  for (size_t i = 0; i < addresses->num_addresses; ++i) {
+    if (!addresses->addresses[i].is_balancer) {
+      ++num_backends;
+    }
+  }
+  // Second pass: actually populate the addresses and (empty) LB tokens.
+  grpc_lb_addresses* backend_addresses =
+      grpc_lb_addresses_create(num_backends, &lb_token_vtable);
+  size_t num_copied = 0;
+  for (size_t i = 0; i < addresses->num_addresses; ++i) {
+    if (addresses->addresses[i].is_balancer) continue;
+    const grpc_resolved_address* addr = &addresses->addresses[i].address;
+    grpc_lb_addresses_set_address(backend_addresses, num_copied, &addr->addr,
+                                  addr->len, false /* is_balancer */,
+                                  nullptr /* balancer_name */,
+                                  (void*)GRPC_MDELEM_LB_TOKEN_EMPTY.payload);
+    ++num_copied;
+  }
+  return backend_addresses;
+}
+
+bool IsServerValid(const xds_grpclb_server* server, size_t idx, bool log) {
+  if (server->drop) return false;
+  const xds_grpclb_ip_address* ip = &server->ip_address;
+  if (GPR_UNLIKELY(server->port >> 16 != 0)) {
+    if (log) {
+      gpr_log(GPR_ERROR,
+              "Invalid port '%d' at index %lu of serverlist. Ignoring.",
+              server->port, (unsigned long)idx);
+    }
+    return false;
+  }
+  if (GPR_UNLIKELY(ip->size != 4 && ip->size != 16)) {
+    if (log) {
+      gpr_log(GPR_ERROR,
+              "Expected IP to be 4 or 16 bytes, got %d at index %lu of "
+              "serverlist. Ignoring",
+              ip->size, (unsigned long)idx);
+    }
+    return false;
+  }
+  return true;
+}
+
+void ParseServer(const xds_grpclb_server* server, grpc_resolved_address* addr) {
+  memset(addr, 0, sizeof(*addr));
+  if (server->drop) return;
+  const uint16_t netorder_port = grpc_htons((uint16_t)server->port);
+  /* the addresses are given in binary format (a in(6)_addr struct) in
+   * server->ip_address.bytes. */
+  const xds_grpclb_ip_address* ip = &server->ip_address;
+  if (ip->size == 4) {
+    addr->len = static_cast<socklen_t>(sizeof(grpc_sockaddr_in));
+    grpc_sockaddr_in* addr4 = reinterpret_cast<grpc_sockaddr_in*>(&addr->addr);
+    addr4->sin_family = GRPC_AF_INET;
+    memcpy(&addr4->sin_addr, ip->bytes, ip->size);
+    addr4->sin_port = netorder_port;
+  } else if (ip->size == 16) {
+    addr->len = static_cast<socklen_t>(sizeof(grpc_sockaddr_in6));
+    grpc_sockaddr_in6* addr6 = (grpc_sockaddr_in6*)&addr->addr;
+    addr6->sin6_family = GRPC_AF_INET6;
+    memcpy(&addr6->sin6_addr, ip->bytes, ip->size);
+    addr6->sin6_port = netorder_port;
+  }
+}
+
+// Returns addresses extracted from \a serverlist.
+grpc_lb_addresses* ProcessServerlist(const xds_grpclb_serverlist* serverlist) {
+  size_t num_valid = 0;
+  /* first pass: count how many are valid in order to allocate the necessary
+   * memory in a single block */
+  for (size_t i = 0; i < serverlist->num_servers; ++i) {
+    if (IsServerValid(serverlist->servers[i], i, true)) ++num_valid;
+  }
+  grpc_lb_addresses* lb_addresses =
+      grpc_lb_addresses_create(num_valid, &lb_token_vtable);
+  /* second pass: actually populate the addresses and LB tokens (aka user data
+   * to the outside world) to be read by the RR policy during its creation.
+   * Given that the validity tests are very cheap, they are performed again
+   * instead of marking the valid ones during the first pass, as this would
+   * incurr in an allocation due to the arbitrary number of server */
+  size_t addr_idx = 0;
+  for (size_t sl_idx = 0; sl_idx < serverlist->num_servers; ++sl_idx) {
+    const xds_grpclb_server* server = serverlist->servers[sl_idx];
+    if (!IsServerValid(serverlist->servers[sl_idx], sl_idx, false)) continue;
+    GPR_ASSERT(addr_idx < num_valid);
+    /* address processing */
+    grpc_resolved_address addr;
+    ParseServer(server, &addr);
+    /* lb token processing */
+    void* user_data;
+    if (server->has_load_balance_token) {
+      const size_t lb_token_max_length =
+          GPR_ARRAY_SIZE(server->load_balance_token);
+      const size_t lb_token_length =
+          strnlen(server->load_balance_token, lb_token_max_length);
+      grpc_slice lb_token_mdstr = grpc_slice_from_copied_buffer(
+          server->load_balance_token, lb_token_length);
+      user_data =
+          (void*)grpc_mdelem_from_slices(GRPC_MDSTR_LB_TOKEN, lb_token_mdstr)
+              .payload;
+    } else {
+      char* uri = grpc_sockaddr_to_uri(&addr);
+      gpr_log(GPR_INFO,
+              "Missing LB token for backend address '%s'. The empty token will "
+              "be used instead",
+              uri);
+      gpr_free(uri);
+      user_data = (void*)GRPC_MDELEM_LB_TOKEN_EMPTY.payload;
+    }
+    grpc_lb_addresses_set_address(lb_addresses, addr_idx, &addr.addr, addr.len,
+                                  false /* is_balancer */,
+                                  nullptr /* balancer_name */, user_data);
+    ++addr_idx;
+  }
+  GPR_ASSERT(addr_idx == num_valid);
+  return lb_addresses;
+}
+
+//
+// XdsLb::BalancerCallState
+//
+
+XdsLb::BalancerCallState::BalancerCallState(
+    RefCountedPtr<LoadBalancingPolicy> parent_xdslb_policy)
+    : InternallyRefCountedWithTracing<BalancerCallState>(&grpc_lb_xds_trace),
+      xdslb_policy_(std::move(parent_xdslb_policy)) {
+  GPR_ASSERT(xdslb_policy_ != nullptr);
+  GPR_ASSERT(!xdslb_policy()->shutting_down_);
+  // Init the LB call. Note that the LB call will progress every time there's
+  // activity in xdslb_policy_->interested_parties(), which is comprised of
+  // the polling entities from client_channel.
+  GPR_ASSERT(xdslb_policy()->server_name_ != nullptr);
+  GPR_ASSERT(xdslb_policy()->server_name_[0] != '\0');
+  const grpc_millis deadline =
+      xdslb_policy()->lb_call_timeout_ms_ == 0
+          ? GRPC_MILLIS_INF_FUTURE
+          : ExecCtx::Get()->Now() + xdslb_policy()->lb_call_timeout_ms_;
+  lb_call_ = grpc_channel_create_pollset_set_call(
+      xdslb_policy()->lb_channel_, nullptr, GRPC_PROPAGATE_DEFAULTS,
+      xdslb_policy_->interested_parties(),
+      GRPC_MDSTR_SLASH_GRPC_DOT_LB_DOT_V1_DOT_LOADBALANCER_SLASH_BALANCELOAD,
+      nullptr, deadline, nullptr);
+  // Init the LB call request payload.
+  xds_grpclb_request* request =
+      xds_grpclb_request_create(xdslb_policy()->server_name_);
+  grpc_slice request_payload_slice = xds_grpclb_request_encode(request);
+  send_message_payload_ =
+      grpc_raw_byte_buffer_create(&request_payload_slice, 1);
+  grpc_slice_unref_internal(request_payload_slice);
+  xds_grpclb_request_destroy(request);
+  // Init other data associated with the LB call.
+  grpc_metadata_array_init(&lb_initial_metadata_recv_);
+  grpc_metadata_array_init(&lb_trailing_metadata_recv_);
+  GRPC_CLOSURE_INIT(&lb_on_initial_request_sent_, OnInitialRequestSentLocked,
+                    this, grpc_combiner_scheduler(xdslb_policy()->combiner()));
+  GRPC_CLOSURE_INIT(&lb_on_balancer_message_received_,
+                    OnBalancerMessageReceivedLocked, this,
+                    grpc_combiner_scheduler(xdslb_policy()->combiner()));
+  GRPC_CLOSURE_INIT(&lb_on_balancer_status_received_,
+                    OnBalancerStatusReceivedLocked, this,
+                    grpc_combiner_scheduler(xdslb_policy()->combiner()));
+}
+
+XdsLb::BalancerCallState::~BalancerCallState() {
+  GPR_ASSERT(lb_call_ != nullptr);
+  grpc_call_unref(lb_call_);
+  grpc_metadata_array_destroy(&lb_initial_metadata_recv_);
+  grpc_metadata_array_destroy(&lb_trailing_metadata_recv_);
+  grpc_byte_buffer_destroy(send_message_payload_);
+  grpc_byte_buffer_destroy(recv_message_payload_);
+  grpc_slice_unref_internal(lb_call_status_details_);
+}
+
+void XdsLb::BalancerCallState::Orphan() {
+  GPR_ASSERT(lb_call_ != nullptr);
+  // If we are here because xdslb_policy wants to cancel the call,
+  // lb_on_balancer_status_received_ will complete the cancellation and clean
+  // up. Otherwise, we are here because xdslb_policy has to orphan a failed
+  // call, then the following cancellation will be a no-op.
+  grpc_call_cancel(lb_call_, nullptr);
+  if (client_load_report_timer_callback_pending_) {
+    grpc_timer_cancel(&client_load_report_timer_);
+  }
+  // Note that the initial ref is hold by lb_on_balancer_status_received_
+  // instead of the caller of this function. So the corresponding unref happens
+  // in lb_on_balancer_status_received_ instead of here.
+}
+
+void XdsLb::BalancerCallState::StartQuery() {
+  GPR_ASSERT(lb_call_ != nullptr);
+  if (grpc_lb_xds_trace.enabled()) {
+    gpr_log(GPR_INFO, "[xdslb %p] Starting LB call (lb_calld: %p, lb_call: %p)",
+            xdslb_policy_.get(), this, lb_call_);
+  }
+  // Create the ops.
+  grpc_call_error call_error;
+  grpc_op ops[3];
+  memset(ops, 0, sizeof(ops));
+  // Op: send initial metadata.
+  grpc_op* op = ops;
+  op->op = GRPC_OP_SEND_INITIAL_METADATA;
+  op->data.send_initial_metadata.count = 0;
+  op->flags = 0;
+  op->reserved = nullptr;
+  op++;
+  // Op: send request message.
+  GPR_ASSERT(send_message_payload_ != nullptr);
+  op->op = GRPC_OP_SEND_MESSAGE;
+  op->data.send_message.send_message = send_message_payload_;
+  op->flags = 0;
+  op->reserved = nullptr;
+  op++;
+  // TODO(roth): We currently track this ref manually.  Once the
+  // ClosureRef API is ready, we should pass the RefCountedPtr<> along
+  // with the callback.
+  auto self = Ref(DEBUG_LOCATION, "on_initial_request_sent");
+  self.release();
+  call_error = grpc_call_start_batch_and_execute(
+      lb_call_, ops, (size_t)(op - ops), &lb_on_initial_request_sent_);
+  GPR_ASSERT(GRPC_CALL_OK == call_error);
+  // Op: recv initial metadata.
+  op = ops;
+  op->op = GRPC_OP_RECV_INITIAL_METADATA;
+  op->data.recv_initial_metadata.recv_initial_metadata =
+      &lb_initial_metadata_recv_;
+  op->flags = 0;
+  op->reserved = nullptr;
+  op++;
+  // Op: recv response.
+  op->op = GRPC_OP_RECV_MESSAGE;
+  op->data.recv_message.recv_message = &recv_message_payload_;
+  op->flags = 0;
+  op->reserved = nullptr;
+  op++;
+  // TODO(roth): We currently track this ref manually.  Once the
+  // ClosureRef API is ready, we should pass the RefCountedPtr<> along
+  // with the callback.
+  self = Ref(DEBUG_LOCATION, "on_message_received");
+  self.release();
+  call_error = grpc_call_start_batch_and_execute(
+      lb_call_, ops, (size_t)(op - ops), &lb_on_balancer_message_received_);
+  GPR_ASSERT(GRPC_CALL_OK == call_error);
+  // Op: recv server status.
+  op = ops;
+  op->op = GRPC_OP_RECV_STATUS_ON_CLIENT;
+  op->data.recv_status_on_client.trailing_metadata =
+      &lb_trailing_metadata_recv_;
+  op->data.recv_status_on_client.status = &lb_call_status_;
+  op->data.recv_status_on_client.status_details = &lb_call_status_details_;
+  op->flags = 0;
+  op->reserved = nullptr;
+  op++;
+  // This callback signals the end of the LB call, so it relies on the initial
+  // ref instead of a new ref. When it's invoked, it's the initial ref that is
+  // unreffed.
+  call_error = grpc_call_start_batch_and_execute(
+      lb_call_, ops, (size_t)(op - ops), &lb_on_balancer_status_received_);
+  GPR_ASSERT(GRPC_CALL_OK == call_error);
+}
+
+void XdsLb::BalancerCallState::ScheduleNextClientLoadReportLocked() {
+  const grpc_millis next_client_load_report_time =
+      ExecCtx::Get()->Now() + client_stats_report_interval_;
+  GRPC_CLOSURE_INIT(&client_load_report_closure_,
+                    MaybeSendClientLoadReportLocked, this,
+                    grpc_combiner_scheduler(xdslb_policy()->combiner()));
+  grpc_timer_init(&client_load_report_timer_, next_client_load_report_time,
+                  &client_load_report_closure_);
+  client_load_report_timer_callback_pending_ = true;
+}
+
+void XdsLb::BalancerCallState::MaybeSendClientLoadReportLocked(
+    void* arg, grpc_error* error) {
+  BalancerCallState* lb_calld = static_cast<BalancerCallState*>(arg);
+  XdsLb* xdslb_policy = lb_calld->xdslb_policy();
+  lb_calld->client_load_report_timer_callback_pending_ = false;
+  if (error != GRPC_ERROR_NONE || lb_calld != xdslb_policy->lb_calld_.get()) {
+    lb_calld->Unref(DEBUG_LOCATION, "client_load_report");
+    return;
+  }
+  // If we've already sent the initial request, then we can go ahead and send
+  // the load report. Otherwise, we need to wait until the initial request has
+  // been sent to send this (see OnInitialRequestSentLocked()).
+  if (lb_calld->send_message_payload_ == nullptr) {
+    lb_calld->SendClientLoadReportLocked();
+  } else {
+    lb_calld->client_load_report_is_due_ = true;
+  }
+}
+
+bool XdsLb::BalancerCallState::LoadReportCountersAreZero(
+    xds_grpclb_request* request) {
+  XdsLbClientStats::DroppedCallCounts* drop_entries =
+      static_cast<XdsLbClientStats::DroppedCallCounts*>(
+          request->client_stats.calls_finished_with_drop.arg);
+  return request->client_stats.num_calls_started == 0 &&
+         request->client_stats.num_calls_finished == 0 &&
+         request->client_stats.num_calls_finished_with_client_failed_to_send ==
+             0 &&
+         request->client_stats.num_calls_finished_known_received == 0 &&
+         (drop_entries == nullptr || drop_entries->empty());
+}
+
+void XdsLb::BalancerCallState::SendClientLoadReportLocked() {
+  // Construct message payload.
+  GPR_ASSERT(send_message_payload_ == nullptr);
+  xds_grpclb_request* request =
+      xds_grpclb_load_report_request_create_locked(client_stats_.get());
+  // Skip client load report if the counters were all zero in the last
+  // report and they are still zero in this one.
+  if (LoadReportCountersAreZero(request)) {
+    if (last_client_load_report_counters_were_zero_) {
+      xds_grpclb_request_destroy(request);
+      ScheduleNextClientLoadReportLocked();
+      return;
+    }
+    last_client_load_report_counters_were_zero_ = true;
+  } else {
+    last_client_load_report_counters_were_zero_ = false;
+  }
+  grpc_slice request_payload_slice = xds_grpclb_request_encode(request);
+  send_message_payload_ =
+      grpc_raw_byte_buffer_create(&request_payload_slice, 1);
+  grpc_slice_unref_internal(request_payload_slice);
+  xds_grpclb_request_destroy(request);
+  // Send the report.
+  grpc_op op;
+  memset(&op, 0, sizeof(op));
+  op.op = GRPC_OP_SEND_MESSAGE;
+  op.data.send_message.send_message = send_message_payload_;
+  GRPC_CLOSURE_INIT(&client_load_report_closure_, ClientLoadReportDoneLocked,
+                    this, grpc_combiner_scheduler(xdslb_policy()->combiner()));
+  grpc_call_error call_error = grpc_call_start_batch_and_execute(
+      lb_call_, &op, 1, &client_load_report_closure_);
+  if (GPR_UNLIKELY(call_error != GRPC_CALL_OK)) {
+    gpr_log(GPR_ERROR, "[xdslb %p] call_error=%d", xdslb_policy_.get(),
+            call_error);
+    GPR_ASSERT(GRPC_CALL_OK == call_error);
+  }
+}
+
+void XdsLb::BalancerCallState::ClientLoadReportDoneLocked(void* arg,
+                                                          grpc_error* error) {
+  BalancerCallState* lb_calld = static_cast<BalancerCallState*>(arg);
+  XdsLb* xdslb_policy = lb_calld->xdslb_policy();
+  grpc_byte_buffer_destroy(lb_calld->send_message_payload_);
+  lb_calld->send_message_payload_ = nullptr;
+  if (error != GRPC_ERROR_NONE || lb_calld != xdslb_policy->lb_calld_.get()) {
+    lb_calld->Unref(DEBUG_LOCATION, "client_load_report");
+    return;
+  }
+  lb_calld->ScheduleNextClientLoadReportLocked();
+}
+
+void XdsLb::BalancerCallState::OnInitialRequestSentLocked(void* arg,
+                                                          grpc_error* error) {
+  BalancerCallState* lb_calld = static_cast<BalancerCallState*>(arg);
+  grpc_byte_buffer_destroy(lb_calld->send_message_payload_);
+  lb_calld->send_message_payload_ = nullptr;
+  // If we attempted to send a client load report before the initial request was
+  // sent (and this lb_calld is still in use), send the load report now.
+  if (lb_calld->client_load_report_is_due_ &&
+      lb_calld == lb_calld->xdslb_policy()->lb_calld_.get()) {
+    lb_calld->SendClientLoadReportLocked();
+    lb_calld->client_load_report_is_due_ = false;
+  }
+  lb_calld->Unref(DEBUG_LOCATION, "on_initial_request_sent");
+}
+
+void XdsLb::BalancerCallState::OnBalancerMessageReceivedLocked(
+    void* arg, grpc_error* error) {
+  BalancerCallState* lb_calld = static_cast<BalancerCallState*>(arg);
+  XdsLb* xdslb_policy = lb_calld->xdslb_policy();
+  // Empty payload means the LB call was cancelled.
+  if (lb_calld != xdslb_policy->lb_calld_.get() ||
+      lb_calld->recv_message_payload_ == nullptr) {
+    lb_calld->Unref(DEBUG_LOCATION, "on_message_received");
+    return;
+  }
+  grpc_byte_buffer_reader bbr;
+  grpc_byte_buffer_reader_init(&bbr, lb_calld->recv_message_payload_);
+  grpc_slice response_slice = grpc_byte_buffer_reader_readall(&bbr);
+  grpc_byte_buffer_reader_destroy(&bbr);
+  grpc_byte_buffer_destroy(lb_calld->recv_message_payload_);
+  lb_calld->recv_message_payload_ = nullptr;
+  xds_grpclb_initial_response* initial_response;
+  xds_grpclb_serverlist* serverlist;
+  if (!lb_calld->seen_initial_response_ &&
+      (initial_response = xds_grpclb_initial_response_parse(response_slice)) !=
+          nullptr) {
+    // Have NOT seen initial response, look for initial response.
+    if (initial_response->has_client_stats_report_interval) {
+      lb_calld->client_stats_report_interval_ = GPR_MAX(
+          GPR_MS_PER_SEC, xds_grpclb_duration_to_millis(
+                              &initial_response->client_stats_report_interval));
+      if (grpc_lb_xds_trace.enabled()) {
+        gpr_log(GPR_INFO,
+                "[xdslb %p] Received initial LB response message; "
+                "client load reporting interval = %" PRId64 " milliseconds",
+                xdslb_policy, lb_calld->client_stats_report_interval_);
+      }
+    } else if (grpc_lb_xds_trace.enabled()) {
+      gpr_log(GPR_INFO,
+              "[xdslb %p] Received initial LB response message; client load "
+              "reporting NOT enabled",
+              xdslb_policy);
+    }
+    xds_grpclb_initial_response_destroy(initial_response);
+    lb_calld->seen_initial_response_ = true;
+  } else if ((serverlist = xds_grpclb_response_parse_serverlist(
+                  response_slice)) != nullptr) {
+    // Have seen initial response, look for serverlist.
+    GPR_ASSERT(lb_calld->lb_call_ != nullptr);
+    if (grpc_lb_xds_trace.enabled()) {
+      gpr_log(GPR_INFO,
+              "[xdslb %p] Serverlist with %" PRIuPTR " servers received",
+              xdslb_policy, serverlist->num_servers);
+      for (size_t i = 0; i < serverlist->num_servers; ++i) {
+        grpc_resolved_address addr;
+        ParseServer(serverlist->servers[i], &addr);
+        char* ipport;
+        grpc_sockaddr_to_string(&ipport, &addr, false);
+        gpr_log(GPR_INFO, "[xdslb %p] Serverlist[%" PRIuPTR "]: %s",
+                xdslb_policy, i, ipport);
+        gpr_free(ipport);
+      }
+    }
+    /* update serverlist */
+    if (serverlist->num_servers > 0) {
+      // Start sending client load report only after we start using the
+      // serverlist returned from the current LB call.
+      if (lb_calld->client_stats_report_interval_ > 0 &&
+          lb_calld->client_stats_ == nullptr) {
+        lb_calld->client_stats_.reset(New<XdsLbClientStats>());
+        // TODO(roth): We currently track this ref manually.  Once the
+        // ClosureRef API is ready, we should pass the RefCountedPtr<> along
+        // with the callback.
+        auto self = lb_calld->Ref(DEBUG_LOCATION, "client_load_report");
+        self.release();
+        lb_calld->ScheduleNextClientLoadReportLocked();
+      }
+      if (xds_grpclb_serverlist_equals(xdslb_policy->serverlist_, serverlist)) {
+        if (grpc_lb_xds_trace.enabled()) {
+          gpr_log(GPR_INFO,
+                  "[xdslb %p] Incoming server list identical to current, "
+                  "ignoring.",
+                  xdslb_policy);
+        }
+        xds_grpclb_destroy_serverlist(serverlist);
+      } else { /* new serverlist */
+        if (xdslb_policy->serverlist_ != nullptr) {
+          /* dispose of the old serverlist */
+          xds_grpclb_destroy_serverlist(xdslb_policy->serverlist_);
+        } else {
+          /* or dispose of the fallback */
+          grpc_lb_addresses_destroy(xdslb_policy->fallback_backend_addresses_);
+          xdslb_policy->fallback_backend_addresses_ = nullptr;
+          if (xdslb_policy->fallback_timer_callback_pending_) {
+            grpc_timer_cancel(&xdslb_policy->lb_fallback_timer_);
+          }
+        }
+        // and update the copy in the XdsLb instance. This
+        // serverlist instance will be destroyed either upon the next
+        // update or when the XdsLb instance is destroyed.
+        xdslb_policy->serverlist_ = serverlist;
+        xdslb_policy->serverlist_index_ = 0;
+        xdslb_policy->CreateOrUpdateRoundRobinPolicyLocked();
+      }
+    } else {
+      if (grpc_lb_xds_trace.enabled()) {
+        gpr_log(GPR_INFO, "[xdslb %p] Received empty server list, ignoring.",
+                xdslb_policy);
+      }
+      xds_grpclb_destroy_serverlist(serverlist);
+    }
+  } else {
+    // No valid initial response or serverlist found.
+    char* response_slice_str =
+        grpc_dump_slice(response_slice, GPR_DUMP_ASCII | GPR_DUMP_HEX);
+    gpr_log(GPR_ERROR,
+            "[xdslb %p] Invalid LB response received: '%s'. Ignoring.",
+            xdslb_policy, response_slice_str);
+    gpr_free(response_slice_str);
+  }
+  grpc_slice_unref_internal(response_slice);
+  if (!xdslb_policy->shutting_down_) {
+    // Keep listening for serverlist updates.
+    grpc_op op;
+    memset(&op, 0, sizeof(op));
+    op.op = GRPC_OP_RECV_MESSAGE;
+    op.data.recv_message.recv_message = &lb_calld->recv_message_payload_;
+    op.flags = 0;
+    op.reserved = nullptr;
+    // Reuse the "OnBalancerMessageReceivedLocked" ref taken in StartQuery().
+    const grpc_call_error call_error = grpc_call_start_batch_and_execute(
+        lb_calld->lb_call_, &op, 1,
+        &lb_calld->lb_on_balancer_message_received_);
+    GPR_ASSERT(GRPC_CALL_OK == call_error);
+  } else {
+    lb_calld->Unref(DEBUG_LOCATION, "on_message_received+grpclb_shutdown");
+  }
+}
+
+void XdsLb::BalancerCallState::OnBalancerStatusReceivedLocked(
+    void* arg, grpc_error* error) {
+  BalancerCallState* lb_calld = static_cast<BalancerCallState*>(arg);
+  XdsLb* xdslb_policy = lb_calld->xdslb_policy();
+  GPR_ASSERT(lb_calld->lb_call_ != nullptr);
+  if (grpc_lb_xds_trace.enabled()) {
+    char* status_details =
+        grpc_slice_to_c_string(lb_calld->lb_call_status_details_);
+    gpr_log(GPR_INFO,
+            "[xdslb %p] Status from LB server received. Status = %d, details "
+            "= '%s', (lb_calld: %p, lb_call: %p), error '%s'",
+            xdslb_policy, lb_calld->lb_call_status_, status_details, lb_calld,
+            lb_calld->lb_call_, grpc_error_string(error));
+    gpr_free(status_details);
+  }
+  xdslb_policy->TryReresolutionLocked(&grpc_lb_xds_trace, GRPC_ERROR_NONE);
+  // If this lb_calld is still in use, this call ended because of a failure so
+  // we want to retry connecting. Otherwise, we have deliberately ended this
+  // call and no further action is required.
+  if (lb_calld == xdslb_policy->lb_calld_.get()) {
+    xdslb_policy->lb_calld_.reset();
+    GPR_ASSERT(!xdslb_policy->shutting_down_);
+    if (lb_calld->seen_initial_response_) {
+      // If we lose connection to the LB server, reset the backoff and restart
+      // the LB call immediately.
+      xdslb_policy->lb_call_backoff_.Reset();
+      xdslb_policy->StartBalancerCallLocked();
+    } else {
+      // If this LB call fails establishing any connection to the LB server,
+      // retry later.
+      xdslb_policy->StartBalancerCallRetryTimerLocked();
+    }
+  }
+  lb_calld->Unref(DEBUG_LOCATION, "lb_call_ended");
+}
+
+//
+// helper code for creating balancer channel
+//
+
+grpc_lb_addresses* ExtractBalancerAddresses(
+    const grpc_lb_addresses* addresses) {
+  size_t num_grpclb_addrs = 0;
+  for (size_t i = 0; i < addresses->num_addresses; ++i) {
+    if (addresses->addresses[i].is_balancer) ++num_grpclb_addrs;
+  }
+  // There must be at least one balancer address, or else the
+  // client_channel would not have chosen this LB policy.
+  GPR_ASSERT(num_grpclb_addrs > 0);
+  grpc_lb_addresses* lb_addresses =
+      grpc_lb_addresses_create(num_grpclb_addrs, nullptr);
+  size_t lb_addresses_idx = 0;
+  for (size_t i = 0; i < addresses->num_addresses; ++i) {
+    if (!addresses->addresses[i].is_balancer) continue;
+    if (GPR_UNLIKELY(addresses->addresses[i].user_data != nullptr)) {
+      gpr_log(GPR_ERROR,
+              "This LB policy doesn't support user data. It will be ignored");
+    }
+    grpc_lb_addresses_set_address(
+        lb_addresses, lb_addresses_idx++, addresses->addresses[i].address.addr,
+        addresses->addresses[i].address.len, false /* is balancer */,
+        addresses->addresses[i].balancer_name, nullptr /* user data */);
+  }
+  GPR_ASSERT(num_grpclb_addrs == lb_addresses_idx);
+  return lb_addresses;
+}
+
+/* Returns the channel args for the LB channel, used to create a bidirectional
+ * stream for the reception of load balancing updates.
+ *
+ * Inputs:
+ *   - \a addresses: corresponding to the balancers.
+ *   - \a response_generator: in order to propagate updates from the resolver
+ *   above the grpclb policy.
+ *   - \a args: other args inherited from the grpclb policy. */
+grpc_channel_args* BuildBalancerChannelArgs(
+    const grpc_lb_addresses* addresses,
+    FakeResolverResponseGenerator* response_generator,
+    const grpc_channel_args* args) {
+  grpc_lb_addresses* lb_addresses = ExtractBalancerAddresses(addresses);
+  // Channel args to remove.
+  static const char* args_to_remove[] = {
+      // LB policy name, since we want to use the default (pick_first) in
+      // the LB channel.
+      GRPC_ARG_LB_POLICY_NAME,
+      // The channel arg for the server URI, since that will be different for
+      // the LB channel than for the parent channel.  The client channel
+      // factory will re-add this arg with the right value.
+      GRPC_ARG_SERVER_URI,
+      // The resolved addresses, which will be generated by the name resolver
+      // used in the LB channel.  Note that the LB channel will use the fake
+      // resolver, so this won't actually generate a query to DNS (or some
+      // other name service).  However, the addresses returned by the fake
+      // resolver will have is_balancer=false, whereas our own addresses have
+      // is_balancer=true.  We need the LB channel to return addresses with
+      // is_balancer=false so that it does not wind up recursively using the
+      // grpclb LB policy, as per the special case logic in client_channel.c.
+      GRPC_ARG_LB_ADDRESSES,
+      // The fake resolver response generator, because we are replacing it
+      // with the one from the grpclb policy, used to propagate updates to
+      // the LB channel.
+      GRPC_ARG_FAKE_RESOLVER_RESPONSE_GENERATOR,
+      // The LB channel should use the authority indicated by the target
+      // authority table (see \a grpc_lb_policy_xds_modify_lb_channel_args),
+      // as opposed to the authority from the parent channel.
+      GRPC_ARG_DEFAULT_AUTHORITY,
+      // Just as for \a GRPC_ARG_DEFAULT_AUTHORITY, the LB channel should be
+      // treated as a stand-alone channel and not inherit this argument from the
+      // args of the parent channel.
+      GRPC_SSL_TARGET_NAME_OVERRIDE_ARG,
+  };
+  // Channel args to add.
+  const grpc_arg args_to_add[] = {
+      // New LB addresses.
+      // Note that we pass these in both when creating the LB channel
+      // and via the fake resolver.  The latter is what actually gets used.
+      grpc_lb_addresses_create_channel_arg(lb_addresses),
+      // The fake resolver response generator, which we use to inject
+      // address updates into the LB channel.
+      grpc_core::FakeResolverResponseGenerator::MakeChannelArg(
+          response_generator),
+      // A channel arg indicating the target is a grpclb load balancer.
+      grpc_channel_arg_integer_create(
+          const_cast<char*>(GRPC_ARG_ADDRESS_IS_XDS_LOAD_BALANCER), 1),
+      // A channel arg indicating this is an internal channels, aka it is
+      // owned by components in Core, not by the user application.
+      grpc_channel_arg_integer_create(
+          const_cast<char*>(GRPC_ARG_CHANNELZ_CHANNEL_IS_INTERNAL_CHANNEL), 1),
+  };
+  // Construct channel args.
+  grpc_channel_args* new_args = grpc_channel_args_copy_and_add_and_remove(
+      args, args_to_remove, GPR_ARRAY_SIZE(args_to_remove), args_to_add,
+      GPR_ARRAY_SIZE(args_to_add));
+  // Make any necessary modifications for security.
+  new_args = grpc_lb_policy_xds_modify_lb_channel_args(new_args);
+  // Clean up.
+  grpc_lb_addresses_destroy(lb_addresses);
+  return new_args;
+}
+
+//
+// ctor and dtor
+//
+
+XdsLb::XdsLb(const grpc_lb_addresses* addresses,
+             const LoadBalancingPolicy::Args& args)
+    : LoadBalancingPolicy(args),
+      response_generator_(MakeRefCounted<FakeResolverResponseGenerator>()),
+      lb_call_backoff_(
+          BackOff::Options()
+              .set_initial_backoff(GRPC_XDS_INITIAL_CONNECT_BACKOFF_SECONDS *
+                                   1000)
+              .set_multiplier(GRPC_XDS_RECONNECT_BACKOFF_MULTIPLIER)
+              .set_jitter(GRPC_XDS_RECONNECT_JITTER)
+              .set_max_backoff(GRPC_XDS_RECONNECT_MAX_BACKOFF_SECONDS * 1000)) {
+  // Initialization.
+  gpr_mu_init(&lb_channel_mu_);
+  grpc_subchannel_index_ref();
+  GRPC_CLOSURE_INIT(&lb_channel_on_connectivity_changed_,
+                    &XdsLb::OnBalancerChannelConnectivityChangedLocked, this,
+                    grpc_combiner_scheduler(args.combiner));
+  GRPC_CLOSURE_INIT(&on_rr_connectivity_changed_,
+                    &XdsLb::OnRoundRobinConnectivityChangedLocked, this,
+                    grpc_combiner_scheduler(args.combiner));
+  GRPC_CLOSURE_INIT(&on_rr_request_reresolution_,
+                    &XdsLb::OnRoundRobinRequestReresolutionLocked, this,
+                    grpc_combiner_scheduler(args.combiner));
+  grpc_connectivity_state_init(&state_tracker_, GRPC_CHANNEL_IDLE, "xds");
+  // Record server name.
+  const grpc_arg* arg = grpc_channel_args_find(args.args, GRPC_ARG_SERVER_URI);
+  const char* server_uri = grpc_channel_arg_get_string(arg);
+  GPR_ASSERT(server_uri != nullptr);
+  grpc_uri* uri = grpc_uri_parse(server_uri, true);
+  GPR_ASSERT(uri->path[0] != '\0');
+  server_name_ = gpr_strdup(uri->path[0] == '/' ? uri->path + 1 : uri->path);
+  if (grpc_lb_xds_trace.enabled()) {
+    gpr_log(GPR_INFO,
+            "[xdslb %p] Will use '%s' as the server name for LB request.", this,
+            server_name_);
+  }
+  grpc_uri_destroy(uri);
+  // Record LB call timeout.
+  arg = grpc_channel_args_find(args.args, GRPC_ARG_GRPCLB_CALL_TIMEOUT_MS);
+  lb_call_timeout_ms_ = grpc_channel_arg_get_integer(arg, {0, 0, INT_MAX});
+  // Record fallback timeout.
+  arg = grpc_channel_args_find(args.args, GRPC_ARG_GRPCLB_FALLBACK_TIMEOUT_MS);
+  lb_fallback_timeout_ms_ = grpc_channel_arg_get_integer(
+      arg, {GRPC_XDS_DEFAULT_FALLBACK_TIMEOUT_MS, 0, INT_MAX});
+  // Process channel args.
+  ProcessChannelArgsLocked(*args.args);
+}
+
+XdsLb::~XdsLb() {
+  GPR_ASSERT(pending_picks_ == nullptr);
+  gpr_mu_destroy(&lb_channel_mu_);
+  gpr_free((void*)server_name_);
+  grpc_channel_args_destroy(args_);
+  grpc_connectivity_state_destroy(&state_tracker_);
+  if (serverlist_ != nullptr) {
+    xds_grpclb_destroy_serverlist(serverlist_);
+  }
+  if (fallback_backend_addresses_ != nullptr) {
+    grpc_lb_addresses_destroy(fallback_backend_addresses_);
+  }
+  grpc_subchannel_index_unref();
+}
+
+void XdsLb::ShutdownLocked() {
+  grpc_error* error = GRPC_ERROR_CREATE_FROM_STATIC_STRING("Channel shutdown");
+  shutting_down_ = true;
+  lb_calld_.reset();
+  if (retry_timer_callback_pending_) {
+    grpc_timer_cancel(&lb_call_retry_timer_);
+  }
+  if (fallback_timer_callback_pending_) {
+    grpc_timer_cancel(&lb_fallback_timer_);
+  }
+  rr_policy_.reset();
+  TryReresolutionLocked(&grpc_lb_xds_trace, GRPC_ERROR_CANCELLED);
+  // We destroy the LB channel here instead of in our destructor because
+  // destroying the channel triggers a last callback to
+  // OnBalancerChannelConnectivityChangedLocked(), and we need to be
+  // alive when that callback is invoked.
+  if (lb_channel_ != nullptr) {
+    gpr_mu_lock(&lb_channel_mu_);
+    grpc_channel_destroy(lb_channel_);
+    lb_channel_ = nullptr;
+    gpr_mu_unlock(&lb_channel_mu_);
+  }
+  grpc_connectivity_state_set(&state_tracker_, GRPC_CHANNEL_SHUTDOWN,
+                              GRPC_ERROR_REF(error), "grpclb_shutdown");
+  // Clear pending picks.
+  PendingPick* pp;
+  while ((pp = pending_picks_) != nullptr) {
+    pending_picks_ = pp->next;
+    pp->pick->connected_subchannel.reset();
+    // Note: pp is deleted in this callback.
+    GRPC_CLOSURE_SCHED(&pp->on_complete, GRPC_ERROR_REF(error));
+  }
+  GRPC_ERROR_UNREF(error);
+}
+
+//
+// public methods
+//
+
+void XdsLb::HandOffPendingPicksLocked(LoadBalancingPolicy* new_policy) {
+  PendingPick* pp;
+  while ((pp = pending_picks_) != nullptr) {
+    pending_picks_ = pp->next;
+    pp->pick->on_complete = pp->original_on_complete;
+    pp->pick->user_data = nullptr;
+    grpc_error* error = GRPC_ERROR_NONE;
+    if (new_policy->PickLocked(pp->pick, &error)) {
+      // Synchronous return; schedule closure.
+      GRPC_CLOSURE_SCHED(pp->pick->on_complete, error);
+    }
+    Delete(pp);
+  }
+}
+
+// Cancel a specific pending pick.
+//
+// A grpclb pick progresses as follows:
+// - If there's a Round Robin policy (rr_policy_) available, it'll be
+//   handed over to the RR policy (in CreateRoundRobinPolicyLocked()). From
+//   that point onwards, it'll be RR's responsibility. For cancellations, that
+//   implies the pick needs also be cancelled by the RR instance.
+// - Otherwise, without an RR instance, picks stay pending at this policy's
+//   level (grpclb), inside the pending_picks_ list. To cancel these,
+//   we invoke the completion closure and set the pick's connected
+//   subchannel to nullptr right here.
+void XdsLb::CancelPickLocked(PickState* pick, grpc_error* error) {
+  PendingPick* pp = pending_picks_;
+  pending_picks_ = nullptr;
+  while (pp != nullptr) {
+    PendingPick* next = pp->next;
+    if (pp->pick == pick) {
+      pick->connected_subchannel.reset();
+      // Note: pp is deleted in this callback.
+      GRPC_CLOSURE_SCHED(&pp->on_complete,
+                         GRPC_ERROR_CREATE_REFERENCING_FROM_STATIC_STRING(
+                             "Pick Cancelled", &error, 1));
+    } else {
+      pp->next = pending_picks_;
+      pending_picks_ = pp;
+    }
+    pp = next;
+  }
+  if (rr_policy_ != nullptr) {
+    rr_policy_->CancelPickLocked(pick, GRPC_ERROR_REF(error));
+  }
+  GRPC_ERROR_UNREF(error);
+}
+
+// Cancel all pending picks.
+//
+// A grpclb pick progresses as follows:
+// - If there's a Round Robin policy (rr_policy_) available, it'll be
+//   handed over to the RR policy (in CreateRoundRobinPolicyLocked()). From
+//   that point onwards, it'll be RR's responsibility. For cancellations, that
+//   implies the pick needs also be cancelled by the RR instance.
+// - Otherwise, without an RR instance, picks stay pending at this policy's
+//   level (grpclb), inside the pending_picks_ list. To cancel these,
+//   we invoke the completion closure and set the pick's connected
+//   subchannel to nullptr right here.
+void XdsLb::CancelMatchingPicksLocked(uint32_t initial_metadata_flags_mask,
+                                      uint32_t initial_metadata_flags_eq,
+                                      grpc_error* error) {
+  PendingPick* pp = pending_picks_;
+  pending_picks_ = nullptr;
+  while (pp != nullptr) {
+    PendingPick* next = pp->next;
+    if ((pp->pick->initial_metadata_flags & initial_metadata_flags_mask) ==
+        initial_metadata_flags_eq) {
+      // Note: pp is deleted in this callback.
+      GRPC_CLOSURE_SCHED(&pp->on_complete,
+                         GRPC_ERROR_CREATE_REFERENCING_FROM_STATIC_STRING(
+                             "Pick Cancelled", &error, 1));
+    } else {
+      pp->next = pending_picks_;
+      pending_picks_ = pp;
+    }
+    pp = next;
+  }
+  if (rr_policy_ != nullptr) {
+    rr_policy_->CancelMatchingPicksLocked(initial_metadata_flags_mask,
+                                          initial_metadata_flags_eq,
+                                          GRPC_ERROR_REF(error));
+  }
+  GRPC_ERROR_UNREF(error);
+}
+
+void XdsLb::ExitIdleLocked() {
+  if (!started_picking_) {
+    StartPickingLocked();
+  }
+}
+
+void XdsLb::ResetBackoffLocked() {
+  if (lb_channel_ != nullptr) {
+    grpc_channel_reset_connect_backoff(lb_channel_);
+  }
+  if (rr_policy_ != nullptr) {
+    rr_policy_->ResetBackoffLocked();
+  }
+}
+
+bool XdsLb::PickLocked(PickState* pick, grpc_error** error) {
+  PendingPick* pp = PendingPickCreate(pick);
+  bool pick_done = false;
+  if (rr_policy_ != nullptr) {
+    if (grpc_lb_xds_trace.enabled()) {
+      gpr_log(GPR_INFO, "[xdslb %p] about to PICK from RR %p", this,
+              rr_policy_.get());
+    }
+    pick_done =
+        PickFromRoundRobinPolicyLocked(false /* force_async */, pp, error);
+  } else {  // rr_policy_ == NULL
+    if (pick->on_complete == nullptr) {
+      *error = GRPC_ERROR_CREATE_FROM_STATIC_STRING(
+          "No pick result available but synchronous result required.");
+      pick_done = true;
+    } else {
+      if (grpc_lb_xds_trace.enabled()) {
+        gpr_log(GPR_INFO,
+                "[xdslb %p] No RR policy. Adding to grpclb's pending picks",
+                this);
+      }
+      AddPendingPick(pp);
+      if (!started_picking_) {
+        StartPickingLocked();
+      }
+      pick_done = false;
+    }
+  }
+  return pick_done;
+}
+
+void XdsLb::FillChildRefsForChannelz(channelz::ChildRefsList* child_subchannels,
+                                     channelz::ChildRefsList* child_channels) {
+  // delegate to the RoundRobin to fill the children subchannels.
+  rr_policy_->FillChildRefsForChannelz(child_subchannels, child_channels);
+  MutexLock lock(&lb_channel_mu_);
+  if (lb_channel_ != nullptr) {
+    grpc_core::channelz::ChannelNode* channel_node =
+        grpc_channel_get_channelz_node(lb_channel_);
+    if (channel_node != nullptr) {
+      child_channels->push_back(channel_node->uuid());
+    }
+  }
+}
+
+grpc_connectivity_state XdsLb::CheckConnectivityLocked(
+    grpc_error** connectivity_error) {
+  return grpc_connectivity_state_get(&state_tracker_, connectivity_error);
+}
+
+void XdsLb::NotifyOnStateChangeLocked(grpc_connectivity_state* current,
+                                      grpc_closure* closure) {
+  grpc_connectivity_state_notify_on_state_change(&state_tracker_, current,
+                                                 closure);
+}
+
+void XdsLb::ProcessChannelArgsLocked(const grpc_channel_args& args) {
+  const grpc_arg* arg = grpc_channel_args_find(&args, GRPC_ARG_LB_ADDRESSES);
+  if (GPR_UNLIKELY(arg == nullptr || arg->type != GRPC_ARG_POINTER)) {
+    // Ignore this update.
+    gpr_log(GPR_ERROR,
+            "[xdslb %p] No valid LB addresses channel arg in update, ignoring.",
+            this);
+    return;
+  }
+  const grpc_lb_addresses* addresses =
+      static_cast<const grpc_lb_addresses*>(arg->value.pointer.p);
+  // Update fallback address list.
+  if (fallback_backend_addresses_ != nullptr) {
+    grpc_lb_addresses_destroy(fallback_backend_addresses_);
+  }
+  fallback_backend_addresses_ = ExtractBackendAddresses(addresses);
+  // Make sure that GRPC_ARG_LB_POLICY_NAME is set in channel args,
+  // since we use this to trigger the client_load_reporting filter.
+  static const char* args_to_remove[] = {GRPC_ARG_LB_POLICY_NAME};
+  grpc_arg new_arg = grpc_channel_arg_string_create(
+      (char*)GRPC_ARG_LB_POLICY_NAME, (char*)"xds");
+  grpc_channel_args_destroy(args_);
+  args_ = grpc_channel_args_copy_and_add_and_remove(
+      &args, args_to_remove, GPR_ARRAY_SIZE(args_to_remove), &new_arg, 1);
+  // Construct args for balancer channel.
+  grpc_channel_args* lb_channel_args =
+      BuildBalancerChannelArgs(addresses, response_generator_.get(), &args);
+  // Create balancer channel if needed.
+  if (lb_channel_ == nullptr) {
+    char* uri_str;
+    gpr_asprintf(&uri_str, "fake:///%s", server_name_);
+    gpr_mu_lock(&lb_channel_mu_);
+    lb_channel_ = grpc_client_channel_factory_create_channel(
+        client_channel_factory(), uri_str,
+        GRPC_CLIENT_CHANNEL_TYPE_LOAD_BALANCING, lb_channel_args);
+    gpr_mu_unlock(&lb_channel_mu_);
+    GPR_ASSERT(lb_channel_ != nullptr);
+    gpr_free(uri_str);
+  }
+  // Propagate updates to the LB channel (pick_first) through the fake
+  // resolver.
+  response_generator_->SetResponse(lb_channel_args);
+  grpc_channel_args_destroy(lb_channel_args);
+}
+
+void XdsLb::UpdateLocked(const grpc_channel_args& args) {
+  ProcessChannelArgsLocked(args);
+  // If fallback is configured and the RR policy already exists, update
+  // it with the new fallback addresses.
+  if (lb_fallback_timeout_ms_ > 0 && rr_policy_ != nullptr) {
+    CreateOrUpdateRoundRobinPolicyLocked();
+  }
+  // Start watching the LB channel connectivity for connection, if not
+  // already doing so.
+  if (!watching_lb_channel_) {
+    lb_channel_connectivity_ = grpc_channel_check_connectivity_state(
+        lb_channel_, true /* try to connect */);
+    grpc_channel_element* client_channel_elem = grpc_channel_stack_last_element(
+        grpc_channel_get_channel_stack(lb_channel_));
+    GPR_ASSERT(client_channel_elem->filter == &grpc_client_channel_filter);
+    watching_lb_channel_ = true;
+    // TODO(roth): We currently track this ref manually.  Once the
+    // ClosureRef API is ready, we should pass the RefCountedPtr<> along
+    // with the callback.
+    auto self = Ref(DEBUG_LOCATION, "watch_lb_channel_connectivity");
+    self.release();
+    grpc_client_channel_watch_connectivity_state(
+        client_channel_elem,
+        grpc_polling_entity_create_from_pollset_set(interested_parties()),
+        &lb_channel_connectivity_, &lb_channel_on_connectivity_changed_,
+        nullptr);
+  }
+}
+
+//
+// code for balancer channel and call
+//
+
+void XdsLb::StartPickingLocked() {
+  // Start a timer to fall back.
+  if (lb_fallback_timeout_ms_ > 0 && serverlist_ == nullptr &&
+      !fallback_timer_callback_pending_) {
+    grpc_millis deadline = ExecCtx::Get()->Now() + lb_fallback_timeout_ms_;
+    // TODO(roth): We currently track this ref manually.  Once the
+    // ClosureRef API is ready, we should pass the RefCountedPtr<> along
+    // with the callback.
+    auto self = Ref(DEBUG_LOCATION, "on_fallback_timer");
+    self.release();
+    GRPC_CLOSURE_INIT(&lb_on_fallback_, &XdsLb::OnFallbackTimerLocked, this,
+                      grpc_combiner_scheduler(combiner()));
+    fallback_timer_callback_pending_ = true;
+    grpc_timer_init(&lb_fallback_timer_, deadline, &lb_on_fallback_);
+  }
+  started_picking_ = true;
+  StartBalancerCallLocked();
+}
+
+void XdsLb::StartBalancerCallLocked() {
+  GPR_ASSERT(lb_channel_ != nullptr);
+  if (shutting_down_) return;
+  // Init the LB call data.
+  GPR_ASSERT(lb_calld_ == nullptr);
+  lb_calld_ = MakeOrphanable<BalancerCallState>(Ref());
+  if (grpc_lb_xds_trace.enabled()) {
+    gpr_log(GPR_INFO,
+            "[xdslb %p] Query for backends (lb_channel: %p, lb_calld: %p)",
+            this, lb_channel_, lb_calld_.get());
+  }
+  lb_calld_->StartQuery();
+}
+
+void XdsLb::OnFallbackTimerLocked(void* arg, grpc_error* error) {
+  XdsLb* xdslb_policy = static_cast<XdsLb*>(arg);
+  xdslb_policy->fallback_timer_callback_pending_ = false;
+  // If we receive a serverlist after the timer fires but before this callback
+  // actually runs, don't fall back.
+  if (xdslb_policy->serverlist_ == nullptr && !xdslb_policy->shutting_down_ &&
+      error == GRPC_ERROR_NONE) {
+    if (grpc_lb_xds_trace.enabled()) {
+      gpr_log(GPR_INFO, "[xdslb %p] Falling back to use backends from resolver",
+              xdslb_policy);
+    }
+    GPR_ASSERT(xdslb_policy->fallback_backend_addresses_ != nullptr);
+    xdslb_policy->CreateOrUpdateRoundRobinPolicyLocked();
+  }
+  xdslb_policy->Unref(DEBUG_LOCATION, "on_fallback_timer");
+}
+
+void XdsLb::StartBalancerCallRetryTimerLocked() {
+  grpc_millis next_try = lb_call_backoff_.NextAttemptTime();
+  if (grpc_lb_xds_trace.enabled()) {
+    gpr_log(GPR_INFO, "[xdslb %p] Connection to LB server lost...", this);
+    grpc_millis timeout = next_try - ExecCtx::Get()->Now();
+    if (timeout > 0) {
+      gpr_log(GPR_INFO, "[xdslb %p] ... retry_timer_active in %" PRId64 "ms.",
+              this, timeout);
+    } else {
+      gpr_log(GPR_INFO, "[xdslb %p] ... retry_timer_active immediately.", this);
+    }
+  }
+  // TODO(roth): We currently track this ref manually.  Once the
+  // ClosureRef API is ready, we should pass the RefCountedPtr<> along
+  // with the callback.
+  auto self = Ref(DEBUG_LOCATION, "on_balancer_call_retry_timer");
+  self.release();
+  GRPC_CLOSURE_INIT(&lb_on_call_retry_, &XdsLb::OnBalancerCallRetryTimerLocked,
+                    this, grpc_combiner_scheduler(combiner()));
+  retry_timer_callback_pending_ = true;
+  grpc_timer_init(&lb_call_retry_timer_, next_try, &lb_on_call_retry_);
+}
+
+void XdsLb::OnBalancerCallRetryTimerLocked(void* arg, grpc_error* error) {
+  XdsLb* xdslb_policy = static_cast<XdsLb*>(arg);
+  xdslb_policy->retry_timer_callback_pending_ = false;
+  if (!xdslb_policy->shutting_down_ && error == GRPC_ERROR_NONE &&
+      xdslb_policy->lb_calld_ == nullptr) {
+    if (grpc_lb_xds_trace.enabled()) {
+      gpr_log(GPR_INFO, "[xdslb %p] Restarting call to LB server",
+              xdslb_policy);
+    }
+    xdslb_policy->StartBalancerCallLocked();
+  }
+  xdslb_policy->Unref(DEBUG_LOCATION, "on_balancer_call_retry_timer");
+}
+
+// Invoked as part of the update process. It continues watching the LB channel
+// until it shuts down or becomes READY. It's invoked even if the LB channel
+// stayed READY throughout the update (for example if the update is identical).
+void XdsLb::OnBalancerChannelConnectivityChangedLocked(void* arg,
+                                                       grpc_error* error) {
+  XdsLb* xdslb_policy = static_cast<XdsLb*>(arg);
+  if (xdslb_policy->shutting_down_) goto done;
+  // Re-initialize the lb_call. This should also take care of updating the
+  // embedded RR policy. Note that the current RR policy, if any, will stay in
+  // effect until an update from the new lb_call is received.
+  switch (xdslb_policy->lb_channel_connectivity_) {
+    case GRPC_CHANNEL_CONNECTING:
+    case GRPC_CHANNEL_TRANSIENT_FAILURE: {
+      // Keep watching the LB channel.
+      grpc_channel_element* client_channel_elem =
+          grpc_channel_stack_last_element(
+              grpc_channel_get_channel_stack(xdslb_policy->lb_channel_));
+      GPR_ASSERT(client_channel_elem->filter == &grpc_client_channel_filter);
+      grpc_client_channel_watch_connectivity_state(
+          client_channel_elem,
+          grpc_polling_entity_create_from_pollset_set(
+              xdslb_policy->interested_parties()),
+          &xdslb_policy->lb_channel_connectivity_,
+          &xdslb_policy->lb_channel_on_connectivity_changed_, nullptr);
+      break;
+    }
+      // The LB channel may be IDLE because it's shut down before the update.
+      // Restart the LB call to kick the LB channel into gear.
+    case GRPC_CHANNEL_IDLE:
+    case GRPC_CHANNEL_READY:
+      xdslb_policy->lb_calld_.reset();
+      if (xdslb_policy->started_picking_) {
+        if (xdslb_policy->retry_timer_callback_pending_) {
+          grpc_timer_cancel(&xdslb_policy->lb_call_retry_timer_);
+        }
+        xdslb_policy->lb_call_backoff_.Reset();
+        xdslb_policy->StartBalancerCallLocked();
+      }
+      [[fallthrough]];
+      // Fall through.
+    case GRPC_CHANNEL_SHUTDOWN:
+    done:
+      xdslb_policy->watching_lb_channel_ = false;
+      xdslb_policy->Unref(DEBUG_LOCATION,
+                          "watch_lb_channel_connectivity_cb_shutdown");
+  }
+}
+
+//
+// PendingPick
+//
+
+// Adds lb_token of selected subchannel (address) to the call's initial
+// metadata.
+grpc_error* AddLbTokenToInitialMetadata(
+    grpc_mdelem lb_token, grpc_linked_mdelem* lb_token_mdelem_storage,
+    grpc_metadata_batch* initial_metadata) {
+  GPR_ASSERT(lb_token_mdelem_storage != nullptr);
+  GPR_ASSERT(!GRPC_MDISNULL(lb_token));
+  return grpc_metadata_batch_add_tail(initial_metadata, lb_token_mdelem_storage,
+                                      lb_token);
+}
+
+// Destroy function used when embedding client stats in call context.
+void DestroyClientStats(void* arg) {
+  static_cast<XdsLbClientStats*>(arg)->Unref();
+}
+
+void XdsLb::PendingPickSetMetadataAndContext(PendingPick* pp) {
+  /* if connected_subchannel is nullptr, no pick has been made by the RR
+   * policy (e.g., all addresses failed to connect). There won't be any
+   * user_data/token available */
+  if (pp->pick->connected_subchannel != nullptr) {
+    if (GPR_LIKELY(!GRPC_MDISNULL(pp->lb_token))) {
+      AddLbTokenToInitialMetadata(GRPC_MDELEM_REF(pp->lb_token),
+                                  &pp->pick->lb_token_mdelem_storage,
+                                  pp->pick->initial_metadata);
+    } else {
+      gpr_log(GPR_ERROR,
+              "[xdslb %p] No LB token for connected subchannel pick %p",
+              pp->xdslb_policy, pp->pick);
+      abort();
+    }
+    // Pass on client stats via context. Passes ownership of the reference.
+    if (pp->client_stats != nullptr) {
+      pp->pick->subchannel_call_context[GRPC_GRPCLB_CLIENT_STATS].value =
+          pp->client_stats.release();
+      pp->pick->subchannel_call_context[GRPC_GRPCLB_CLIENT_STATS].destroy =
+          DestroyClientStats;
+    }
+  } else {
+    pp->client_stats.reset();
+  }
+}
+
+/* The \a on_complete closure passed as part of the pick requires keeping a
+ * reference to its associated round robin instance. We wrap this closure in
+ * order to unref the round robin instance upon its invocation */
+void XdsLb::OnPendingPickComplete(void* arg, grpc_error* error) {
+  PendingPick* pp = static_cast<PendingPick*>(arg);
+  PendingPickSetMetadataAndContext(pp);
+  GRPC_CLOSURE_SCHED(pp->original_on_complete, GRPC_ERROR_REF(error));
+  Delete(pp);
+}
+
+XdsLb::PendingPick* XdsLb::PendingPickCreate(PickState* pick) {
+  PendingPick* pp = New<PendingPick>();
+  pp->xdslb_policy = this;
+  pp->pick = pick;
+  GRPC_CLOSURE_INIT(&pp->on_complete, &XdsLb::OnPendingPickComplete, pp,
+                    grpc_schedule_on_exec_ctx);
+  pp->original_on_complete = pick->on_complete;
+  pick->on_complete = &pp->on_complete;
+  return pp;
+}
+
+void XdsLb::AddPendingPick(PendingPick* pp) {
+  pp->next = pending_picks_;
+  pending_picks_ = pp;
+}
+
+//
+// code for interacting with the RR policy
+//
+
+// Performs a pick over \a rr_policy_. Given that a pick can return
+// immediately (ignoring its completion callback), we need to perform the
+// cleanups this callback would otherwise be responsible for.
+// If \a force_async is true, then we will manually schedule the
+// completion callback even if the pick is available immediately.
+bool XdsLb::PickFromRoundRobinPolicyLocked(bool force_async, PendingPick* pp,
+                                           grpc_error** error) {
+  // Check for drops if we are not using fallback backend addresses.
+  if (serverlist_ != nullptr) {
+    // Look at the index into the serverlist to see if we should drop this call.
+    xds_grpclb_server* server = serverlist_->servers[serverlist_index_++];
+    if (serverlist_index_ == serverlist_->num_servers) {
+      serverlist_index_ = 0;  // Wrap-around.
+    }
+    if (server->drop) {
+      // Update client load reporting stats to indicate the number of
+      // dropped calls.  Note that we have to do this here instead of in
+      // the client_load_reporting filter, because we do not create a
+      // subchannel call (and therefore no client_load_reporting filter)
+      // for dropped calls.
+      if (lb_calld_ != nullptr && lb_calld_->client_stats() != nullptr) {
+        lb_calld_->client_stats()->AddCallDroppedLocked(
+            server->load_balance_token);
+      }
+      if (force_async) {
+        GRPC_CLOSURE_SCHED(pp->original_on_complete, GRPC_ERROR_NONE);
+        Delete(pp);
+        return false;
+      }
+      Delete(pp);
+      return true;
+    }
+  }
+  // Set client_stats and user_data.
+  if (lb_calld_ != nullptr && lb_calld_->client_stats() != nullptr) {
+    pp->client_stats = lb_calld_->client_stats()->Ref();
+  }
+  GPR_ASSERT(pp->pick->user_data == nullptr);
+  pp->pick->user_data = (void**)&pp->lb_token;
+  // Pick via the RR policy.
+  bool pick_done = rr_policy_->PickLocked(pp->pick, error);
+  if (pick_done) {
+    PendingPickSetMetadataAndContext(pp);
+    if (force_async) {
+      GRPC_CLOSURE_SCHED(pp->original_on_complete, *error);
+      *error = GRPC_ERROR_NONE;
+      pick_done = false;
+    }
+    Delete(pp);
+  }
+  // else, the pending pick will be registered and taken care of by the
+  // pending pick list inside the RR policy.  Eventually,
+  // OnPendingPickComplete() will be called, which will (among other
+  // things) add the LB token to the call's initial metadata.
+  return pick_done;
+}
+
+void XdsLb::CreateRoundRobinPolicyLocked(const Args& args) {
+  GPR_ASSERT(rr_policy_ == nullptr);
+  rr_policy_ = LoadBalancingPolicyRegistry::CreateLoadBalancingPolicy(
+      "round_robin", args);
+  if (GPR_UNLIKELY(rr_policy_ == nullptr)) {
+    gpr_log(GPR_ERROR, "[xdslb %p] Failure creating a RoundRobin policy", this);
+    return;
+  }
+  // TODO(roth): We currently track this ref manually.  Once the new
+  // ClosureRef API is done, pass the RefCountedPtr<> along with the closure.
+  auto self = Ref(DEBUG_LOCATION, "on_rr_reresolution_requested");
+  self.release();
+  rr_policy_->SetReresolutionClosureLocked(&on_rr_request_reresolution_);
+  grpc_error* rr_state_error = nullptr;
+  rr_connectivity_state_ = rr_policy_->CheckConnectivityLocked(&rr_state_error);
+  // Connectivity state is a function of the RR policy updated/created.
+  UpdateConnectivityStateFromRoundRobinPolicyLocked(rr_state_error);
+  // Add the gRPC LB's interested_parties pollset_set to that of the newly
+  // created RR policy. This will make the RR policy progress upon activity on
+  // gRPC LB, which in turn is tied to the application's call.
+  grpc_pollset_set_add_pollset_set(rr_policy_->interested_parties(),
+                                   interested_parties());
+  // Subscribe to changes to the connectivity of the new RR.
+  // TODO(roth): We currently track this ref manually.  Once the new
+  // ClosureRef API is done, pass the RefCountedPtr<> along with the closure.
+  self = Ref(DEBUG_LOCATION, "on_rr_connectivity_changed");
+  self.release();
+  rr_policy_->NotifyOnStateChangeLocked(&rr_connectivity_state_,
+                                        &on_rr_connectivity_changed_);
+  rr_policy_->ExitIdleLocked();
+  // Send pending picks to RR policy.
+  PendingPick* pp;
+  while ((pp = pending_picks_)) {
+    pending_picks_ = pp->next;
+    if (grpc_lb_xds_trace.enabled()) {
+      gpr_log(GPR_INFO,
+              "[xdslb %p] Pending pick about to (async) PICK from RR %p", this,
+              rr_policy_.get());
+    }
+    grpc_error* error = GRPC_ERROR_NONE;
+    PickFromRoundRobinPolicyLocked(true /* force_async */, pp, &error);
+  }
+}
+
+grpc_channel_args* XdsLb::CreateRoundRobinPolicyArgsLocked() {
+  grpc_lb_addresses* addresses;
+  bool is_backend_from_grpclb_load_balancer = false;
+  if (serverlist_ != nullptr) {
+    GPR_ASSERT(serverlist_->num_servers > 0);
+    addresses = ProcessServerlist(serverlist_);
+    is_backend_from_grpclb_load_balancer = true;
+  } else {
+    // If CreateOrUpdateRoundRobinPolicyLocked() is invoked when we haven't
+    // received any serverlist from the balancer, we use the fallback backends
+    // returned by the resolver. Note that the fallback backend list may be
+    // empty, in which case the new round_robin policy will keep the requested
+    // picks pending.
+    GPR_ASSERT(fallback_backend_addresses_ != nullptr);
+    addresses = grpc_lb_addresses_copy(fallback_backend_addresses_);
+  }
+  GPR_ASSERT(addresses != nullptr);
+  // Replace the LB addresses in the channel args that we pass down to
+  // the subchannel.
+  static const char* keys_to_remove[] = {GRPC_ARG_LB_ADDRESSES};
+  const grpc_arg args_to_add[] = {
+      grpc_lb_addresses_create_channel_arg(addresses),
+      // A channel arg indicating if the target is a backend inferred from a
+      // grpclb load balancer.
+      grpc_channel_arg_integer_create(
+          const_cast<char*>(GRPC_ARG_ADDRESS_IS_BACKEND_FROM_XDS_LOAD_BALANCER),
+          is_backend_from_grpclb_load_balancer),
+  };
+  grpc_channel_args* args = grpc_channel_args_copy_and_add_and_remove(
+      args_, keys_to_remove, GPR_ARRAY_SIZE(keys_to_remove), args_to_add,
+      GPR_ARRAY_SIZE(args_to_add));
+  grpc_lb_addresses_destroy(addresses);
+  return args;
+}
+
+void XdsLb::CreateOrUpdateRoundRobinPolicyLocked() {
+  if (shutting_down_) return;
+  grpc_channel_args* args = CreateRoundRobinPolicyArgsLocked();
+  GPR_ASSERT(args != nullptr);
+  if (rr_policy_ != nullptr) {
+    if (grpc_lb_xds_trace.enabled()) {
+      gpr_log(GPR_INFO, "[xdslb %p] Updating RR policy %p", this,
+              rr_policy_.get());
+    }
+    rr_policy_->UpdateLocked(*args);
+  } else {
+    LoadBalancingPolicy::Args lb_policy_args;
+    lb_policy_args.combiner = combiner();
+    lb_policy_args.client_channel_factory = client_channel_factory();
+    lb_policy_args.args = args;
+    CreateRoundRobinPolicyLocked(lb_policy_args);
+    if (grpc_lb_xds_trace.enabled()) {
+      gpr_log(GPR_INFO, "[xdslb %p] Created new RR policy %p", this,
+              rr_policy_.get());
+    }
+  }
+  grpc_channel_args_destroy(args);
+}
+
+void XdsLb::OnRoundRobinRequestReresolutionLocked(void* arg,
+                                                  grpc_error* error) {
+  XdsLb* xdslb_policy = static_cast<XdsLb*>(arg);
+  if (xdslb_policy->shutting_down_ || error != GRPC_ERROR_NONE) {
+    xdslb_policy->Unref(DEBUG_LOCATION, "on_rr_reresolution_requested");
+    return;
+  }
+  if (grpc_lb_xds_trace.enabled()) {
+    gpr_log(
+        GPR_INFO,
+        "[xdslb %p] Re-resolution requested from the internal RR policy (%p).",
+        xdslb_policy, xdslb_policy->rr_policy_.get());
+  }
+  // If we are talking to a balancer, we expect to get updated addresses form
+  // the balancer, so we can ignore the re-resolution request from the RR
+  // policy. Otherwise, handle the re-resolution request using the
+  // grpclb policy's original re-resolution closure.
+  if (xdslb_policy->lb_calld_ == nullptr ||
+      !xdslb_policy->lb_calld_->seen_initial_response()) {
+    xdslb_policy->TryReresolutionLocked(&grpc_lb_xds_trace, GRPC_ERROR_NONE);
+  }
+  // Give back the wrapper closure to the RR policy.
+  xdslb_policy->rr_policy_->SetReresolutionClosureLocked(
+      &xdslb_policy->on_rr_request_reresolution_);
+}
+
+void XdsLb::UpdateConnectivityStateFromRoundRobinPolicyLocked(
+    grpc_error* rr_state_error) {
+  const grpc_connectivity_state curr_glb_state =
+      grpc_connectivity_state_check(&state_tracker_);
+  /* The new connectivity status is a function of the previous one and the new
+   * input coming from the status of the RR policy.
+   *
+   *  current state (grpclb's)
+   *  |
+   *  v  || I  |  C  |  R  |  TF  |  SD  |  <- new state (RR's)
+   *  ===++====+=====+=====+======+======+
+   *   I || I  |  C  |  R  | [I]  | [I]  |
+   *  ---++----+-----+-----+------+------+
+   *   C || I  |  C  |  R  | [C]  | [C]  |
+   *  ---++----+-----+-----+------+------+
+   *   R || I  |  C  |  R  | [R]  | [R]  |
+   *  ---++----+-----+-----+------+------+
+   *  TF || I  |  C  |  R  | [TF] | [TF] |
+   *  ---++----+-----+-----+------+------+
+   *  SD || NA |  NA |  NA |  NA  |  NA  | (*)
+   *  ---++----+-----+-----+------+------+
+   *
+   * A [STATE] indicates that the old RR policy is kept. In those cases, STATE
+   * is the current state of grpclb, which is left untouched.
+   *
+   *  In summary, if the new state is TRANSIENT_FAILURE or SHUTDOWN, stick to
+   *  the previous RR instance.
+   *
+   *  Note that the status is never updated to SHUTDOWN as a result of calling
+   *  this function. Only glb_shutdown() has the power to set that state.
+   *
+   *  (*) This function mustn't be called during shutting down. */
+  GPR_ASSERT(curr_glb_state != GRPC_CHANNEL_SHUTDOWN);
+  switch (rr_connectivity_state_) {
+    case GRPC_CHANNEL_TRANSIENT_FAILURE:
+    case GRPC_CHANNEL_SHUTDOWN:
+      GPR_ASSERT(rr_state_error != GRPC_ERROR_NONE);
+      break;
+    case GRPC_CHANNEL_IDLE:
+    case GRPC_CHANNEL_CONNECTING:
+    case GRPC_CHANNEL_READY:
+      GPR_ASSERT(rr_state_error == GRPC_ERROR_NONE);
+  }
+  if (grpc_lb_xds_trace.enabled()) {
+    gpr_log(
+        GPR_INFO,
+        "[xdslb %p] Setting grpclb's state to %s from new RR policy %p state.",
+        this, grpc_connectivity_state_name(rr_connectivity_state_),
+        rr_policy_.get());
+  }
+  grpc_connectivity_state_set(&state_tracker_, rr_connectivity_state_,
+                              rr_state_error,
+                              "update_lb_connectivity_status_locked");
+}
+
+void XdsLb::OnRoundRobinConnectivityChangedLocked(void* arg,
+                                                  grpc_error* error) {
+  XdsLb* xdslb_policy = static_cast<XdsLb*>(arg);
+  if (xdslb_policy->shutting_down_) {
+    xdslb_policy->Unref(DEBUG_LOCATION, "on_rr_connectivity_changed");
+    return;
+  }
+  xdslb_policy->UpdateConnectivityStateFromRoundRobinPolicyLocked(
+      GRPC_ERROR_REF(error));
+  // Resubscribe. Reuse the "on_rr_connectivity_changed" ref.
+  xdslb_policy->rr_policy_->NotifyOnStateChangeLocked(
+      &xdslb_policy->rr_connectivity_state_,
+      &xdslb_policy->on_rr_connectivity_changed_);
+}
+
+//
+// factory
+//
+
+class XdsFactory : public LoadBalancingPolicyFactory {
+ public:
+  OrphanablePtr<LoadBalancingPolicy> CreateLoadBalancingPolicy(
+      const LoadBalancingPolicy::Args& args) const override {
+    /* Count the number of gRPC-LB addresses. There must be at least one. */
+    const grpc_arg* arg =
+        grpc_channel_args_find(args.args, GRPC_ARG_LB_ADDRESSES);
+    if (arg == nullptr || arg->type != GRPC_ARG_POINTER) {
+      return nullptr;
+    }
+    grpc_lb_addresses* addresses =
+        static_cast<grpc_lb_addresses*>(arg->value.pointer.p);
+    size_t num_grpclb_addrs = 0;
+    for (size_t i = 0; i < addresses->num_addresses; ++i) {
+      if (addresses->addresses[i].is_balancer) ++num_grpclb_addrs;
+    }
+    if (num_grpclb_addrs == 0) return nullptr;
+    return OrphanablePtr<LoadBalancingPolicy>(New<XdsLb>(addresses, args));
+  }
+
+  const char* name() const override { return "xds"; }
+};
+
+}  // namespace
+
+}  // namespace grpc_core
+
+//
+// Plugin registration
+//
+
+namespace {
+
+// Only add client_load_reporting filter if the grpclb LB policy is used.
+bool maybe_add_client_load_reporting_filter(grpc_channel_stack_builder* builder,
+                                            void* arg) {
+  const grpc_channel_args* args =
+      grpc_channel_stack_builder_get_channel_arguments(builder);
+  const grpc_arg* channel_arg =
+      grpc_channel_args_find(args, GRPC_ARG_LB_POLICY_NAME);
+  if (channel_arg != nullptr && channel_arg->type == GRPC_ARG_STRING &&
+      strcmp(channel_arg->value.string, "grpclb") == 0) {
+    return grpc_channel_stack_builder_append_filter(
+        builder, (const grpc_channel_filter*)arg, nullptr, nullptr);
+  }
+  return true;
+}
+
+}  // namespace
+
+void grpc_lb_policy_xds_init() {
+  grpc_core::LoadBalancingPolicyRegistry::Builder::
+      RegisterLoadBalancingPolicyFactory(
+          grpc_core::UniquePtr<grpc_core::LoadBalancingPolicyFactory>(
+              grpc_core::New<grpc_core::XdsFactory>()));
+  grpc_channel_init_register_stage(GRPC_CLIENT_SUBCHANNEL,
+                                   GRPC_CHANNEL_INIT_BUILTIN_PRIORITY,
+                                   maybe_add_client_load_reporting_filter,
+                                   (void*)&xds_client_load_reporting_filter);
+}
+
+void grpc_lb_policy_xds_shutdown() {}
diff --git a/src/core/ext/filters/client_channel/lb_policy/xds/xds.h b/src/core/ext/filters/client_channel/lb_policy/xds/xds.h
new file mode 100644
index 0000000000..8b20680f2d
--- /dev/null
+++ b/src/core/ext/filters/client_channel/lb_policy/xds/xds.h
@@ -0,0 +1,36 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#ifndef GRPC_CORE_EXT_FILTERS_CLIENT_CHANNEL_LB_POLICY_XDS_XDS_H
+#define GRPC_CORE_EXT_FILTERS_CLIENT_CHANNEL_LB_POLICY_XDS_XDS_H
+
+#include <grpc/support/port_platform.h>
+
+/** Channel arg indicating if a target corresponding to the address is grpclb
+ * loadbalancer. The type of this arg is an integer and the value is treated as
+ * a bool. */
+#define GRPC_ARG_ADDRESS_IS_XDS_LOAD_BALANCER \
+  "grpc.address_is_xds_load_balancer"
+/** Channel arg indicating if a target corresponding to the address is a backend
+ * received from a balancer. The type of this arg is an integer and the value is
+ * treated as a bool. */
+#define GRPC_ARG_ADDRESS_IS_BACKEND_FROM_XDS_LOAD_BALANCER \
+  "grpc.address_is_backend_from_xds_load_balancer"
+
+#endif /* GRPC_CORE_EXT_FILTERS_CLIENT_CHANNEL_LB_POLICY_XDS_XDS_H \
+        */
diff --git a/src/core/ext/filters/client_channel/lb_policy/xds/xds_channel.cc b/src/core/ext/filters/client_channel/lb_policy/xds/xds_channel.cc
new file mode 100644
index 0000000000..0aa145a24e
--- /dev/null
+++ b/src/core/ext/filters/client_channel/lb_policy/xds/xds_channel.cc
@@ -0,0 +1,26 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#include <grpc/support/port_platform.h>
+
+#include "src/core/ext/filters/client_channel/lb_policy/xds/xds_channel.h"
+
+grpc_channel_args* grpc_lb_policy_xds_modify_lb_channel_args(
+    grpc_channel_args* args) {
+  return args;
+}
diff --git a/src/core/ext/filters/client_channel/lb_policy/xds/xds_channel.h b/src/core/ext/filters/client_channel/lb_policy/xds/xds_channel.h
new file mode 100644
index 0000000000..32c4acc8a3
--- /dev/null
+++ b/src/core/ext/filters/client_channel/lb_policy/xds/xds_channel.h
@@ -0,0 +1,36 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#ifndef GRPC_CORE_EXT_FILTERS_CLIENT_CHANNEL_LB_POLICY_XDS_XDS_CHANNEL_H
+#define GRPC_CORE_EXT_FILTERS_CLIENT_CHANNEL_LB_POLICY_XDS_XDS_CHANNEL_H
+
+#include <grpc/support/port_platform.h>
+
+#include "src/core/ext/filters/client_channel/lb_policy_factory.h"
+
+/// Makes any necessary modifications to \a args for use in the xds
+/// balancer channel.
+///
+/// Takes ownership of \a args.
+///
+/// Caller takes ownership of the returned args.
+grpc_channel_args* grpc_lb_policy_xds_modify_lb_channel_args(
+    grpc_channel_args* args);
+
+#endif /* GRPC_CORE_EXT_FILTERS_CLIENT_CHANNEL_LB_POLICY_XDS_XDS_CHANNEL_H \
+        */
diff --git a/src/core/ext/filters/client_channel/lb_policy/xds/xds_channel_secure.cc b/src/core/ext/filters/client_channel/lb_policy/xds/xds_channel_secure.cc
new file mode 100644
index 0000000000..5ab72efce4
--- /dev/null
+++ b/src/core/ext/filters/client_channel/lb_policy/xds/xds_channel_secure.cc
@@ -0,0 +1,107 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#include <grpc/support/port_platform.h>
+
+#include "src/core/ext/filters/client_channel/lb_policy/xds/xds_channel.h"
+
+#include <grpc/support/alloc.h>
+#include <grpc/support/string_util.h>
+#include <string.h>
+
+#include "src/core/ext/filters/client_channel/client_channel.h"
+#include "src/core/lib/channel/channel_args.h"
+#include "src/core/lib/gpr/string.h"
+#include "src/core/lib/iomgr/sockaddr_utils.h"
+#include "src/core/lib/security/credentials/credentials.h"
+#include "src/core/lib/security/transport/target_authority_table.h"
+#include "src/core/lib/slice/slice_internal.h"
+
+namespace grpc_core {
+namespace {
+
+int BalancerNameCmp(const grpc_core::UniquePtr<char>& a,
+                    const grpc_core::UniquePtr<char>& b) {
+  return strcmp(a.get(), b.get());
+}
+
+RefCountedPtr<TargetAuthorityTable> CreateTargetAuthorityTable(
+    grpc_lb_addresses* addresses) {
+  TargetAuthorityTable::Entry* target_authority_entries =
+      static_cast<TargetAuthorityTable::Entry*>(gpr_zalloc(
+          sizeof(*target_authority_entries) * addresses->num_addresses));
+  for (size_t i = 0; i < addresses->num_addresses; ++i) {
+    char* addr_str;
+    GPR_ASSERT(grpc_sockaddr_to_string(
+                   &addr_str, &addresses->addresses[i].address, true) > 0);
+    target_authority_entries[i].key = grpc_slice_from_copied_string(addr_str);
+    target_authority_entries[i].value.reset(
+        gpr_strdup(addresses->addresses[i].balancer_name));
+    gpr_free(addr_str);
+  }
+  RefCountedPtr<TargetAuthorityTable> target_authority_table =
+      TargetAuthorityTable::Create(addresses->num_addresses,
+                                   target_authority_entries, BalancerNameCmp);
+  gpr_free(target_authority_entries);
+  return target_authority_table;
+}
+
+}  // namespace
+}  // namespace grpc_core
+
+grpc_channel_args* grpc_lb_policy_xds_modify_lb_channel_args(
+    grpc_channel_args* args) {
+  const char* args_to_remove[1];
+  size_t num_args_to_remove = 0;
+  grpc_arg args_to_add[2];
+  size_t num_args_to_add = 0;
+  // Add arg for targets info table.
+  const grpc_arg* arg = grpc_channel_args_find(args, GRPC_ARG_LB_ADDRESSES);
+  GPR_ASSERT(arg != nullptr);
+  GPR_ASSERT(arg->type == GRPC_ARG_POINTER);
+  grpc_lb_addresses* addresses =
+      static_cast<grpc_lb_addresses*>(arg->value.pointer.p);
+  grpc_core::RefCountedPtr<grpc_core::TargetAuthorityTable>
+      target_authority_table = grpc_core::CreateTargetAuthorityTable(addresses);
+  args_to_add[num_args_to_add++] =
+      grpc_core::CreateTargetAuthorityTableChannelArg(
+          target_authority_table.get());
+  // Substitute the channel credentials with a version without call
+  // credentials: the load balancer is not necessarily trusted to handle
+  // bearer token credentials.
+  grpc_channel_credentials* channel_credentials =
+      grpc_channel_credentials_find_in_args(args);
+  grpc_channel_credentials* creds_sans_call_creds = nullptr;
+  if (channel_credentials != nullptr) {
+    creds_sans_call_creds =
+        grpc_channel_credentials_duplicate_without_call_credentials(
+            channel_credentials);
+    GPR_ASSERT(creds_sans_call_creds != nullptr);
+    args_to_remove[num_args_to_remove++] = GRPC_ARG_CHANNEL_CREDENTIALS;
+    args_to_add[num_args_to_add++] =
+        grpc_channel_credentials_to_arg(creds_sans_call_creds);
+  }
+  grpc_channel_args* result = grpc_channel_args_copy_and_add_and_remove(
+      args, args_to_remove, num_args_to_remove, args_to_add, num_args_to_add);
+  // Clean up.
+  grpc_channel_args_destroy(args);
+  if (creds_sans_call_creds != nullptr) {
+    grpc_channel_credentials_unref(creds_sans_call_creds);
+  }
+  return result;
+}
diff --git a/src/core/ext/filters/client_channel/lb_policy/xds/xds_client_stats.cc b/src/core/ext/filters/client_channel/lb_policy/xds/xds_client_stats.cc
new file mode 100644
index 0000000000..cdf5408be3
--- /dev/null
+++ b/src/core/ext/filters/client_channel/lb_policy/xds/xds_client_stats.cc
@@ -0,0 +1,85 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#include <grpc/support/port_platform.h>
+
+#include "src/core/ext/filters/client_channel/lb_policy/xds/xds_client_stats.h"
+
+#include <grpc/support/atm.h>
+#include <grpc/support/string_util.h>
+#include <string.h>
+
+namespace grpc_core {
+
+void XdsLbClientStats::AddCallStarted() {
+  gpr_atm_full_fetch_add(&num_calls_started_, (gpr_atm)1);
+}
+
+void XdsLbClientStats::AddCallFinished(bool finished_with_client_failed_to_send,
+                                       bool finished_known_received) {
+  gpr_atm_full_fetch_add(&num_calls_finished_, (gpr_atm)1);
+  if (finished_with_client_failed_to_send) {
+    gpr_atm_full_fetch_add(&num_calls_finished_with_client_failed_to_send_,
+                           (gpr_atm)1);
+  }
+  if (finished_known_received) {
+    gpr_atm_full_fetch_add(&num_calls_finished_known_received_, (gpr_atm)1);
+  }
+}
+
+void XdsLbClientStats::AddCallDroppedLocked(char* token) {
+  // Increment num_calls_started and num_calls_finished.
+  gpr_atm_full_fetch_add(&num_calls_started_, (gpr_atm)1);
+  gpr_atm_full_fetch_add(&num_calls_finished_, (gpr_atm)1);
+  // Record the drop.
+  if (drop_token_counts_ == nullptr) {
+    drop_token_counts_.reset(New<DroppedCallCounts>());
+  }
+  for (size_t i = 0; i < drop_token_counts_->size(); ++i) {
+    if (strcmp((*drop_token_counts_)[i].token.get(), token) == 0) {
+      ++(*drop_token_counts_)[i].count;
+      return;
+    }
+  }
+  // Not found, so add a new entry.
+  drop_token_counts_->emplace_back(UniquePtr<char>(gpr_strdup(token)), 1);
+}
+
+namespace {
+
+void AtomicGetAndResetCounter(int64_t* value, gpr_atm* counter) {
+  *value = static_cast<int64_t>(gpr_atm_full_xchg(counter, (gpr_atm)0));
+}
+
+}  // namespace
+
+void XdsLbClientStats::GetLocked(
+    int64_t* num_calls_started, int64_t* num_calls_finished,
+    int64_t* num_calls_finished_with_client_failed_to_send,
+    int64_t* num_calls_finished_known_received,
+    UniquePtr<DroppedCallCounts>* drop_token_counts) {
+  AtomicGetAndResetCounter(num_calls_started, &num_calls_started_);
+  AtomicGetAndResetCounter(num_calls_finished, &num_calls_finished_);
+  AtomicGetAndResetCounter(num_calls_finished_with_client_failed_to_send,
+                           &num_calls_finished_with_client_failed_to_send_);
+  AtomicGetAndResetCounter(num_calls_finished_known_received,
+                           &num_calls_finished_known_received_);
+  *drop_token_counts = std::move(drop_token_counts_);
+}
+
+}  // namespace grpc_core
diff --git a/src/core/ext/filters/client_channel/lb_policy/xds/xds_client_stats.h b/src/core/ext/filters/client_channel/lb_policy/xds/xds_client_stats.h
new file mode 100644
index 0000000000..fa0b9f4b63
--- /dev/null
+++ b/src/core/ext/filters/client_channel/lb_policy/xds/xds_client_stats.h
@@ -0,0 +1,72 @@
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#ifndef GRPC_CORE_EXT_FILTERS_CLIENT_CHANNEL_LB_POLICY_XDS_XDS_CLIENT_STATS_H
+#define GRPC_CORE_EXT_FILTERS_CLIENT_CHANNEL_LB_POLICY_XDS_XDS_CLIENT_STATS_H
+
+#include <grpc/support/port_platform.h>
+
+#include <grpc/support/atm.h>
+
+#include "src/core/lib/gprpp/inlined_vector.h"
+#include "src/core/lib/gprpp/memory.h"
+#include "src/core/lib/gprpp/ref_counted.h"
+
+namespace grpc_core {
+
+class XdsLbClientStats : public RefCounted<XdsLbClientStats> {
+ public:
+  struct DropTokenCount {
+    UniquePtr<char> token;
+    int64_t count;
+
+    DropTokenCount(UniquePtr<char> token, int64_t count)
+        : token(std::move(token)), count(count) {}
+  };
+
+  typedef InlinedVector<DropTokenCount, 10> DroppedCallCounts;
+
+  XdsLbClientStats() {}
+
+  void AddCallStarted();
+  void AddCallFinished(bool finished_with_client_failed_to_send,
+                       bool finished_known_received);
+
+  // This method is not thread-safe; caller must synchronize.
+  void AddCallDroppedLocked(char* token);
+
+  // This method is not thread-safe; caller must synchronize.
+  void GetLocked(int64_t* num_calls_started, int64_t* num_calls_finished,
+                 int64_t* num_calls_finished_with_client_failed_to_send,
+                 int64_t* num_calls_finished_known_received,
+                 UniquePtr<DroppedCallCounts>* drop_token_counts);
+
+ private:
+  // This field must only be accessed via *_locked() methods.
+  UniquePtr<DroppedCallCounts> drop_token_counts_;
+  // These fields may be accessed from multiple threads at a time.
+  gpr_atm num_calls_started_ = 0;
+  gpr_atm num_calls_finished_ = 0;
+  gpr_atm num_calls_finished_with_client_failed_to_send_ = 0;
+  gpr_atm num_calls_finished_known_received_ = 0;
+};
+
+}  // namespace grpc_core
+
+#endif /* GRPC_CORE_EXT_FILTERS_CLIENT_CHANNEL_LB_POLICY_XDS_XDS_CLIENT_STATS_H \
+        */
diff --git a/src/core/ext/filters/client_channel/subchannel.cc b/src/core/ext/filters/client_channel/subchannel.cc
index 4a668b0fa7..a0a40eb2b3 100644
--- a/src/core/ext/filters/client_channel/subchannel.cc
+++ b/src/core/ext/filters/client_channel/subchannel.cc
@@ -49,6 +49,8 @@
 #include "src/core/lib/surface/channel.h"
 #include "src/core/lib/surface/channel_init.h"
 #include "src/core/lib/transport/connectivity_state.h"
+#include "src/core/lib/transport/error_utils.h"
+#include "src/core/lib/transport/status_metadata.h"
 
 #define INTERNAL_REF_BITS 16
 #define STRONG_REF_MASK (~(gpr_atm)((1 << INTERNAL_REF_BITS) - 1))
@@ -144,6 +146,11 @@ struct grpc_subchannel {
 struct grpc_subchannel_call {
   grpc_core::ConnectedSubchannel* connection;
   grpc_closure* schedule_closure_after_destroy;
+  // state needed to support channelz interception of recv trailing metadata.
+  grpc_closure recv_trailing_metadata_ready;
+  grpc_closure* original_recv_trailing_metadata;
+  grpc_metadata_batch* recv_trailing_metadata;
+  grpc_millis deadline;
 };
 
 #define SUBCHANNEL_CALL_TO_CALL_STACK(call)                          \
@@ -421,6 +428,35 @@ intptr_t grpc_subchannel_get_child_socket_uuid(grpc_subchannel* subchannel) {
   }
 }
 
+static const char* subchannel_connectivity_state_change_string(
+    grpc_connectivity_state state) {
+  switch (state) {
+    case GRPC_CHANNEL_IDLE:
+      return "Subchannel state change to IDLE";
+    case GRPC_CHANNEL_CONNECTING:
+      return "Subchannel state change to CONNECTING";
+    case GRPC_CHANNEL_READY:
+      return "Subchannel state change to READY";
+    case GRPC_CHANNEL_TRANSIENT_FAILURE:
+      return "Subchannel state change to TRANSIENT_FAILURE";
+    case GRPC_CHANNEL_SHUTDOWN:
+      return "Subchannel state change to SHUTDOWN";
+  }
+  GPR_UNREACHABLE_CODE(return "UNKNOWN");
+}
+
+static void set_subchannel_connectivity_state_locked(
+    grpc_subchannel* c, grpc_connectivity_state state, grpc_error* error,
+    const char* reason) {
+  if (c->channelz_subchannel != nullptr) {
+    c->channelz_subchannel->AddTraceEvent(
+        grpc_core::channelz::ChannelTrace::Severity::Info,
+        grpc_slice_from_static_string(
+            subchannel_connectivity_state_change_string(state)));
+  }
+  grpc_connectivity_state_set(&c->state_tracker, state, error, reason);
+}
+
 static void continue_connect_locked(grpc_subchannel* c) {
   grpc_connect_in_args args;
   args.interested_parties = c->pollset_set;
@@ -429,8 +465,8 @@ static void continue_connect_locked(grpc_subchannel* c) {
   c->next_attempt_deadline = c->backoff->NextAttemptTime();
   args.deadline = std::max(c->next_attempt_deadline, min_deadline);
   args.channel_args = c->args;
-  grpc_connectivity_state_set(&c->state_tracker, GRPC_CHANNEL_CONNECTING,
-                              GRPC_ERROR_NONE, "connecting");
+  set_subchannel_connectivity_state_locked(c, GRPC_CHANNEL_CONNECTING,
+                                           GRPC_ERROR_NONE, "connecting");
   grpc_connector_connect(c->connector, &args, &c->connecting_result,
                          &c->on_connected);
 }
@@ -580,9 +616,9 @@ static void on_connected_subchannel_connectivity_changed(void* p,
                       connected_subchannel_watcher->connectivity_state));
         }
         c->connected_subchannel.reset();
-        grpc_connectivity_state_set(&c->state_tracker,
-                                    GRPC_CHANNEL_TRANSIENT_FAILURE,
-                                    GRPC_ERROR_REF(error), "reflect_child");
+        set_subchannel_connectivity_state_locked(
+            c, GRPC_CHANNEL_TRANSIENT_FAILURE, GRPC_ERROR_REF(error),
+            "reflect_child");
         c->backoff_begun = false;
         c->backoff->Reset();
         maybe_start_connecting_locked(c);
@@ -593,8 +629,8 @@ static void on_connected_subchannel_connectivity_changed(void* p,
       break;
     }
     default: {
-      grpc_connectivity_state_set(
-          &c->state_tracker, connected_subchannel_watcher->connectivity_state,
+      set_subchannel_connectivity_state_locked(
+          c, connected_subchannel_watcher->connectivity_state,
           GRPC_ERROR_REF(error), "reflect_child");
       GRPC_SUBCHANNEL_WEAK_REF(c, "state_watcher");
       c->connected_subchannel->NotifyOnStateChange(
@@ -652,7 +688,7 @@ static bool publish_transport_locked(grpc_subchannel* c) {
 
   /* publish */
   c->connected_subchannel.reset(grpc_core::New<grpc_core::ConnectedSubchannel>(
-      stk, c->channelz_subchannel.get(), socket_uuid));
+      stk, c->channelz_subchannel, socket_uuid));
   gpr_log(GPR_INFO, "New connected subchannel at %p for subchannel %p",
           c->connected_subchannel.get(), c);
 
@@ -665,8 +701,8 @@ static bool publish_transport_locked(grpc_subchannel* c) {
       &connected_subchannel_watcher->closure);
 
   /* signal completion */
-  grpc_connectivity_state_set(&c->state_tracker, GRPC_CHANNEL_READY,
-                              GRPC_ERROR_NONE, "connected");
+  set_subchannel_connectivity_state_locked(c, GRPC_CHANNEL_READY,
+                                           GRPC_ERROR_NONE, "connected");
   return true;
 }
 
@@ -683,8 +719,8 @@ static void on_subchannel_connected(void* arg, grpc_error* error) {
   } else if (c->disconnected) {
     GRPC_SUBCHANNEL_WEAK_UNREF(c, "connecting");
   } else {
-    grpc_connectivity_state_set(
-        &c->state_tracker, GRPC_CHANNEL_TRANSIENT_FAILURE,
+    set_subchannel_connectivity_state_locked(
+        c, GRPC_CHANNEL_TRANSIENT_FAILURE,
         grpc_error_set_int(GRPC_ERROR_CREATE_REFERENCING_FROM_STATIC_STRING(
                                "Connect Failed", &error, 1),
                            GRPC_ERROR_INT_GRPC_STATUS, GRPC_STATUS_UNAVAILABLE),
@@ -745,9 +781,71 @@ void grpc_subchannel_call_unref(
   GRPC_CALL_STACK_UNREF(SUBCHANNEL_CALL_TO_CALL_STACK(c), REF_REASON);
 }
 
+// Sets *status based on md_batch and error.
+static void get_call_status(grpc_subchannel_call* call,
+                            grpc_metadata_batch* md_batch, grpc_error* error,
+                            grpc_status_code* status) {
+  if (error != GRPC_ERROR_NONE) {
+    grpc_error_get_status(error, call->deadline, status, nullptr, nullptr,
+                          nullptr);
+  } else {
+    if (md_batch->idx.named.grpc_status != nullptr) {
+      *status = grpc_get_status_code_from_metadata(
+          md_batch->idx.named.grpc_status->md);
+    } else {
+      *status = GRPC_STATUS_UNKNOWN;
+    }
+  }
+  GRPC_ERROR_UNREF(error);
+}
+
+static void recv_trailing_metadata_ready(void* arg, grpc_error* error) {
+  grpc_subchannel_call* call = static_cast<grpc_subchannel_call*>(arg);
+  GPR_ASSERT(call->recv_trailing_metadata != nullptr);
+  grpc_status_code status = GRPC_STATUS_OK;
+  grpc_metadata_batch* md_batch = call->recv_trailing_metadata;
+  get_call_status(call, md_batch, GRPC_ERROR_REF(error), &status);
+  grpc_core::channelz::SubchannelNode* channelz_subchannel =
+      call->connection->channelz_subchannel();
+  GPR_ASSERT(channelz_subchannel != nullptr);
+  if (status == GRPC_STATUS_OK) {
+    channelz_subchannel->RecordCallSucceeded();
+  } else {
+    channelz_subchannel->RecordCallFailed();
+  }
+  GRPC_CLOSURE_RUN(call->original_recv_trailing_metadata,
+                   GRPC_ERROR_REF(error));
+}
+
+// If channelz is enabled, intercept recv_trailing so that we may check the
+// status and associate it to a subchannel.
+static void maybe_intercept_recv_trailing_metadata(
+    grpc_subchannel_call* call, grpc_transport_stream_op_batch* batch) {
+  // only intercept payloads with recv trailing.
+  if (!batch->recv_trailing_metadata) {
+    return;
+  }
+  // only add interceptor is channelz is enabled.
+  if (call->connection->channelz_subchannel() == nullptr) {
+    return;
+  }
+  GRPC_CLOSURE_INIT(&call->recv_trailing_metadata_ready,
+                    recv_trailing_metadata_ready, call,
+                    grpc_schedule_on_exec_ctx);
+  // save some state needed for the interception callback.
+  GPR_ASSERT(call->recv_trailing_metadata == nullptr);
+  call->recv_trailing_metadata =
+      batch->payload->recv_trailing_metadata.recv_trailing_metadata;
+  call->original_recv_trailing_metadata =
+      batch->payload->recv_trailing_metadata.recv_trailing_metadata_ready;
+  batch->payload->recv_trailing_metadata.recv_trailing_metadata_ready =
+      &call->recv_trailing_metadata_ready;
+}
+
 void grpc_subchannel_call_process_op(grpc_subchannel_call* call,
                                      grpc_transport_stream_op_batch* batch) {
   GPR_TIMER_SCOPE("grpc_subchannel_call_process_op", 0);
+  maybe_intercept_recv_trailing_metadata(call, batch);
   grpc_call_stack* call_stack = SUBCHANNEL_CALL_TO_CALL_STACK(call);
   grpc_call_element* top_elem = grpc_call_stack_element(call_stack, 0);
   GRPC_CALL_LOG_OP(GPR_INFO, top_elem, batch);
@@ -822,10 +920,12 @@ namespace grpc_core {
 
 ConnectedSubchannel::ConnectedSubchannel(
     grpc_channel_stack* channel_stack,
-    channelz::SubchannelNode* channelz_subchannel, intptr_t socket_uuid)
+    grpc_core::RefCountedPtr<grpc_core::channelz::SubchannelNode>
+        channelz_subchannel,
+    intptr_t socket_uuid)
     : RefCountedWithTracing<ConnectedSubchannel>(&grpc_trace_stream_refcount),
       channel_stack_(channel_stack),
-      channelz_subchannel_(channelz_subchannel),
+      channelz_subchannel_(std::move(channelz_subchannel)),
       socket_uuid_(socket_uuid) {}
 
 ConnectedSubchannel::~ConnectedSubchannel() {
@@ -872,6 +972,7 @@ grpc_error* ConnectedSubchannel::CreateCall(const CallArgs& args,
       Ref(DEBUG_LOCATION, "subchannel_call");
   connection.release();  // Ref is passed to the grpc_subchannel_call object.
   (*call)->connection = this;
+  (*call)->deadline = args.deadline;
   const grpc_call_element_args call_args = {
       callstk,           /* call_stack */
       nullptr,           /* server_transport_data */
diff --git a/src/core/ext/filters/client_channel/subchannel.h b/src/core/ext/filters/client_channel/subchannel.h
index 699f93a8e7..c53b13e37e 100644
--- a/src/core/ext/filters/client_channel/subchannel.h
+++ b/src/core/ext/filters/client_channel/subchannel.h
@@ -85,9 +85,11 @@ class ConnectedSubchannel : public RefCountedWithTracing<ConnectedSubchannel> {
     size_t parent_data_size;
   };
 
-  explicit ConnectedSubchannel(grpc_channel_stack* channel_stack,
-                               channelz::SubchannelNode* channelz_subchannel,
-                               intptr_t socket_uuid);
+  explicit ConnectedSubchannel(
+      grpc_channel_stack* channel_stack,
+      grpc_core::RefCountedPtr<grpc_core::channelz::SubchannelNode>
+          channelz_subchannel,
+      intptr_t socket_uuid);
   ~ConnectedSubchannel();
 
   grpc_channel_stack* channel_stack() { return channel_stack_; }
@@ -97,15 +99,16 @@ class ConnectedSubchannel : public RefCountedWithTracing<ConnectedSubchannel> {
   void Ping(grpc_closure* on_initiate, grpc_closure* on_ack);
   grpc_error* CreateCall(const CallArgs& args, grpc_subchannel_call** call);
   channelz::SubchannelNode* channelz_subchannel() {
-    return channelz_subchannel_;
+    return channelz_subchannel_.get();
   }
   intptr_t socket_uuid() { return socket_uuid_; }
 
  private:
   grpc_channel_stack* channel_stack_;
-  // backpointer to the channelz node in this connected subchannel's
+  // ref counted pointer to the channelz node in this connected subchannel's
   // owning subchannel.
-  channelz::SubchannelNode* channelz_subchannel_;
+  grpc_core::RefCountedPtr<grpc_core::channelz::SubchannelNode>
+      channelz_subchannel_;
   // uuid of this subchannel's socket. 0 if this subchannel is not connected.
   const intptr_t socket_uuid_;
 };
diff --git a/src/core/ext/filters/http/client_authority_filter.cc b/src/core/ext/filters/http/client_authority_filter.cc
index 1ca20ebb26..6383f12594 100644
--- a/src/core/ext/filters/http/client_authority_filter.cc
+++ b/src/core/ext/filters/http/client_authority_filter.cc
@@ -59,9 +59,8 @@ void authority_start_transport_stream_op_batch(
       initial_metadata->idx.named.authority == nullptr) {
     grpc_error* error = grpc_metadata_batch_add_head(
         initial_metadata, &calld->authority_storage,
-        grpc_mdelem_from_slices(
-            GRPC_MDSTR_AUTHORITY,
-            grpc_slice_ref_internal(chand->default_authority)));
+        grpc_mdelem_create(GRPC_MDSTR_AUTHORITY, chand->default_authority,
+                           nullptr));
     if (error != GRPC_ERROR_NONE) {
       grpc_transport_stream_op_batch_finish_with_failure(batch, error,
                                                          calld->call_combiner);
diff --git a/src/core/ext/transport/chttp2/client/chttp2_connector.cc b/src/core/ext/transport/chttp2/client/chttp2_connector.cc
index 0ac84032fd..5229304fa4 100644
--- a/src/core/ext/transport/chttp2/client/chttp2_connector.cc
+++ b/src/core/ext/transport/chttp2/client/chttp2_connector.cc
@@ -160,7 +160,7 @@ static void on_handshake_done(void* arg, grpc_error* error) {
 static void start_handshake_locked(chttp2_connector* c) {
   c->handshake_mgr = grpc_handshake_manager_create();
   grpc_handshakers_add(HANDSHAKER_CLIENT, c->args.channel_args,
-                       c->handshake_mgr);
+                       c->args.interested_parties, c->handshake_mgr);
   grpc_endpoint_add_to_pollset_set(c->endpoint, c->args.interested_parties);
   grpc_handshake_manager_do_handshake(
       c->handshake_mgr, c->args.interested_parties, c->endpoint,
diff --git a/src/core/ext/transport/chttp2/server/chttp2_server.cc b/src/core/ext/transport/chttp2/server/chttp2_server.cc
index 3f8a26ae32..6ed88dfb5e 100644
--- a/src/core/ext/transport/chttp2/server/chttp2_server.cc
+++ b/src/core/ext/transport/chttp2/server/chttp2_server.cc
@@ -53,6 +53,8 @@ typedef struct {
   grpc_closure tcp_server_shutdown_complete;
   grpc_closure* server_destroy_listener_done;
   grpc_handshake_manager* pending_handshake_mgrs;
+  grpc_core::RefCountedPtr<grpc_core::channelz::ListenSocketNode>
+      channelz_listen_socket;
 } server_state;
 
 typedef struct {
@@ -67,6 +69,7 @@ typedef struct {
   grpc_timer timer;
   grpc_closure on_timeout;
   grpc_closure on_receive_settings;
+  grpc_pollset_set* interested_parties;
 } server_connection_state;
 
 static void server_connection_state_unref(
@@ -76,6 +79,9 @@ static void server_connection_state_unref(
       GRPC_CHTTP2_UNREF_TRANSPORT(connection_state->transport,
                                   "receive settings timeout");
     }
+    grpc_pollset_set_del_pollset(connection_state->interested_parties,
+                                 connection_state->accepting_pollset);
+    grpc_pollset_set_destroy(connection_state->interested_parties);
     gpr_free(connection_state);
   }
 }
@@ -133,7 +139,8 @@ static void on_handshake_done(void* arg, grpc_error* error) {
           grpc_create_chttp2_transport(args->args, args->endpoint, false);
       grpc_server_setup_transport(
           connection_state->svr_state->server, transport,
-          connection_state->accepting_pollset, args->args);
+          connection_state->accepting_pollset, args->args,
+          grpc_chttp2_transport_get_socket_uuid(transport));
       // Use notify_on_receive_settings callback to enforce the
       // handshake deadline.
       connection_state->transport =
@@ -189,7 +196,11 @@ static void on_accept(void* arg, grpc_endpoint* tcp,
   connection_state->accepting_pollset = accepting_pollset;
   connection_state->acceptor = acceptor;
   connection_state->handshake_mgr = handshake_mgr;
+  connection_state->interested_parties = grpc_pollset_set_create();
+  grpc_pollset_set_add_pollset(connection_state->interested_parties,
+                               connection_state->accepting_pollset);
   grpc_handshakers_add(HANDSHAKER_SERVER, state->args,
+                       connection_state->interested_parties,
                        connection_state->handshake_mgr);
   const grpc_arg* timeout_arg =
       grpc_channel_args_find(state->args, GRPC_ARG_SERVER_HANDSHAKE_TIMEOUT_MS);
@@ -223,6 +234,7 @@ static void tcp_server_shutdown_complete(void* arg, grpc_error* error) {
   GPR_ASSERT(state->shutdown);
   grpc_handshake_manager_pending_list_shutdown_all(
       state->pending_handshake_mgrs, GRPC_ERROR_REF(error));
+  state->channelz_listen_socket.reset();
   gpr_mu_unlock(&state->mu);
   // Flush queued work before destroying handshaker factory, since that
   // may do a synchronous unref.
@@ -262,6 +274,8 @@ grpc_error* grpc_chttp2_server_add_port(grpc_server* server, const char* addr,
   server_state* state = nullptr;
   grpc_error** errors = nullptr;
   size_t naddrs = 0;
+  const grpc_arg* arg = nullptr;
+  intptr_t socket_uuid = 0;
 
   *port_num = -1;
 
@@ -323,9 +337,16 @@ grpc_error* grpc_chttp2_server_add_port(grpc_server* server, const char* addr,
   }
   grpc_resolved_addresses_destroy(resolved);
 
+  arg = grpc_channel_args_find(args, GRPC_ARG_ENABLE_CHANNELZ);
+  if (grpc_channel_arg_get_bool(arg, false)) {
+    state->channelz_listen_socket =
+        grpc_core::MakeRefCounted<grpc_core::channelz::ListenSocketNode>();
+    socket_uuid = state->channelz_listen_socket->uuid();
+  }
+
   /* Register with the server only upon success */
   grpc_server_add_listener(server, state, server_start_listener,
-                           server_destroy_listener);
+                           server_destroy_listener, socket_uuid);
   goto done;
 
 /* Error path: cleanup and return */
diff --git a/src/core/ext/transport/chttp2/server/insecure/server_chttp2_posix.cc b/src/core/ext/transport/chttp2/server/insecure/server_chttp2_posix.cc
index e4bd91d07b..b9024a87e2 100644
--- a/src/core/ext/transport/chttp2/server/insecure/server_chttp2_posix.cc
+++ b/src/core/ext/transport/chttp2/server/insecure/server_chttp2_posix.cc
@@ -61,7 +61,7 @@ void grpc_server_add_insecure_channel_from_fd(grpc_server* server,
     grpc_endpoint_add_to_pollset(server_endpoint, pollsets[i]);
   }
 
-  grpc_server_setup_transport(server, transport, nullptr, server_args);
+  grpc_server_setup_transport(server, transport, nullptr, server_args, 0);
   grpc_chttp2_transport_start_reading(transport, nullptr, nullptr);
 }
 
diff --git a/src/core/ext/transport/chttp2/transport/chttp2_transport.cc b/src/core/ext/transport/chttp2/transport/chttp2_transport.cc
index 2d4b4da4c6..8a481bb7d5 100644
--- a/src/core/ext/transport/chttp2/transport/chttp2_transport.cc
+++ b/src/core/ext/transport/chttp2/transport/chttp2_transport.cc
@@ -2128,8 +2128,7 @@ void grpc_chttp2_fake_status(grpc_chttp2_transport* t, grpc_chttp2_stream* s,
           "add_status_message",
           grpc_chttp2_incoming_metadata_buffer_replace_or_add(
               &s->metadata_buffer[1],
-              grpc_mdelem_from_slices(GRPC_MDSTR_GRPC_MESSAGE,
-                                      grpc_slice_ref_internal(slice))));
+              grpc_mdelem_create(GRPC_MDSTR_GRPC_MESSAGE, slice, nullptr)));
     }
     s->published_metadata[1] = GRPC_METADATA_SYNTHESIZED_FROM_FAKE;
     grpc_chttp2_maybe_complete_recv_trailing_metadata(t, s);
diff --git a/src/core/ext/transport/inproc/inproc_transport.cc b/src/core/ext/transport/inproc/inproc_transport.cc
index b0ca7f8207..9dbd095843 100644
--- a/src/core/ext/transport/inproc/inproc_transport.cc
+++ b/src/core/ext/transport/inproc/inproc_transport.cc
@@ -1256,7 +1256,9 @@ grpc_channel* grpc_inproc_channel_create(grpc_server* server,
   inproc_transports_create(&server_transport, server_args, &client_transport,
                            client_args);
 
-  grpc_server_setup_transport(server, server_transport, nullptr, server_args);
+  // TODO(ncteisen): design and support channelz GetSocket for inproc.
+  grpc_server_setup_transport(server, server_transport, nullptr, server_args,
+                              0);
   grpc_channel* channel = grpc_channel_create(
       "inproc", client_args, GRPC_CLIENT_DIRECT_CHANNEL, client_transport);
 
diff --git a/src/core/lib/channel/channelz.cc b/src/core/lib/channel/channelz.cc
index 573292fba1..33577d890a 100644
--- a/src/core/lib/channel/channelz.cc
+++ b/src/core/lib/channel/channelz.cc
@@ -37,13 +37,16 @@
 #include "src/core/lib/iomgr/exec_ctx.h"
 #include "src/core/lib/slice/slice_internal.h"
 #include "src/core/lib/surface/channel.h"
+#include "src/core/lib/surface/server.h"
 #include "src/core/lib/transport/error_utils.h"
 
 namespace grpc_core {
 namespace channelz {
 
-BaseNode::BaseNode(EntityType type)
-    : type_(type), uuid_(ChannelzRegistry::Register(this)) {}
+BaseNode::BaseNode(EntityType type) : type_(type), uuid_(-1) {
+  // The registry will set uuid_ under its lock.
+  ChannelzRegistry::Register(this);
+}
 
 BaseNode::~BaseNode() { ChannelzRegistry::Unregister(uuid_); }
 
@@ -190,11 +193,45 @@ RefCountedPtr<ChannelNode> ChannelNode::MakeChannelNode(
       channel, channel_tracer_max_nodes, is_top_level_channel);
 }
 
-ServerNode::ServerNode(size_t channel_tracer_max_nodes)
-    : BaseNode(EntityType::kServer), trace_(channel_tracer_max_nodes) {}
+ServerNode::ServerNode(grpc_server* server, size_t channel_tracer_max_nodes)
+    : BaseNode(EntityType::kServer),
+      server_(server),
+      trace_(channel_tracer_max_nodes) {}
 
 ServerNode::~ServerNode() {}
 
+char* ServerNode::RenderServerSockets(intptr_t start_socket_id) {
+  grpc_json* top_level_json = grpc_json_create(GRPC_JSON_OBJECT);
+  grpc_json* json = top_level_json;
+  grpc_json* json_iterator = nullptr;
+  ChildRefsList socket_refs;
+  // uuids index into entities one-off (idx 0 is really uuid 1, since 0 is
+  // reserved). However, we want to support requests coming in with
+  // start_server_id=0, which signifies "give me everything."
+  size_t start_idx = start_socket_id == 0 ? 0 : start_socket_id - 1;
+  grpc_server_populate_server_sockets(server_, &socket_refs, start_idx);
+  if (!socket_refs.empty()) {
+    // create list of socket refs
+    grpc_json* array_parent = grpc_json_create_child(
+        nullptr, json, "socketRef", nullptr, GRPC_JSON_ARRAY, false);
+    for (size_t i = 0; i < socket_refs.size(); ++i) {
+      json_iterator =
+          grpc_json_create_child(json_iterator, array_parent, nullptr, nullptr,
+                                 GRPC_JSON_OBJECT, false);
+      grpc_json_add_number_string_child(json_iterator, nullptr, "socketId",
+                                        socket_refs[i]);
+    }
+  }
+  // For now we do not have any pagination rules. In the future we could
+  // pick a constant for max_channels_sent for a GetServers request.
+  // Tracking: https://github.com/grpc/grpc/issues/16019.
+  json_iterator = grpc_json_create_child(nullptr, json, "end", nullptr,
+                                         GRPC_JSON_TRUE, false);
+  char* json_str = grpc_json_dump_to_string(top_level_json, 0);
+  grpc_json_destroy(top_level_json);
+  return json_str;
+}
+
 grpc_json* ServerNode::RenderJson() {
   // We need to track these three json objects to build our object
   grpc_json* top_level_json = grpc_json_create(GRPC_JSON_OBJECT);
@@ -223,6 +260,20 @@ grpc_json* ServerNode::RenderJson() {
   }
   // ask CallCountingHelper to populate trace and call count data.
   call_counter_.PopulateCallCounts(json);
+  json = top_level_json;
+  ChildRefsList listen_sockets;
+  grpc_server_populate_listen_sockets(server_, &listen_sockets);
+  if (!listen_sockets.empty()) {
+    grpc_json* array_parent = grpc_json_create_child(
+        nullptr, json, "listenSocket", nullptr, GRPC_JSON_ARRAY, false);
+    for (size_t i = 0; i < listen_sockets.size(); ++i) {
+      json_iterator =
+          grpc_json_create_child(json_iterator, array_parent, nullptr, nullptr,
+                                 GRPC_JSON_OBJECT, false);
+      grpc_json_add_number_string_child(json_iterator, nullptr, "socketId",
+                                        listen_sockets[i]);
+    }
+  }
   return top_level_json;
 }
 
@@ -323,5 +374,22 @@ grpc_json* SocketNode::RenderJson() {
   return top_level_json;
 }
 
+ListenSocketNode::ListenSocketNode() : BaseNode(EntityType::kSocket) {}
+
+grpc_json* ListenSocketNode::RenderJson() {
+  // We need to track these three json objects to build our object
+  grpc_json* top_level_json = grpc_json_create(GRPC_JSON_OBJECT);
+  grpc_json* json = top_level_json;
+  grpc_json* json_iterator = nullptr;
+  // create and fill the ref child
+  json_iterator = grpc_json_create_child(json_iterator, json, "ref", nullptr,
+                                         GRPC_JSON_OBJECT, false);
+  json = json_iterator;
+  json_iterator = nullptr;
+  json_iterator = grpc_json_add_number_string_child(json, json_iterator,
+                                                    "socketId", uuid());
+  return top_level_json;
+}
+
 }  // namespace channelz
 }  // namespace grpc_core
diff --git a/src/core/lib/channel/channelz.h b/src/core/lib/channel/channelz.h
index 3f728cda6d..88551befc8 100644
--- a/src/core/lib/channel/channelz.h
+++ b/src/core/lib/channel/channelz.h
@@ -24,6 +24,7 @@
 #include <grpc/grpc.h>
 
 #include "src/core/lib/channel/channel_trace.h"
+#include "src/core/lib/gprpp/inlined_vector.h"
 #include "src/core/lib/gprpp/manual_constructor.h"
 #include "src/core/lib/gprpp/ref_counted.h"
 #include "src/core/lib/gprpp/ref_counted_ptr.h"
@@ -41,17 +42,23 @@
 
 /** This is the default value for whether or not to enable channelz. If
  * GRPC_ARG_ENABLE_CHANNELZ is set, it will override this default value. */
-#define GRPC_ENABLE_CHANNELZ_DEFAULT false
+#define GRPC_ENABLE_CHANNELZ_DEFAULT true
 
 /** This is the default value for the maximum amount of memory used by trace
  * events per channel trace node. If
  * GRPC_ARG_MAX_CHANNEL_TRACE_EVENT_MEMORY_PER_NODE is set, it will override
  * this default value. */
-#define GRPC_MAX_CHANNEL_TRACE_EVENT_MEMORY_PER_NODE_DEFAULT 0
+#define GRPC_MAX_CHANNEL_TRACE_EVENT_MEMORY_PER_NODE_DEFAULT 1024 * 4
 
 namespace grpc_core {
+
 namespace channelz {
 
+// TODO(ncteisen), this only contains the uuids of the children for now,
+// since that is all that is strictly needed. In a future enhancement we will
+// add human readable names as in the channelz.proto
+typedef InlinedVector<intptr_t, 10> ChildRefsList;
+
 namespace testing {
 class CallCountingHelperPeer;
 class ChannelNodePeer;
@@ -85,8 +92,10 @@ class BaseNode : public RefCounted<BaseNode> {
   intptr_t uuid() const { return uuid_; }
 
  private:
+  // to allow the ChannelzRegistry to set uuid_ under its lock.
+  friend class ChannelzRegistry;
   const EntityType type_;
-  const intptr_t uuid_;
+  intptr_t uuid_;
 };
 
 // This class is a helper class for channelz entities that deal with Channels,
@@ -193,11 +202,13 @@ class ChannelNode : public BaseNode {
 // Handles channelz bookkeeping for servers
 class ServerNode : public BaseNode {
  public:
-  explicit ServerNode(size_t channel_tracer_max_nodes);
+  ServerNode(grpc_server* server, size_t channel_tracer_max_nodes);
   ~ServerNode() override;
 
   grpc_json* RenderJson() override;
 
+  char* RenderServerSockets(intptr_t start_socket_id);
+
   // proxy methods to composed classes.
   void AddTraceEvent(ChannelTrace::Severity severity, grpc_slice data) {
     trace_.AddTraceEvent(severity, data);
@@ -213,6 +224,7 @@ class ServerNode : public BaseNode {
   void RecordCallSucceeded() { call_counter_.RecordCallSucceeded(); }
 
  private:
+  grpc_server* server_;
   CallCountingHelper call_counter_;
   ChannelTrace trace_;
 };
@@ -253,6 +265,15 @@ class SocketNode : public BaseNode {
   UniquePtr<char> peer_string_;
 };
 
+// Handles channelz bookkeeping for listen sockets
+class ListenSocketNode : public BaseNode {
+ public:
+  ListenSocketNode();
+  ~ListenSocketNode() override {}
+
+  grpc_json* RenderJson() override;
+};
+
 // Creation functions
 
 typedef RefCountedPtr<ChannelNode> (*ChannelNodeCreationFunc)(grpc_channel*,
diff --git a/src/core/lib/channel/channelz_registry.cc b/src/core/lib/channel/channelz_registry.cc
index 841f1c6104..e90a9e1f7f 100644
--- a/src/core/lib/channel/channelz_registry.cc
+++ b/src/core/lib/channel/channelz_registry.cc
@@ -38,6 +38,8 @@ namespace {
 // singleton instance of the registry.
 ChannelzRegistry* g_channelz_registry = nullptr;
 
+const int kPaginationLimit = 100;
+
 }  // anonymous namespace
 
 void ChannelzRegistry::Init() { g_channelz_registry = New<ChannelzRegistry>(); }
@@ -53,29 +55,78 @@ ChannelzRegistry::ChannelzRegistry() { gpr_mu_init(&mu_); }
 
 ChannelzRegistry::~ChannelzRegistry() { gpr_mu_destroy(&mu_); }
 
-intptr_t ChannelzRegistry::InternalRegister(BaseNode* node) {
+void ChannelzRegistry::InternalRegister(BaseNode* node) {
   MutexLock lock(&mu_);
   entities_.push_back(node);
-  intptr_t uuid = entities_.size();
-  return uuid;
+  node->uuid_ = ++uuid_generator_;
+}
+
+void ChannelzRegistry::MaybePerformCompactionLocked() {
+  constexpr double kEmptinessTheshold = 1 / 3;
+  double emptiness_ratio =
+      double(num_empty_slots_) / double(entities_.capacity());
+  if (emptiness_ratio > kEmptinessTheshold) {
+    int front = 0;
+    for (size_t i = 0; i < entities_.size(); ++i) {
+      if (entities_[i] != nullptr) {
+        entities_[front++] = entities_[i];
+      }
+    }
+    for (int i = 0; i < num_empty_slots_; ++i) {
+      entities_.pop_back();
+    }
+    num_empty_slots_ = 0;
+  }
+}
+
+int ChannelzRegistry::FindByUuidLocked(intptr_t target_uuid) {
+  size_t left = 0;
+  size_t right = entities_.size() - 1;
+  while (left <= right) {
+    size_t true_middle = left + (right - left) / 2;
+    size_t first_non_null = true_middle;
+    while (first_non_null < right && entities_[first_non_null] == nullptr) {
+      first_non_null++;
+    }
+    if (entities_[first_non_null] == nullptr) {
+      right = true_middle - 1;
+      continue;
+    }
+    intptr_t uuid = entities_[first_non_null]->uuid();
+    if (uuid == target_uuid) {
+      return int(first_non_null);
+    }
+    if (uuid < target_uuid) {
+      left = first_non_null + 1;
+    } else {
+      right = true_middle - 1;
+    }
+  }
+  return -1;
 }
 
 void ChannelzRegistry::InternalUnregister(intptr_t uuid) {
   GPR_ASSERT(uuid >= 1);
   MutexLock lock(&mu_);
-  GPR_ASSERT(static_cast<size_t>(uuid) <= entities_.size());
-  entities_[uuid - 1] = nullptr;
+  GPR_ASSERT(uuid <= uuid_generator_);
+  int idx = FindByUuidLocked(uuid);
+  GPR_ASSERT(idx >= 0);
+  entities_[idx] = nullptr;
+  num_empty_slots_++;
+  MaybePerformCompactionLocked();
 }
 
 BaseNode* ChannelzRegistry::InternalGet(intptr_t uuid) {
   MutexLock lock(&mu_);
-  if (uuid < 1 || uuid > static_cast<intptr_t>(entities_.size())) {
+  if (uuid < 1 || uuid > uuid_generator_) {
     return nullptr;
   }
-  return entities_[uuid - 1];
+  int idx = FindByUuidLocked(uuid);
+  return idx < 0 ? nullptr : entities_[idx];
 }
 
 char* ChannelzRegistry::InternalGetTopChannels(intptr_t start_channel_id) {
+  MutexLock lock(&mu_);
   grpc_json* top_level_json = grpc_json_create(GRPC_JSON_OBJECT);
   grpc_json* json = top_level_json;
   grpc_json* json_iterator = nullptr;
@@ -85,10 +136,18 @@ char* ChannelzRegistry::InternalGetTopChannels(intptr_t start_channel_id) {
   // start_channel_id=0, which signifies "give me everything." Hence this
   // funky looking line below.
   size_t start_idx = start_channel_id == 0 ? 0 : start_channel_id - 1;
+  bool reached_pagination_limit = false;
   for (size_t i = start_idx; i < entities_.size(); ++i) {
     if (entities_[i] != nullptr &&
         entities_[i]->type() ==
             grpc_core::channelz::BaseNode::EntityType::kTopLevelChannel) {
+      // check if we are over pagination limit to determine if we need to set
+      // the "end" element. If we don't go through this block, we know that
+      // when the loop terminates, we have <= to kPaginationLimit.
+      if (top_level_channels.size() == kPaginationLimit) {
+        reached_pagination_limit = true;
+        break;
+      }
       top_level_channels.push_back(entities_[i]);
     }
   }
@@ -102,17 +161,17 @@ char* ChannelzRegistry::InternalGetTopChannels(intptr_t start_channel_id) {
           grpc_json_link_child(array_parent, channel_json, json_iterator);
     }
   }
-  // For now we do not have any pagination rules. In the future we could
-  // pick a constant for max_channels_sent for a GetTopChannels request.
-  // Tracking: https://github.com/grpc/grpc/issues/16019.
-  json_iterator = grpc_json_create_child(nullptr, json, "end", nullptr,
-                                         GRPC_JSON_TRUE, false);
+  if (!reached_pagination_limit) {
+    grpc_json_create_child(nullptr, json, "end", nullptr, GRPC_JSON_TRUE,
+                           false);
+  }
   char* json_str = grpc_json_dump_to_string(top_level_json, 0);
   grpc_json_destroy(top_level_json);
   return json_str;
 }
 
 char* ChannelzRegistry::InternalGetServers(intptr_t start_server_id) {
+  MutexLock lock(&mu_);
   grpc_json* top_level_json = grpc_json_create(GRPC_JSON_OBJECT);
   grpc_json* json = top_level_json;
   grpc_json* json_iterator = nullptr;
@@ -121,10 +180,18 @@ char* ChannelzRegistry::InternalGetServers(intptr_t start_server_id) {
   // reserved). However, we want to support requests coming in with
   // start_server_id=0, which signifies "give me everything."
   size_t start_idx = start_server_id == 0 ? 0 : start_server_id - 1;
+  bool reached_pagination_limit = false;
   for (size_t i = start_idx; i < entities_.size(); ++i) {
     if (entities_[i] != nullptr &&
         entities_[i]->type() ==
             grpc_core::channelz::BaseNode::EntityType::kServer) {
+      // check if we are over pagination limit to determine if we need to set
+      // the "end" element. If we don't go through this block, we know that
+      // when the loop terminates, we have <= to kPaginationLimit.
+      if (servers.size() == kPaginationLimit) {
+        reached_pagination_limit = true;
+        break;
+      }
       servers.push_back(entities_[i]);
     }
   }
@@ -138,11 +205,10 @@ char* ChannelzRegistry::InternalGetServers(intptr_t start_server_id) {
           grpc_json_link_child(array_parent, server_json, json_iterator);
     }
   }
-  // For now we do not have any pagination rules. In the future we could
-  // pick a constant for max_channels_sent for a GetServers request.
-  // Tracking: https://github.com/grpc/grpc/issues/16019.
-  json_iterator = grpc_json_create_child(nullptr, json, "end", nullptr,
-                                         GRPC_JSON_TRUE, false);
+  if (!reached_pagination_limit) {
+    grpc_json_create_child(nullptr, json, "end", nullptr, GRPC_JSON_TRUE,
+                           false);
+  }
   char* json_str = grpc_json_dump_to_string(top_level_json, 0);
   grpc_json_destroy(top_level_json);
   return json_str;
@@ -160,6 +226,21 @@ char* grpc_channelz_get_servers(intptr_t start_server_id) {
   return grpc_core::channelz::ChannelzRegistry::GetServers(start_server_id);
 }
 
+char* grpc_channelz_get_server_sockets(intptr_t server_id,
+                                       intptr_t start_socket_id) {
+  grpc_core::channelz::BaseNode* base_node =
+      grpc_core::channelz::ChannelzRegistry::Get(server_id);
+  if (base_node == nullptr ||
+      base_node->type() != grpc_core::channelz::BaseNode::EntityType::kServer) {
+    return nullptr;
+  }
+  // This cast is ok since we have just checked to make sure base_node is
+  // actually a server node
+  grpc_core::channelz::ServerNode* server_node =
+      static_cast<grpc_core::channelz::ServerNode*>(base_node);
+  return server_node->RenderServerSockets(start_socket_id);
+}
+
 char* grpc_channelz_get_channel(intptr_t channel_id) {
   grpc_core::channelz::BaseNode* channel_node =
       grpc_core::channelz::ChannelzRegistry::Get(channel_id);
diff --git a/src/core/lib/channel/channelz_registry.h b/src/core/lib/channel/channelz_registry.h
index d0d660600d..ea6ab6c8e5 100644
--- a/src/core/lib/channel/channelz_registry.h
+++ b/src/core/lib/channel/channelz_registry.h
@@ -30,6 +30,10 @@
 namespace grpc_core {
 namespace channelz {
 
+namespace testing {
+class ChannelzRegistryPeer;
+}
+
 // singleton registry object to track all objects that are needed to support
 // channelz bookkeeping. All objects share globally distributed uuids.
 class ChannelzRegistry {
@@ -40,7 +44,7 @@ class ChannelzRegistry {
   // To be called in grpc_shutdown();
   static void Shutdown();
 
-  static intptr_t Register(BaseNode* node) {
+  static void Register(BaseNode* node) {
     return Default()->InternalRegister(node);
   }
   static void Unregister(intptr_t uuid) { Default()->InternalUnregister(uuid); }
@@ -61,6 +65,7 @@ class ChannelzRegistry {
  private:
   GPRC_ALLOW_CLASS_TO_USE_NON_PUBLIC_NEW
   GPRC_ALLOW_CLASS_TO_USE_NON_PUBLIC_DELETE
+  friend class testing::ChannelzRegistryPeer;
 
   ChannelzRegistry();
   ~ChannelzRegistry();
@@ -69,7 +74,7 @@ class ChannelzRegistry {
   static ChannelzRegistry* Default();
 
   // globally registers an Entry. Returns its unique uuid
-  intptr_t InternalRegister(BaseNode* node);
+  void InternalRegister(BaseNode* node);
 
   // globally unregisters the object that is associated to uuid. Also does
   // sanity check that an object doesn't try to unregister the wrong type.
@@ -82,9 +87,18 @@ class ChannelzRegistry {
   char* InternalGetTopChannels(intptr_t start_channel_id);
   char* InternalGetServers(intptr_t start_server_id);
 
-  // protects entities_ and uuid_
+  // If entities_ has over a certain threshold of empty slots, it will
+  // compact the vector and move all used slots to the front.
+  void MaybePerformCompactionLocked();
+
+  // Performs binary search on entities_ to find the index with that uuid.
+  int FindByUuidLocked(intptr_t uuid);
+
+  // protects members
   gpr_mu mu_;
   InlinedVector<BaseNode*, 20> entities_;
+  intptr_t uuid_generator_ = 0;
+  int num_empty_slots_ = 0;
 };
 
 }  // namespace channelz
diff --git a/src/core/lib/channel/handshaker_factory.cc b/src/core/lib/channel/handshaker_factory.cc
index 4fd43635b6..8ade8fe4e2 100644
--- a/src/core/lib/channel/handshaker_factory.cc
+++ b/src/core/lib/channel/handshaker_factory.cc
@@ -24,11 +24,12 @@
 
 void grpc_handshaker_factory_add_handshakers(
     grpc_handshaker_factory* handshaker_factory, const grpc_channel_args* args,
+    grpc_pollset_set* interested_parties,
     grpc_handshake_manager* handshake_mgr) {
   if (handshaker_factory != nullptr) {
     GPR_ASSERT(handshaker_factory->vtable != nullptr);
-    handshaker_factory->vtable->add_handshakers(handshaker_factory, args,
-                                                handshake_mgr);
+    handshaker_factory->vtable->add_handshakers(
+        handshaker_factory, args, interested_parties, handshake_mgr);
   }
 }
 
diff --git a/src/core/lib/channel/handshaker_factory.h b/src/core/lib/channel/handshaker_factory.h
index 3e45fcf20e..e17a678179 100644
--- a/src/core/lib/channel/handshaker_factory.h
+++ b/src/core/lib/channel/handshaker_factory.h
@@ -32,6 +32,7 @@ typedef struct grpc_handshaker_factory grpc_handshaker_factory;
 typedef struct {
   void (*add_handshakers)(grpc_handshaker_factory* handshaker_factory,
                           const grpc_channel_args* args,
+                          grpc_pollset_set* interested_parties,
                           grpc_handshake_manager* handshake_mgr);
   void (*destroy)(grpc_handshaker_factory* handshaker_factory);
 } grpc_handshaker_factory_vtable;
@@ -42,6 +43,7 @@ struct grpc_handshaker_factory {
 
 void grpc_handshaker_factory_add_handshakers(
     grpc_handshaker_factory* handshaker_factory, const grpc_channel_args* args,
+    grpc_pollset_set* interested_parties,
     grpc_handshake_manager* handshake_mgr);
 
 void grpc_handshaker_factory_destroy(
diff --git a/src/core/lib/channel/handshaker_registry.cc b/src/core/lib/channel/handshaker_registry.cc
index eec3e1b352..fbafc43e79 100644
--- a/src/core/lib/channel/handshaker_registry.cc
+++ b/src/core/lib/channel/handshaker_registry.cc
@@ -51,9 +51,11 @@ static void grpc_handshaker_factory_list_register(
 
 static void grpc_handshaker_factory_list_add_handshakers(
     grpc_handshaker_factory_list* list, const grpc_channel_args* args,
+    grpc_pollset_set* interested_parties,
     grpc_handshake_manager* handshake_mgr) {
   for (size_t i = 0; i < list->num_factories; ++i) {
-    grpc_handshaker_factory_add_handshakers(list->list[i], args, handshake_mgr);
+    grpc_handshaker_factory_add_handshakers(list->list[i], args,
+                                            interested_parties, handshake_mgr);
   }
 }
 
@@ -91,7 +93,9 @@ void grpc_handshaker_factory_register(bool at_start,
 
 void grpc_handshakers_add(grpc_handshaker_type handshaker_type,
                           const grpc_channel_args* args,
+                          grpc_pollset_set* interested_parties,
                           grpc_handshake_manager* handshake_mgr) {
   grpc_handshaker_factory_list_add_handshakers(
-      &g_handshaker_factory_lists[handshaker_type], args, handshake_mgr);
+      &g_handshaker_factory_lists[handshaker_type], args, interested_parties,
+      handshake_mgr);
 }
diff --git a/src/core/lib/channel/handshaker_registry.h b/src/core/lib/channel/handshaker_registry.h
index 82ad9c5b9a..3dd4316de6 100644
--- a/src/core/lib/channel/handshaker_registry.h
+++ b/src/core/lib/channel/handshaker_registry.h
@@ -43,6 +43,7 @@ void grpc_handshaker_factory_register(bool at_start,
 
 void grpc_handshakers_add(grpc_handshaker_type handshaker_type,
                           const grpc_channel_args* args,
+                          grpc_pollset_set* interested_parties,
                           grpc_handshake_manager* handshake_mgr);
 
 #endif /* GRPC_CORE_LIB_CHANNEL_HANDSHAKER_REGISTRY_H */
diff --git a/src/core/lib/gprpp/inlined_vector.h b/src/core/lib/gprpp/inlined_vector.h
index 76e2f0a785..65c2b9634f 100644
--- a/src/core/lib/gprpp/inlined_vector.h
+++ b/src/core/lib/gprpp/inlined_vector.h
@@ -123,6 +123,14 @@ class InlinedVector {
 
   void push_back(T&& value) { emplace_back(std::move(value)); }
 
+  void pop_back() {
+    assert(!empty());
+    size_t s = size();
+    T& value = data()[s - 1];
+    value.~T();
+    size_--;
+  }
+
   void copy_from(const InlinedVector& v) {
     // if v is allocated, copy over the buffer.
     if (v.dynamic_ != nullptr) {
diff --git a/src/core/lib/http/httpcli_security_connector.cc b/src/core/lib/http/httpcli_security_connector.cc
index 50078c37a1..5a5e0b72d5 100644
--- a/src/core/lib/http/httpcli_security_connector.cc
+++ b/src/core/lib/http/httpcli_security_connector.cc
@@ -29,6 +29,7 @@
 #include "src/core/lib/channel/channel_args.h"
 #include "src/core/lib/channel/handshaker_registry.h"
 #include "src/core/lib/gpr/string.h"
+#include "src/core/lib/iomgr/pollset.h"
 #include "src/core/lib/security/transport/security_handshaker.h"
 #include "src/core/lib/slice/slice_internal.h"
 #include "src/core/tsi/ssl_transport_security.h"
@@ -51,6 +52,7 @@ static void httpcli_ssl_destroy(grpc_security_connector* sc) {
 }
 
 static void httpcli_ssl_add_handshakers(grpc_channel_security_connector* sc,
+                                        grpc_pollset_set* interested_parties,
                                         grpc_handshake_manager* handshake_mgr) {
   grpc_httpcli_ssl_channel_security_connector* c =
       reinterpret_cast<grpc_httpcli_ssl_channel_security_connector*>(sc);
@@ -189,7 +191,8 @@ static void ssl_handshake(void* arg, grpc_endpoint* tcp, const char* host,
   grpc_arg channel_arg = grpc_security_connector_to_arg(&sc->base);
   grpc_channel_args args = {1, &channel_arg};
   c->handshake_mgr = grpc_handshake_manager_create();
-  grpc_handshakers_add(HANDSHAKER_CLIENT, &args, c->handshake_mgr);
+  grpc_handshakers_add(HANDSHAKER_CLIENT, &args,
+                       nullptr /* interested_parties */, c->handshake_mgr);
   grpc_handshake_manager_do_handshake(
       c->handshake_mgr, nullptr /* interested_parties */, tcp,
       nullptr /* channel_args */, deadline, nullptr /* acceptor */,
diff --git a/src/core/lib/iomgr/ev_posix.cc b/src/core/lib/iomgr/ev_posix.cc
index 764fb08142..8a7dc7b004 100644
--- a/src/core/lib/iomgr/ev_posix.cc
+++ b/src/core/lib/iomgr/ev_posix.cc
@@ -395,6 +395,4 @@ void grpc_pollset_set_del_fd(grpc_pollset_set* pollset_set, grpc_fd* fd) {
   g_event_engine->pollset_set_del_fd(pollset_set, fd);
 }
 
-void grpc_use_signal(int signum) {}
-
 #endif  // GRPC_POSIX_SOCKET_EV
diff --git a/src/core/lib/iomgr/socket_utils_common_posix.cc b/src/core/lib/iomgr/socket_utils_common_posix.cc
index 50674b0845..bdfc1d70c3 100644
--- a/src/core/lib/iomgr/socket_utils_common_posix.cc
+++ b/src/core/lib/iomgr/socket_utils_common_posix.cc
@@ -307,7 +307,10 @@ grpc_error* grpc_set_socket_tcp_user_timeout(
     }
   }
 #else
-  gpr_log(GPR_INFO, "TCP_USER_TIMEOUT not supported for this platform");
+  extern grpc_core::TraceFlag grpc_tcp_trace;
+  if (grpc_tcp_trace.enabled()) {
+    gpr_log(GPR_INFO, "TCP_USER_TIMEOUT not supported for this platform");
+  }
 #endif /* GRPC_HAVE_TCP_USER_TIMEOUT */
   return GRPC_ERROR_NONE;
 }
diff --git a/src/core/lib/iomgr/tcp_posix.cc b/src/core/lib/iomgr/tcp_posix.cc
index e40bf81c90..aa2704ce26 100644
--- a/src/core/lib/iomgr/tcp_posix.cc
+++ b/src/core/lib/iomgr/tcp_posix.cc
@@ -468,7 +468,9 @@ static void tcp_do_read(grpc_tcp* tcp) {
     GRPC_STATS_INC_TCP_READ_SIZE(read_bytes);
     add_to_estimate(tcp, static_cast<size_t>(read_bytes));
     GPR_ASSERT((size_t)read_bytes <= tcp->incoming_buffer->length);
-    if (static_cast<size_t>(read_bytes) < tcp->incoming_buffer->length) {
+    if (static_cast<size_t>(read_bytes) == tcp->incoming_buffer->length) {
+      finish_estimate(tcp);
+    } else if (static_cast<size_t>(read_bytes) < tcp->incoming_buffer->length) {
       grpc_slice_buffer_trim_end(
           tcp->incoming_buffer,
           tcp->incoming_buffer->length - static_cast<size_t>(read_bytes),
@@ -498,7 +500,7 @@ static void tcp_read_allocation_done(void* tcpp, grpc_error* error) {
 
 static void tcp_continue_read(grpc_tcp* tcp) {
   size_t target_read_size = get_target_read_size(tcp);
-  if (tcp->incoming_buffer->length < target_read_size &&
+  if (tcp->incoming_buffer->length < target_read_size / 2 &&
       tcp->incoming_buffer->count < MAX_READ_IOVEC) {
     if (grpc_tcp_trace.enabled()) {
       gpr_log(GPR_INFO, "TCP:%p alloc_slices", tcp);
diff --git a/src/core/lib/iomgr/timer_manager.cc b/src/core/lib/iomgr/timer_manager.cc
index 54f19a9259..ceba79f678 100644
--- a/src/core/lib/iomgr/timer_manager.cc
+++ b/src/core/lib/iomgr/timer_manager.cc
@@ -245,7 +245,7 @@ static void timer_main_loop() {
           gpr_log(GPR_INFO, "timers not checked: expect another thread to");
         }
         next = GRPC_MILLIS_INF_FUTURE;
-      /* fall through */
+      // fallthrough
       case GRPC_TIMERS_CHECKED_AND_EMPTY:
         if (!wait_until(next)) {
           return;
diff --git a/src/core/lib/iomgr/wakeup_fd_eventfd.cc b/src/core/lib/iomgr/wakeup_fd_eventfd.cc
index dcf7dab71f..d68c9ada1f 100644
--- a/src/core/lib/iomgr/wakeup_fd_eventfd.cc
+++ b/src/core/lib/iomgr/wakeup_fd_eventfd.cc
@@ -32,12 +32,11 @@
 #include "src/core/lib/profiling/timers.h"
 
 static grpc_error* eventfd_create(grpc_wakeup_fd* fd_info) {
-  int efd = eventfd(0, EFD_NONBLOCK | EFD_CLOEXEC);
-  if (efd < 0) {
+  fd_info->read_fd = eventfd(0, EFD_NONBLOCK | EFD_CLOEXEC);
+  fd_info->write_fd = -1;
+  if (fd_info->read_fd < 0) {
     return GRPC_OS_ERROR(errno, "eventfd");
   }
-  fd_info->read_fd = efd;
-  fd_info->write_fd = -1;
   return GRPC_ERROR_NONE;
 }
 
diff --git a/src/core/lib/security/credentials/plugin/plugin_credentials.cc b/src/core/lib/security/credentials/plugin/plugin_credentials.cc
index 73946ce039..4015124298 100644
--- a/src/core/lib/security/credentials/plugin/plugin_credentials.cc
+++ b/src/core/lib/security/credentials/plugin/plugin_credentials.cc
@@ -102,8 +102,7 @@ static grpc_error* process_plugin_result(
     } else {
       for (size_t i = 0; i < num_md; ++i) {
         grpc_mdelem mdelem =
-            grpc_mdelem_from_slices(grpc_slice_ref_internal(md[i].key),
-                                    grpc_slice_ref_internal(md[i].value));
+            grpc_mdelem_create(md[i].key, md[i].value, nullptr);
         grpc_credentials_mdelem_array_add(r->md_array, mdelem);
         GRPC_MDELEM_UNREF(mdelem);
       }
diff --git a/src/core/lib/security/security_connector/alts_security_connector.cc b/src/core/lib/security/security_connector/alts_security_connector.cc
index 35a787871a..d38c0ff044 100644
--- a/src/core/lib/security/security_connector/alts_security_connector.cc
+++ b/src/core/lib/security/security_connector/alts_security_connector.cc
@@ -64,29 +64,29 @@ static void alts_server_destroy(grpc_security_connector* sc) {
 }
 
 static void alts_channel_add_handshakers(
-    grpc_channel_security_connector* sc,
+    grpc_channel_security_connector* sc, grpc_pollset_set* interested_parties,
     grpc_handshake_manager* handshake_manager) {
   tsi_handshaker* handshaker = nullptr;
   auto c = reinterpret_cast<grpc_alts_channel_security_connector*>(sc);
   grpc_alts_credentials* creds =
       reinterpret_cast<grpc_alts_credentials*>(c->base.channel_creds);
-  GPR_ASSERT(alts_tsi_handshaker_create(creds->options, c->target_name,
-                                        creds->handshaker_service_url, true,
-                                        &handshaker) == TSI_OK);
+  GPR_ASSERT(alts_tsi_handshaker_create(
+                 creds->options, c->target_name, creds->handshaker_service_url,
+                 true, interested_parties, &handshaker) == TSI_OK);
   grpc_handshake_manager_add(handshake_manager, grpc_security_handshaker_create(
                                                     handshaker, &sc->base));
 }
 
 static void alts_server_add_handshakers(
-    grpc_server_security_connector* sc,
+    grpc_server_security_connector* sc, grpc_pollset_set* interested_parties,
     grpc_handshake_manager* handshake_manager) {
   tsi_handshaker* handshaker = nullptr;
   auto c = reinterpret_cast<grpc_alts_server_security_connector*>(sc);
   grpc_alts_server_credentials* creds =
       reinterpret_cast<grpc_alts_server_credentials*>(c->base.server_creds);
-  GPR_ASSERT(alts_tsi_handshaker_create(creds->options, nullptr,
-                                        creds->handshaker_service_url, false,
-                                        &handshaker) == TSI_OK);
+  GPR_ASSERT(alts_tsi_handshaker_create(
+                 creds->options, nullptr, creds->handshaker_service_url, false,
+                 interested_parties, &handshaker) == TSI_OK);
   grpc_handshake_manager_add(handshake_manager, grpc_security_handshaker_create(
                                                     handshaker, &sc->base));
 }
diff --git a/src/core/lib/security/security_connector/local_security_connector.cc b/src/core/lib/security/security_connector/local_security_connector.cc
index c436a7906b..911013ae58 100644
--- a/src/core/lib/security/security_connector/local_security_connector.cc
+++ b/src/core/lib/security/security_connector/local_security_connector.cc
@@ -30,6 +30,7 @@
 
 #include "src/core/ext/filters/client_channel/client_channel.h"
 #include "src/core/lib/channel/channel_args.h"
+#include "src/core/lib/iomgr/pollset.h"
 #include "src/core/lib/security/credentials/local/local_credentials.h"
 #include "src/core/lib/security/transport/security_handshaker.h"
 #include "src/core/tsi/local_transport_security.h"
@@ -68,7 +69,7 @@ static void local_server_destroy(grpc_security_connector* sc) {
 }
 
 static void local_channel_add_handshakers(
-    grpc_channel_security_connector* sc,
+    grpc_channel_security_connector* sc, grpc_pollset_set* interested_parties,
     grpc_handshake_manager* handshake_manager) {
   tsi_handshaker* handshaker = nullptr;
   GPR_ASSERT(local_tsi_handshaker_create(true /* is_client */, &handshaker) ==
@@ -78,7 +79,7 @@ static void local_channel_add_handshakers(
 }
 
 static void local_server_add_handshakers(
-    grpc_server_security_connector* sc,
+    grpc_server_security_connector* sc, grpc_pollset_set* interested_parties,
     grpc_handshake_manager* handshake_manager) {
   tsi_handshaker* handshaker = nullptr;
   GPR_ASSERT(local_tsi_handshaker_create(false /* is_client */, &handshaker) ==
diff --git a/src/core/lib/security/security_connector/security_connector.cc b/src/core/lib/security/security_connector/security_connector.cc
index 6246613e7b..7028ae8d16 100644
--- a/src/core/lib/security/security_connector/security_connector.cc
+++ b/src/core/lib/security/security_connector/security_connector.cc
@@ -120,17 +120,19 @@ const tsi_peer_property* tsi_peer_get_property_by_name(const tsi_peer* peer,
 
 void grpc_channel_security_connector_add_handshakers(
     grpc_channel_security_connector* connector,
+    grpc_pollset_set* interested_parties,
     grpc_handshake_manager* handshake_mgr) {
   if (connector != nullptr) {
-    connector->add_handshakers(connector, handshake_mgr);
+    connector->add_handshakers(connector, interested_parties, handshake_mgr);
   }
 }
 
 void grpc_server_security_connector_add_handshakers(
     grpc_server_security_connector* connector,
+    grpc_pollset_set* interested_parties,
     grpc_handshake_manager* handshake_mgr) {
   if (connector != nullptr) {
-    connector->add_handshakers(connector, handshake_mgr);
+    connector->add_handshakers(connector, interested_parties, handshake_mgr);
   }
 }
 
@@ -519,7 +521,7 @@ static void fake_channel_cancel_check_call_host(
 }
 
 static void fake_channel_add_handshakers(
-    grpc_channel_security_connector* sc,
+    grpc_channel_security_connector* sc, grpc_pollset_set* interested_parties,
     grpc_handshake_manager* handshake_mgr) {
   grpc_handshake_manager_add(
       handshake_mgr,
@@ -528,6 +530,7 @@ static void fake_channel_add_handshakers(
 }
 
 static void fake_server_add_handshakers(grpc_server_security_connector* sc,
+                                        grpc_pollset_set* interested_parties,
                                         grpc_handshake_manager* handshake_mgr) {
   grpc_handshake_manager_add(
       handshake_mgr,
@@ -669,6 +672,7 @@ static void ssl_server_destroy(grpc_security_connector* sc) {
 }
 
 static void ssl_channel_add_handshakers(grpc_channel_security_connector* sc,
+                                        grpc_pollset_set* interested_parties,
                                         grpc_handshake_manager* handshake_mgr) {
   grpc_ssl_channel_security_connector* c =
       reinterpret_cast<grpc_ssl_channel_security_connector*>(sc);
@@ -779,6 +783,7 @@ static bool try_fetch_ssl_server_credentials(
 }
 
 static void ssl_server_add_handshakers(grpc_server_security_connector* sc,
+                                       grpc_pollset_set* interested_parties,
                                        grpc_handshake_manager* handshake_mgr) {
   grpc_ssl_server_security_connector* c =
       reinterpret_cast<grpc_ssl_server_security_connector*>(sc);
diff --git a/src/core/lib/security/security_connector/security_connector.h b/src/core/lib/security/security_connector/security_connector.h
index 67a506b576..d8df3cd72f 100644
--- a/src/core/lib/security/security_connector/security_connector.h
+++ b/src/core/lib/security/security_connector/security_connector.h
@@ -27,6 +27,7 @@
 
 #include "src/core/lib/channel/handshaker.h"
 #include "src/core/lib/iomgr/endpoint.h"
+#include "src/core/lib/iomgr/pollset.h"
 #include "src/core/lib/iomgr/tcp_server.h"
 #include "src/core/tsi/ssl_transport_security.h"
 #include "src/core/tsi/transport_security_interface.h"
@@ -125,6 +126,7 @@ struct grpc_channel_security_connector {
                                  grpc_closure* on_call_host_checked,
                                  grpc_error* error);
   void (*add_handshakers)(grpc_channel_security_connector* sc,
+                          grpc_pollset_set* interested_parties,
                           grpc_handshake_manager* handshake_mgr);
 };
 
@@ -151,6 +153,7 @@ void grpc_channel_security_connector_cancel_check_call_host(
 /* Registers handshakers with \a handshake_mgr. */
 void grpc_channel_security_connector_add_handshakers(
     grpc_channel_security_connector* connector,
+    grpc_pollset_set* interested_parties,
     grpc_handshake_manager* handshake_mgr);
 
 /* --- server_security_connector object. ---
@@ -164,6 +167,7 @@ struct grpc_server_security_connector {
   grpc_security_connector base;
   grpc_server_credentials* server_creds;
   void (*add_handshakers)(grpc_server_security_connector* sc,
+                          grpc_pollset_set* interested_parties,
                           grpc_handshake_manager* handshake_mgr);
 };
 
@@ -172,7 +176,8 @@ int grpc_server_security_connector_cmp(grpc_server_security_connector* sc1,
                                        grpc_server_security_connector* sc2);
 
 void grpc_server_security_connector_add_handshakers(
-    grpc_server_security_connector* sc, grpc_handshake_manager* handshake_mgr);
+    grpc_server_security_connector* sc, grpc_pollset_set* interested_parties,
+    grpc_handshake_manager* handshake_mgr);
 
 /* --- Creation security connectors. --- */
 
diff --git a/src/core/lib/security/transport/security_handshaker.cc b/src/core/lib/security/transport/security_handshaker.cc
index d76d582638..4d6b133809 100644
--- a/src/core/lib/security/transport/security_handshaker.cc
+++ b/src/core/lib/security/transport/security_handshaker.cc
@@ -475,22 +475,24 @@ static grpc_handshaker* fail_handshaker_create() {
 
 static void client_handshaker_factory_add_handshakers(
     grpc_handshaker_factory* handshaker_factory, const grpc_channel_args* args,
+    grpc_pollset_set* interested_parties,
     grpc_handshake_manager* handshake_mgr) {
   grpc_channel_security_connector* security_connector =
       reinterpret_cast<grpc_channel_security_connector*>(
           grpc_security_connector_find_in_args(args));
-  grpc_channel_security_connector_add_handshakers(security_connector,
-                                                  handshake_mgr);
+  grpc_channel_security_connector_add_handshakers(
+      security_connector, interested_parties, handshake_mgr);
 }
 
 static void server_handshaker_factory_add_handshakers(
     grpc_handshaker_factory* hf, const grpc_channel_args* args,
+    grpc_pollset_set* interested_parties,
     grpc_handshake_manager* handshake_mgr) {
   grpc_server_security_connector* security_connector =
       reinterpret_cast<grpc_server_security_connector*>(
           grpc_security_connector_find_in_args(args));
-  grpc_server_security_connector_add_handshakers(security_connector,
-                                                 handshake_mgr);
+  grpc_server_security_connector_add_handshakers(
+      security_connector, interested_parties, handshake_mgr);
 }
 
 static void handshaker_factory_destroy(
diff --git a/src/core/lib/surface/channel.cc b/src/core/lib/surface/channel.cc
index 4294434504..d7095c24d4 100644
--- a/src/core/lib/surface/channel.cc
+++ b/src/core/lib/surface/channel.cc
@@ -336,9 +336,8 @@ grpc_call* grpc_channel_create_call(grpc_channel* channel,
   grpc_core::ExecCtx exec_ctx;
   grpc_call* call = grpc_channel_create_call_internal(
       channel, parent_call, propagation_mask, cq, nullptr,
-      grpc_mdelem_from_slices(GRPC_MDSTR_PATH, grpc_slice_ref_internal(method)),
-      host != nullptr ? grpc_mdelem_from_slices(GRPC_MDSTR_AUTHORITY,
-                                                grpc_slice_ref_internal(*host))
+      grpc_mdelem_create(GRPC_MDSTR_PATH, method, nullptr),
+      host != nullptr ? grpc_mdelem_create(GRPC_MDSTR_AUTHORITY, *host, nullptr)
                       : GRPC_MDNULL,
       grpc_timespec_to_millis_round_up(deadline));
 
@@ -347,14 +346,13 @@ grpc_call* grpc_channel_create_call(grpc_channel* channel,
 
 grpc_call* grpc_channel_create_pollset_set_call(
     grpc_channel* channel, grpc_call* parent_call, uint32_t propagation_mask,
-    grpc_pollset_set* pollset_set, grpc_slice method, const grpc_slice* host,
-    grpc_millis deadline, void* reserved) {
+    grpc_pollset_set* pollset_set, const grpc_slice& method,
+    const grpc_slice* host, grpc_millis deadline, void* reserved) {
   GPR_ASSERT(!reserved);
   return grpc_channel_create_call_internal(
       channel, parent_call, propagation_mask, nullptr, pollset_set,
-      grpc_mdelem_from_slices(GRPC_MDSTR_PATH, grpc_slice_ref_internal(method)),
-      host != nullptr ? grpc_mdelem_from_slices(GRPC_MDSTR_AUTHORITY,
-                                                grpc_slice_ref_internal(*host))
+      grpc_mdelem_create(GRPC_MDSTR_PATH, method, nullptr),
+      host != nullptr ? grpc_mdelem_create(GRPC_MDSTR_AUTHORITY, *host, nullptr)
                       : GRPC_MDNULL,
       deadline);
 }
diff --git a/src/core/lib/surface/channel.h b/src/core/lib/surface/channel.h
index e5ff2c3596..4ac76b8a29 100644
--- a/src/core/lib/surface/channel.h
+++ b/src/core/lib/surface/channel.h
@@ -45,8 +45,8 @@ grpc_channel* grpc_channel_create_with_builder(
     value of \a propagation_mask (see propagation_bits.h for possible values) */
 grpc_call* grpc_channel_create_pollset_set_call(
     grpc_channel* channel, grpc_call* parent_call, uint32_t propagation_mask,
-    grpc_pollset_set* pollset_set, grpc_slice method, const grpc_slice* host,
-    grpc_millis deadline, void* reserved);
+    grpc_pollset_set* pollset_set, const grpc_slice& method,
+    const grpc_slice* host, grpc_millis deadline, void* reserved);
 
 /** Get a (borrowed) pointer to this channels underlying channel stack */
 grpc_channel_stack* grpc_channel_get_channel_stack(grpc_channel* channel);
diff --git a/src/core/lib/surface/completion_queue.cc b/src/core/lib/surface/completion_queue.cc
index 5dc9991f70..b81ae73b4d 100644
--- a/src/core/lib/surface/completion_queue.cc
+++ b/src/core/lib/surface/completion_queue.cc
@@ -79,6 +79,7 @@ typedef struct non_polling_worker {
 
 typedef struct {
   gpr_mu mu;
+  bool kicked_without_poller;
   non_polling_worker* root;
   grpc_closure* shutdown;
 } non_polling_poller;
@@ -103,6 +104,10 @@ static grpc_error* non_polling_poller_work(grpc_pollset* pollset,
                                            grpc_millis deadline) {
   non_polling_poller* npp = reinterpret_cast<non_polling_poller*>(pollset);
   if (npp->shutdown) return GRPC_ERROR_NONE;
+  if (npp->kicked_without_poller) {
+    npp->kicked_without_poller = false;
+    return GRPC_ERROR_NONE;
+  }
   non_polling_worker w;
   gpr_cv_init(&w.cv);
   if (worker != nullptr) *worker = reinterpret_cast<grpc_pollset_worker*>(&w);
@@ -148,6 +153,8 @@ static grpc_error* non_polling_poller_kick(
       w->kicked = true;
       gpr_cv_signal(&w->cv);
     }
+  } else {
+    p->kicked_without_poller = true;
   }
   return GRPC_ERROR_NONE;
 }
diff --git a/src/core/lib/surface/server.cc b/src/core/lib/surface/server.cc
index 449aef768e..35ab2c3bce 100644
--- a/src/core/lib/surface/server.cc
+++ b/src/core/lib/surface/server.cc
@@ -54,6 +54,7 @@ struct listener {
                 size_t pollset_count);
   void (*destroy)(grpc_server* server, void* arg, grpc_closure* closure);
   struct listener* next;
+  intptr_t socket_uuid;
   grpc_closure destroy_done;
 };
 
@@ -104,6 +105,7 @@ struct channel_data {
   uint32_t registered_method_max_probes;
   grpc_closure finish_destroy_channel_closure;
   grpc_closure channel_connectivity_changed;
+  intptr_t socket_uuid;
 };
 
 typedef struct shutdown_tag {
@@ -1016,7 +1018,7 @@ grpc_server* grpc_server_create(const grpc_channel_args* args, void* reserved) {
         {GRPC_MAX_CHANNEL_TRACE_EVENT_MEMORY_PER_NODE_DEFAULT, 0, INT_MAX});
     server->channelz_server =
         grpc_core::MakeRefCounted<grpc_core::channelz::ServerNode>(
-            channel_tracer_max_memory);
+            server, channel_tracer_max_memory);
     server->channelz_server->AddTraceEvent(
         grpc_core::channelz::ChannelTrace::Severity::Info,
         grpc_slice_from_static_string("Server created"));
@@ -1119,7 +1121,8 @@ void grpc_server_get_pollsets(grpc_server* server, grpc_pollset*** pollsets,
 
 void grpc_server_setup_transport(grpc_server* s, grpc_transport* transport,
                                  grpc_pollset* accepting_pollset,
-                                 const grpc_channel_args* args) {
+                                 const grpc_channel_args* args,
+                                 intptr_t socket_uuid) {
   size_t num_registered_methods;
   size_t alloc;
   registered_method* rm;
@@ -1139,6 +1142,7 @@ void grpc_server_setup_transport(grpc_server* s, grpc_transport* transport,
   chand->server = s;
   server_ref(s);
   chand->channel = channel;
+  chand->socket_uuid = socket_uuid;
 
   size_t cq_idx;
   for (cq_idx = 0; cq_idx < s->cq_count; cq_idx++) {
@@ -1213,6 +1217,29 @@ void grpc_server_setup_transport(grpc_server* s, grpc_transport* transport,
   grpc_transport_perform_op(transport, op);
 }
 
+void grpc_server_populate_server_sockets(
+    grpc_server* s, grpc_core::channelz::ChildRefsList* server_sockets,
+    intptr_t start_idx) {
+  gpr_mu_lock(&s->mu_global);
+  channel_data* c = nullptr;
+  for (c = s->root_channel_data.next; c != &s->root_channel_data; c = c->next) {
+    intptr_t socket_uuid = c->socket_uuid;
+    if (socket_uuid >= start_idx) {
+      server_sockets->push_back(socket_uuid);
+    }
+  }
+  gpr_mu_unlock(&s->mu_global);
+}
+
+void grpc_server_populate_listen_sockets(
+    grpc_server* server, grpc_core::channelz::ChildRefsList* listen_sockets) {
+  gpr_mu_lock(&server->mu_global);
+  for (listener* l = server->listeners; l != nullptr; l = l->next) {
+    listen_sockets->push_back(l->socket_uuid);
+  }
+  gpr_mu_unlock(&server->mu_global);
+}
+
 void done_published_shutdown(void* done_arg, grpc_cq_completion* storage) {
   (void)done_arg;
   gpr_free(storage);
@@ -1346,11 +1373,13 @@ void grpc_server_add_listener(grpc_server* server, void* arg,
                                             grpc_pollset** pollsets,
                                             size_t pollset_count),
                               void (*destroy)(grpc_server* server, void* arg,
-                                              grpc_closure* on_done)) {
+                                              grpc_closure* on_done),
+                              intptr_t socket_uuid) {
   listener* l = static_cast<listener*>(gpr_malloc(sizeof(listener)));
   l->arg = arg;
   l->start = start;
   l->destroy = destroy;
+  l->socket_uuid = socket_uuid;
   l->next = server->listeners;
   server->listeners = l;
 }
diff --git a/src/core/lib/surface/server.h b/src/core/lib/surface/server.h
index 0196743ff9..33c205417e 100644
--- a/src/core/lib/surface/server.h
+++ b/src/core/lib/surface/server.h
@@ -39,13 +39,24 @@ void grpc_server_add_listener(grpc_server* server, void* listener,
                                             grpc_pollset** pollsets,
                                             size_t npollsets),
                               void (*destroy)(grpc_server* server, void* arg,
-                                              grpc_closure* on_done));
+                                              grpc_closure* on_done),
+                              intptr_t socket_uuid);
 
 /* Setup a transport - creates a channel stack, binds the transport to the
    server */
 void grpc_server_setup_transport(grpc_server* server, grpc_transport* transport,
                                  grpc_pollset* accepting_pollset,
-                                 const grpc_channel_args* args);
+                                 const grpc_channel_args* args,
+                                 intptr_t socket_uuid);
+
+/* fills in the uuids of all sockets used for connections on this server */
+void grpc_server_populate_server_sockets(
+    grpc_server* server, grpc_core::channelz::ChildRefsList* server_sockets,
+    intptr_t start_idx);
+
+/* fills in the uuids of all listen sockets on this server */
+void grpc_server_populate_listen_sockets(
+    grpc_server* server, grpc_core::channelz::ChildRefsList* listen_sockets);
 
 grpc_core::channelz::ServerNode* grpc_server_get_channelz_node(
     grpc_server* server);
diff --git a/src/core/lib/surface/version.cc b/src/core/lib/surface/version.cc
index a44f9acdc3..66890ce65a 100644
--- a/src/core/lib/surface/version.cc
+++ b/src/core/lib/surface/version.cc
@@ -23,6 +23,6 @@
 
 #include <grpc/grpc.h>
 
-const char* grpc_version_string(void) { return "6.0.0-dev"; }
+const char* grpc_version_string(void) { return "7.0.0-dev"; }
 
-const char* grpc_g_stands_for(void) { return "gao"; }
+const char* grpc_g_stands_for(void) { return "gizmo"; }
diff --git a/src/core/lib/transport/metadata.cc b/src/core/lib/transport/metadata.cc
index d164502280..60af22393e 100644
--- a/src/core/lib/transport/metadata.cc
+++ b/src/core/lib/transport/metadata.cc
@@ -237,7 +237,7 @@ static void rehash_mdtab(mdtab_shard* shard) {
 }
 
 grpc_mdelem grpc_mdelem_create(
-    grpc_slice key, grpc_slice value,
+    const grpc_slice& key, const grpc_slice& value,
     grpc_mdelem_data* compatible_external_backing_store) {
   if (!grpc_slice_is_interned(key) || !grpc_slice_is_interned(value)) {
     if (compatible_external_backing_store != nullptr) {
@@ -324,7 +324,8 @@ grpc_mdelem grpc_mdelem_create(
   return GRPC_MAKE_MDELEM(md, GRPC_MDELEM_STORAGE_INTERNED);
 }
 
-grpc_mdelem grpc_mdelem_from_slices(grpc_slice key, grpc_slice value) {
+grpc_mdelem grpc_mdelem_from_slices(const grpc_slice& key,
+                                    const grpc_slice& value) {
   grpc_mdelem out = grpc_mdelem_create(key, value, nullptr);
   grpc_slice_unref_internal(key);
   grpc_slice_unref_internal(value);
diff --git a/src/core/lib/transport/metadata.h b/src/core/lib/transport/metadata.h
index 338082276c..989c7544c1 100644
--- a/src/core/lib/transport/metadata.h
+++ b/src/core/lib/transport/metadata.h
@@ -109,7 +109,8 @@ struct grpc_mdelem {
                               (uintptr_t)GRPC_MDELEM_STORAGE_INTERNED_BIT))
 
 /* Unrefs the slices. */
-grpc_mdelem grpc_mdelem_from_slices(grpc_slice key, grpc_slice value);
+grpc_mdelem grpc_mdelem_from_slices(const grpc_slice& key,
+                                    const grpc_slice& value);
 
 /* Cheaply convert a grpc_metadata to a grpc_mdelem; may use the grpc_metadata
    object as backing storage (so lifetimes should align) */
@@ -120,7 +121,7 @@ grpc_mdelem grpc_mdelem_from_grpc_metadata(grpc_metadata* metadata);
    compatible_external_backing_store if it is non-NULL (in which case it's the
    users responsibility to ensure that it outlives usage) */
 grpc_mdelem grpc_mdelem_create(
-    grpc_slice key, grpc_slice value,
+    const grpc_slice& key, const grpc_slice& value,
     grpc_mdelem_data* compatible_external_backing_store);
 
 bool grpc_mdelem_eq(grpc_mdelem a, grpc_mdelem b);
diff --git a/src/core/lib/transport/metadata_batch.cc b/src/core/lib/transport/metadata_batch.cc
index 761aad19c4..928ed73cda 100644
--- a/src/core/lib/transport/metadata_batch.cc
+++ b/src/core/lib/transport/metadata_batch.cc
@@ -139,6 +139,7 @@ static void link_head(grpc_mdelem_list* list, grpc_linked_mdelem* storage) {
   GPR_ASSERT(!GRPC_MDISNULL(storage->md));
   storage->prev = nullptr;
   storage->next = list->head;
+  storage->reserved = nullptr;
   if (list->head != nullptr) {
     list->head->prev = storage;
   } else {
diff --git a/src/core/tsi/alts/handshaker/alts_tsi_handshaker.cc b/src/core/tsi/alts/handshaker/alts_tsi_handshaker.cc
index 34608a3de1..dfdd659b87 100644
--- a/src/core/tsi/alts/handshaker/alts_tsi_handshaker.cc
+++ b/src/core/tsi/alts/handshaker/alts_tsi_handshaker.cc
@@ -347,7 +347,8 @@ static void init_shared_resources(const char* handshaker_service_url) {
 
 tsi_result alts_tsi_handshaker_create(
     const grpc_alts_credentials_options* options, const char* target_name,
-    const char* handshaker_service_url, bool is_client, tsi_handshaker** self) {
+    const char* handshaker_service_url, bool is_client,
+    grpc_pollset_set* interested_parties, tsi_handshaker** self) {
   if (handshaker_service_url == nullptr || self == nullptr ||
       options == nullptr || (is_client && target_name == nullptr)) {
     gpr_log(GPR_ERROR, "Invalid arguments to alts_tsi_handshaker_create()");
diff --git a/src/core/tsi/alts/handshaker/alts_tsi_handshaker.h b/src/core/tsi/alts/handshaker/alts_tsi_handshaker.h
index 227b30ce53..48ce69b1da 100644
--- a/src/core/tsi/alts/handshaker/alts_tsi_handshaker.h
+++ b/src/core/tsi/alts/handshaker/alts_tsi_handshaker.h
@@ -23,6 +23,7 @@
 
 #include <grpc/grpc.h>
 
+#include "src/core/lib/iomgr/pollset_set.h"
 #include "src/core/lib/security/credentials/alts/grpc_alts_credentials_options.h"
 #include "src/core/tsi/alts_transport_security.h"
 #include "src/core/tsi/transport_security.h"
@@ -51,6 +52,7 @@ typedef struct alts_tsi_handshaker alts_tsi_handshaker;
  *   "host:port".
  * - is_client: boolean value indicating if the handshaker is used at the client
  *   (is_client = true) or server (is_client = false) side.
+ * - interested_parties: set of pollsets interested in this connection.
  * - self: address of ALTS TSI handshaker instance to be returned from the
  *   method.
  *
@@ -58,7 +60,8 @@ typedef struct alts_tsi_handshaker alts_tsi_handshaker;
  */
 tsi_result alts_tsi_handshaker_create(
     const grpc_alts_credentials_options* options, const char* target_name,
-    const char* handshaker_service_url, bool is_client, tsi_handshaker** self);
+    const char* handshaker_service_url, bool is_client,
+    grpc_pollset_set* interested_parties, tsi_handshaker** self);
 
 /**
  * This method handles handshaker response returned from ALTS handshaker
diff --git a/src/cpp/common/version_cc.cc b/src/cpp/common/version_cc.cc
index cc797f1546..8abd45efb7 100644
--- a/src/cpp/common/version_cc.cc
+++ b/src/cpp/common/version_cc.cc
@@ -22,5 +22,5 @@
 #include <grpcpp/grpcpp.h>
 
 namespace grpc {
-grpc::string Version() { return "1.16.0-dev"; }
+grpc::string Version() { return "1.17.0-dev"; }
 }  // namespace grpc
diff --git a/src/cpp/server/channelz/channelz_service.cc b/src/cpp/server/channelz/channelz_service.cc
index 4e3fe8c1c9..79ed9102e5 100644
--- a/src/cpp/server/channelz/channelz_service.cc
+++ b/src/cpp/server/channelz/channelz_service.cc
@@ -60,6 +60,23 @@ Status ChannelzService::GetServers(
   return Status::OK;
 }
 
+Status ChannelzService::GetServerSockets(
+    ServerContext* unused, const channelz::v1::GetServerSocketsRequest* request,
+    channelz::v1::GetServerSocketsResponse* response) {
+  char* json_str = grpc_channelz_get_server_sockets(request->server_id(),
+                                                    request->start_socket_id());
+  if (json_str == nullptr) {
+    return Status(INTERNAL, "grpc_channelz_get_server_sockets returned null");
+  }
+  google::protobuf::util::Status s =
+      google::protobuf::util::JsonStringToMessage(json_str, response);
+  gpr_free(json_str);
+  if (s != google::protobuf::util::Status::OK) {
+    return Status(INTERNAL, s.ToString());
+  }
+  return Status::OK;
+}
+
 Status ChannelzService::GetChannel(
     ServerContext* unused, const channelz::v1::GetChannelRequest* request,
     channelz::v1::GetChannelResponse* response) {
@@ -96,7 +113,6 @@ Status ChannelzService::GetSocket(ServerContext* unused,
                                   const channelz::v1::GetSocketRequest* request,
                                   channelz::v1::GetSocketResponse* response) {
   char* json_str = grpc_channelz_get_socket(request->socket_id());
-  gpr_log(GPR_ERROR, "%s", json_str);
   if (json_str == nullptr) {
     return Status(NOT_FOUND, "No object found for that SocketId");
   }
diff --git a/src/cpp/server/channelz/channelz_service.h b/src/cpp/server/channelz/channelz_service.h
index 1be4e01c73..590b5d492e 100644
--- a/src/cpp/server/channelz/channelz_service.h
+++ b/src/cpp/server/channelz/channelz_service.h
@@ -36,6 +36,11 @@ class ChannelzService final : public channelz::v1::Channelz::Service {
   Status GetServers(ServerContext* unused,
                     const channelz::v1::GetServersRequest* request,
                     channelz::v1::GetServersResponse* response) override;
+  // implementation of GetServerSockets rpc
+  Status GetServerSockets(
+      ServerContext* unused,
+      const channelz::v1::GetServerSocketsRequest* request,
+      channelz::v1::GetServerSocketsResponse* response) override;
   // implementation of GetChannel rpc
   Status GetChannel(ServerContext* unused,
                     const channelz::v1::GetChannelRequest* request,
diff --git a/src/csharp/.editorconfig b/src/csharp/.editorconfig
index fabce7f5ba..c9a2c48a7d 100644
--- a/src/csharp/.editorconfig
+++ b/src/csharp/.editorconfig
@@ -6,3 +6,26 @@ indent_style = space
 indent_size = 4
 insert_final_newline = true
 tab_width = 4
+
+; https://docs.microsoft.com/visualstudio/ide/editorconfig-code-style-settings-reference
+[*.cs]
+dotnet_sort_system_directives_first = true
+csharp_new_line_before_open_brace = accessors, anonymous_methods, control_blocks, events, indexers, local_functions, methods, properties, types
+csharp_new_line_before_else = true
+csharp_new_line_before_catch = true
+csharp_new_line_before_finally = true
+csharp_indent_case_contents = true
+csharp_indent_switch_labels = true
+csharp_space_after_cast = false
+csharp_space_after_keywords_in_control_flow_statements = true
+csharp_space_between_method_declaration_parameter_list_parentheses = false
+csharp_space_between_method_call_parameter_list_parentheses = false
+csharp_space_between_parentheses = false
+csharp_space_before_colon_in_inheritance_clause = true
+csharp_space_after_colon_in_inheritance_clause = true
+csharp_space_around_binary_operators = before_and_after
+csharp_space_between_method_declaration_empty_parameter_list_parentheses = false
+csharp_space_between_method_call_name_and_opening_parenthesis = false
+csharp_space_between_method_call_empty_parameter_list_parentheses = false
+csharp_preserve_single_line_statements = true
+csharp_preserve_single_line_blocks = true
diff --git a/src/csharp/Grpc.Core.Tests/SanityTest.cs b/src/csharp/Grpc.Core.Tests/SanityTest.cs
index eaad409ec0..0904453b6e 100644
--- a/src/csharp/Grpc.Core.Tests/SanityTest.cs
+++ b/src/csharp/Grpc.Core.Tests/SanityTest.cs
@@ -102,6 +102,7 @@ namespace Grpc.Core.Tests
                 "Grpc.HealthCheck.Tests",
                 "Grpc.IntegrationTesting",
                 "Grpc.Reflection.Tests",
+                "Grpc.Tools.Tests",
             };
             foreach (var assemblyName in otherAssemblies)
             {
diff --git a/src/csharp/Grpc.Core/Internal/UnmanagedLibrary.cs b/src/csharp/Grpc.Core/Internal/UnmanagedLibrary.cs
index 7185d68efe..1786fc2e3f 100644
--- a/src/csharp/Grpc.Core/Internal/UnmanagedLibrary.cs
+++ b/src/csharp/Grpc.Core/Internal/UnmanagedLibrary.cs
@@ -51,11 +51,12 @@ namespace Grpc.Core.Internal
 
             Logger.Debug("Attempting to load native library \"{0}\"", this.libraryPath);
 
-            this.handle = PlatformSpecificLoadLibrary(this.libraryPath);
+            this.handle = PlatformSpecificLoadLibrary(this.libraryPath, out string loadLibraryErrorDetail);
 
             if (this.handle == IntPtr.Zero)
             {
-                throw new IOException(string.Format("Error loading native library \"{0}\"", this.libraryPath));
+                throw new IOException(string.Format("Error loading native library \"{0}\". {1}",
+                                                    this.libraryPath, loadLibraryErrorDetail));
             }
         }
 
@@ -129,31 +130,44 @@ namespace Grpc.Core.Internal
         /// <summary>
         /// Loads library in a platform specific way.
         /// </summary>
-        private static IntPtr PlatformSpecificLoadLibrary(string libraryPath)
+        private static IntPtr PlatformSpecificLoadLibrary(string libraryPath, out string errorMsg)
         {
             if (PlatformApis.IsWindows)
             {
+                // TODO(jtattermusch): populate the error on Windows
+                errorMsg = null;
                 return Windows.LoadLibrary(libraryPath);
             }
             if (PlatformApis.IsLinux)
             {
                 if (PlatformApis.IsMono)
                 {
-                    return Mono.dlopen(libraryPath, RTLD_GLOBAL + RTLD_LAZY);
+                    return LoadLibraryPosix(Mono.dlopen, Mono.dlerror, libraryPath, out errorMsg);
                 }
                 if (PlatformApis.IsNetCore)
                 {
-                    return CoreCLR.dlopen(libraryPath, RTLD_GLOBAL + RTLD_LAZY);
+                    return LoadLibraryPosix(CoreCLR.dlopen, CoreCLR.dlerror, libraryPath, out errorMsg);
                 }
-                return Linux.dlopen(libraryPath, RTLD_GLOBAL + RTLD_LAZY);
+                return LoadLibraryPosix(Linux.dlopen, Linux.dlerror, libraryPath, out errorMsg);
             }
             if (PlatformApis.IsMacOSX)
             {
-                return MacOSX.dlopen(libraryPath, RTLD_GLOBAL + RTLD_LAZY);
+                return LoadLibraryPosix(MacOSX.dlopen, MacOSX.dlerror, libraryPath, out errorMsg);
             }
             throw new InvalidOperationException("Unsupported platform.");
         }
 
+        private static IntPtr LoadLibraryPosix(Func<string, int, IntPtr> dlopenFunc, Func<IntPtr> dlerrorFunc, string libraryPath, out string errorMsg)
+        {
+            errorMsg = null;
+            IntPtr ret = dlopenFunc(libraryPath, RTLD_GLOBAL + RTLD_LAZY);
+            if (ret == IntPtr.Zero)
+            {
+                errorMsg = Marshal.PtrToStringAnsi(dlerrorFunc());
+            }
+            return ret;
+        }
+
         private static string FirstValidLibraryPath(string[] libraryPathAlternatives)
         {
             GrpcPreconditions.CheckArgument(libraryPathAlternatives.Length > 0, "libraryPathAlternatives cannot be empty.");
@@ -184,6 +198,9 @@ namespace Grpc.Core.Internal
             internal static extern IntPtr dlopen(string filename, int flags);
 
             [DllImport("libdl.so")]
+            internal static extern IntPtr dlerror();
+
+            [DllImport("libdl.so")]
             internal static extern IntPtr dlsym(IntPtr handle, string symbol);
         }
 
@@ -193,6 +210,9 @@ namespace Grpc.Core.Internal
             internal static extern IntPtr dlopen(string filename, int flags);
 
             [DllImport("libSystem.dylib")]
+            internal static extern IntPtr dlerror();
+
+            [DllImport("libSystem.dylib")]
             internal static extern IntPtr dlsym(IntPtr handle, string symbol);
         }
 
@@ -209,6 +229,9 @@ namespace Grpc.Core.Internal
             internal static extern IntPtr dlopen(string filename, int flags);
 
             [DllImport("__Internal")]
+            internal static extern IntPtr dlerror();
+
+            [DllImport("__Internal")]
             internal static extern IntPtr dlsym(IntPtr handle, string symbol);
         }
 
@@ -223,6 +246,9 @@ namespace Grpc.Core.Internal
             internal static extern IntPtr dlopen(string filename, int flags);
 
             [DllImport("libcoreclr.so")]
+            internal static extern IntPtr dlerror();
+
+            [DllImport("libcoreclr.so")]
             internal static extern IntPtr dlsym(IntPtr handle, string symbol);
         }
     }
diff --git a/src/csharp/Grpc.Core/Version.csproj.include b/src/csharp/Grpc.Core/Version.csproj.include
index 18515ea1e8..ed0d884365 100755
--- a/src/csharp/Grpc.Core/Version.csproj.include
+++ b/src/csharp/Grpc.Core/Version.csproj.include
@@ -1,7 +1,7 @@
 <!-- This file is generated -->
 <Project>
   <PropertyGroup>
-    <GrpcCsharpVersion>1.16.0-dev</GrpcCsharpVersion>
+    <GrpcCsharpVersion>1.17.0-dev</GrpcCsharpVersion>
     <GoogleProtobufVersion>3.6.1</GoogleProtobufVersion>
   </PropertyGroup>
 </Project>
diff --git a/src/csharp/Grpc.Core/VersionInfo.cs b/src/csharp/Grpc.Core/VersionInfo.cs
index 55d09dda7a..14714c8c4a 100644
--- a/src/csharp/Grpc.Core/VersionInfo.cs
+++ b/src/csharp/Grpc.Core/VersionInfo.cs
@@ -33,11 +33,11 @@ namespace Grpc.Core
         /// <summary>
         /// Current <c>AssemblyFileVersion</c> of gRPC C# assemblies
         /// </summary>
-        public const string CurrentAssemblyFileVersion = "1.16.0.0";
+        public const string CurrentAssemblyFileVersion = "1.17.0.0";
 
         /// <summary>
         /// Current version of gRPC C#
         /// </summary>
-        public const string CurrentVersion = "1.16.0-dev";
+        public const string CurrentVersion = "1.17.0-dev";
     }
 }
diff --git a/src/csharp/Grpc.Tools.Tests/CSharpGeneratorTest.cs b/src/csharp/Grpc.Tools.Tests/CSharpGeneratorTest.cs
new file mode 100644
index 0000000000..e4c9b2fa84
--- /dev/null
+++ b/src/csharp/Grpc.Tools.Tests/CSharpGeneratorTest.cs
@@ -0,0 +1,85 @@
+#region Copyright notice and license
+
+// Copyright 2018 gRPC authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#endregion
+
+using NUnit.Framework;
+
+namespace Grpc.Tools.Tests
+{
+    public class CSharpGeneratorTest : GeneratorTest
+    {
+        GeneratorServices _generator;
+
+        [SetUp]
+        public new void SetUp()
+        {
+            _generator = GeneratorServices.GetForLanguage("CSharp", _log);
+        }
+
+        [TestCase("foo.proto", "Foo.cs", "FooGrpc.cs")]
+        [TestCase("sub/foo.proto", "Foo.cs", "FooGrpc.cs")]
+        [TestCase("one_two.proto", "OneTwo.cs", "OneTwoGrpc.cs")]
+        [TestCase("__one_two!.proto", "OneTwo!.cs", "OneTwo!Grpc.cs")]
+        [TestCase("one(two).proto", "One(two).cs", "One(two)Grpc.cs")]
+        [TestCase("one_(two).proto", "One(two).cs", "One(two)Grpc.cs")]
+        [TestCase("one two.proto", "One two.cs", "One twoGrpc.cs")]
+        [TestCase("one_ two.proto", "One two.cs", "One twoGrpc.cs")]
+        [TestCase("one .proto", "One .cs", "One Grpc.cs")]
+        public void NameMangling(string proto, string expectCs, string expectGrpcCs)
+        {
+            var poss = _generator.GetPossibleOutputs(Utils.MakeItem(proto, "grpcservices", "both"));
+            Assert.AreEqual(2, poss.Length);
+            Assert.Contains(expectCs, poss);
+            Assert.Contains(expectGrpcCs, poss);
+        }
+
+        [Test]
+        public void NoGrpcOneOutput()
+        {
+            var poss = _generator.GetPossibleOutputs(Utils.MakeItem("foo.proto"));
+            Assert.AreEqual(1, poss.Length);
+        }
+
+        [TestCase("none")]
+        [TestCase("")]
+        public void GrpcNoneOneOutput(string grpc)
+        {
+            var item = Utils.MakeItem("foo.proto", "grpcservices", grpc);
+            var poss = _generator.GetPossibleOutputs(item);
+            Assert.AreEqual(1, poss.Length);
+        }
+
+        [TestCase("client")]
+        [TestCase("server")]
+        [TestCase("both")]
+        public void GrpcEnabledTwoOutputs(string grpc)
+        {
+            var item = Utils.MakeItem("foo.proto", "grpcservices", grpc);
+            var poss = _generator.GetPossibleOutputs(item);
+            Assert.AreEqual(2, poss.Length);
+        }
+
+        [Test]
+        public void OutputDirMetadataRecognized()
+        {
+            var item = Utils.MakeItem("foo.proto", "OutputDir", "out");
+            var poss = _generator.GetPossibleOutputs(item);
+            Assert.AreEqual(1, poss.Length);
+            Assert.That(poss[0], Is.EqualTo("out/Foo.cs") | Is.EqualTo("out\\Foo.cs"));
+        }
+    };
+}
diff --git a/src/csharp/Grpc.Tools.Tests/CppGeneratorTest.cs b/src/csharp/Grpc.Tools.Tests/CppGeneratorTest.cs
new file mode 100644
index 0000000000..bd0405a03a
--- /dev/null
+++ b/src/csharp/Grpc.Tools.Tests/CppGeneratorTest.cs
@@ -0,0 +1,88 @@
+#region Copyright notice and license
+
+// Copyright 2018 gRPC authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#endregion
+
+using System.IO;
+using NUnit.Framework;
+
+namespace Grpc.Tools.Tests
+{
+    public class CppGeneratorTest : GeneratorTest
+    {
+        GeneratorServices _generator;
+
+        [SetUp]
+        public new void SetUp()
+        {
+            _generator = GeneratorServices.GetForLanguage("Cpp", _log);
+        }
+
+        [TestCase("foo.proto", "", "foo")]
+        [TestCase("foo.proto", ".", "foo")]
+        [TestCase("foo.proto", "./", "foo")]
+        [TestCase("sub/foo.proto", "", "sub/foo")]
+        [TestCase("root/sub/foo.proto", "root", "sub/foo")]
+        [TestCase("root/sub/foo.proto", "root", "sub/foo")]
+        [TestCase("/root/sub/foo.proto", "/root", "sub/foo")]
+        public void RelativeDirectoryCompute(string proto, string root, string expectStem)
+        {
+            if (Path.DirectorySeparatorChar == '\\')
+                expectStem = expectStem.Replace('/', '\\');
+            var poss = _generator.GetPossibleOutputs(Utils.MakeItem(proto, "ProtoRoot", root));
+            Assert.AreEqual(2, poss.Length);
+            Assert.Contains(expectStem + ".pb.cc", poss);
+            Assert.Contains(expectStem + ".pb.h", poss);
+        }
+
+        [Test]
+        public void NoGrpcTwoOutputs()
+        {
+            var poss = _generator.GetPossibleOutputs(Utils.MakeItem("foo.proto"));
+            Assert.AreEqual(2, poss.Length);
+        }
+
+        [TestCase("false")]
+        [TestCase("")]
+        public void GrpcDisabledTwoOutput(string grpc)
+        {
+            var item = Utils.MakeItem("foo.proto", "grpcservices", grpc);
+            var poss = _generator.GetPossibleOutputs(item);
+            Assert.AreEqual(2, poss.Length);
+        }
+
+        [TestCase("true")]
+        public void GrpcEnabledFourOutputs(string grpc)
+        {
+            var item = Utils.MakeItem("foo.proto", "grpcservices", grpc);
+            var poss = _generator.GetPossibleOutputs(item);
+            Assert.AreEqual(4, poss.Length);
+            Assert.Contains("foo.pb.cc", poss);
+            Assert.Contains("foo.pb.h", poss);
+            Assert.Contains("foo_grpc.pb.cc", poss);
+            Assert.Contains("foo_grpc.pb.h", poss);
+        }
+
+        [Test]
+        public void OutputDirMetadataRecognized()
+        {
+            var item = Utils.MakeItem("foo.proto", "OutputDir", "out");
+            var poss = _generator.GetPossibleOutputs(item);
+            Assert.AreEqual(2, poss.Length);
+            Assert.That(Path.GetDirectoryName(poss[0]), Is.EqualTo("out"));
+        }
+    };
+}
diff --git a/src/csharp/Grpc.Tools.Tests/DepFileUtilTest.cs b/src/csharp/Grpc.Tools.Tests/DepFileUtilTest.cs
new file mode 100644
index 0000000000..e89a8f4b5d
--- /dev/null
+++ b/src/csharp/Grpc.Tools.Tests/DepFileUtilTest.cs
@@ -0,0 +1,146 @@
+#region Copyright notice and license
+
+// Copyright 2018 gRPC authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#endregion
+
+using System.IO;
+using Microsoft.Build.Framework;
+using Microsoft.Build.Utilities;
+using NUnit.Framework;
+
+namespace Grpc.Tools.Tests
+{
+    public class DepFileUtilTest
+    {
+
+        [Test]
+        public void HashString64Hex_IsSane()
+        {
+            string hashFoo1 = DepFileUtil.HashString64Hex("foo");
+            string hashEmpty = DepFileUtil.HashString64Hex("");
+            string hashFoo2 = DepFileUtil.HashString64Hex("foo");
+
+            StringAssert.IsMatch("^[a-f0-9]{16}$", hashFoo1);
+            Assert.AreEqual(hashFoo1, hashFoo2);
+            Assert.AreNotEqual(hashFoo1, hashEmpty);
+        }
+
+        [Test]
+        public void GetDepFilenameForProto_IsSane()
+        {
+            StringAssert.IsMatch(@"^out[\\/][a-f0-9]{16}_foo.protodep$",
+                DepFileUtil.GetDepFilenameForProto("out", "foo.proto"));
+            StringAssert.IsMatch(@"^[a-f0-9]{16}_foo.protodep$",
+                DepFileUtil.GetDepFilenameForProto("", "foo.proto"));
+        }
+
+        [Test]
+        public void GetDepFilenameForProto_HashesDir()
+        {
+            string PickHash(string fname) =>
+                DepFileUtil.GetDepFilenameForProto("", fname).Substring(0, 16);
+
+            string same1 = PickHash("dir1/dir2/foo.proto");
+            string same2 = PickHash("dir1/dir2/proto.foo");
+            string same3 = PickHash("dir1/dir2/proto");
+            string same4 = PickHash("dir1/dir2/.proto");
+            string unsame1 = PickHash("dir2/foo.proto");
+            string unsame2 = PickHash("/dir2/foo.proto");
+
+            Assert.AreEqual(same1, same2);
+            Assert.AreEqual(same1, same3);
+            Assert.AreEqual(same1, same4);
+            Assert.AreNotEqual(same1, unsame1);
+            Assert.AreNotEqual(unsame1, unsame2);
+        }
+
+        //////////////////////////////////////////////////////////////////////////
+        // Full file reading tests
+
+        // Generated by protoc on Windows. Slashes vary.
+        const string depFile1 =
+    @"C:\projects\foo\src\./foo.grpc.pb.cc \
+C:\projects\foo\src\./foo.grpc.pb.h \
+C:\projects\foo\src\./foo.pb.cc \
+ C:\projects\foo\src\./foo.pb.h: C:/usr/include/google/protobuf/wrappers.proto\
+   C:/usr/include/google/protobuf/any.proto\
+C:/usr/include/google/protobuf/source_context.proto\
+   C:/usr/include/google/protobuf/type.proto\
+   foo.proto";
+
+        // This has a nasty output directory with a space.
+        const string depFile2 =
+    @"obj\Release x64\net45\/Foo.cs \
+obj\Release x64\net45\/FooGrpc.cs: C:/usr/include/google/protobuf/wrappers.proto\
+ C:/projects/foo/src//foo.proto";
+
+        [Test]
+        public void ReadDependencyInput_FullFile1()
+        {
+            string[] deps = ReadDependencyInputFromFileData(depFile1, "foo.proto");
+
+            Assert.NotNull(deps);
+            Assert.That(deps, Has.Length.InRange(4, 5));  // foo.proto may or may not be listed.
+            Assert.That(deps, Has.One.EndsWith("wrappers.proto"));
+            Assert.That(deps, Has.One.EndsWith("type.proto"));
+            Assert.That(deps, Has.None.StartWith(" "));
+        }
+
+        [Test]
+        public void ReadDependencyInput_FullFile2()
+        {
+            string[] deps = ReadDependencyInputFromFileData(depFile2, "C:/projects/foo/src/foo.proto");
+
+            Assert.NotNull(deps);
+            Assert.That(deps, Has.Length.InRange(1, 2));
+            Assert.That(deps, Has.One.EndsWith("wrappers.proto"));
+            Assert.That(deps, Has.None.StartWith(" "));
+        }
+
+        [Test]
+        public void ReadDependencyInput_FullFileUnparsable()
+        {
+            string[] deps = ReadDependencyInputFromFileData("a:/foo.proto", "/foo.proto");
+            Assert.NotNull(deps);
+            Assert.Zero(deps.Length);
+        }
+
+        // NB in our tests files are put into the temp directory but all have
+        // different names. Avoid adding files with the same directory path and
+        // name, or add reasonable handling for it if required. Tests are run in
+        // parallel and will collide otherwise.
+        private string[] ReadDependencyInputFromFileData(string fileData, string protoName)
+        {
+            string tempPath = Path.GetTempPath();
+            string tempfile = DepFileUtil.GetDepFilenameForProto(tempPath, protoName);
+            try
+            {
+                File.WriteAllText(tempfile, fileData);
+                var mockEng = new Moq.Mock<IBuildEngine>();
+                var log = new TaskLoggingHelper(mockEng.Object, "x");
+                return DepFileUtil.ReadDependencyInputs(tempPath, protoName, log);
+            }
+            finally
+            {
+                try
+                {
+                    File.Delete(tempfile);
+                }
+                catch { }
+            }
+        }
+    };
+}
diff --git a/src/csharp/Grpc.Tools.Tests/GeneratorTest.cs b/src/csharp/Grpc.Tools.Tests/GeneratorTest.cs
new file mode 100644
index 0000000000..8a8fc81aba
--- /dev/null
+++ b/src/csharp/Grpc.Tools.Tests/GeneratorTest.cs
@@ -0,0 +1,55 @@
+#region Copyright notice and license
+
+// Copyright 2018 gRPC authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#endregion
+
+using Microsoft.Build.Framework;
+using Microsoft.Build.Utilities;
+using Moq;
+using NUnit.Framework;
+
+namespace Grpc.Tools.Tests
+{
+    public class GeneratorTest
+    {
+        protected Mock<IBuildEngine> _mockEngine;
+        protected TaskLoggingHelper _log;
+
+        [SetUp]
+        public void SetUp()
+        {
+            _mockEngine = new Mock<IBuildEngine>();
+            _log = new TaskLoggingHelper(_mockEngine.Object, "dummy");
+        }
+
+        [TestCase("csharp")]
+        [TestCase("CSharp")]
+        [TestCase("cpp")]
+        public void ValidLanguages(string lang)
+        {
+            Assert.IsNotNull(GeneratorServices.GetForLanguage(lang, _log));
+            _mockEngine.Verify(me => me.LogErrorEvent(It.IsAny<BuildErrorEventArgs>()), Times.Never);
+        }
+
+        [TestCase("")]
+        [TestCase("COBOL")]
+        public void InvalidLanguages(string lang)
+        {
+            Assert.IsNull(GeneratorServices.GetForLanguage(lang, _log));
+            _mockEngine.Verify(me => me.LogErrorEvent(It.IsAny<BuildErrorEventArgs>()), Times.Once);
+        }
+    };
+}
diff --git a/src/csharp/Grpc.Tools.Tests/Grpc.Tools.Tests.csproj b/src/csharp/Grpc.Tools.Tests/Grpc.Tools.Tests.csproj
new file mode 100644
index 0000000000..a2d4874eec
--- /dev/null
+++ b/src/csharp/Grpc.Tools.Tests/Grpc.Tools.Tests.csproj
@@ -0,0 +1,78 @@
+<Project Sdk="Microsoft.NET.Sdk" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+
+  <Import Project="..\Grpc.Core\Version.csproj.include" />
+
+  <PropertyGroup>
+    <TargetFrameworks>net45;netcoreapp1.0</TargetFrameworks>
+    <OutputType>Exe</OutputType>
+  </PropertyGroup>
+
+  <Import Project="..\Grpc.Core\SourceLink.csproj.include" />
+
+  <!-- This is copied verbatim from Grpc.Core/Common.csproj.include. Other settings
+       in that file conflict with the intent of this build, as it cannot be signed,
+       and may not compile Grpc.Core/Version.cs, as that file references constants
+       in Grpc.Core.dll.
+       TODO(kkm): Refactor imports. -->
+  <PropertyGroup Condition=" '$(OS)' != 'Windows_NT' and '$(MSBuildRuntimeType)' == 'Core' ">
+    <!-- Use Mono reference assemblies in SDK build: https://github.com/dotnet/sdk/issues/335 -->
+    <FrameworkPathOverride Condition="Exists('/usr/lib/mono/4.5-api')">/usr/lib/mono/4.5-api</FrameworkPathOverride>
+    <FrameworkPathOverride Condition="Exists('/usr/local/lib/mono/4.5-api')">/usr/local/lib/mono/4.5-api</FrameworkPathOverride>
+    <FrameworkPathOverride Condition="Exists('/Library/Frameworks/Mono.framework/Versions/Current/lib/mono/4.5-api')">/Library/Frameworks/Mono.framework/Versions/Current/lib/mono/4.5-api</FrameworkPathOverride>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\Grpc.Tools\Grpc.Tools.csproj" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Moq" Version="4.8.3" />
+    <PackageReference Include="NUnit; NUnitLite" Version="3.10.1" />
+    <PackageReference Include="System.Runtime.InteropServices.RuntimeInformation" Version="4.3.0" />
+  </ItemGroup>
+
+  <PropertyGroup Condition=" '$(TargetFramework)' != 'net45' ">
+    <DefineConstants>$(DefineConstants);NETCORE</DefineConstants>
+  </PropertyGroup>
+
+  <ItemGroup Condition=" '$(TargetFramework)' == 'net45' ">
+    <Reference Include="Microsoft.Build.Framework; Microsoft.Build.Utilities.v4.0" />
+  </ItemGroup>
+
+  <ItemGroup Condition=" '$(TargetFramework)' != 'net45' ">
+    <PackageReference Include="Microsoft.Build.Framework; Microsoft.Build.Utilities.Core" Version="15.6.*" />
+  </ItemGroup>
+
+  <!-- Groups below is a hack to allow the test to run under Mono Framework build.
+       ========================================================================== -->
+
+  <!-- Mono unfortunately comes with broken Microsoft.Build.* assemblies installed in
+       the GAC, but fortunately searches for runtime assemblies in a different order
+       than Windows CLR host: the GAC assemblies have the lowest search priority, (see
+       https://www.mono-project.com/docs/advanced/assemblies-and-the-gac/), not the
+       highest as is in Windows (documented at
+       https://docs.microsoft.com/dotnet/framework/deployment/how-the-runtime-locates-assemblies).
+       To run the tests under Mono, we need correct assemblies in the same directory as
+       the test executable. Correct versions are in the MSBuild directory under Mono. -->
+  <ItemGroup Condition=" '$(TargetFramework)' == 'net45' and '$(OS)' != 'Windows_NT' ">
+    <None Include="$(_MSBuildAssemblyPath)/Microsoft.Build.Framework.dll;
+                   $(_MSBuildAssemblyPath)/Microsoft.Build.Utilities.v4.0.dll;
+                   $(_MSBuildAssemblyPath)/Microsoft.Build.Utilities.Core.dll"
+          CopyToOutputDirectory="Always" Visible="false" />
+  </ItemGroup>
+  <PropertyGroup Condition=" '$(TargetFramework)' == 'net45' and '$(OS)' != 'Windows_NT' ">
+    <!-- The None items are included into assembly candidate resolution by default, and
+         we do not want that, as they are not valid as reference assemblies (the version of
+         Microsoft.Build.Utilities.v4.0 is a pure facade for Microsoft.Build.Utilities.Core,
+         and does not define any types at all). Exclude them from assembly resolution. See
+         https://github.com/Microsoft/msbuild/blob/50639058f/documentation/wiki/ResolveAssemblyReference.md -->
+    <AssemblySearchPaths>{HintPathFromItem};{TargetFrameworkDirectory};{RawFileName}</AssemblySearchPaths>
+    <!-- Mono knows better where its MSBuild is. -->
+    <_MSBuildAssemblyPath Condition=" '$(MSBuildRuntimeType)' != 'Core' "
+                          >$(MSBuildToolsPath)</_MSBuildAssemblyPath>
+    <!-- Under dotnet, make the best guess we can. -->
+    <_MSBuildAssemblyPath Condition=" '$(MSBuildRuntimeType)' == 'Core' "
+                          >$(FrameworkPathOverride)/../msbuild/$(MSBuildToolsVersion)/bin</_MSBuildAssemblyPath>
+  </PropertyGroup>
+
+</Project>
diff --git a/src/csharp/Grpc.Tools.Tests/NUnitMain.cs b/src/csharp/Grpc.Tools.Tests/NUnitMain.cs
new file mode 100644
index 0000000000..418c33820e
--- /dev/null
+++ b/src/csharp/Grpc.Tools.Tests/NUnitMain.cs
@@ -0,0 +1,33 @@
+#region Copyright notice and license
+
+// Copyright 2018 gRPC authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#endregion
+
+using System.Reflection;
+using NUnitLite;
+
+namespace Grpc.Tools.Tests
+{
+    static class NUnitMain
+    {
+        public static int Main(string[] args) =>
+#if NETCOREAPP1_0 || NETCOREAPP1_1
+            new AutoRun(typeof(NUnitMain).GetTypeInfo().Assembly).Execute(args);
+#else
+            new AutoRun().Execute(args);
+#endif
+    };
+}
diff --git a/src/csharp/Grpc.Tools.Tests/ProtoCompileBasicTest.cs b/src/csharp/Grpc.Tools.Tests/ProtoCompileBasicTest.cs
new file mode 100644
index 0000000000..ea763f4e40
--- /dev/null
+++ b/src/csharp/Grpc.Tools.Tests/ProtoCompileBasicTest.cs
@@ -0,0 +1,76 @@
+#region Copyright notice and license
+
+// Copyright 2018 gRPC authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#endregion
+
+using System.Reflection;  // UWYU: Object.GetType() extension.
+using Microsoft.Build.Framework;
+using Moq;
+using NUnit.Framework;
+
+namespace Grpc.Tools.Tests
+{
+    public class ProtoCompileBasicTest
+    {
+        // Mock task class that stops right before invoking protoc.
+        public class ProtoCompileTestable : ProtoCompile
+        {
+            public string LastPathToTool { get; private set; }
+            public string[] LastResponseFile { get; private set; }
+
+            protected override int ExecuteTool(string pathToTool,
+                                               string response,
+                                               string commandLine)
+            {
+                // We should never be using command line commands.
+                Assert.That(commandLine, Is.Null | Is.Empty);
+
+                // Must receive a path to tool
+                Assert.That(pathToTool, Is.Not.Null & Is.Not.Empty);
+                Assert.That(response, Is.Not.Null & Does.EndWith("\n"));
+
+                LastPathToTool = pathToTool;
+                LastResponseFile = response.Remove(response.Length - 1).Split('\n');
+
+                // Do not run the tool, but pretend it ran successfully.
+                return 0;
+            }
+        };
+
+        protected Mock<IBuildEngine> _mockEngine;
+        protected ProtoCompileTestable _task;
+
+        [SetUp]
+        public void SetUp()
+        {
+            _mockEngine = new Mock<IBuildEngine>();
+            _task = new ProtoCompileTestable {
+                BuildEngine = _mockEngine.Object
+            };
+        }
+
+        [TestCase("ProtoBuf")]
+        [TestCase("Generator")]
+        [TestCase("OutputDir")]
+        [Description("We trust MSBuild to initialize these properties.")]
+        public void RequiredAttributePresentOnProperty(string prop)
+        {
+            var pinfo = _task.GetType()?.GetProperty(prop);
+            Assert.NotNull(pinfo);
+            Assert.That(pinfo, Has.Attribute<RequiredAttribute>());
+        }
+    };
+}
diff --git a/src/csharp/Grpc.Tools.Tests/ProtoCompileCommandLineGeneratorTest.cs b/src/csharp/Grpc.Tools.Tests/ProtoCompileCommandLineGeneratorTest.cs
new file mode 100644
index 0000000000..cac7146634
--- /dev/null
+++ b/src/csharp/Grpc.Tools.Tests/ProtoCompileCommandLineGeneratorTest.cs
@@ -0,0 +1,179 @@
+#region Copyright notice and license
+
+// Copyright 2018 gRPC authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#endregion
+
+using System.IO;
+using Microsoft.Build.Framework;
+using Moq;
+using NUnit.Framework;
+
+namespace Grpc.Tools.Tests
+{
+    public class ProtoCompileCommandLineGeneratorTest : ProtoCompileBasicTest
+    {
+        [SetUp]
+        public new void SetUp()
+        {
+            _task.Generator = "csharp";
+            _task.OutputDir = "outdir";
+            _task.ProtoBuf = Utils.MakeSimpleItems("a.proto");
+        }
+
+        void ExecuteExpectSuccess()
+        {
+            _mockEngine
+              .Setup(me => me.LogErrorEvent(It.IsAny<BuildErrorEventArgs>()))
+              .Callback((BuildErrorEventArgs e) =>
+                  Assert.Fail($"Error logged by build engine:\n{e.Message}"));
+            bool result = _task.Execute();
+            Assert.IsTrue(result);
+        }
+
+        [Test]
+        public void MinimalCompile()
+        {
+            ExecuteExpectSuccess();
+            Assert.That(_task.LastPathToTool, Does.Match(@"protoc(.exe)?$"));
+            Assert.That(_task.LastResponseFile, Is.EqualTo(new[] {
+                "--csharp_out=outdir", "a.proto" }));
+        }
+
+        [Test]
+        public void CompileTwoFiles()
+        {
+            _task.ProtoBuf = Utils.MakeSimpleItems("a.proto", "foo/b.proto");
+            ExecuteExpectSuccess();
+            Assert.That(_task.LastResponseFile, Is.EqualTo(new[] {
+                "--csharp_out=outdir", "a.proto", "foo/b.proto" }));
+        }
+
+        [Test]
+        public void CompileWithProtoPaths()
+        {
+            _task.ProtoPath = new[] { "/path1", "/path2" };
+            ExecuteExpectSuccess();
+            Assert.That(_task.LastResponseFile, Is.EqualTo(new[] {
+                "--csharp_out=outdir", "--proto_path=/path1",
+                "--proto_path=/path2", "a.proto" }));
+        }
+
+        [TestCase("Cpp")]
+        [TestCase("CSharp")]
+        [TestCase("Java")]
+        [TestCase("Javanano")]
+        [TestCase("Js")]
+        [TestCase("Objc")]
+        [TestCase("Php")]
+        [TestCase("Python")]
+        [TestCase("Ruby")]
+        public void CompileWithOptions(string gen)
+        {
+            _task.Generator = gen;
+            _task.OutputOptions = new[] { "foo", "bar" };
+            ExecuteExpectSuccess();
+            gen = gen.ToLowerInvariant();
+            Assert.That(_task.LastResponseFile, Is.EqualTo(new[] {
+                $"--{gen}_out=outdir", $"--{gen}_opt=foo,bar", "a.proto" }));
+        }
+
+        [Test]
+        public void OutputDependencyFile()
+        {
+            _task.DependencyOut = "foo/my.protodep";
+            // Task fails trying to read the non-generated file; we ignore that.
+            _task.Execute();
+            Assert.That(_task.LastResponseFile,
+                Does.Contain("--dependency_out=foo/my.protodep"));
+        }
+
+        [Test]
+        public void OutputDependencyWithProtoDepDir()
+        {
+            _task.ProtoDepDir = "foo";
+            // Task fails trying to read the non-generated file; we ignore that.
+            _task.Execute();
+            Assert.That(_task.LastResponseFile,
+                Has.One.Match(@"^--dependency_out=foo[/\\].+_a.protodep$"));
+        }
+
+        [Test]
+        public void GenerateGrpc()
+        {
+            _task.GrpcPluginExe = "/foo/grpcgen";
+            ExecuteExpectSuccess();
+            Assert.That(_task.LastResponseFile, Is.SupersetOf(new[] {
+                "--csharp_out=outdir", "--grpc_out=outdir",
+                "--plugin=protoc-gen-grpc=/foo/grpcgen" }));
+        }
+
+        [Test]
+        public void GenerateGrpcWithOutDir()
+        {
+            _task.GrpcPluginExe = "/foo/grpcgen";
+            _task.GrpcOutputDir = "gen-out";
+            ExecuteExpectSuccess();
+            Assert.That(_task.LastResponseFile, Is.SupersetOf(new[] {
+                "--csharp_out=outdir", "--grpc_out=gen-out" }));
+        }
+
+        [Test]
+        public void GenerateGrpcWithOptions()
+        {
+            _task.GrpcPluginExe = "/foo/grpcgen";
+            _task.GrpcOutputOptions = new[] { "baz", "quux" };
+            ExecuteExpectSuccess();
+            Assert.That(_task.LastResponseFile,
+                        Does.Contain("--grpc_opt=baz,quux"));
+        }
+
+        [Test]
+        public void DirectoryArgumentsSlashTrimmed()
+        {
+            _task.GrpcPluginExe = "/foo/grpcgen";
+            _task.GrpcOutputDir = "gen-out/";
+            _task.OutputDir = "outdir/";
+            _task.ProtoPath = new[] { "/path1/", "/path2/" };
+            ExecuteExpectSuccess();
+            Assert.That(_task.LastResponseFile, Is.SupersetOf(new[] {
+        "--proto_path=/path1", "--proto_path=/path2",
+        "--csharp_out=outdir", "--grpc_out=gen-out" }));
+        }
+
+        [TestCase(".", ".")]
+        [TestCase("/", "/")]
+        [TestCase("//", "/")]
+        [TestCase("/foo/", "/foo")]
+        [TestCase("/foo", "/foo")]
+        [TestCase("foo/", "foo")]
+        [TestCase("foo//", "foo")]
+        [TestCase("foo/\\", "foo")]
+        [TestCase("foo\\/", "foo")]
+        [TestCase("C:\\foo", "C:\\foo")]
+        [TestCase("C:", "C:")]
+        [TestCase("C:\\", "C:\\")]
+        [TestCase("C:\\\\", "C:\\")]
+        public void DirectorySlashTrimmingCases(string given, string expect)
+        {
+            if (Path.DirectorySeparatorChar == '/')
+                expect = expect.Replace('\\', '/');
+            _task.OutputDir = given;
+            ExecuteExpectSuccess();
+            Assert.That(_task.LastResponseFile,
+                        Does.Contain("--csharp_out=" + expect));
+        }
+    };
+}
diff --git a/src/csharp/Grpc.Tools.Tests/ProtoCompileCommandLinePrinterTest.cs b/src/csharp/Grpc.Tools.Tests/ProtoCompileCommandLinePrinterTest.cs
new file mode 100644
index 0000000000..1773dcb875
--- /dev/null
+++ b/src/csharp/Grpc.Tools.Tests/ProtoCompileCommandLinePrinterTest.cs
@@ -0,0 +1,51 @@
+#region Copyright notice and license
+
+// Copyright 2018 gRPC authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#endregion
+
+using Microsoft.Build.Framework;
+using Moq;
+using NUnit.Framework;
+
+namespace Grpc.Tools.Tests
+{
+    public class ProtoCompileCommandLinePrinterTest : ProtoCompileBasicTest
+    {
+        [SetUp]
+        public new void SetUp()
+        {
+            _task.Generator = "csharp";
+            _task.OutputDir = "outdir";
+            _task.ProtoBuf = Utils.MakeSimpleItems("a.proto");
+
+            _mockEngine
+              .Setup(me => me.LogMessageEvent(It.IsAny<BuildMessageEventArgs>()))
+              .Callback((BuildMessageEventArgs e) =>
+                  Assert.Fail($"Error logged by build engine:\n{e.Message}"))
+              .Verifiable("Command line was not output by the task.");
+        }
+
+        void ExecuteExpectSuccess()
+        {
+            _mockEngine
+              .Setup(me => me.LogErrorEvent(It.IsAny<BuildErrorEventArgs>()))
+              .Callback((BuildErrorEventArgs e) =>
+                  Assert.Fail($"Error logged by build engine:\n{e.Message}"));
+            bool result = _task.Execute();
+            Assert.IsTrue(result);
+        }
+    };
+}
diff --git a/src/csharp/Grpc.Tools.Tests/ProtoToolsPlatformTaskTest.cs b/src/csharp/Grpc.Tools.Tests/ProtoToolsPlatformTaskTest.cs
new file mode 100644
index 0000000000..54723b74fc
--- /dev/null
+++ b/src/csharp/Grpc.Tools.Tests/ProtoToolsPlatformTaskTest.cs
@@ -0,0 +1,139 @@
+#region Copyright notice and license
+
+// Copyright 2018 gRPC authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#endregion
+
+using System.Runtime.InteropServices;  // For NETCORE tests.
+using Microsoft.Build.Framework;
+using Moq;
+using NUnit.Framework;
+
+namespace Grpc.Tools.Tests
+{
+    public class ProtoToolsPlatformTaskTest
+    {
+        ProtoToolsPlatform _task;
+        int _cpuMatched, _osMatched;
+
+        [OneTimeSetUp]
+        public void SetUp()
+        {
+            var mockEng = new Mock<IBuildEngine>();
+            _task = new ProtoToolsPlatform() { BuildEngine = mockEng.Object };
+            _task.Execute();
+        }
+
+        [OneTimeTearDown]
+        public void TearDown()
+        {
+            Assert.AreEqual(1, _cpuMatched, "CPU type detection failed");
+            Assert.AreEqual(1, _osMatched, "OS detection failed");
+        }
+
+#if NETCORE
+        // PlatformAttribute not yet available in NUnit, coming soon:
+        // https://github.com/nunit/nunit/pull/3003.
+        // Use same test case names as under the full framework.
+        [Test]
+        public void CpuIsX86()
+        {
+            if (RuntimeInformation.OSArchitecture == Architecture.X86)
+            {
+                _cpuMatched++;
+                Assert.AreEqual("x86", _task.Cpu);
+            }
+        }
+
+        [Test]
+        public void CpuIsX64()
+        {
+            if (RuntimeInformation.OSArchitecture == Architecture.X64)
+            {
+                _cpuMatched++;
+                Assert.AreEqual("x64", _task.Cpu);
+            }
+        }
+
+        [Test]
+        public void OsIsWindows()
+        {
+            if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
+            {
+                _osMatched++;
+                Assert.AreEqual("windows", _task.Os);
+            }
+        }
+
+        [Test]
+        public void OsIsLinux()
+        {
+            if (RuntimeInformation.IsOSPlatform(OSPlatform.Linux))
+            {
+                _osMatched++;
+                Assert.AreEqual("linux", _task.Os);
+            }
+        }
+
+        [Test]
+        public void OsIsMacOsX()
+        {
+            if (RuntimeInformation.IsOSPlatform(OSPlatform.OSX))
+            {
+                _osMatched++;
+                Assert.AreEqual("macosx", _task.Os);
+            }
+        }
+
+#else  // !NETCORE, i.e. full framework.
+
+        [Test, Platform("32-Bit")]
+        public void CpuIsX86()
+        {
+            _cpuMatched++;
+            Assert.AreEqual("x86", _task.Cpu);
+        }
+
+        [Test, Platform("64-Bit")]
+        public void CpuIsX64()
+        {
+            _cpuMatched++;
+            Assert.AreEqual("x64", _task.Cpu);
+        }
+
+        [Test, Platform("Win")]
+        public void OsIsWindows()
+        {
+            _osMatched++;
+            Assert.AreEqual("windows", _task.Os);
+        }
+
+        [Test, Platform("Linux")]
+        public void OsIsLinux()
+        {
+            _osMatched++;
+            Assert.AreEqual("linux", _task.Os);
+        }
+
+        [Test, Platform("MacOSX")]
+        public void OsIsMacOsX()
+        {
+            _osMatched++;
+            Assert.AreEqual("macosx", _task.Os);
+        }
+
+#endif  // NETCORE
+    };
+}
diff --git a/src/csharp/Grpc.Tools.Tests/Utils.cs b/src/csharp/Grpc.Tools.Tests/Utils.cs
new file mode 100644
index 0000000000..6e0f1cffd5
--- /dev/null
+++ b/src/csharp/Grpc.Tools.Tests/Utils.cs
@@ -0,0 +1,46 @@
+#region Copyright notice and license
+
+// Copyright 2018 gRPC authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#endregion
+
+using System.Linq;
+using Microsoft.Build.Framework;
+using Microsoft.Build.Utilities;
+
+namespace Grpc.Tools.Tests
+{
+    static class Utils
+    {
+        // Build an item with a name from args[0] and metadata key-value pairs
+        // from the rest of args, interleaved.
+        // This does not do any checking, and expects an odd number of args.
+        public static ITaskItem MakeItem(params string[] args)
+        {
+            var item = new TaskItem(args[0]);
+            for (int i = 1; i < args.Length; i += 2)
+            {
+                item.SetMetadata(args[i], args[i + 1]);
+            }
+            return item;
+        }
+
+        // Return an array of items from given itemspecs.
+        public static ITaskItem[] MakeSimpleItems(params string[] specs)
+        {
+            return specs.Select(s => new TaskItem(s)).ToArray();
+        }
+    };
+}
diff --git a/src/csharp/Grpc.Tools.nuspec b/src/csharp/Grpc.Tools.nuspec
deleted file mode 100644
index 0cae5572fd..0000000000
--- a/src/csharp/Grpc.Tools.nuspec
+++ /dev/null
@@ -1,33 +0,0 @@
-<?xml version="1.0" encoding="utf-8"?>
-<package>
-  <metadata>
-    <id>Grpc.Tools</id>
-    <title>gRPC C# Tools</title>
-    <summary>Tools for C# implementation of gRPC - an RPC library and framework</summary>
-    <description>Precompiled protobuf compiler and gRPC protobuf compiler plugin for generating gRPC client/server C# code. Binaries are available for Windows, Linux and MacOS.</description>
-    <version>$version$</version>
-    <authors>Google Inc.</authors>
-    <owners>grpc-packages</owners>
-    <licenseUrl>https://github.com/grpc/grpc/blob/master/LICENSE</licenseUrl>
-    <projectUrl>https://github.com/grpc/grpc</projectUrl>
-    <requireLicenseAcceptance>false</requireLicenseAcceptance>
-    <releaseNotes>Release $version$</releaseNotes>
-    <copyright>Copyright 2015, Google Inc.</copyright>
-    <tags>gRPC RPC Protocol HTTP/2</tags>
-  </metadata>
-  <files>
-    <!-- forward slashes in src path enable building on Linux -->
-    <file src="protoc_plugins/protoc_windows_x86/protoc.exe" target="tools/windows_x86/protoc.exe" />
-    <file src="protoc_plugins/protoc_windows_x86/grpc_csharp_plugin.exe" target="tools/windows_x86/grpc_csharp_plugin.exe" />
-    <file src="protoc_plugins/protoc_windows_x64/protoc.exe" target="tools/windows_x64/protoc.exe" />
-    <file src="protoc_plugins/protoc_windows_x64/grpc_csharp_plugin.exe" target="tools/windows_x64/grpc_csharp_plugin.exe" />
-    <file src="protoc_plugins/protoc_linux_x86/protoc" target="tools/linux_x86/protoc" />
-    <file src="protoc_plugins/protoc_linux_x86/grpc_csharp_plugin" target="tools/linux_x86/grpc_csharp_plugin" />
-    <file src="protoc_plugins/protoc_linux_x64/protoc" target="tools/linux_x64/protoc" />
-    <file src="protoc_plugins/protoc_linux_x64/grpc_csharp_plugin" target="tools/linux_x64/grpc_csharp_plugin" />
-    <file src="protoc_plugins/protoc_macos_x86/protoc" target="tools/macosx_x86/protoc" />
-    <file src="protoc_plugins/protoc_macos_x86/grpc_csharp_plugin" target="tools/macosx_x86/grpc_csharp_plugin" />
-    <file src="protoc_plugins/protoc_macos_x64/protoc" target="tools/macosx_x64/protoc" />
-    <file src="protoc_plugins/protoc_macos_x64/grpc_csharp_plugin" target="tools/macosx_x64/grpc_csharp_plugin" />
-  </files>
-</package>
diff --git a/src/csharp/Grpc.Tools/Common.cs b/src/csharp/Grpc.Tools/Common.cs
new file mode 100644
index 0000000000..e6acdd6393
--- /dev/null
+++ b/src/csharp/Grpc.Tools/Common.cs
@@ -0,0 +1,114 @@
+#region Copyright notice and license
+
+// Copyright 2018 gRPC authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#endregion
+
+using System;
+using System.IO;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+using System.Security;
+
+[assembly: InternalsVisibleTo("Grpc.Tools.Tests")]
+
+namespace Grpc.Tools
+{
+    // Metadata names (MSBuild item attributes) that we refer to often.
+    static class Metadata
+    {
+        // On output dependency lists.
+        public static string Source = "Source";
+        // On ProtoBuf items.
+        public static string ProtoRoot = "ProtoRoot";
+        public static string OutputDir = "OutputDir";
+        public static string GrpcServices = "GrpcServices";
+        public static string GrpcOutputDir = "GrpcOutputDir";
+    };
+
+    // A few flags used to control the behavior under various platforms.
+    internal static class Platform
+    {
+        public enum OsKind { Unknown, Windows, Linux, MacOsX };
+        public static readonly OsKind Os;
+
+        public enum CpuKind { Unknown, X86, X64 };
+        public static readonly CpuKind Cpu;
+
+        // This is not necessarily true, but good enough. BCL lacks a per-FS
+        // API to determine file case sensitivity.
+        public static bool IsFsCaseInsensitive => Os == OsKind.Windows;
+        public static bool IsWindows => Os == OsKind.Windows;
+
+        static Platform()
+        {
+#if NETCORE
+            Os = RuntimeInformation.IsOSPlatform(OSPlatform.Windows) ? OsKind.Windows
+               : RuntimeInformation.IsOSPlatform(OSPlatform.Linux) ? OsKind.Linux
+               : RuntimeInformation.IsOSPlatform(OSPlatform.OSX) ? OsKind.MacOsX
+               : OsKind.Unknown;
+
+            switch (RuntimeInformation.OSArchitecture)
+            {
+                case Architecture.X86: Cpu = CpuKind.X86; break;
+                case Architecture.X64: Cpu = CpuKind.X64; break;
+                // We do not have build tools for other architectures.
+                default: Cpu = CpuKind.Unknown; break;
+            }
+#else
+            // Running under either Mono or full MS framework.
+            Os = OsKind.Windows;
+            if (Type.GetType("Mono.Runtime", throwOnError: false) != null)
+            {
+                // Congratulations. We are running under Mono.
+                var plat = Environment.OSVersion.Platform;
+                if (plat == PlatformID.MacOSX)
+                {
+                    Os = OsKind.MacOsX;
+                }
+                else if (plat == PlatformID.Unix || (int)plat == 128)
+                {
+                    // This is how Mono detects OSX internally.
+                    Os = File.Exists("/usr/lib/libc.dylib") ? OsKind.MacOsX : OsKind.Linux;
+                }
+            }
+
+            // Hope we are not building on ARM under Xamarin!
+            Cpu = Environment.Is64BitOperatingSystem ? CpuKind.X64 : CpuKind.X86;
+#endif
+        }
+    };
+
+    // Exception handling helpers.
+    static class Exceptions
+    {
+        // Returns true iff the exception indicates an error from an I/O call. See
+        // https://github.com/Microsoft/msbuild/blob/v15.4.8.50001/src/Shared/ExceptionHandling.cs#L101
+        static public bool IsIoRelated(Exception ex) =>
+            ex is IOException ||
+            (ex is ArgumentException && !(ex is ArgumentNullException)) ||
+            ex is SecurityException ||
+            ex is UnauthorizedAccessException ||
+            ex is NotSupportedException;
+    };
+
+    // String helpers.
+    static class Strings
+    {
+        // Compare string to argument using OrdinalIgnoreCase comparison.
+        public static bool EqualNoCase(this string a, string b) =>
+            string.Equals(a, b, StringComparison.OrdinalIgnoreCase);
+    }
+}
diff --git a/src/csharp/Grpc.Tools/DepFileUtil.cs b/src/csharp/Grpc.Tools/DepFileUtil.cs
new file mode 100644
index 0000000000..440d3d535c
--- /dev/null
+++ b/src/csharp/Grpc.Tools/DepFileUtil.cs
@@ -0,0 +1,273 @@
+#region Copyright notice and license
+
+// Copyright 2018 gRPC authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#endregion
+
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Text;
+using Microsoft.Build.Framework;
+using Microsoft.Build.Utilities;
+
+namespace Grpc.Tools
+{
+    internal static class DepFileUtil
+    {
+        /*
+           Sample dependency files. Notable features we have to deal with:
+            * Slash doubling, must normalize them.
+            * Spaces in file names. Cannot just "unwrap" the line on backslash at eof;
+              rather, treat every line as containing one file name except for one with
+              the ':' separator, as containing exactly two.
+            * Deal with ':' also being drive letter separator (second example).
+
+        obj\Release\net45\/Foo.cs \
+        obj\Release\net45\/FooGrpc.cs: C:/foo/include/google/protobuf/wrappers.proto\
+         C:/projects/foo/src//foo.proto
+
+        C:\projects\foo\src\./foo.grpc.pb.cc \
+        C:\projects\foo\src\./foo.grpc.pb.h \
+        C:\projects\foo\src\./foo.pb.cc \
+        C:\projects\foo\src\./foo.pb.h: C:/foo/include/google/protobuf/wrappers.proto\
+         C:/foo/include/google/protobuf/any.proto\
+         C:/foo/include/google/protobuf/source_context.proto\
+         C:/foo/include/google/protobuf/type.proto\
+         foo.proto
+        */
+
+        /// <summary>
+        /// Read file names from the dependency file to the right of ':'
+        /// </summary>
+        /// <param name="protoDepDir">Relative path to the dependency cache, e. g. "out"</param>
+        /// <param name="proto">Relative path to the proto item, e. g. "foo/file.proto"</param>
+        /// <param name="log">A <see cref="TaskLoggingHelper"/> for logging</param>
+        /// <returns>
+        /// Array of the proto file <b>input</b> dependencies as written by protoc, or empty
+        /// array if the dependency file does not exist or cannot be parsed.
+        /// </returns>
+        public static string[] ReadDependencyInputs(string protoDepDir, string proto,
+                                                    TaskLoggingHelper log)
+        {
+            string depFilename = GetDepFilenameForProto(protoDepDir, proto);
+            string[] lines = ReadDepFileLines(depFilename, false, log);
+            if (lines.Length == 0)
+            {
+                return lines;
+            }
+
+            var result = new List<string>();
+            bool skip = true;
+            foreach (string line in lines)
+            {
+                // Start at the only line separating dependency outputs from inputs.
+                int ix = skip ? FindLineSeparator(line) : -1;
+                skip = skip && ix < 0;
+                if (skip) { continue; }
+                string file = ExtractFilenameFromLine(line, ix + 1, line.Length);
+                if (file == "")
+                {
+                    log.LogMessage(MessageImportance.Low,
+              $"Skipping unparsable dependency file {depFilename}.\nLine with error: '{line}'");
+                    return new string[0];
+                }
+
+                // Do not bend over backwards trying not to include a proto into its
+                // own list of dependencies. Since a file is not older than self,
+                // it is safe to add; this is purely a memory optimization.
+                if (file != proto)
+                {
+                    result.Add(file);
+                }
+            }
+            return result.ToArray();
+        }
+
+        /// <summary>
+        /// Read file names from the dependency file to the left of ':'
+        /// </summary>
+        /// <param name="depFilename">Path to dependency file written by protoc</param>
+        /// <param name="log">A <see cref="TaskLoggingHelper"/> for logging</param>
+        /// <returns>
+        /// Array of the protoc-generated outputs from the given dependency file
+        /// written by protoc, or empty array if the file does not exist or cannot
+        /// be parsed.
+        /// </returns>
+        /// <remarks>
+        /// Since this is called after a protoc invocation, an unparsable or missing
+        /// file causes an error-level message to be logged.
+        /// </remarks>
+        public static string[] ReadDependencyOutputs(string depFilename,
+                                                    TaskLoggingHelper log)
+        {
+            string[] lines = ReadDepFileLines(depFilename, true, log);
+            if (lines.Length == 0)
+            {
+                return lines;
+            }
+
+            var result = new List<string>();
+            foreach (string line in lines)
+            {
+                int ix = FindLineSeparator(line);
+                string file = ExtractFilenameFromLine(line, 0, ix >= 0 ? ix : line.Length);
+                if (file == "")
+                {
+                    log.LogError("Unable to parse generated dependency file {0}.\n" +
+                                 "Line with error: '{1}'", depFilename, line);
+                    return new string[0];
+                }
+                result.Add(file);
+
+                // If this is the line with the separator, do not read further.
+                if (ix >= 0) { break; }
+            }
+            return result.ToArray();
+        }
+
+        /// <summary>
+        /// Construct relative dependency file name from directory hash and file name
+        /// </summary>
+        /// <param name="protoDepDir">Relative path to the dependency cache, e. g. "out"</param>
+        /// <param name="proto">Relative path to the proto item, e. g. "foo/file.proto"</param>
+        /// <returns>
+        /// Full relative path to the dependency file, e. g.
+        /// "out/deadbeef12345678_file.protodep"
+        /// </returns>
+        /// <remarks>
+        /// Since a project may contain proto files with the same filename but in different
+        /// directories, a unique filename for the dependency file is constructed based on the
+        /// proto file name both name and directory. The directory path can be arbitrary,
+        /// for example, it can be outside of the project, or an absolute path including
+        /// a drive letter, or a UNC network path. A name constructed from such a path by,
+        /// for example, replacing disallowed name characters with an underscore, may well
+        /// be over filesystem's allowed path length, since it will be located under the
+        /// project and solution directories, which are also some level deep from the root.
+        /// Instead of creating long and unwieldy names for these proto sources, we cache
+        /// the full path of the name without the filename, and append the filename to it,
+        /// as in e. g. "foo/file.proto" will yield the name "deadbeef12345678_file", where
+        /// "deadbeef12345678" is a presumed hash value of the string "foo/". This allows
+        /// the file names be short, unique (up to a hash collision), and still allowing
+        /// the user to guess their provenance.
+        /// </remarks>
+        public static string GetDepFilenameForProto(string protoDepDir, string proto)
+        {
+            string dirname = Path.GetDirectoryName(proto);
+            if (Platform.IsFsCaseInsensitive)
+            {
+                dirname = dirname.ToLowerInvariant();
+            }
+            string dirhash = HashString64Hex(dirname);
+            string filename = Path.GetFileNameWithoutExtension(proto);
+            return Path.Combine(protoDepDir, $"{dirhash}_{filename}.protodep");
+        }
+
+        // Get a 64-bit hash for a directory string. We treat it as if it were
+        // unique, since there are not so many distinct proto paths in a project.
+        // We take the first 64 bit of the string SHA1.
+        // Internal for tests access only.
+        internal static string HashString64Hex(string str)
+        {
+            using (var sha1 = System.Security.Cryptography.SHA1.Create())
+            {
+                byte[] hash = sha1.ComputeHash(Encoding.UTF8.GetBytes(str));
+                var hashstr = new StringBuilder(16);
+                for (int i = 0; i < 8; i++)
+                {
+                    hashstr.Append(hash[i].ToString("x2"));
+                }
+                return hashstr.ToString();
+            }
+        }
+
+        // Extract filename between 'beg' (inclusive) and 'end' (exclusive) from
+        // line 'line', skipping over trailing and leading whitespace, and, when
+        // 'end' is immediately past end of line 'line', also final '\' (used
+        // as a line continuation token in the dep file).
+        // Returns an empty string if the filename cannot be extracted.
+        static string ExtractFilenameFromLine(string line, int beg, int end)
+        {
+            while (beg < end && char.IsWhiteSpace(line[beg])) beg++;
+            if (beg < end && end == line.Length && line[end - 1] == '\\') end--;
+            while (beg < end && char.IsWhiteSpace(line[end - 1])) end--;
+            if (beg == end) return "";
+
+            string filename = line.Substring(beg, end - beg);
+            try
+            {
+                // Normalize file name.
+                return Path.Combine(Path.GetDirectoryName(filename), Path.GetFileName(filename));
+            }
+            catch (Exception ex) when (Exceptions.IsIoRelated(ex))
+            {
+                return "";
+            }
+        }
+
+        // Finds the index of the ':' separating dependency clauses in the line,
+        // not taking Windows drive spec into account. Returns the index of the
+        // separating ':', or -1 if no separator found.
+        static int FindLineSeparator(string line)
+        {
+            // Mind this case where the first ':' is not separator:
+            // C:\foo\bar\.pb.h: C:/protobuf/wrappers.proto\
+            int ix = line.IndexOf(':');
+            if (ix <= 0 || ix == line.Length - 1
+                || (line[ix + 1] != '/' && line[ix + 1] != '\\')
+                || !char.IsLetter(line[ix - 1]))
+            {
+                return ix;  // Not a windows drive: no letter before ':', or no '\' after.
+            }
+            for (int j = ix - 1; --j >= 0;)
+            {
+                if (!char.IsWhiteSpace(line[j]))
+                {
+                    return ix;  // Not space or BOL only before "X:/".
+                }
+            }
+            return line.IndexOf(':', ix + 1);
+        }
+
+        // Read entire dependency file. The 'required' parameter controls error
+        // logging behavior in case the file not found. We require this file when
+        // compiling, but reading it is optional when computing dependencies.
+        static string[] ReadDepFileLines(string filename, bool required,
+                                         TaskLoggingHelper log)
+        {
+            try
+            {
+                var result = File.ReadAllLines(filename);
+                if (!required)
+                {
+                    log.LogMessage(MessageImportance.Low, $"Using dependency file {filename}");
+                }
+                return result;
+            }
+            catch (Exception ex) when (Exceptions.IsIoRelated(ex))
+            {
+                if (required)
+                {
+                    log.LogError($"Unable to load {filename}: {ex.GetType().Name}: {ex.Message}");
+                }
+                else
+                {
+                    log.LogMessage(MessageImportance.Low, $"Skipping {filename}: {ex.Message}");
+                }
+                return new string[0];
+            }
+        }
+    };
+}
diff --git a/src/csharp/Grpc.Tools/GeneratorServices.cs b/src/csharp/Grpc.Tools/GeneratorServices.cs
new file mode 100644
index 0000000000..536ec43c83
--- /dev/null
+++ b/src/csharp/Grpc.Tools/GeneratorServices.cs
@@ -0,0 +1,194 @@
+#region Copyright notice and license
+
+// Copyright 2018 gRPC authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#endregion
+
+using System;
+using System.IO;
+using System.Text;
+using Microsoft.Build.Framework;
+using Microsoft.Build.Utilities;
+
+namespace Grpc.Tools
+{
+    // Abstract class for language-specific analysis behavior, such
+    // as guessing the generated files the same way protoc does.
+    internal abstract class GeneratorServices
+    {
+        protected readonly TaskLoggingHelper Log;
+        protected GeneratorServices(TaskLoggingHelper log) { Log = log; }
+
+        // Obtain a service for the given language (csharp, cpp).
+        public static GeneratorServices GetForLanguage(string lang, TaskLoggingHelper log)
+        {
+            if (lang.EqualNoCase("csharp")) { return new CSharpGeneratorServices(log); }
+            if (lang.EqualNoCase("cpp")) { return new CppGeneratorServices(log); }
+
+            log.LogError("Invalid value '{0}' for task property 'Generator'. " +
+                "Supported generator languages: CSharp, Cpp.", lang);
+            return null;
+        }
+
+        // Guess whether item's metadata suggests gRPC stub generation.
+        // When "gRPCServices" is not defined, assume gRPC is not used.
+        // When defined, C# uses "none" to skip gRPC, C++ uses "false", so
+        // recognize both. Since the value is tightly coupled to the scripts,
+        // we do not try to validate the value; scripts take care of that.
+        // It is safe to assume that gRPC is requested for any other value.
+        protected bool GrpcOutputPossible(ITaskItem proto)
+        {
+            string gsm = proto.GetMetadata(Metadata.GrpcServices);
+            return !gsm.EqualNoCase("") && !gsm.EqualNoCase("none")
+                && !gsm.EqualNoCase("false");
+        }
+
+        public abstract string[] GetPossibleOutputs(ITaskItem proto);
+    };
+
+    // C# generator services.
+    internal class CSharpGeneratorServices : GeneratorServices
+    {
+        public CSharpGeneratorServices(TaskLoggingHelper log) : base(log) { }
+
+        public override string[] GetPossibleOutputs(ITaskItem protoItem)
+        {
+            bool doGrpc = GrpcOutputPossible(protoItem);
+            string filename = LowerUnderscoreToUpperCamel(
+                Path.GetFileNameWithoutExtension(protoItem.ItemSpec));
+
+            var outputs = new string[doGrpc ? 2 : 1];
+            string outdir = protoItem.GetMetadata(Metadata.OutputDir);
+            string fileStem = Path.Combine(outdir, filename);
+            outputs[0] = fileStem + ".cs";
+            if (doGrpc)
+            {
+                // Override outdir if kGrpcOutputDir present, default to proto output.
+                outdir = protoItem.GetMetadata(Metadata.GrpcOutputDir);
+                if (outdir != "")
+                {
+                    fileStem = Path.Combine(outdir, filename);
+                }
+                outputs[1] = fileStem + "Grpc.cs";
+            }
+            return outputs;
+        }
+
+        string LowerUnderscoreToUpperCamel(string str)
+        {
+            // See src/compiler/generator_helpers.h:118
+            var result = new StringBuilder(str.Length, str.Length);
+            bool cap = true;
+            foreach (char c in str)
+            {
+                if (c == '_')
+                {
+                    cap = true;
+                }
+                else if (cap)
+                {
+                    result.Append(char.ToUpperInvariant(c));
+                    cap = false;
+                }
+                else
+                {
+                    result.Append(c);
+                }
+            }
+            return result.ToString();
+        }
+    };
+
+    // C++ generator services.
+    internal class CppGeneratorServices : GeneratorServices
+    {
+        public CppGeneratorServices(TaskLoggingHelper log) : base(log) { }
+
+        public override string[] GetPossibleOutputs(ITaskItem protoItem)
+        {
+            bool doGrpc = GrpcOutputPossible(protoItem);
+            string root = protoItem.GetMetadata(Metadata.ProtoRoot);
+            string proto = protoItem.ItemSpec;
+            string filename = Path.GetFileNameWithoutExtension(proto);
+            // E. g., ("foo/", "foo/bar/x.proto") => "bar"
+            string relative = GetRelativeDir(root, proto);
+
+            var outputs = new string[doGrpc ? 4 : 2];
+            string outdir = protoItem.GetMetadata(Metadata.OutputDir);
+            string fileStem = Path.Combine(outdir, relative, filename);
+            outputs[0] = fileStem + ".pb.cc";
+            outputs[1] = fileStem + ".pb.h";
+            if (doGrpc)
+            {
+                // Override outdir if kGrpcOutputDir present, default to proto output.
+                outdir = protoItem.GetMetadata(Metadata.GrpcOutputDir);
+                if (outdir != "")
+                {
+                    fileStem = Path.Combine(outdir, relative, filename);
+                }
+                outputs[2] = fileStem + "_grpc.pb.cc";
+                outputs[3] = fileStem + "_grpc.pb.h";
+            }
+            return outputs;
+        }
+
+        // Calculate part of proto path relative to root. Protoc is very picky
+        // about them matching exactly, so can be we. Expect root be exact prefix
+        // to proto, minus some slash normalization.
+        string GetRelativeDir(string root, string proto)
+        {
+            string protoDir = Path.GetDirectoryName(proto);
+            string rootDir = EndWithSlash(Path.GetDirectoryName(EndWithSlash(root)));
+            if (rootDir == s_dotSlash)
+            {
+                // Special case, otherwise we can return "./" instead of "" below!
+                return protoDir;
+            }
+            if (Platform.IsFsCaseInsensitive)
+            {
+                protoDir = protoDir.ToLowerInvariant();
+                rootDir = rootDir.ToLowerInvariant();
+            }
+            protoDir = EndWithSlash(protoDir);
+            if (!protoDir.StartsWith(rootDir))
+            {
+                Log.LogWarning("ProtoBuf item '{0}' has the ProtoRoot metadata '{1}' " +
+                  "which is not prefix to its path. Cannot compute relative path.",
+                  proto, root);
+                return "";
+            }
+            return protoDir.Substring(rootDir.Length);
+        }
+
+        // './' or '.\', normalized per system.
+        static string s_dotSlash = "." + Path.DirectorySeparatorChar;
+
+        static string EndWithSlash(string str)
+        {
+            if (str == "")
+            {
+                return s_dotSlash;
+            }
+            else if (str[str.Length - 1] != '\\' && str[str.Length - 1] != '/')
+            {
+                return str + Path.DirectorySeparatorChar;
+            }
+            else
+            {
+                return str;
+            }
+        }
+    };
+}
diff --git a/src/csharp/Grpc.Tools/Grpc.Tools.csproj b/src/csharp/Grpc.Tools/Grpc.Tools.csproj
new file mode 100644
index 0000000000..61fa75a4ec
--- /dev/null
+++ b/src/csharp/Grpc.Tools/Grpc.Tools.csproj
@@ -0,0 +1,101 @@
+<Project Sdk="Microsoft.NET.Sdk" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+
+  <Import Project="..\Grpc.Core\Version.csproj.include" />
+
+  <PropertyGroup>
+    <AssemblyName>Protobuf.MSBuild</AssemblyName>
+    <Version>$(GrpcCsharpVersion)</Version>
+    <!-- If changing targets, change also paths in Google.Protobuf.Tools.targets. -->
+    <TargetFrameworks>net45;netstandard1.3</TargetFrameworks>
+  </PropertyGroup>
+
+  <!-- This is copied verbatim from Grpc.Core/Common.csproj.include. Other settings
+       in that file conflict with the intent of this build, as it cannot be signed,
+       and may not compile Grpc.Core/Version.cs, as that file references constants
+       in Grpc.Core.dll.
+       TODO(kkm): Refactor imports. -->
+  <PropertyGroup Condition=" '$(OS)' != 'Windows_NT' and '$(MSBuildRuntimeType)' == 'Core' ">
+    <!-- Use Mono reference assemblies in SDK build: https://github.com/dotnet/sdk/issues/335 -->
+    <FrameworkPathOverride Condition="Exists('/usr/lib/mono/4.5-api')">/usr/lib/mono/4.5-api</FrameworkPathOverride>
+    <FrameworkPathOverride Condition="Exists('/usr/local/lib/mono/4.5-api')">/usr/local/lib/mono/4.5-api</FrameworkPathOverride>
+    <FrameworkPathOverride Condition="Exists('/Library/Frameworks/Mono.framework/Versions/Current/lib/mono/4.5-api')">/Library/Frameworks/Mono.framework/Versions/Current/lib/mono/4.5-api</FrameworkPathOverride>
+  </PropertyGroup>
+
+  <PropertyGroup Label="Asset root folders. TODO(kkm): Change with package separation.">
+    <!-- TODO(kkm): Rework whole section when splitting packages.  -->
+    <!-- GRPC: ../../third_party/protobuf/src/google/protobuf/  -->
+    <!-- GPB:  ../src/google/protobuf/ -->
+    <Assets_ProtoInclude>../../../third_party/protobuf/src/google/protobuf/</Assets_ProtoInclude>
+
+    <!-- GPB:  ../protoc/ -->
+    <!-- GRPC: ../protoc_plugins/protoc_ -->
+    <Assets_ProtoCompiler>../protoc_plugins/protoc_</Assets_ProtoCompiler>
+
+    <!-- GRPC: ../protoc_plugins/ -->
+    <Assets_GrpcPlugins>../protoc_plugins/</Assets_GrpcPlugins>
+  </PropertyGroup>
+
+  <PropertyGroup Condition=" '$(TargetFramework)' != 'net45' ">
+    <DefineConstants>$(DefineConstants);NETCORE</DefineConstants>
+  </PropertyGroup>
+
+  <PropertyGroup Label="NuGet package definition" Condition=" '$(Configuration)' == 'Release' ">
+    <!-- TODO(kkm): Change to "build\" after splitting. -->
+    <BuildOutputTargetFolder>build\_protobuf\</BuildOutputTargetFolder>
+    <DevelopmentDependency>true</DevelopmentDependency>
+    <NoPackageAnalysis>true</NoPackageAnalysis>
+    <PackageId>Grpc.Tools</PackageId>
+    <Description>gRPC and Protocol Buffer compiler for managed C# and native C++ projects.
+
+Add this package to a project that contains .proto files to be compiled to code.
+It contains the compilers, include files and project system integration for gRPC
+and Protocol buffer service description files necessary to build them on Windows,
+Linux and MacOS. Managed runtime is supplied separately in the Grpc.Core package.</Description>
+    <Copyright>Copyright 2018 gRPC authors</Copyright>
+    <Authors>gRPC authors</Authors>
+    <PackageLicenseUrl>https://github.com/grpc/grpc/blob/master/LICENSE</PackageLicenseUrl>
+    <PackageProjectUrl>https://github.com/grpc/grpc</PackageProjectUrl>
+    <PackageTags>gRPC RPC protocol HTTP/2</PackageTags>
+  </PropertyGroup>
+
+  <ItemGroup Label="NuGet package assets">
+    <None Pack="true" PackagePath="build\" Include="build\**\*.xml; build\**\*.props; build\**\*.targets;" />
+
+    <!-- Protobuf assets (for Google.Protobuf.Tools) -->
+    <_ProtoAssetName Include="any;api;descriptor;duration;empty;field_mask;
+                              source_context;struct;timestamp;type;wrappers" />
+    <_Asset PackagePath="build/native/include/google/protobuf/" Include="@(_ProtoAssetName->'$(Assets_ProtoInclude)%(Identity).proto')" />
+
+    <!-- TODO(kkm): GPB builds assets into "macosx", GRPC into "macos". -->
+    <!-- TODO(kkm): Do not place non-tools under tools/, use build/native/bin/. -->
+    <!-- TODO(kkm): Do not package windows x64 builds (#13098). -->
+    <_Asset PackagePath="tools/windows_x86/protoc.exe" Include="$(Assets_ProtoCompiler)windows_x86/protoc.exe" />
+    <_Asset PackagePath="tools/windows_x64/protoc.exe" Include="$(Assets_ProtoCompiler)windows_x64/protoc.exe" />
+    <_Asset PackagePath="tools/linux_x86/protoc" Include="$(Assets_ProtoCompiler)linux_x86/protoc" />
+    <_Asset PackagePath="tools/linux_x64/protoc" Include="$(Assets_ProtoCompiler)linux_x64/protoc" />
+    <_Asset PackagePath="tools/macosx_x86/protoc" Include="$(Assets_ProtoCompiler)macos_x86/protoc" /> <!-- GPB: macosx-->
+    <_Asset PackagePath="tools/macosx_x64/protoc" Include="$(Assets_ProtoCompiler)macos_x64/protoc" /> <!-- GPB: macosx-->
+
+    <!-- gRPC assets (for Grpc.Tools) -->
+    <_Asset PackagePath="tools/windows_x86/grpc_csharp_plugin.exe" Include="$(Assets_GrpcPlugins)protoc_windows_x86/grpc_csharp_plugin.exe" />
+    <_Asset PackagePath="tools/windows_x64/grpc_csharp_plugin.exe" Include="$(Assets_GrpcPlugins)protoc_windows_x64/grpc_csharp_plugin.exe" />
+    <_Asset PackagePath="tools/linux_x86/grpc_csharp_plugin" Include="$(Assets_GrpcPlugins)protoc_linux_x86/grpc_csharp_plugin" />
+    <_Asset PackagePath="tools/linux_x64/grpc_csharp_plugin" Include="$(Assets_GrpcPlugins)protoc_linux_x64/grpc_csharp_plugin" />
+    <_Asset PackagePath="tools/macosx_x86/grpc_csharp_plugin" Include="$(Assets_GrpcPlugins)protoc_macos_x86/grpc_csharp_plugin" />
+    <_Asset PackagePath="tools/macosx_x64/grpc_csharp_plugin" Include="$(Assets_GrpcPlugins)protoc_macos_x64/grpc_csharp_plugin" />
+
+    <None Include="@(_Asset)" Pack="true" Visible="false" />
+  </ItemGroup>
+
+  <ItemGroup Condition=" '$(TargetFramework)' == 'net45' ">
+    <Reference Include="Microsoft.Build.Framework; Microsoft.Build.Utilities.v4.0" Pack="false" />
+  </ItemGroup>
+
+  <ItemGroup Condition=" '$(TargetFramework)' != 'net45' ">
+    <PackageReference Include="Microsoft.Build.Framework; Microsoft.Build.Utilities.Core" Version="15.6.*" />
+    <!--  Set PrivateAssets="All" on all items, even those implicitly added,
+          so that they do not become dependencies of this package. -->
+    <PackageReference Update="@(PackageReference)" PrivateAssets="All" />
+  </ItemGroup>
+
+</Project>
diff --git a/src/csharp/Grpc.Tools/ProtoCompile.cs b/src/csharp/Grpc.Tools/ProtoCompile.cs
new file mode 100644
index 0000000000..93608e1ac0
--- /dev/null
+++ b/src/csharp/Grpc.Tools/ProtoCompile.cs
@@ -0,0 +1,441 @@
+#region Copyright notice and license
+
+// Copyright 2018 gRPC authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#endregion
+
+using System.Text;
+using Microsoft.Build.Framework;
+using Microsoft.Build.Utilities;
+
+namespace Grpc.Tools
+{
+    /// <summary>
+    /// Run Google proto compiler (protoc).
+    ///
+    /// After a successful run, the task reads the dependency file if specified
+    /// to be saved by the compiler, and returns its output files.
+    ///
+    /// This task (unlike PrepareProtoCompile) does not attempt to guess anything
+    /// about language-specific behavior of protoc, and therefore can be used for
+    /// any language outputs.
+    /// </summary>
+    public class ProtoCompile : ToolTask
+    {
+        /*
+
+        Usage: /home/kkm/work/protobuf/src/.libs/lt-protoc [OPTION] PROTO_FILES
+        Parse PROTO_FILES and generate output based on the options given:
+          -IPATH, --proto_path=PATH   Specify the directory in which to search for
+                                      imports.  May be specified multiple times;
+                                      directories will be searched in order.  If not
+                                      given, the current working directory is used.
+          --version                   Show version info and exit.
+          -h, --help                  Show this text and exit.
+          --encode=MESSAGE_TYPE       Read a text-format message of the given type
+                                      from standard input and write it in binary
+                                      to standard output.  The message type must
+                                      be defined in PROTO_FILES or their imports.
+          --decode=MESSAGE_TYPE       Read a binary message of the given type from
+                                      standard input and write it in text format
+                                      to standard output.  The message type must
+                                      be defined in PROTO_FILES or their imports.
+          --decode_raw                Read an arbitrary protocol message from
+                                      standard input and write the raw tag/value
+                                      pairs in text format to standard output.  No
+                                      PROTO_FILES should be given when using this
+                                      flag.
+          --descriptor_set_in=FILES   Specifies a delimited list of FILES
+                                      each containing a FileDescriptorSet (a
+                                      protocol buffer defined in descriptor.proto).
+                                      The FileDescriptor for each of the PROTO_FILES
+                                      provided will be loaded from these
+                                      FileDescriptorSets. If a FileDescriptor
+                                      appears multiple times, the first occurrence
+                                      will be used.
+          -oFILE,                     Writes a FileDescriptorSet (a protocol buffer,
+            --descriptor_set_out=FILE defined in descriptor.proto) containing all of
+                                      the input files to FILE.
+          --include_imports           When using --descriptor_set_out, also include
+                                      all dependencies of the input files in the
+                                      set, so that the set is self-contained.
+          --include_source_info       When using --descriptor_set_out, do not strip
+                                      SourceCodeInfo from the FileDescriptorProto.
+                                      This results in vastly larger descriptors that
+                                      include information about the original
+                                      location of each decl in the source file as
+                                      well as surrounding comments.
+          --dependency_out=FILE       Write a dependency output file in the format
+                                      expected by make. This writes the transitive
+                                      set of input file paths to FILE
+          --error_format=FORMAT       Set the format in which to print errors.
+                                      FORMAT may be 'gcc' (the default) or 'msvs'
+                                      (Microsoft Visual Studio format).
+          --print_free_field_numbers  Print the free field numbers of the messages
+                                      defined in the given proto files. Groups share
+                                      the same field number space with the parent
+                                      message. Extension ranges are counted as
+                                      occupied fields numbers.
+
+          --plugin=EXECUTABLE         Specifies a plugin executable to use.
+                                      Normally, protoc searches the PATH for
+                                      plugins, but you may specify additional
+                                      executables not in the path using this flag.
+                                      Additionally, EXECUTABLE may be of the form
+                                      NAME=PATH, in which case the given plugin name
+                                      is mapped to the given executable even if
+                                      the executable's own name differs.
+          --cpp_out=OUT_DIR           Generate C++ header and source.
+          --csharp_out=OUT_DIR        Generate C# source file.
+          --java_out=OUT_DIR          Generate Java source file.
+          --javanano_out=OUT_DIR      Generate Java Nano source file.
+          --js_out=OUT_DIR            Generate JavaScript source.
+          --objc_out=OUT_DIR          Generate Objective C header and source.
+          --php_out=OUT_DIR           Generate PHP source file.
+          --python_out=OUT_DIR        Generate Python source file.
+          --ruby_out=OUT_DIR          Generate Ruby source file.
+          @<filename>                 Read options and filenames from file. If a
+                                      relative file path is specified, the file
+                                      will be searched in the working directory.
+                                      The --proto_path option will not affect how
+                                      this argument file is searched. Content of
+                                      the file will be expanded in the position of
+                                      @<filename> as in the argument list. Note
+                                      that shell expansion is not applied to the
+                                      content of the file (i.e., you cannot use
+                                      quotes, wildcards, escapes, commands, etc.).
+                                      Each line corresponds to a single argument,
+                                      even if it contains spaces.
+        */
+        static string[] s_supportedGenerators = new[] { "cpp", "csharp", "java",
+                                                        "javanano", "js", "objc",
+                                                        "php", "python", "ruby" };
+
+        /// <summary>
+        /// Code generator.
+        /// </summary>
+        [Required]
+        public string Generator { get; set; }
+
+        /// <summary>
+        /// Protobuf files to compile.
+        /// </summary>
+        [Required]
+        public ITaskItem[] ProtoBuf { get; set; }
+
+        /// <summary>
+        /// Directory where protoc dependency files are cached. If provided, dependency
+        /// output filename is autogenerated from source directory hash and file name.
+        /// Mutually exclusive with DependencyOut.
+        /// Switch: --dependency_out (with autogenerated file name).
+        /// </summary>
+        public string ProtoDepDir { get; set; }
+
+        /// <summary>
+        /// Dependency file full name. Mutually exclusive with ProtoDepDir.
+        /// Autogenerated file name is available in this property after execution.
+        /// Switch: --dependency_out.
+        /// </summary>
+        [Output]
+        public string DependencyOut { get; set; }
+
+        /// <summary>
+        /// The directories to search for imports. Directories will be searched
+        /// in order. If not given, the current working directory is used.
+        /// Switch: --proto_path.
+        /// </summary>
+        public string[] ProtoPath { get; set; }
+
+        /// <summary>
+        /// Generated code directory. The generator property determines the language.
+        /// Switch: --GEN-out= (for different generators GEN).
+        /// </summary>
+        [Required]
+        public string OutputDir { get; set; }
+
+        /// <summary>
+        /// Codegen options. See also OptionsFromMetadata.
+        /// Switch: --GEN_out= (for different generators GEN).
+        /// </summary>
+        public string[] OutputOptions { get; set; }
+
+        /// <summary>
+        /// Full path to the gRPC plugin executable. If specified, gRPC generation
+        /// is enabled for the files.
+        /// Switch: --plugin=protoc-gen-grpc=
+        /// </summary>
+        public string GrpcPluginExe { get; set; }
+
+        /// <summary>
+        /// Generated gRPC  directory. The generator property determines the
+        /// language. If gRPC is enabled but this is not given, OutputDir is used.
+        /// Switch: --grpc_out=
+        /// </summary>
+        public string GrpcOutputDir { get; set; }
+
+        /// <summary>
+        /// gRPC Codegen options. See also OptionsFromMetadata.
+        /// --grpc_opt=opt1,opt2=val (comma-separated).
+        /// </summary>
+        public string[] GrpcOutputOptions { get; set; }
+
+        /// <summary>
+        /// List of files written in addition to generated outputs. Includes a
+        /// single item for the dependency file if written.
+        /// </summary>
+        [Output]
+        public ITaskItem[] AdditionalFileWrites { get; private set; }
+
+        /// <summary>
+        /// List of language files generated by protoc. Empty unless DependencyOut
+        /// or ProtoDepDir is set, since the file writes are extracted from protoc
+        /// dependency output file.
+        /// </summary>
+        [Output]
+        public ITaskItem[] GeneratedFiles { get; private set; }
+
+        // Hide this property from MSBuild, we should never use a shell script.
+        private new bool UseCommandProcessor { get; set; }
+
+        protected override string ToolName => Platform.IsWindows ? "protoc.exe" : "protoc";
+
+        // Since we never try to really locate protoc.exe somehow, just try ToolExe
+        // as the full tool location. It will be either just protoc[.exe] from
+        // ToolName above if not set by the user, or a user-supplied full path. The
+        // base class will then resolve the former using system PATH.
+        protected override string GenerateFullPathToTool() => ToolExe;
+
+        // Log protoc errors with the High priority (bold white in MsBuild,
+        // printed with -v:n, and shown in the Output windows in VS).
+        protected override MessageImportance StandardErrorLoggingImportance => MessageImportance.High;
+
+        // Called by base class to validate arguments and make them consistent.
+        protected override bool ValidateParameters()
+        {
+            // Part of proto command line switches, must be lowercased.
+            Generator = Generator.ToLowerInvariant();
+            if (!System.Array.Exists(s_supportedGenerators, g => g == Generator))
+            {
+                Log.LogError("Invalid value for Generator='{0}'. Supported generators: {1}",
+                             Generator, string.Join(", ", s_supportedGenerators));
+            }
+
+            if (ProtoDepDir != null && DependencyOut != null)
+            {
+                Log.LogError("Properties ProtoDepDir and DependencyOut may not be both specified");
+            }
+
+            if (ProtoBuf.Length > 1 && (ProtoDepDir != null || DependencyOut != null))
+            {
+                Log.LogError("Proto compiler currently allows only one input when " +
+                             "--dependency_out is specified (via ProtoDepDir or DependencyOut). " +
+                             "Tracking issue: https://github.com/google/protobuf/pull/3959");
+            }
+
+            // Use ProtoDepDir to autogenerate DependencyOut
+            if (ProtoDepDir != null)
+            {
+                DependencyOut = DepFileUtil.GetDepFilenameForProto(ProtoDepDir, ProtoBuf[0].ItemSpec);
+            }
+
+            if (GrpcPluginExe == null)
+            {
+                GrpcOutputOptions = null;
+                GrpcOutputDir = null;
+            }
+            else if (GrpcOutputDir == null)
+            {
+                // Use OutputDir for gRPC output if not specified otherwise by user.
+                GrpcOutputDir = OutputDir;
+            }
+
+            return !Log.HasLoggedErrors && base.ValidateParameters();
+        }
+
+        // Protoc chokes on BOM, naturally. I would!
+        static readonly Encoding s_utf8WithoutBom = new UTF8Encoding(false);
+        protected override Encoding ResponseFileEncoding => s_utf8WithoutBom;
+
+        // Protoc takes one argument per line from the response file, and does not
+        // require any quoting whatsoever. Otherwise, this is similar to the
+        // standard CommandLineBuilder
+        class ProtocResponseFileBuilder
+        {
+            StringBuilder _data = new StringBuilder(1000);
+            public override string ToString() => _data.ToString();
+
+            // If 'value' is not empty, append '--name=value\n'.
+            public void AddSwitchMaybe(string name, string value)
+            {
+                if (!string.IsNullOrEmpty(value))
+                {
+                    _data.Append("--").Append(name).Append("=")
+                         .Append(value).Append('\n');
+                }
+            }
+
+            // Add switch with the 'values' separated by commas, for options.
+            public void AddSwitchMaybe(string name, string[] values)
+            {
+                if (values?.Length > 0)
+                {
+                    _data.Append("--").Append(name).Append("=")
+                         .Append(string.Join(",", values)).Append('\n');
+                }
+            }
+
+            // Add a positional argument to the file data.
+            public void AddArg(string arg)
+            {
+                _data.Append(arg).Append('\n');
+            }
+        };
+
+        // Called by the base ToolTask to get response file contents.
+        protected override string GenerateResponseFileCommands()
+        {
+            var cmd = new ProtocResponseFileBuilder();
+            cmd.AddSwitchMaybe(Generator + "_out", TrimEndSlash(OutputDir));
+            cmd.AddSwitchMaybe(Generator + "_opt", OutputOptions);
+            cmd.AddSwitchMaybe("plugin=protoc-gen-grpc", GrpcPluginExe);
+            cmd.AddSwitchMaybe("grpc_out", TrimEndSlash(GrpcOutputDir));
+            cmd.AddSwitchMaybe("grpc_opt", GrpcOutputOptions);
+            if (ProtoPath != null)
+            {
+                foreach (string path in ProtoPath)
+                    cmd.AddSwitchMaybe("proto_path", TrimEndSlash(path));
+            }
+            cmd.AddSwitchMaybe("dependency_out", DependencyOut);
+            foreach (var proto in ProtoBuf)
+            {
+                cmd.AddArg(proto.ItemSpec);
+            }
+            return cmd.ToString();
+        }
+
+        // Protoc cannot digest trailing slashes in directory names,
+        // curiously under Linux, but not in Windows.
+        static string TrimEndSlash(string dir)
+        {
+            if (dir == null || dir.Length <= 1)
+            {
+                return dir;
+            }
+            string trim = dir.TrimEnd('/', '\\');
+            // Do not trim the root slash, drive letter possible.
+            if (trim.Length == 0)
+            {
+                // Slashes all the way down.
+                return dir.Substring(0, 1);
+            }
+            if (trim.Length == 2 && dir.Length > 2 && trim[1] == ':')
+            {
+                // We have a drive letter and root, e. g. 'C:\'
+                return dir.Substring(0, 3);
+            }
+            return trim;
+        }
+
+        // Called by the base class to log tool's command line.
+        //
+        // Protoc command file is peculiar, with one argument per line, separated
+        // by newlines. Unwrap it for log readability into a single line, and also
+        // quote arguments, lest it look weird and so it may be copied and pasted
+        // into shell. Since this is for logging only, correct enough is correct.
+        protected override void LogToolCommand(string cmd)
+        {
+            var printer = new StringBuilder(1024);
+
+            // Print 'str' slice into 'printer', wrapping in quotes if contains some
+            // interesting characters in file names, or if empty string. The list of
+            // characters requiring quoting is not by any means exhaustive; we are
+            // just striving to be nice, not guaranteeing to be nice.
+            var quotable = new[] { ' ', '!', '$', '&', '\'', '^' };
+            void PrintQuoting(string str, int start, int count)
+            {
+                bool wrap = count == 0 || str.IndexOfAny(quotable, start, count) >= 0;
+                if (wrap) printer.Append('"');
+                printer.Append(str, start, count);
+                if (wrap) printer.Append('"');
+            }
+
+            for (int ib = 0, ie; (ie = cmd.IndexOf('\n', ib)) >= 0; ib = ie + 1)
+            {
+                // First line only contains both the program name and the first switch.
+                // We can rely on at least the '--out_dir' switch being always present.
+                if (ib == 0)
+                {
+                    int iep = cmd.IndexOf(" --");
+                    if (iep > 0)
+                    {
+                        PrintQuoting(cmd, 0, iep);
+                        ib = iep + 1;
+                    }
+                }
+                printer.Append(' ');
+                if (cmd[ib] == '-')
+                {
+                    // Print switch unquoted, including '=' if any.
+                    int iarg = cmd.IndexOf('=', ib, ie - ib);
+                    if (iarg < 0)
+                    {
+                        // Bare switch without a '='.
+                        printer.Append(cmd, ib, ie - ib);
+                        continue;
+                    }
+                    printer.Append(cmd, ib, iarg + 1 - ib);
+                    ib = iarg + 1;
+                }
+                // A positional argument or switch value.
+                PrintQuoting(cmd, ib, ie - ib);
+            }
+
+            base.LogToolCommand(printer.ToString());
+        }
+
+        // Main task entry point.
+        public override bool Execute()
+        {
+            base.UseCommandProcessor = false;
+
+            bool ok = base.Execute();
+            if (!ok)
+            {
+                return false;
+            }
+
+            // Read dependency output file from the compiler to retrieve the
+            // definitive list of created files. Report the dependency file
+            // itself as having been written to.
+            if (DependencyOut != null)
+            {
+                string[] outputs = DepFileUtil.ReadDependencyOutputs(DependencyOut, Log);
+                if (HasLoggedErrors)
+                {
+                    return false;
+                }
+
+                GeneratedFiles = new ITaskItem[outputs.Length];
+                for (int i = 0; i < outputs.Length; i++)
+                {
+                    GeneratedFiles[i] = new TaskItem(outputs[i]);
+                }
+                AdditionalFileWrites = new ITaskItem[] { new TaskItem(DependencyOut) };
+            }
+
+            return true;
+        }
+    };
+}
diff --git a/src/csharp/Grpc.Tools/ProtoCompilerOutputs.cs b/src/csharp/Grpc.Tools/ProtoCompilerOutputs.cs
new file mode 100644
index 0000000000..915be3421e
--- /dev/null
+++ b/src/csharp/Grpc.Tools/ProtoCompilerOutputs.cs
@@ -0,0 +1,86 @@
+#region Copyright notice and license
+
+// Copyright 2018 gRPC authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#endregion
+
+using System.Collections.Generic;
+using Microsoft.Build.Framework;
+using Microsoft.Build.Utilities;
+
+namespace Grpc.Tools
+{
+    public class ProtoCompilerOutputs : Task
+    {
+        /// <summary>
+        /// Code generator. Currently supported are "csharp", "cpp".
+        /// </summary>
+        [Required]
+        public string Generator { get; set; }
+
+        /// <summary>
+        /// All Proto files in the project. The task computes possible outputs
+        /// from these proto files, and returns them in the PossibleOutputs list.
+        /// Not all of these might be actually produced by protoc; this is dealt
+        /// with later in the ProtoCompile task which returns the list of
+        /// files actually produced by the compiler.
+        /// </summary>
+        [Required]
+        public ITaskItem[] ProtoBuf { get; set; }
+
+        /// <summary>
+        /// Output items per each potential output. We do not look at existing
+        /// cached dependency even if they exist, since file may be refactored,
+        /// affecting whether or not gRPC code file is generated from a given proto.
+        /// Instead, all potentially possible generated sources are collected.
+        /// It is a wise idea to generate empty files later for those potentials
+        /// that are not actually created by protoc, so the dependency checks
+        /// result in a minimal recompilation. The Protoc task can output the
+        /// list of files it actually produces, given right combination of its
+        /// properties.
+        /// Output items will have the Source metadata set on them:
+        ///     <ItemName Include="MyProto.cs" Source="my_proto.proto" />
+        /// </summary>
+        [Output]
+        public ITaskItem[] PossibleOutputs { get; private set; }
+
+        public override bool Execute()
+        {
+            var generator = GeneratorServices.GetForLanguage(Generator, Log);
+            if (generator == null)
+            {
+                // Error already logged, just return.
+                return false;
+            }
+
+            // Get language-specific possible output. The generator expects certain
+            // metadata be set on the proto item.
+            var possible = new List<ITaskItem>();
+            foreach (var proto in ProtoBuf)
+            {
+                var outputs = generator.GetPossibleOutputs(proto);
+                foreach (string output in outputs)
+                {
+                    var ti = new TaskItem(output);
+                    ti.SetMetadata(Metadata.Source, proto.ItemSpec);
+                    possible.Add(ti);
+                }
+            }
+            PossibleOutputs = possible.ToArray();
+
+            return !Log.HasLoggedErrors;
+        }
+    };
+}
diff --git a/src/csharp/Grpc.Tools/ProtoReadDependencies.cs b/src/csharp/Grpc.Tools/ProtoReadDependencies.cs
new file mode 100644
index 0000000000..963837e8b7
--- /dev/null
+++ b/src/csharp/Grpc.Tools/ProtoReadDependencies.cs
@@ -0,0 +1,78 @@
+#region Copyright notice and license
+
+// Copyright 2018 gRPC authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#endregion
+
+using System.Collections.Generic;
+using Microsoft.Build.Framework;
+using Microsoft.Build.Utilities;
+
+namespace Grpc.Tools
+{
+    public class ProtoReadDependencies : Task
+    {
+        /// <summary>
+        /// The collection is used to collect possible additional dependencies
+        /// of proto files cached under ProtoDepDir.
+        /// </summary>
+        [Required]
+        public ITaskItem[] ProtoBuf { get; set; }
+
+        /// <summary>
+        /// Directory where protoc dependency files are cached.
+        /// </summary>
+        [Required]
+        public string ProtoDepDir { get; set; }
+
+        /// <summary>
+        /// Additional items that a proto file depends on. This list may include
+        /// extra dependencies; we do our best to include as few extra positives
+        /// as reasonable to avoid missing any. The collection item is the
+        /// dependency, and its Source metadatum is the dependent proto file, like
+        ///     <ItemName Include="/usr/include/proto/wrapper.proto"
+        ///               Source="my_proto.proto" />
+        /// </summary>
+        [Output]
+        public ITaskItem[] Dependencies { get; private set; }
+
+        public override bool Execute()
+        {
+            // Read dependency files, where available. There might be none,
+            // just use a best effort.
+            if (ProtoDepDir != null)
+            {
+                var dependencies = new List<ITaskItem>();
+                foreach (var proto in ProtoBuf)
+                {
+                    string[] deps = DepFileUtil.ReadDependencyInputs(ProtoDepDir, proto.ItemSpec, Log);
+                    foreach (string dep in deps)
+                    {
+                        var ti = new TaskItem(dep);
+                        ti.SetMetadata(Metadata.Source, proto.ItemSpec);
+                        dependencies.Add(ti);
+                    }
+                }
+                Dependencies = dependencies.ToArray();
+            }
+            else
+            {
+                Dependencies = new ITaskItem[0];
+            }
+
+            return !Log.HasLoggedErrors;
+        }
+    };
+}
diff --git a/src/csharp/Grpc.Tools/ProtoToolsPlatform.cs b/src/csharp/Grpc.Tools/ProtoToolsPlatform.cs
new file mode 100644
index 0000000000..aed8a66339
--- /dev/null
+++ b/src/csharp/Grpc.Tools/ProtoToolsPlatform.cs
@@ -0,0 +1,63 @@
+#region Copyright notice and license
+
+// Copyright 2018 gRPC authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#endregion
+
+using Microsoft.Build.Framework;
+using Microsoft.Build.Utilities;
+
+namespace Grpc.Tools
+{
+    /// <summary>
+    /// A helper task to resolve actual OS type and bitness.
+    /// </summary>
+    public class ProtoToolsPlatform : Task
+    {
+        /// <summary>
+        /// Return one of 'linux', 'macosx' or 'windows'.
+        /// If the OS is unknown, the property is not set.
+        /// </summary>
+        [Output]
+        public string Os { get; set; }
+
+        /// <summary>
+        /// Return one of 'x64' or 'x86'.
+        /// If the CPU is unknown, the property is not set.
+        /// </summary>
+        [Output]
+        public string Cpu { get; set; }
+
+
+        public override bool Execute()
+        {
+            switch (Platform.Os)
+            {
+                case Platform.OsKind.Linux: Os = "linux"; break;
+                case Platform.OsKind.MacOsX: Os = "macosx"; break;
+                case Platform.OsKind.Windows: Os = "windows"; break;
+                default: Os = ""; break;
+            }
+
+            switch (Platform.Cpu)
+            {
+                case Platform.CpuKind.X86: Cpu = "x86"; break;
+                case Platform.CpuKind.X64: Cpu = "x64"; break;
+                default: Cpu = ""; break;
+            }
+            return true;
+        }
+    };
+}
diff --git a/src/csharp/Grpc.Tools/build/Grpc.Tools.props b/src/csharp/Grpc.Tools/build/Grpc.Tools.props
new file mode 100644
index 0000000000..dbcd8bf494
--- /dev/null
+++ b/src/csharp/Grpc.Tools/build/Grpc.Tools.props
@@ -0,0 +1,11 @@
+<?xml version="1.0"?>
+<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <PropertyGroup>
+    <MSBuildAllProjects>$(MSBuildAllProjects);$(MSBuildThisFileFullPath)</MSBuildAllProjects>
+  </PropertyGroup>
+
+  <!-- Name of this file must match package ID. -->
+  <!-- Packages will be split later. -->
+  <Import Project="_grpc/_Grpc.Tools.props"/>
+  <Import Project="_protobuf/Google.Protobuf.Tools.props"/>
+</Project>
diff --git a/src/csharp/Grpc.Tools/build/Grpc.Tools.targets b/src/csharp/Grpc.Tools/build/Grpc.Tools.targets
new file mode 100644
index 0000000000..c0a5b1e2c5
--- /dev/null
+++ b/src/csharp/Grpc.Tools/build/Grpc.Tools.targets
@@ -0,0 +1,11 @@
+<?xml version="1.0"?>
+<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <PropertyGroup>
+    <MSBuildAllProjects>$(MSBuildAllProjects);$(MSBuildThisFileFullPath)</MSBuildAllProjects>
+  </PropertyGroup>
+
+  <!-- Name of this file must match package ID. -->
+  <!-- Packages will be split later. -->
+  <Import Project="_grpc/_Grpc.Tools.targets"/>
+  <Import Project="_protobuf/Google.Protobuf.Tools.targets"/>
+</Project>
diff --git a/src/csharp/Grpc.Tools/build/_grpc/Grpc.CSharp.xml b/src/csharp/Grpc.Tools/build/_grpc/Grpc.CSharp.xml
new file mode 100644
index 0000000000..54468eb5ef
--- /dev/null
+++ b/src/csharp/Grpc.Tools/build/_grpc/Grpc.CSharp.xml
@@ -0,0 +1,30 @@
+<ProjectSchemaDefinitions xmlns="http://schemas.microsoft.com/build/2009/properties">
+  <Rule Name="ProtoBuf"
+        DisplayName="File Properties"
+        PageTemplate="generic"
+        Description="File Properties"
+        OverrideMode="Extend">
+    <Rule.DataSource>
+      <DataSource Persistence="ProjectFile" Label="Configuration" ItemType="ProtoBuf"
+                  HasConfigurationCondition="false" SourceOfDefaultValue="AfterContext" />
+    </Rule.DataSource>
+
+    <Rule.Categories>
+      <Category Name="gRPC" DisplayName="gRPC" />
+    </Rule.Categories>
+
+    <EnumProperty Name="GrpcServices" DisplayName="gRPC Stub Classes"
+                  Category="gRPC" Default="Both"
+                  Description="Generate gRPC server and client stub classes.">
+      <EnumValue Name="Both" DisplayName="Client and Server" IsDefault="true" />
+      <EnumValue Name="Client" DisplayName="Client only" />
+      <EnumValue Name="Server" DisplayName="Server only" />
+      <EnumValue Name="None" DisplayName="Do not generate" />
+      <EnumProperty.DataSource>
+        <DataSource ItemType="ProtoBuf" SourceOfDefaultValue="AfterContext"
+                    PersistenceStyle="Attribute" />
+      </EnumProperty.DataSource>
+    </EnumProperty>
+
+  </Rule>
+</ProjectSchemaDefinitions>
diff --git a/src/csharp/Grpc.Tools/build/_grpc/README b/src/csharp/Grpc.Tools/build/_grpc/README
new file mode 100644
index 0000000000..4a7204b9ff
--- /dev/null
+++ b/src/csharp/Grpc.Tools/build/_grpc/README
@@ -0,0 +1,3 @@
+TODO(kkm): These file will go into Grpc.Tools/build after package split.
+           Remove leading underscores from file names; they are hiding the
+           files from some NuGet versions which pull them into project.
diff --git a/src/csharp/Grpc.Tools/build/_grpc/_Grpc.Tools.props b/src/csharp/Grpc.Tools/build/_grpc/_Grpc.Tools.props
new file mode 100644
index 0000000000..8ce07c48ab
--- /dev/null
+++ b/src/csharp/Grpc.Tools/build/_grpc/_Grpc.Tools.props
@@ -0,0 +1,6 @@
+<?xml version="1.0"?>
+<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <PropertyGroup>
+    <MSBuildAllProjects>$(MSBuildAllProjects);$(MSBuildThisFileFullPath)</MSBuildAllProjects>
+  </PropertyGroup>
+</Project>
diff --git a/src/csharp/Grpc.Tools/build/_grpc/_Grpc.Tools.targets b/src/csharp/Grpc.Tools/build/_grpc/_Grpc.Tools.targets
new file mode 100644
index 0000000000..5f76c03ce5
--- /dev/null
+++ b/src/csharp/Grpc.Tools/build/_grpc/_Grpc.Tools.targets
@@ -0,0 +1,48 @@
+<?xml version="1.0"?>
+<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <PropertyGroup>
+    <MSBuildAllProjects>$(MSBuildAllProjects);$(MSBuildThisFileFullPath)</MSBuildAllProjects>
+    <gRPC_PluginFileName Condition=" '$(gRPC_PluginFileName)' == '' and '$(Language)' == 'C#' ">grpc_csharp_plugin</gRPC_PluginFileName>
+  </PropertyGroup>
+
+  <ItemGroup Condition=" '$(Protobuf_ProjectSupported)' == 'true' and '$(Language)' == 'C#' ">
+    <!-- Extend property pages with gRPC properties. -->
+    <PropertyPageSchema Include="$(MSBuildThisFileDirectory)Grpc.CSharp.xml">
+      <Context>File;BrowseObject</Context>
+    </PropertyPageSchema>
+  </ItemGroup>
+
+  <ItemDefinitionGroup Condition=" '$(Protobuf_ProjectSupported)' == 'true' and '$(Language)' == 'C#' ">
+    <ProtoBuf>
+      <GrpcServices Condition=" '%(ProtoBuf.GrpcServices)' == '' ">Both</GrpcServices>
+    </ProtoBuf>
+  </ItemDefinitionGroup>
+
+  <!-- This target is invoked in a C# project, or can be called in a customized project. -->
+  <Target Name="gRPC_ResolvePluginFullPath" AfterTargets="Protobuf_ResolvePlatform">
+    <PropertyGroup>
+      <!-- TODO(kkm): Do not use Protobuf_PackagedToolsPath, roll gRPC's own. -->
+      <!-- TODO(kkm): Do not package windows x64 builds (#13098). -->
+      <gRPC_PluginFullPath Condition=" '$(gRPC_PluginFullPath)' == '' and '$(Protobuf_ToolsOs)' == 'windows' "
+           >$(Protobuf_PackagedToolsPath)\$(Protobuf_ToolsOs)_x86\$(gRPC_PluginFileName).exe</gRPC_PluginFullPath>
+      <gRPC_PluginFullPath Condition=" '$(gRPC_PluginFullPath)' == '' "
+           >$(Protobuf_PackagedToolsPath)/$(Protobuf_ToolsOs)_$(Protobuf_ToolsCpu)/$(gRPC_PluginFileName)</gRPC_PluginFullPath>
+    </PropertyGroup>
+  </Target>
+
+  <Target Name="_gRPC_PrepareCompileOptions" AfterTargets="Protobuf_PrepareCompileOptions">
+    <ItemGroup Condition=" '$(Language)' == 'C#' ">
+      <Protobuf_Compile Condition=" %(Protobuf_Compile.GrpcServices) != 'None' ">
+        <GrpcPluginExe Condition=" '%(Protobuf_Compile.GrpcPluginExe)' == '' ">$(gRPC_PluginFullPath)</GrpcPluginExe>
+        <GrpcOutputDir Condition=" '%(Protobuf_Compile.GrpcOutputDir)' == '' " >%(Protobuf_Compile.OutputDir)</GrpcOutputDir>
+        <_GrpcOutputOptions Condition=" '%(Protobuf_Compile.Access)' == 'Internal' ">%(Protobuf_Compile._GrpcOutputOptions);internal_access</_GrpcOutputOptions>
+      </Protobuf_Compile>
+      <Protobuf_Compile Condition=" '%(Protobuf_Compile.GrpcServices)' == 'Client' ">
+        <_GrpcOutputOptions>%(Protobuf_Compile._GrpcOutputOptions);no_server</_GrpcOutputOptions>
+      </Protobuf_Compile>
+      <Protobuf_Compile Condition=" '%(Protobuf_Compile.GrpcServices)' == 'Server' ">
+        <_GrpcOutputOptions>%(Protobuf_Compile._GrpcOutputOptions);no_client</_GrpcOutputOptions>
+      </Protobuf_Compile>
+    </ItemGroup>
+  </Target>
+</Project>
diff --git a/src/csharp/Grpc.Tools/build/_protobuf/Google.Protobuf.Tools.props b/src/csharp/Grpc.Tools/build/_protobuf/Google.Protobuf.Tools.props
new file mode 100644
index 0000000000..9f2d8bb4b5
--- /dev/null
+++ b/src/csharp/Grpc.Tools/build/_protobuf/Google.Protobuf.Tools.props
@@ -0,0 +1,24 @@
+<?xml version="1.0"?>
+<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <PropertyGroup>
+    <MSBuildAllProjects>$(MSBuildAllProjects);$(MSBuildThisFileFullPath)</MSBuildAllProjects>
+
+    <!-- Revision number of this package conventions (as if "API" version). -->
+    <Protobuf_ToolingRevision>1</Protobuf_ToolingRevision>
+
+    <!-- TODO(kkm): Remove one "../" when separating packages. -->
+    <!-- TODO(kkm): Do not place non-tools under tools/, use build/native/bin/. -->
+    <Protobuf_PackagedToolsPath>$( [System.IO.Path]::GetFullPath($(MSBuildThisFileDirectory)../../tools) )</Protobuf_PackagedToolsPath>
+    <Protobuf_StandardImportsPath>$( [System.IO.Path]::GetFullPath($(MSBuildThisFileDirectory)../native/include) )</Protobuf_StandardImportsPath>
+  </PropertyGroup>
+
+  <!-- NET SDK projects only: include proto files by default. Other project
+       types are not setting or using $(EnableDefaultItems).
+       Note that MSBuild evaluates all ItemGroups and their conditions in the
+       final pass over the build script, so properties like EnableDefaultProtoBufItems
+       here can be changed later in the project. -->
+  <ItemGroup Condition=" '$(Protobuf_ProjectSupported)' == 'true' ">
+    <ProtoBuf Include="**/*.proto"
+              Condition=" '$(EnableDefaultItems)' == 'true' and '$(EnableDefaultProtoBufItems)' == 'true' " />
+  </ItemGroup>
+</Project>
diff --git a/src/csharp/Grpc.Tools/build/_protobuf/Google.Protobuf.Tools.targets b/src/csharp/Grpc.Tools/build/_protobuf/Google.Protobuf.Tools.targets
new file mode 100644
index 0000000000..1d233d23a8
--- /dev/null
+++ b/src/csharp/Grpc.Tools/build/_protobuf/Google.Protobuf.Tools.targets
@@ -0,0 +1,384 @@
+<?xml version="1.0"?>
+<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <PropertyGroup>
+    <MSBuildAllProjects>$(MSBuildAllProjects);$(MSBuildThisFileFullPath)</MSBuildAllProjects>
+    <!-- We allow a non-C# generator be set by the user, but skip adding outputs to Compile in this case. -->
+    <Protobuf_Generator Condition=" '$(Protobuf_Generator)' == '' and '$(Language)' == 'C#' ">CSharp</Protobuf_Generator>
+    <!-- Configuration is passing the smoke test. -->
+    <Protobuf_ProjectSupported Condition=" '$(Protobuf_Generator)' != '' ">true</Protobuf_ProjectSupported>
+    <_Protobuf_MsBuildAssembly Condition=" '$(MSBuildRuntimeType)' == 'Core' ">netstandard1.3\Protobuf.MSBuild.dll</_Protobuf_MsBuildAssembly>
+    <_Protobuf_MsBuildAssembly Condition=" '$(MSBuildRuntimeType)' != 'Core' ">net45\Protobuf.MSBuild.dll</_Protobuf_MsBuildAssembly>
+  </PropertyGroup>
+
+  <UsingTask AssemblyFile="$(_Protobuf_MsBuildAssembly)" TaskName="Grpc.Tools.ProtoToolsPlatform" />
+  <UsingTask AssemblyFile="$(_Protobuf_MsBuildAssembly)" TaskName="Grpc.Tools.ProtoCompilerOutputs" />
+  <UsingTask AssemblyFile="$(_Protobuf_MsBuildAssembly)" TaskName="Grpc.Tools.ProtoReadDependencies" />
+  <UsingTask AssemblyFile="$(_Protobuf_MsBuildAssembly)" TaskName="Grpc.Tools.ProtoCompile" />
+
+  <PropertyGroup Condition=" '$(Protobuf_ProjectSupported)' == 'true' ">
+    <Protobuf_IntermediatePath Condition=" '$(Protobuf_IntermediatePath)' == '' ">$(IntermediateOutputPath)</Protobuf_IntermediatePath>
+    <Protobuf_OutputPath Condition=" '$(Protobuf_OutputPath)' == '' ">$(Protobuf_IntermediatePath)</Protobuf_OutputPath>
+    <Protobuf_DepFilesPath Condition=" '$(Protobuf_DepFilesPath)' == '' ">$(Protobuf_IntermediatePath)</Protobuf_DepFilesPath>
+  </PropertyGroup>
+
+  <ItemDefinitionGroup Condition=" '$(Protobuf_ProjectSupported)' == 'true' and '$(Language)' == 'C#' ">
+    <ProtoBuf>
+      <Access Condition="'%(ProtoBuf.Access)' == '' ">Public</Access>
+      <ProtoCompile Condition="'%(ProtoBuf.ProtoCompile)' == '' ">True</ProtoCompile>
+      <ProtoRoot Condition="'%(ProtoBuf.ProtoRoot)' == '' " />
+      <CompileOutputs Condition="'%(ProtoBuf.CompileOutputs)' == ''">True</CompileOutputs>
+      <OutputDir Condition="'%(ProtoBuf.OutputDir)' == '' ">$(Protobuf_OutputPath)</OutputDir>
+    </ProtoBuf>
+  </ItemDefinitionGroup>
+
+  <ItemGroup Condition=" '$(Protobuf_ProjectSupported)' == 'true' and '$(Language)' == 'C#' ">
+    <PropertyPageSchema Include="$(MSBuildThisFileDirectory)Protobuf.CSharp.xml">
+      <Context>File;BrowseObject</Context>
+    </PropertyPageSchema>
+    <AvailableItemName Include="ProtoBuf" />
+  </ItemGroup>
+
+  <PropertyGroup>
+    <!-- NET SDK: by default, do not include proto files in the directory.
+         Current Microsoft's recommendation is against globbing:
+         https://docs.microsoft.com/en-us/dotnet/core/tools/csproj#recommendation -->
+    <EnableDefaultProtoBufItems Condition=" '$(EnableDefaultProtoBufItems)' == '' ">false</EnableDefaultProtoBufItems>
+  </PropertyGroup>
+
+  <!-- Check configuration sanity before build. -->
+  <Target Name="_Protobuf_SanityCheck" BeforeTargets="PrepareForBuild">
+    <Error
+      Condition=" '$(Protobuf_ProjectSupported)' != 'true' "
+      Text="Google.Protobuf.Tools proto compilation is only supported by default in a C# project (extension .csproj)" />
+  </Target>
+
+  <!--================================================================================
+                                     Tool path resolution
+   =================================================================================-->
+
+  <!-- Extension point for plugin packages: use Protobuf_ToolsOs and Protobuf_ToolsCpu
+       to resolve executable. Either or both may be blank, however, if resolution
+       fails; do check them before using. -->
+  <Target Name="Protobuf_ResolvePlatform">
+    <ProtoToolsPlatform>
+      <Output TaskParameter="Os" PropertyName="_Protobuf_ToolsOs"/>
+      <Output TaskParameter="Cpu" PropertyName="_Protobuf_ToolsCpu"/>
+    </ProtoToolsPlatform>
+
+    <PropertyGroup>
+      <!-- First try environment variable. -->
+      <Protobuf_ToolsOs>$(PROTOBUF_TOOLS_OS)</Protobuf_ToolsOs>
+      <Protobuf_ToolsCpu>$(PROTOBUF_TOOLS_CPU)</Protobuf_ToolsCpu>
+      <Protobuf_ProtocFullPath>$(PROTOBUF_PROTOC)</Protobuf_ProtocFullPath>
+
+      <!-- Next try OS and CPU resolved by ProtoToolsPlatform. -->
+      <Protobuf_ToolsOs Condition=" '$(Protobuf_ToolsOs)' == '' ">$(_Protobuf_ToolsOs)</Protobuf_ToolsOs>
+      <Protobuf_ToolsCpu Condition=" '$(Protobuf_ToolsCpu)' == '' ">$(_Protobuf_ToolsCpu)</Protobuf_ToolsCpu>
+      <!-- TODO(kkm): Do not package windows x64 builds (#13098). -->
+      <Protobuf_ProtocFullPath Condition=" '$(Protobuf_ProtocFullPath)' == '' and '$(Protobuf_ToolsOs)' == 'windows' "
+           >$(Protobuf_PackagedToolsPath)\$(Protobuf_ToolsOs)_x86\protoc.exe</Protobuf_ProtocFullPath>
+      <Protobuf_ProtocFullPath Condition=" '$(Protobuf_ProtocFullPath)' == '' "
+           >$(Protobuf_PackagedToolsPath)/$(Protobuf_ToolsOs)_$(Protobuf_ToolsCpu)/protoc</Protobuf_ProtocFullPath>
+    </PropertyGroup>
+
+    <Error Condition=" '$(DesignTimeBuild)' != 'true' and '$(PROTOBUF_PROTOC)' == ''
+                        and ( '$(Protobuf_ToolsOs)' == '' or '$(Protobuf_ToolsCpu)' == '' ) "
+      Text="Google.Protobuf.Tools cannot determine host OS and CPU.&#10;Use environment variables PROTOBUF_TOOLS_OS={linux|macosx|windows} and PROTOBUF_TOOLS_CPU={x86|x64} to try the closest match to your system.&#10;You may also set PROTOBUF_PROTOC to specify full path to the host-provided compiler (v3.5+ is required)." />
+  </Target>
+
+  <!--================================================================================
+                                     Proto compilation
+   =================================================================================-->
+
+  <!-- Extension points. -->
+  <Target Name="Protobuf_BeforeCompile" />
+  <Target Name="Protobuf_AfterCompile" />
+
+  <!-- Main compile sequence. Certain steps are gated by the value $(DesignTimeBuild),
+       so the sequence is good for either design time or build time. -->
+  <Target Name="Protobuf_Compile"
+          Condition=" '@(ProtoBuf)' != '' "
+          DependsOnTargets=" Protobuf_BeforeCompile;
+                             Protobuf_ResolvePlatform;
+                             _Protobuf_SelectFiles;
+                             Protobuf_PrepareCompile;
+                             _Protobuf_AugmentLanguageCompile;
+                             _Protobuf_CoreCompile;
+                             Protobuf_ReconcileOutputs;
+                             Protobuf_AfterCompile" />
+
+  <!-- Do proto compilation by default in a C# project. In other types, the user invoke
+       Protobuf_Compile directly where required. -->
+  <!-- TODO(kkm): Do shared compile in outer multitarget project? -->
+  <Target Name="_Protobuf_Compile_BeforeCsCompile"
+          BeforeTargets="BeforeCompile"
+          DependsOnTargets="Protobuf_Compile"
+          Condition=" '$(Language)' == 'C#' " />
+
+  <Target Name="_Protobuf_SelectFiles">
+    <!-- Guess .proto root for the files. Whenever the root is set for a file explicitly,
+         leave it as is. Otherwise, for files under the project directory, set the root
+         to "." for the project's directory, as it is the current when compiling; for the
+         files outside of project directory, use each .proto file's directory as the root. -->
+    <FindUnderPath Path="$(MSBuildProjectDirectory)"
+                   Files="@(ProtoBuf->WithMetadataValue('ProtoRoot',''))">
+      <Output TaskParameter="InPath" ItemName="_Protobuf_NoRootInProject"/>
+      <Output TaskParameter="OutOfPath" ItemName="_Protobuf_NoRootElsewhere"/>
+    </FindUnderPath>
+    <ItemGroup>
+      <!-- Files with explicit metadata. -->
+      <Protobuf_Compile Include="@(ProtoBuf->HasMetadata('ProtoRoot'))" />
+      <!-- In-project files will have ProtoRoot='.'. -->
+      <Protobuf_Compile Include="@(_Protobuf_NoRootInProject)">
+        <ProtoRoot>.</ProtoRoot>
+      </Protobuf_Compile>
+      <!-- Out-of-project files will have respective ProtoRoot='%(RelativeDir)'. -->
+      <Protobuf_Compile Include="@(_Protobuf_NoRootElsewhere)">
+        <ProtoRoot>%(RelativeDir)</ProtoRoot>
+      </Protobuf_Compile>
+      <!-- Remove files not for compile. -->
+      <Protobuf_Compile Remove="@(Protobuf_Compile)" Condition=" !%(ProtoCompile) " />
+      <!-- Ensure invariant Source=%(Identity). -->
+      <Protobuf_Compile>
+        <Source>%(Identity)</Source>
+      </Protobuf_Compile>
+    </ItemGroup>
+  </Target>
+
+  <!-- Extension point for non-C# project. Protobuf_Generator should be supported
+       by the ProtoCompile task, but we skip inferring expected outputs. All proto
+       files will be always recompiled with a warning, unless you add expectations
+       to the Protobuf_ExpectedOutputs collection.
+
+       All inferred ExpectedOutputs will be added to code compile (C#) in a C# project
+       by default. This is controlled per-proto by the CompileOutputs metadata. -->
+  <Target Name="Protobuf_PrepareCompile" Condition=" '@(Protobuf_Compile)' != '' ">
+    <!-- Predict expected names. -->
+    <ProtoCompilerOutputs Condition=" '$(Language)' == 'C#' "
+                          ProtoBuf="@(Protobuf_Compile)"
+                          Generator="$(Protobuf_Generator)">
+      <Output TaskParameter="PossibleOutputs" ItemName="Protobuf_ExpectedOutputs" />
+    </ProtoCompilerOutputs>
+    <!-- Read any dependency files from previous compiles. -->
+    <ProtoReadDependencies Condition=" '$(Protobuf_DepFilesPath)' != '' and '$(DesignTimeBuild)' != 'true' "
+                           ProtoBuf="@(Protobuf_Compile)"
+                           ProtoDepDir="$(Protobuf_DepFilesPath)" >
+      <Output TaskParameter="Dependencies" ItemName="Protobuf_Dependencies" />
+    </ProtoReadDependencies>
+  </Target>
+
+  <!-- Add all expected outputs, and only these, to language compile.  -->
+  <Target Name="_Protobuf_AugmentLanguageCompile"
+          DependsOnTargets="_Protobuf_EnforceInvariants"
+          Condition=" '$(Language)' == 'C#' ">
+    <ItemGroup>
+      <_Protobuf_CodeCompile Include="@(Protobuf_ExpectedOutputs->Distinct())"
+         Condition=" '%(Source)' != '' and '@(Protobuf_Compile->WithMetadataValue('CompileOutputs', 'true'))' != '' " />
+      <Compile Include="@(_Protobuf_CodeCompile)" />
+    </ItemGroup>
+  </Target>
+
+  <!-- These invariants must be kept for compile up-to-date check to work. -->
+  <Target Name="_Protobuf_EnforceInvariants">
+    <!-- Enforce Source=Identity on proto files. The 'Source' metadata is used as a common
+         key to match dependencies/expected outputs in the lists for up-to-date checks. -->
+    <ItemGroup>
+      <Protobuf_Compile>
+        <Source>%(Identity)</Source>
+      </Protobuf_Compile>
+    </ItemGroup>
+
+    <!-- Remove possible output and dependency declarations that have no Source set, or those
+         not matching any proto marked for compilation. -->
+    <ItemGroup>
+      <Protobuf_ExpectedOutputs Remove="@(Protobuf_ExpectedOutputs)" Condition=" '%(Protobuf_ExpectedOutputs.Source)' == '' " />
+      <Protobuf_ExpectedOutputs Remove="@(Protobuf_ExpectedOutputs)" Condition=" '%(Source)' != '' and '@(Protobuf_Compile)' == '' " />
+      <Protobuf_Dependencies Remove="@(Protobuf_Dependencies)" Condition=" '%(Protobuf_Dependencies.Source)' == '' " />
+      <Protobuf_Dependencies Remove="@(Protobuf_Dependencies)" Condition=" '%(Source)' != '' and '@(Protobuf_Compile)' == '' " />
+    </ItemGroup>
+  </Target>
+
+  <!-- Gather files with and without known outputs, separately. -->
+  <Target Name="_Protobuf_GatherStaleFiles"
+          Condition=" '@(Protobuf_Compile)' != '' "
+          DependsOnTargets="_Protobuf_EnforceInvariants; _Protobuf_GatherStaleSimple; _Protobuf_GatherStaleBatched">
+    <ItemGroup>
+      <!-- Drop outputs from MSBuild inference (they won't have the '_Exec' metadata).  -->
+      <_Protobuf_OutOfDateProto Remove="@(_Protobuf_OutOfDateProto->WithMetadataValue('_Exec',''))" />
+    </ItemGroup>
+  </Target>
+
+  <Target Name="_Protobuf_GatherStaleSimple">
+    <!-- Simple selection: always compile files that have no declared outputs (but warn below). -->
+    <ItemGroup>
+      <_Protobuf_OutOfDateProto Include="@(Protobuf_Compile)"
+                                Condition = " '%(Source)' != '' and '@(Protobuf_ExpectedOutputs)' == '' ">
+        <_Exec>true</_Exec>
+      </_Protobuf_OutOfDateProto>
+    </ItemGroup>
+
+    <!-- You are seeing this warning because there was no Protobuf_ExpectedOutputs items with
+         their Source attribute pointing to the proto files listed in the warning. Such files
+         will be recompiled on every build, as there is nothing to run up-to-date check against.
+         Set Protobuf_NoOrphanWarning to 'true' to suppress if this is what you want. -->
+    <Warning Condition=" '@(_Protobuf_OutOfDateProto)' != '' and '$(Protobuf_NoOrphanWarning)' != 'true' "
+             Text="The following files have no known outputs, and will be always recompiled as if out-of-date:&#10;@(_Protobuf_Orphans->'&#10;    %(Identity)', '')" />
+  </Target>
+
+  <Target Name="_Protobuf_GatherStaleBatched"
+          Inputs="@(Protobuf_Compile);%(Source);@(Protobuf_Dependencies);$(MSBuildAllProjects)"
+          Outputs="@(Protobuf_ExpectedOutputs)" >
+    <!-- The '_Exec' metadatum is set to distinguish really executed items from those MSBuild so
+         "helpfully" infers in a bucketed task. For the same reason, cannot use the intrinsic
+         ItemGroup task here. -->
+    <CreateItem Include="@(Protobuf_Compile)" AdditionalMetadata="_Exec=true">
+      <Output TaskParameter="Include" ItemName="_Protobuf_OutOfDateProto"/>
+    </CreateItem>
+  </Target>
+
+  <!-- Extension point: Plugins massage metadata into recognized metadata
+       values passed to the ProtoCompile task. -->
+  <Target Name="Protobuf_PrepareCompileOptions" Condition=" '@(Protobuf_Compile)' != '' ">
+    <ItemGroup>
+      <Protobuf_Compile>
+        <_OutputOptions Condition=" '%(Protobuf_Compile.Access)' == 'Internal' ">%(Protobuf_Compile._OutputOptions);internal_access</_OutputOptions>
+      </Protobuf_Compile>
+    </ItemGroup>
+  </Target>
+
+  <Target Name="_Protobuf_CoreCompile"
+          Condition=" '$(DesignTimeBuild)' != 'true' "
+          DependsOnTargets="Protobuf_PrepareCompileOptions;_Protobuf_GatherStaleFiles">
+    <!-- Ensure output directories. -->
+    <MakeDir Directories="%(_Protobuf_OutOfDateProto.OutputDir)" />
+    <MakeDir Directories="%(_Protobuf_OutOfDateProto.GrpcOutputDir)" />
+    <MakeDir Directories="$(Protobuf_DepFilesPath)" />
+
+    <!-- Force output to the current directory if the user has set it to empty. -->
+    <ItemGroup>
+      <_Protobuf_OutOfDateProto>
+        <OutputDir Condition=" '%(OutputDir)' == '' ">.</OutputDir>
+      </_Protobuf_OutOfDateProto>
+    </ItemGroup>
+
+    <ProtoCompile Condition=" '@(_Protobuf_OutOfDateProto)' != '' "
+      ToolExe="$(Protobuf_ProtocFullPath)"
+      Generator="$(Protobuf_Generator)"
+      ProtoBuf="%(_Protobuf_OutOfDateProto.Source)"
+      ProtoPath="%(_Protobuf_OutOfDateProto.AdditionalImportDirs);$(Protobuf_StandardImportsPath);%(_Protobuf_OutOfDateProto.ProtoRoot)"
+      ProtoDepDir="$(Protobuf_DepFilesPath)"
+      OutputDir="%(_Protobuf_OutOfDateProto.OutputDir)"
+      OutputOptions="%(_Protobuf_OutOfDateProto._OutputOptions)"
+      GrpcPluginExe="%(_Protobuf_OutOfDateProto.GrpcPluginExe)"
+      GrpcOutputDir="%(_Protobuf_OutOfDateProto.GrpcOutputDir)"
+      GrpcOutputOptions="%(_Protobuf_OutOfDateProto._GrpcOutputOptions)"
+    >
+      <Output TaskParameter="GeneratedFiles" ItemName="_Protobuf_GeneratedFiles"/>
+    </ProtoCompile>
+
+    <!-- Compute files expected but not in fact produced by protoc. -->
+    <ItemGroup Condition=" '@(_Protobuf_OutOfDateProto)' != '' ">
+      <Protobuf_ExpectedNotGenerated Include="@(Protobuf_ExpectedOutputs)"
+                                     Condition=" '%(Source)' != '' and '@(_Protobuf_OutOfDateProto)' != '' " />
+      <Protobuf_ExpectedNotGenerated Remove="@(_Protobuf_GeneratedFiles)" />
+    </ItemGroup>
+  </Target>
+
+  <!-- Extension point. Plugins and/or unsupported projects may take special care of the
+       Protobuf_ExpectedNotGenerated list in BeforeTargets. We just silently create the
+       missing outputs so that out-of-date checks work (we do not add them to language
+       compile though). You can empty this collection in your Before targets to do nothing.
+       The target is not executed if the proto compiler is not executed. -->
+  <Target Name="Protobuf_ReconcileOutputs"
+          Condition=" '$(DesignTimeBuild)' != 'true' ">
+    <!-- Warn about unexpected/missing files outside object file directory only.
+         This should have happened because build was incorrectly customized. -->
+    <FindUnderPath Path="$(BaseIntermediateOutputPath)" Files="@(Protobuf_ExpectedNotGenerated)">
+      <Output TaskParameter="InPath" ItemName="_Protobuf_ExpectedNotGeneratedInTemp"/>
+      <Output TaskParameter="OutOfPath" ItemName="_Protobuf_ExpectedNotGeneratedElsewhere"/>
+    </FindUnderPath>
+
+    <!-- Prevent unnecessary recompilation by silently creating empty files. This probably
+         has happened because a proto file with an rpc service was processed by the gRPC
+         plugin, and the user did not set GrpcOutput to None. When we treat outputs as
+         transient, we can do it permissively. -->
+    <Touch Files="@(_Protobuf_ExpectedNotGeneratedInTemp)" AlwaysCreate="true" />
+
+    <!-- Also create empty files outside of the intermediate directory, if the user wants so. -->
+    <Touch Files="@(_Protobuf_ExpectedNotGeneratedElsewhere)" AlwaysCreate="true"
+           Condition=" '$(Protobuf_TouchMissingExpected)' == 'true' "/>
+
+    <!-- You are seeing this warning because there were some Protobuf_ExpectedOutputs items
+         (outside of the transient directory under obj/) not in fact produced by protoc. -->
+    <Warning Condition=" '@(_Protobuf_ExpectedNotGeneratedElsewhere)' != '' and $(Protobuf_NoWarnMissingExpected) != 'true' "
+             Text="Some expected protoc outputs were not generated.&#10;@(_Protobuf_ExpectedNotGeneratedElsewhere->'&#10;    %(Identity)', '')" />
+  </Target>
+
+  <!--================================================================================
+                                   Proto cleanup
+   =================================================================================-->
+
+  <!-- We fully support cleanup only in a C# project. If extending the build for other
+       generators/plugins, then mostly roll your own. -->
+
+  <!-- Extension points. -->
+  <Target Name="Protobuf_BeforeClean" />
+  <Target Name="Protobuf_AfterClean" />
+
+  <!-- Main cleanup sequence. -->
+  <Target Name="Protobuf_Clean"
+          Condition=" '@(ProtoBuf)' != '' "
+          DependsOnTargets=" Protobuf_BeforeClean;
+                             Protobuf_PrepareClean;
+                             _Protobuf_CoreClean;
+                             Protobuf_AfterClean" />
+
+  <!-- Do proto cleanup by default in a C# project. In other types, the user should
+       invoke Protobuf_Clean directly if required. -->
+  <Target Name="_Protobuf_Clean_AfterCsClean"
+          AfterTargets="CoreClean"
+          DependsOnTargets="Protobuf_Clean"
+          Condition=" '$(Protobuf_ProjectSupported)' == 'true' and '$(Language)' == 'C#' " />
+
+  <!-- Extension point for non-C# project. ProtoCompilerOutputs is not invoked for
+       non-C# projects, since inferring protoc outputs is required, so this is a
+       no-op in other project types. In your extension target populate the
+       Protobuf_ExpectedOutputs with all possible output. An option is to include
+       all existing outputs using Include with a wildcard, if you know where to look.
+
+       Note this is like Protobuf_PrepareCompile, but uses @(Protobuf) regardless
+       of the Compile metadata, to remove all possible outputs. Plugins should err
+       on the side of overextending the Protobuf_ExpectedOutputs here.
+
+       All ExpectedOutputs will be removed. -->
+  <Target Name="Protobuf_PrepareClean" Condition=" '@(Protobuf)' != '' ">
+    <!-- Predict expected names. -->
+    <ProtoCompilerOutputs Condition=" '$(Language)' == 'C#' "
+                          ProtoBuf="@(Protobuf)"
+                          Generator="$(Protobuf_Generator)">
+      <Output TaskParameter="PossibleOutputs" ItemName="Protobuf_ExpectedOutputs" />
+    </ProtoCompilerOutputs>
+  </Target>
+
+  <Target Name="_Protobuf_CoreClean">
+    <ItemGroup>
+      <_Protobuf_Protodep Include="$(Protobuf_DepFilesPath)*.protodep" />
+    </ItemGroup>
+    <Delete Files="@(Protobuf_ExpectedOutputs);@(_Protobuf_Protodep)" TreatErrorsAsWarnings="true" />
+  </Target>
+
+  <!--================================================================================
+                                  Design-time support
+   =================================================================================-->
+
+  <!-- Add all .proto files to the SourceFilesProjectOutputGroupOutput, so that:
+       * Visual Studio triggers a build when any of them changed;
+       * The Pack target includes .proto files into the source package.  -->
+  <Target Name="_Protobuf_SourceFilesProjectOutputGroup"
+          BeforeTargets="SourceFilesProjectOutputGroup"
+          Condition=" '@(ProtoBuf)' != '' " >
+    <ItemGroup>
+      <SourceFilesProjectOutputGroupOutput Include="@(ProtoBuf->'%(FullPath)')" />
+    </ItemGroup>
+  </Target>
+</Project>
diff --git a/src/csharp/Grpc.Tools/build/_protobuf/Protobuf.CSharp.xml b/src/csharp/Grpc.Tools/build/_protobuf/Protobuf.CSharp.xml
new file mode 100644
index 0000000000..2c41fbcbd0
--- /dev/null
+++ b/src/csharp/Grpc.Tools/build/_protobuf/Protobuf.CSharp.xml
@@ -0,0 +1,99 @@
+<ProjectSchemaDefinitions xmlns="http://schemas.microsoft.com/build/2009/properties">
+  <FileExtension Name=".proto"
+                 ContentType="ProtoFile" />
+
+  <ContentType Name="ProtoFile"
+               DisplayName="Protocol buffer definitions file"
+               ItemType="ProtoBuf" />
+
+  <ItemType Name="ProtoBuf"
+            DisplayName="Protobuf compiler" />
+
+  <Rule Name="ProtoBuf"
+        DisplayName="File Properties"
+        PageTemplate="generic"
+        Description="File Properties"
+        OverrideMode="Extend">
+    <Rule.DataSource>
+      <DataSource Persistence="ProjectFile" Label="Configuration" ItemType="ProtoBuf"
+                  HasConfigurationCondition="false" SourceOfDefaultValue="AfterContext" />
+    </Rule.DataSource>
+
+    <Rule.Categories>
+      <Category Name="Advanced" DisplayName="Advanced" />
+      <Category Name="Protobuf" DisplayName="Protobuf" />
+      <Category Name="Misc" DisplayName="Misc" />
+    </Rule.Categories>
+
+    <DynamicEnumProperty Name="{}{ItemType}" DisplayName="Build Action"  Category="Advanced"
+                   Description="How the file relates to the build and deployment processes."
+                   EnumProvider="ItemTypes" />
+
+    <StringProperty Name="Identity" Visible="false" ReadOnly="true">
+      <StringProperty.DataSource>
+        <DataSource Persistence="Intrinsic" ItemType="ProtoBuf"
+                    PersistedName="Identity" SourceOfDefaultValue="AfterContext" />
+      </StringProperty.DataSource>
+    </StringProperty>
+
+    <StringProperty Name="FullPath"
+                    DisplayName="Full Path"
+                    ReadOnly="true"
+                    Category="Misc"
+                    Description="Location of the file.">
+      <StringProperty.DataSource>
+        <DataSource Persistence="Intrinsic" ItemType="ProtoBuf"
+                    PersistedName="FullPath" SourceOfDefaultValue="AfterContext" />
+      </StringProperty.DataSource>
+    </StringProperty>
+
+    <StringProperty Name="FileNameAndExtension"
+                    DisplayName="File Name"
+                    ReadOnly="true"
+                    Category="Misc"
+                    Description="Name of the file or folder.">
+      <StringProperty.DataSource>
+        <DataSource Persistence="Intrinsic" ItemType="ProtoBuf"
+                    PersistedName="FileNameAndExtension" SourceOfDefaultValue="AfterContext" />
+      </StringProperty.DataSource>
+    </StringProperty>
+
+    <BoolProperty Name="Visible" Visible="false" Default="true" />
+
+    <StringProperty Name="DependentUpon" Visible="false">
+      <StringProperty.Metadata>
+        <NameValuePair Name="DoNotCopyAcrossProjects" Value="true" />
+      </StringProperty.Metadata>
+    </StringProperty>
+
+    <StringProperty Name="Link" Visible="false">
+      <StringProperty.DataSource>
+        <DataSource SourceOfDefaultValue="AfterContext" />
+      </StringProperty.DataSource>
+      <StringProperty.Metadata>
+        <NameValuePair Name="DoNotCopyAcrossProjects" Value="true" />
+      </StringProperty.Metadata>
+    </StringProperty>
+
+    <EnumProperty Name="Access" DisplayName="Class Access"
+                  Category="Protobuf"
+                  Description="Public or internal access modifier on generated classes.">
+      <EnumValue Name="Public" DisplayName="Public" IsDefault="true" />
+      <EnumValue Name="Internal" DisplayName="Internal" />
+      <EnumProperty.DataSource>
+        <DataSource ItemType="ProtoBuf" SourceOfDefaultValue="AfterContext"
+                    PersistenceStyle="Attribute" />
+      </EnumProperty.DataSource>
+    </EnumProperty>
+
+    <BoolProperty Name="ProtoCompile" DisplayName="Compile Protobuf"
+                  Category="Protobuf" Default="true"
+                  Description="Specifies if this file is compiled or only imported by other files.">
+      <BoolProperty.DataSource>
+        <DataSource ItemType="ProtoBuf" SourceOfDefaultValue="AfterContext"
+                    PersistenceStyle="Attribute" />
+      </BoolProperty.DataSource>
+    </BoolProperty>
+
+  </Rule>
+</ProjectSchemaDefinitions>
diff --git a/src/csharp/Grpc.Tools/build/_protobuf/README b/src/csharp/Grpc.Tools/build/_protobuf/README
new file mode 100644
index 0000000000..e6e358a218
--- /dev/null
+++ b/src/csharp/Grpc.Tools/build/_protobuf/README
@@ -0,0 +1 @@
+TODO(kkm): These file will go into Google.Protobuf.Tools/build after package split.
diff --git a/src/csharp/Grpc.Tools/build/native/Grpc.Tools.props b/src/csharp/Grpc.Tools/build/native/Grpc.Tools.props
new file mode 100644
index 0000000000..f83c4d135a
--- /dev/null
+++ b/src/csharp/Grpc.Tools/build/native/Grpc.Tools.props
@@ -0,0 +1,17 @@
+<?xml version="1.0"?>
+<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <PropertyGroup>
+    <MSBuildAllProjects>$(MSBuildAllProjects);$(MSBuildThisFileFullPath)</MSBuildAllProjects>
+
+    <!-- Revision number of this package conventions (as if "API" version). -->
+    <Protobuf_ToolingRevision>1</Protobuf_ToolingRevision>
+
+    <!-- For a Visual Studio C++ native project we currently only resolve tools and import paths. -->
+    <!-- TODO(kkm): Do not place non-tools under tools/, use build/native/bin/. -->
+    <!-- TODO(kkm): Do not package windows x64 builds (#13098). -->
+    <Protobuf_ProtocFullPath>$(MSBuildThisFileDirectory)..\..\tools\windows_x86\protoc.exe</Protobuf_ProtocFullPath>
+    <Protobuf_StandardImportsPath>$(MSBuildThisFileDirectory)include\</Protobuf_StandardImportsPath>
+    <gRPC_PluginFileName>grpc_cpp_plugin</gRPC_PluginFileName>
+    <gRPC_PluginFullPath>$(MSBuildThisFileDirectory)..\..\tools\windows_x86\grpc_cpp_plugin.exe</gRPC_PluginFullPath>
+  </PropertyGroup>
+</Project>
diff --git a/src/csharp/Grpc.sln b/src/csharp/Grpc.sln
index d9a7b8d556..6c1b2e9998 100644
--- a/src/csharp/Grpc.sln
+++ b/src/csharp/Grpc.sln
@@ -39,6 +39,10 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Grpc.Reflection.Tests", "Gr
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Grpc.Microbenchmarks", "Grpc.Microbenchmarks\Grpc.Microbenchmarks.csproj", "{84C17746-4727-4290-8E8B-A380793DAE1E}"
 EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Grpc.Tools", "Grpc.Tools\Grpc.Tools.csproj", "{8A643A1B-B85C-4E3D-BFD3-719FE04D7E91}"
+EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Grpc.Tools.Tests", "Grpc.Tools.Tests\Grpc.Tools.Tests.csproj", "{AEBE9BD8-E433-45B7-8B3D-D458EDBBCFC4}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -117,6 +121,14 @@ Global
 		{84C17746-4727-4290-8E8B-A380793DAE1E}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{84C17746-4727-4290-8E8B-A380793DAE1E}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{84C17746-4727-4290-8E8B-A380793DAE1E}.Release|Any CPU.Build.0 = Release|Any CPU
+		{8A643A1B-B85C-4E3D-BFD3-719FE04D7E91}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{8A643A1B-B85C-4E3D-BFD3-719FE04D7E91}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{8A643A1B-B85C-4E3D-BFD3-719FE04D7E91}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{8A643A1B-B85C-4E3D-BFD3-719FE04D7E91}.Release|Any CPU.Build.0 = Release|Any CPU
+		{AEBE9BD8-E433-45B7-8B3D-D458EDBBCFC4}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{AEBE9BD8-E433-45B7-8B3D-D458EDBBCFC4}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{AEBE9BD8-E433-45B7-8B3D-D458EDBBCFC4}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{AEBE9BD8-E433-45B7-8B3D-D458EDBBCFC4}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
diff --git a/src/csharp/build_packages_dotnetcli.bat b/src/csharp/build_packages_dotnetcli.bat
index 24d016104c..27688360e9 100755
--- a/src/csharp/build_packages_dotnetcli.bat
+++ b/src/csharp/build_packages_dotnetcli.bat
@@ -13,7 +13,7 @@
 @rem limitations under the License.
 
 @rem Current package versions
-set VERSION=1.16.0-dev
+set VERSION=1.17.0-dev
 
 @rem Adjust the location of nuget.exe
 set NUGET=C:\nuget\nuget.exe
@@ -39,10 +39,10 @@ xcopy /Y /I nativelibs\csharp_ext_windows_x64\grpc_csharp_ext.dll ..\..\cmake\bu
 %DOTNET% pack --configuration Release Grpc.Auth --output ..\..\..\artifacts || goto :error
 %DOTNET% pack --configuration Release Grpc.HealthCheck --output ..\..\..\artifacts || goto :error
 %DOTNET% pack --configuration Release Grpc.Reflection --output ..\..\..\artifacts || goto :error
+%DOTNET% pack --configuration Release Grpc.Tools --output ..\..\..\artifacts || goto :error
 
 %NUGET% pack Grpc.nuspec -Version %VERSION% -OutputDirectory ..\..\artifacts || goto :error
 %NUGET% pack Grpc.Core.NativeDebug.nuspec -Version %VERSION% -OutputDirectory ..\..\artifacts
-%NUGET% pack Grpc.Tools.nuspec -Version %VERSION% -OutputDirectory ..\..\artifacts
 
 @rem copy resulting nuget packages to artifacts directory
 xcopy /Y /I *.nupkg ..\..\artifacts\ || goto :error
diff --git a/src/csharp/build_unitypackage.bat b/src/csharp/build_unitypackage.bat
index 4e7ac4e414..dd74de0491 100644
--- a/src/csharp/build_unitypackage.bat
+++ b/src/csharp/build_unitypackage.bat
@@ -13,7 +13,7 @@
 @rem limitations under the License.
 
 @rem Current package versions
-set VERSION=1.16.0-dev
+set VERSION=1.17.0-dev
 
 @rem Adjust the location of nuget.exe
 set NUGET=C:\nuget\nuget.exe
diff --git a/src/csharp/tests.json b/src/csharp/tests.json
index 5683d164c6..760776f9e7 100644
--- a/src/csharp/tests.json
+++ b/src/csharp/tests.json
@@ -64,5 +64,15 @@
   "Grpc.Reflection.Tests": [
     "Grpc.Reflection.Tests.ReflectionClientServerTest",
     "Grpc.Reflection.Tests.SymbolRegistryTest"
+  ],
+  "Grpc.Tools.Tests": [
+    "Grpc.Tools.Tests.CppGeneratorTest",
+    "Grpc.Tools.Tests.CSharpGeneratorTest",
+    "Grpc.Tools.Tests.DepFileUtilTest",
+    "Grpc.Tools.Tests.GeneratorTest",
+    "Grpc.Tools.Tests.ProtoCompileBasicTest",
+    "Grpc.Tools.Tests.ProtoCompileCommandLineGeneratorTest",
+    "Grpc.Tools.Tests.ProtoCompileCommandLinePrinterTest",
+    "Grpc.Tools.Tests.ProtoToolsPlatformTaskTest"
   ]
 }
diff --git a/src/objective-c/!ProtoCompiler-gRPCPlugin.podspec b/src/objective-c/!ProtoCompiler-gRPCPlugin.podspec
index 200cee5b7b..a95a120d21 100644
--- a/src/objective-c/!ProtoCompiler-gRPCPlugin.podspec
+++ b/src/objective-c/!ProtoCompiler-gRPCPlugin.podspec
@@ -42,7 +42,7 @@ Pod::Spec.new do |s|
   # exclamation mark ensures that other "regular" pods will be able to find it as it'll be installed
   # before them.
   s.name     = '!ProtoCompiler-gRPCPlugin'
-  v = '1.16.0-dev'
+  v = '1.17.0-dev'
   s.version  = v
   s.summary  = 'The gRPC ProtoC plugin generates Objective-C files from .proto services.'
   s.description = <<-DESC
diff --git a/src/objective-c/GRPCClient/private/GRPCHost.m b/src/objective-c/GRPCClient/private/GRPCHost.m
index de6f09a44b..7c31b10636 100644
--- a/src/objective-c/GRPCClient/private/GRPCHost.m
+++ b/src/objective-c/GRPCClient/private/GRPCHost.m
@@ -58,7 +58,7 @@ static NSMutableDictionary *kHostCache;
   // gRPC library.
   // TODO(jcanizales): Add unit tests for the types of addresses we want to let pass untouched.
   NSURL *hostURL = [NSURL URLWithString:[@"https://" stringByAppendingString:address]];
-  if (hostURL.host && !hostURL.port) {
+  if (hostURL.host && hostURL.port == nil) {
     address = [hostURL.host stringByAppendingString:@":443"];
   }
 
diff --git a/src/objective-c/GRPCClient/private/version.h b/src/objective-c/GRPCClient/private/version.h
index 38862e102a..d5463c0b4c 100644
--- a/src/objective-c/GRPCClient/private/version.h
+++ b/src/objective-c/GRPCClient/private/version.h
@@ -22,4 +22,4 @@
 // instead. This file can be regenerated from the template by running
 // `tools/buildgen/generate_projects.sh`.
 
-#define GRPC_OBJC_VERSION_STRING @"1.16.0-dev"
+#define GRPC_OBJC_VERSION_STRING @"1.17.0-dev"
diff --git a/src/objective-c/tests/version.h b/src/objective-c/tests/version.h
index 82833102ad..ca27c03b3c 100644
--- a/src/objective-c/tests/version.h
+++ b/src/objective-c/tests/version.h
@@ -22,5 +22,5 @@
 // instead. This file can be regenerated from the template by running
 // `tools/buildgen/generate_projects.sh`.
 
-#define GRPC_OBJC_VERSION_STRING @"1.16.0-dev"
-#define GRPC_C_VERSION_STRING @"6.0.0-dev"
+#define GRPC_OBJC_VERSION_STRING @"1.17.0-dev"
+#define GRPC_C_VERSION_STRING @"7.0.0-dev"
diff --git a/src/php/composer.json b/src/php/composer.json
index f31423f8c0..d54db91b5f 100644
--- a/src/php/composer.json
+++ b/src/php/composer.json
@@ -2,7 +2,7 @@
   "name": "grpc/grpc-dev",
   "description": "gRPC library for PHP - for Developement use only",
   "license": "Apache-2.0",
-  "version": "1.16.0",
+  "version": "1.17.0",
   "require": {
     "php": ">=5.5.0",
     "google/protobuf": "^v3.3.0"
diff --git a/src/php/ext/grpc/version.h b/src/php/ext/grpc/version.h
index 469a48e782..70f8bbbf40 100644
--- a/src/php/ext/grpc/version.h
+++ b/src/php/ext/grpc/version.h
@@ -20,6 +20,6 @@
 #ifndef VERSION_H
 #define VERSION_H
 
-#define PHP_GRPC_VERSION "1.16.0dev"
+#define PHP_GRPC_VERSION "1.17.0dev"
 
 #endif /* VERSION_H */
diff --git a/src/proto/grpc/health/v1/BUILD b/src/proto/grpc/health/v1/BUILD
index d234842883..97642985c9 100644
--- a/src/proto/grpc/health/v1/BUILD
+++ b/src/proto/grpc/health/v1/BUILD
@@ -22,3 +22,11 @@ grpc_proto_library(
     name = "health_proto",
     srcs = ["health.proto"],
 )
+
+filegroup(
+    name = "health_proto_file",
+    srcs = [
+        "health.proto",
+    ],
+)
+
diff --git a/src/proto/grpc/testing/control.proto b/src/proto/grpc/testing/control.proto
index a4a9c8fe57..4cfdc2cafb 100644
--- a/src/proto/grpc/testing/control.proto
+++ b/src/proto/grpc/testing/control.proto
@@ -25,6 +25,7 @@ enum ClientType {
   SYNC_CLIENT = 0;
   ASYNC_CLIENT = 1;
   OTHER_CLIENT = 2; // used for some language-specific variants
+  CALLBACK_CLIENT = 3;
 }
 
 enum ServerType {
diff --git a/src/python/grpcio/grpc/_channel.py b/src/python/grpcio/grpc/_channel.py
index 3494c9b15a..eeeb4ddb33 100644
--- a/src/python/grpcio/grpc/_channel.py
+++ b/src/python/grpcio/grpc/_channel.py
@@ -981,4 +981,7 @@ class Channel(grpc.Channel):
         # then deletion of this grpc._channel.Channel instance can be made to
         # effect closure of the underlying cygrpc.Channel instance.
         cygrpc.fork_unregister_channel(self)
-        _moot(self._connectivity_state)
+        # This prevent the failed-at-initializing object removal from failing.
+        # Though the __init__ failed, the removal will still trigger __del__.
+        if hasattr(self, "_connectivity_state"):
+            _moot(self._connectivity_state)
diff --git a/src/python/grpcio/grpc/_cython/_cygrpc/arguments.pxd.pxi b/src/python/grpcio/grpc/_cython/_cygrpc/arguments.pxd.pxi
index 6cb1bc0c05..e0e068e452 100644
--- a/src/python/grpcio/grpc/_cython/_cygrpc/arguments.pxd.pxi
+++ b/src/python/grpcio/grpc/_cython/_cygrpc/arguments.pxd.pxi
@@ -32,7 +32,7 @@ cdef class _ArgumentProcessor:
 
   cdef grpc_arg c_argument
 
-  cdef void c(self, argument, grpc_arg_pointer_vtable *vtable, references)
+  cdef void c(self, argument, grpc_arg_pointer_vtable *vtable, references) except *
 
 
 cdef class _ArgumentsProcessor:
@@ -42,5 +42,5 @@ cdef class _ArgumentsProcessor:
   cdef readonly list _references
   cdef grpc_channel_args _c_arguments
 
-  cdef grpc_channel_args *c(self, grpc_arg_pointer_vtable *vtable)
+  cdef grpc_channel_args *c(self, grpc_arg_pointer_vtable *vtable) except *
   cdef un_c(self)
diff --git a/src/python/grpcio/grpc/_cython/_cygrpc/arguments.pyx.pxi b/src/python/grpcio/grpc/_cython/_cygrpc/arguments.pyx.pxi
index 2239e26b32..b7a4277ff6 100644
--- a/src/python/grpcio/grpc/_cython/_cygrpc/arguments.pyx.pxi
+++ b/src/python/grpcio/grpc/_cython/_cygrpc/arguments.pyx.pxi
@@ -52,7 +52,7 @@ cdef grpc_arg _unwrap_grpc_arg(tuple wrapped_arg):
 
 cdef class _ArgumentProcessor:
 
-  cdef void c(self, argument, grpc_arg_pointer_vtable *vtable, references):
+  cdef void c(self, argument, grpc_arg_pointer_vtable *vtable, references) except *:
     key, value = argument
     cdef bytes encoded_key = _encode(key)
     if encoded_key is not key:
@@ -89,7 +89,7 @@ cdef class _ArgumentsProcessor:
     self._argument_processors = []
     self._references = []
 
-  cdef grpc_channel_args *c(self, grpc_arg_pointer_vtable *vtable):
+  cdef grpc_channel_args *c(self, grpc_arg_pointer_vtable *vtable) except *:
     self._c_arguments.arguments_length = len(self._arguments)
     if self._c_arguments.arguments_length == 0:
       return NULL
diff --git a/src/python/grpcio/grpc/_grpcio_metadata.py b/src/python/grpcio/grpc/_grpcio_metadata.py
index 24e1557578..42b3a1ad49 100644
--- a/src/python/grpcio/grpc/_grpcio_metadata.py
+++ b/src/python/grpcio/grpc/_grpcio_metadata.py
@@ -14,4 +14,4 @@
 
 # AUTO-GENERATED FROM `$REPO_ROOT/templates/src/python/grpcio/grpc/_grpcio_metadata.py.template`!!!
 
-__version__ = """1.16.0.dev0"""
+__version__ = """1.17.0.dev0"""
diff --git a/src/python/grpcio/grpc_version.py b/src/python/grpcio/grpc_version.py
index 6ffe1eb827..71113e68d9 100644
--- a/src/python/grpcio/grpc_version.py
+++ b/src/python/grpcio/grpc_version.py
@@ -14,4 +14,4 @@
 
 # AUTO-GENERATED FROM `$REPO_ROOT/templates/src/python/grpcio/grpc_version.py.template`!!!
 
-VERSION = '1.16.0.dev0'
+VERSION = '1.17.0.dev0'
diff --git a/src/python/grpcio_health_checking/grpc_health/v1/BUILD.bazel b/src/python/grpcio_health_checking/grpc_health/v1/BUILD.bazel
new file mode 100644
index 0000000000..ce3121fa90
--- /dev/null
+++ b/src/python/grpcio_health_checking/grpc_health/v1/BUILD.bazel
@@ -0,0 +1,33 @@
+load("@grpc_python_dependencies//:requirements.bzl", "requirement")
+load("@org_pubref_rules_protobuf//python:rules.bzl", "py_proto_library")
+
+package(default_visibility = ["//visibility:public"])
+
+genrule(
+    name = "mv_health_proto",
+    srcs = [
+        "//src/proto/grpc/health/v1:health_proto_file",
+    ],
+    outs = ["health.proto",],
+    cmd = "cp $< $@",
+)
+
+py_proto_library(
+    name = "py_health_proto",
+    protos = [":mv_health_proto",],
+    with_grpc = True,
+    deps = [
+        requirement('protobuf'),
+    ],
+)
+
+py_library(
+    name = "grpc_health",
+    srcs = ["health.py",],
+    deps = [
+        ":py_health_proto",
+        "//src/python/grpcio/grpc:grpcio",
+    ],
+    imports=["../../",],
+)
+
diff --git a/src/python/grpcio_health_checking/grpc_version.py b/src/python/grpcio_health_checking/grpc_version.py
index e080bf2cbc..a30aac2e0b 100644
--- a/src/python/grpcio_health_checking/grpc_version.py
+++ b/src/python/grpcio_health_checking/grpc_version.py
@@ -14,4 +14,4 @@
 
 # AUTO-GENERATED FROM `$REPO_ROOT/templates/src/python/grpcio_health_checking/grpc_version.py.template`!!!
 
-VERSION = '1.16.0.dev0'
+VERSION = '1.17.0.dev0'
diff --git a/src/python/grpcio_reflection/grpc_version.py b/src/python/grpcio_reflection/grpc_version.py
index 4b3b95fee9..aafea9fe76 100644
--- a/src/python/grpcio_reflection/grpc_version.py
+++ b/src/python/grpcio_reflection/grpc_version.py
@@ -14,4 +14,4 @@
 
 # AUTO-GENERATED FROM `$REPO_ROOT/templates/src/python/grpcio_reflection/grpc_version.py.template`!!!
 
-VERSION = '1.16.0.dev0'
+VERSION = '1.17.0.dev0'
diff --git a/src/python/grpcio_testing/grpc_version.py b/src/python/grpcio_testing/grpc_version.py
index c12aa153a4..876acd3142 100644
--- a/src/python/grpcio_testing/grpc_version.py
+++ b/src/python/grpcio_testing/grpc_version.py
@@ -14,4 +14,4 @@
 
 # AUTO-GENERATED FROM `$REPO_ROOT/templates/src/python/grpcio_testing/grpc_version.py.template`!!!
 
-VERSION = '1.16.0.dev0'
+VERSION = '1.17.0.dev0'
diff --git a/src/python/grpcio_tests/commands.py b/src/python/grpcio_tests/commands.py
index 0dfbf3180b..6931d93ef0 100644
--- a/src/python/grpcio_tests/commands.py
+++ b/src/python/grpcio_tests/commands.py
@@ -116,6 +116,8 @@ class TestGevent(setuptools.Command):
         # eventually succeed, but need to dig into performance issues.
         'unit._cython._no_messages_server_completion_queue_per_call_test.Test.test_rpcs',
         'unit._cython._no_messages_single_server_completion_queue_test.Test.test_rpcs',
+        # TODO(https://github.com/grpc/grpc/issues/16890) enable this test
+        'unit._cython._channel_test.ChannelTest.test_multiple_channels_lonely_connectivity',
         # I have no idea why this doesn't work in gevent, but it shouldn't even be
         # using the c-core
         'testing._client_test.ClientTest.test_infinite_request_stream_real_time',
diff --git a/src/python/grpcio_tests/grpc_version.py b/src/python/grpcio_tests/grpc_version.py
index f4b8a34a46..cc9b41587c 100644
--- a/src/python/grpcio_tests/grpc_version.py
+++ b/src/python/grpcio_tests/grpc_version.py
@@ -14,4 +14,4 @@
 
 # AUTO-GENERATED FROM `$REPO_ROOT/templates/src/python/grpcio_tests/grpc_version.py.template`!!!
 
-VERSION = '1.16.0.dev0'
+VERSION = '1.17.0.dev0'
diff --git a/src/python/grpcio_tests/tests/health_check/BUILD.bazel b/src/python/grpcio_tests/tests/health_check/BUILD.bazel
new file mode 100644
index 0000000000..19e1e1b2e1
--- /dev/null
+++ b/src/python/grpcio_tests/tests/health_check/BUILD.bazel
@@ -0,0 +1,15 @@
+package(default_visibility = ["//visibility:public"])
+
+py_test(
+    name = "health_servicer_test",
+    srcs = ["_health_servicer_test.py"],
+    main = "_health_servicer_test.py",
+    size = "small",
+    deps = [
+        "//src/python/grpcio/grpc:grpcio",
+        "//src/python/grpcio_health_checking/grpc_health/v1:grpc_health",
+        "//src/python/grpcio_tests/tests/unit:test_common",
+    ],
+    imports = ["../../",],
+)
+
diff --git a/src/python/grpcio_tests/tests/unit/_channel_args_test.py b/src/python/grpcio_tests/tests/unit/_channel_args_test.py
index 869c2f4d2f..dd1d2969a2 100644
--- a/src/python/grpcio_tests/tests/unit/_channel_args_test.py
+++ b/src/python/grpcio_tests/tests/unit/_channel_args_test.py
@@ -33,6 +33,14 @@ TEST_CHANNEL_ARGS = (
     ('arg6', TestPointerWrapper()),
 )
 
+INVALID_TEST_CHANNEL_ARGS = [
+    {
+        'foo': 'bar'
+    },
+    (('key',),),
+    'str',
+]
+
 
 class ChannelArgsTest(unittest.TestCase):
 
@@ -44,6 +52,14 @@ class ChannelArgsTest(unittest.TestCase):
             futures.ThreadPoolExecutor(max_workers=1),
             options=TEST_CHANNEL_ARGS)
 
+    def test_invalid_client_args(self):
+        for invalid_arg in INVALID_TEST_CHANNEL_ARGS:
+            self.assertRaises(
+                ValueError,
+                grpc.insecure_channel,
+                'localhost:8080',
+                options=invalid_arg)
+
 
 if __name__ == '__main__':
     unittest.main(verbosity=2)
diff --git a/src/ruby/ext/grpc/rb_grpc_imports.generated.c b/src/ruby/ext/grpc/rb_grpc_imports.generated.c
index 1e7d7f687f..0e192b6201 100644
--- a/src/ruby/ext/grpc/rb_grpc_imports.generated.c
+++ b/src/ruby/ext/grpc/rb_grpc_imports.generated.c
@@ -98,12 +98,12 @@ grpc_resource_quota_set_max_threads_type grpc_resource_quota_set_max_threads_imp
 grpc_resource_quota_arg_vtable_type grpc_resource_quota_arg_vtable_import;
 grpc_channelz_get_top_channels_type grpc_channelz_get_top_channels_import;
 grpc_channelz_get_servers_type grpc_channelz_get_servers_import;
+grpc_channelz_get_server_sockets_type grpc_channelz_get_server_sockets_import;
 grpc_channelz_get_channel_type grpc_channelz_get_channel_import;
 grpc_channelz_get_subchannel_type grpc_channelz_get_subchannel_import;
 grpc_channelz_get_socket_type grpc_channelz_get_socket_import;
 grpc_insecure_channel_create_from_fd_type grpc_insecure_channel_create_from_fd_import;
 grpc_server_add_insecure_channel_from_fd_type grpc_server_add_insecure_channel_from_fd_import;
-grpc_use_signal_type grpc_use_signal_import;
 grpc_auth_property_iterator_next_type grpc_auth_property_iterator_next_import;
 grpc_auth_context_property_iterator_type grpc_auth_context_property_iterator_import;
 grpc_auth_context_peer_identity_type grpc_auth_context_peer_identity_import;
@@ -355,12 +355,12 @@ void grpc_rb_load_imports(HMODULE library) {
   grpc_resource_quota_arg_vtable_import = (grpc_resource_quota_arg_vtable_type) GetProcAddress(library, "grpc_resource_quota_arg_vtable");
   grpc_channelz_get_top_channels_import = (grpc_channelz_get_top_channels_type) GetProcAddress(library, "grpc_channelz_get_top_channels");
   grpc_channelz_get_servers_import = (grpc_channelz_get_servers_type) GetProcAddress(library, "grpc_channelz_get_servers");
+  grpc_channelz_get_server_sockets_import = (grpc_channelz_get_server_sockets_type) GetProcAddress(library, "grpc_channelz_get_server_sockets");
   grpc_channelz_get_channel_import = (grpc_channelz_get_channel_type) GetProcAddress(library, "grpc_channelz_get_channel");
   grpc_channelz_get_subchannel_import = (grpc_channelz_get_subchannel_type) GetProcAddress(library, "grpc_channelz_get_subchannel");
   grpc_channelz_get_socket_import = (grpc_channelz_get_socket_type) GetProcAddress(library, "grpc_channelz_get_socket");
   grpc_insecure_channel_create_from_fd_import = (grpc_insecure_channel_create_from_fd_type) GetProcAddress(library, "grpc_insecure_channel_create_from_fd");
   grpc_server_add_insecure_channel_from_fd_import = (grpc_server_add_insecure_channel_from_fd_type) GetProcAddress(library, "grpc_server_add_insecure_channel_from_fd");
-  grpc_use_signal_import = (grpc_use_signal_type) GetProcAddress(library, "grpc_use_signal");
   grpc_auth_property_iterator_next_import = (grpc_auth_property_iterator_next_type) GetProcAddress(library, "grpc_auth_property_iterator_next");
   grpc_auth_context_property_iterator_import = (grpc_auth_context_property_iterator_type) GetProcAddress(library, "grpc_auth_context_property_iterator");
   grpc_auth_context_peer_identity_import = (grpc_auth_context_peer_identity_type) GetProcAddress(library, "grpc_auth_context_peer_identity");
diff --git a/src/ruby/ext/grpc/rb_grpc_imports.generated.h b/src/ruby/ext/grpc/rb_grpc_imports.generated.h
index ed4b6264b0..e075db89e8 100644
--- a/src/ruby/ext/grpc/rb_grpc_imports.generated.h
+++ b/src/ruby/ext/grpc/rb_grpc_imports.generated.h
@@ -269,6 +269,9 @@ extern grpc_channelz_get_top_channels_type grpc_channelz_get_top_channels_import
 typedef char*(*grpc_channelz_get_servers_type)(intptr_t start_server_id);
 extern grpc_channelz_get_servers_type grpc_channelz_get_servers_import;
 #define grpc_channelz_get_servers grpc_channelz_get_servers_import
+typedef char*(*grpc_channelz_get_server_sockets_type)(intptr_t server_id, intptr_t start_socket_id);
+extern grpc_channelz_get_server_sockets_type grpc_channelz_get_server_sockets_import;
+#define grpc_channelz_get_server_sockets grpc_channelz_get_server_sockets_import
 typedef char*(*grpc_channelz_get_channel_type)(intptr_t channel_id);
 extern grpc_channelz_get_channel_type grpc_channelz_get_channel_import;
 #define grpc_channelz_get_channel grpc_channelz_get_channel_import
@@ -284,9 +287,6 @@ extern grpc_insecure_channel_create_from_fd_type grpc_insecure_channel_create_fr
 typedef void(*grpc_server_add_insecure_channel_from_fd_type)(grpc_server* server, void* reserved, int fd);
 extern grpc_server_add_insecure_channel_from_fd_type grpc_server_add_insecure_channel_from_fd_import;
 #define grpc_server_add_insecure_channel_from_fd grpc_server_add_insecure_channel_from_fd_import
-typedef void(*grpc_use_signal_type)(int signum);
-extern grpc_use_signal_type grpc_use_signal_import;
-#define grpc_use_signal grpc_use_signal_import
 typedef const grpc_auth_property*(*grpc_auth_property_iterator_next_type)(grpc_auth_property_iterator* it);
 extern grpc_auth_property_iterator_next_type grpc_auth_property_iterator_next_import;
 #define grpc_auth_property_iterator_next grpc_auth_property_iterator_next_import
diff --git a/src/ruby/lib/grpc/version.rb b/src/ruby/lib/grpc/version.rb
index 0c3e1ef734..243d566645 100644
--- a/src/ruby/lib/grpc/version.rb
+++ b/src/ruby/lib/grpc/version.rb
@@ -14,5 +14,5 @@
 
 # GRPC contains the General RPC module.
 module GRPC
-  VERSION = '1.16.0.dev'
+  VERSION = '1.17.0.dev'
 end
diff --git a/src/ruby/tools/version.rb b/src/ruby/tools/version.rb
index 03d977c064..92e85eb882 100644
--- a/src/ruby/tools/version.rb
+++ b/src/ruby/tools/version.rb
@@ -14,6 +14,6 @@
 
 module GRPC
   module Tools
-    VERSION = '1.16.0.dev'
+    VERSION = '1.17.0.dev'
   end
 end