Merge pull request #11145 from vjpai/inproc3

In-process transport

8 files changed, 1367 insertions, 1 deletions

diff --git a/src/core/ext/transport/chttp2/transport/chttp2_transport.c b/src/core/ext/transport/chttp2/transport/chttp2_transport.c
index 0859ce8942..bd25f69a1d 100644
--- a/src/core/ext/transport/chttp2/transport/chttp2_transport.c
+++ b/src/core/ext/transport/chttp2/transport/chttp2_transport.c
@@ -1224,7 +1224,7 @@ static void do_nothing(grpc_exec_ctx *exec_ctx, void *arg, grpc_error *error) {}
 
 static void log_metadata(const grpc_metadata_batch *md_batch, uint32_t id,
                          bool is_client, bool is_initial) {
-  for (grpc_linked_mdelem *md = md_batch->list.head; md != md_batch->list.tail;
+  for (grpc_linked_mdelem *md = md_batch->list.head; md != NULL;
        md = md->next) {
     char *key = grpc_slice_to_c_string(GRPC_MDKEY(md->md));
     char *value = grpc_slice_to_c_string(GRPC_MDVALUE(md->md));
diff --git a/src/core/ext/transport/inproc/inproc_plugin.c b/src/core/ext/transport/inproc/inproc_plugin.c
new file mode 100644
index 0000000000..6a796a0b19
--- /dev/null
+++ b/src/core/ext/transport/inproc/inproc_plugin.c
@@ -0,0 +1,29 @@
+/*
+ *
+ * Copyright 2017 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 "src/core/ext/transport/inproc/inproc_transport.h"
+#include "src/core/lib/debug/trace.h"
+
+grpc_tracer_flag grpc_inproc_trace = GRPC_TRACER_INITIALIZER(false, "inproc");
+
+void grpc_inproc_plugin_init(void) {
+  grpc_register_tracer(&grpc_inproc_trace);
+  grpc_inproc_transport_init();
+}
+
+void grpc_inproc_plugin_shutdown(void) { grpc_inproc_transport_shutdown(); }
diff --git a/src/core/ext/transport/inproc/inproc_transport.c b/src/core/ext/transport/inproc/inproc_transport.c
new file mode 100644
index 0000000000..4df64d81e2
--- /dev/null
+++ b/src/core/ext/transport/inproc/inproc_transport.c
@@ -0,0 +1,1277 @@
+/*
+ *
+ * Copyright 2017 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 "src/core/ext/transport/inproc/inproc_transport.h"
+#include <grpc/support/alloc.h>
+#include <grpc/support/string_util.h>
+#include <grpc/support/sync.h>
+#include <grpc/support/time.h>
+#include <string.h>
+#include "src/core/lib/channel/channel_args.h"
+#include "src/core/lib/slice/slice_internal.h"
+#include "src/core/lib/surface/api_trace.h"
+#include "src/core/lib/surface/channel.h"
+#include "src/core/lib/surface/channel_stack_type.h"
+#include "src/core/lib/surface/server.h"
+#include "src/core/lib/transport/connectivity_state.h"
+#include "src/core/lib/transport/error_utils.h"
+#include "src/core/lib/transport/transport_impl.h"
+
+#define INPROC_LOG(...)                                          \
+  do {                                                           \
+    if (GRPC_TRACER_ON(grpc_inproc_trace)) gpr_log(__VA_ARGS__); \
+  } while (0)
+
+static const grpc_transport_vtable inproc_vtable;
+static grpc_slice g_empty_slice;
+static grpc_slice g_fake_path_key;
+static grpc_slice g_fake_path_value;
+static grpc_slice g_fake_auth_key;
+static grpc_slice g_fake_auth_value;
+
+typedef struct {
+  gpr_mu mu;
+  gpr_refcount refs;
+} shared_mu;
+
+typedef struct inproc_transport {
+  grpc_transport base;
+  shared_mu *mu;
+  gpr_refcount refs;
+  bool is_client;
+  grpc_connectivity_state_tracker connectivity;
+  void (*accept_stream_cb)(grpc_exec_ctx *exec_ctx, void *user_data,
+                           grpc_transport *transport, const void *server_data);
+  void *accept_stream_data;
+  bool is_closed;
+  struct inproc_transport *other_side;
+  struct inproc_stream *stream_list;
+} inproc_transport;
+
+typedef struct sb_list_entry {
+  grpc_slice_buffer sb;
+  struct sb_list_entry *next;
+} sb_list_entry;
+
+// Specialize grpc_byte_stream for our use case
+typedef struct {
+  grpc_byte_stream base;
+  sb_list_entry *le;
+} inproc_slice_byte_stream;
+
+typedef struct {
+  // TODO (vjpai): Add some inlined elements to avoid alloc in simple cases
+  sb_list_entry *head;
+  sb_list_entry *tail;
+} slice_buffer_list;
+
+static void slice_buffer_list_init(slice_buffer_list *l) {
+  l->head = NULL;
+  l->tail = NULL;
+}
+
+static void sb_list_entry_destroy(grpc_exec_ctx *exec_ctx, sb_list_entry *le) {
+  grpc_slice_buffer_destroy_internal(exec_ctx, &le->sb);
+  gpr_free(le);
+}
+
+static void slice_buffer_list_destroy(grpc_exec_ctx *exec_ctx,
+                                      slice_buffer_list *l) {
+  sb_list_entry *curr = l->head;
+  while (curr != NULL) {
+    sb_list_entry *le = curr;
+    curr = curr->next;
+    sb_list_entry_destroy(exec_ctx, le);
+  }
+  l->head = NULL;
+  l->tail = NULL;
+}
+
+static bool slice_buffer_list_empty(slice_buffer_list *l) {
+  return l->head == NULL;
+}
+
+static void slice_buffer_list_append_entry(slice_buffer_list *l,
+                                           sb_list_entry *next) {
+  next->next = NULL;
+  if (l->tail) {
+    l->tail->next = next;
+    l->tail = next;
+  } else {
+    l->head = next;
+    l->tail = next;
+  }
+}
+
+static grpc_slice_buffer *slice_buffer_list_append(slice_buffer_list *l) {
+  sb_list_entry *next = gpr_malloc(sizeof(*next));
+  grpc_slice_buffer_init(&next->sb);
+  slice_buffer_list_append_entry(l, next);
+  return &next->sb;
+}
+
+static sb_list_entry *slice_buffer_list_pophead(slice_buffer_list *l) {
+  sb_list_entry *ret = l->head;
+  l->head = l->head->next;
+  if (l->head == NULL) {
+    l->tail = NULL;
+  }
+  return ret;
+}
+
+typedef struct inproc_stream {
+  inproc_transport *t;
+  grpc_metadata_batch to_read_initial_md;
+  uint32_t to_read_initial_md_flags;
+  bool to_read_initial_md_filled;
+  slice_buffer_list to_read_message;
+  grpc_metadata_batch to_read_trailing_md;
+  bool to_read_trailing_md_filled;
+  bool reads_needed;
+  bool read_closure_scheduled;
+  grpc_closure read_closure;
+  // Write buffer used only during gap at init time when client-side
+  // stream is set up but server side stream is not yet set up
+  grpc_metadata_batch write_buffer_initial_md;
+  bool write_buffer_initial_md_filled;
+  uint32_t write_buffer_initial_md_flags;
+  gpr_timespec write_buffer_deadline;
+  slice_buffer_list write_buffer_message;
+  grpc_metadata_batch write_buffer_trailing_md;
+  bool write_buffer_trailing_md_filled;
+  grpc_error *write_buffer_cancel_error;
+
+  struct inproc_stream *other_side;
+  bool other_side_closed;               // won't talk anymore
+  bool write_buffer_other_side_closed;  // on hold
+  grpc_stream_refcount *refs;
+  grpc_closure *closure_at_destroy;
+
+  gpr_arena *arena;
+
+  grpc_transport_stream_op_batch *recv_initial_md_op;
+  grpc_transport_stream_op_batch *recv_message_op;
+  grpc_transport_stream_op_batch *recv_trailing_md_op;
+
+  inproc_slice_byte_stream recv_message_stream;
+
+  bool initial_md_sent;
+  bool trailing_md_sent;
+  bool initial_md_recvd;
+  bool trailing_md_recvd;
+
+  bool closed;
+
+  grpc_error *cancel_self_error;
+  grpc_error *cancel_other_error;
+
+  gpr_timespec deadline;
+
+  bool listed;
+  struct inproc_stream *stream_list_prev;
+  struct inproc_stream *stream_list_next;
+} inproc_stream;
+
+static bool inproc_slice_byte_stream_next(grpc_exec_ctx *exec_ctx,
+                                          grpc_byte_stream *bs, size_t max,
+                                          grpc_closure *on_complete) {
+  inproc_slice_byte_stream *stream = (inproc_slice_byte_stream *)bs;
+  return (stream->le->sb.count != 0);
+}
+
+static grpc_error *inproc_slice_byte_stream_pull(grpc_exec_ctx *exec_ctx,
+                                                 grpc_byte_stream *bs,
+                                                 grpc_slice *slice) {
+  inproc_slice_byte_stream *stream = (inproc_slice_byte_stream *)bs;
+  *slice = grpc_slice_buffer_take_first(&stream->le->sb);
+  return GRPC_ERROR_NONE;
+}
+
+static void inproc_slice_byte_stream_destroy(grpc_exec_ctx *exec_ctx,
+                                             grpc_byte_stream *bs) {
+  inproc_slice_byte_stream *stream = (inproc_slice_byte_stream *)bs;
+  sb_list_entry_destroy(exec_ctx, stream->le);
+}
+
+void inproc_slice_byte_stream_init(inproc_slice_byte_stream *s,
+                                   sb_list_entry *le) {
+  s->base.length = (uint32_t)le->sb.length;
+  s->base.flags = 0;
+  s->base.next = inproc_slice_byte_stream_next;
+  s->base.pull = inproc_slice_byte_stream_pull;
+  s->base.destroy = inproc_slice_byte_stream_destroy;
+  s->le = le;
+}
+
+static void ref_transport(inproc_transport *t) {
+  INPROC_LOG(GPR_DEBUG, "ref_transport %p", t);
+  gpr_ref(&t->refs);
+}
+
+static void really_destroy_transport(grpc_exec_ctx *exec_ctx,
+                                     inproc_transport *t) {
+  INPROC_LOG(GPR_DEBUG, "really_destroy_transport %p", t);
+  grpc_connectivity_state_destroy(exec_ctx, &t->connectivity);
+  if (gpr_unref(&t->mu->refs)) {
+    gpr_free(t->mu);
+  }
+  gpr_free(t);
+}
+
+static void unref_transport(grpc_exec_ctx *exec_ctx, inproc_transport *t) {
+  INPROC_LOG(GPR_DEBUG, "unref_transport %p", t);
+  if (gpr_unref(&t->refs)) {
+    really_destroy_transport(exec_ctx, t);
+  }
+}
+
+#ifndef NDEBUG
+#define STREAM_REF(refs, reason) grpc_stream_ref(refs, reason)
+#define STREAM_UNREF(e, refs, reason) grpc_stream_unref(e, refs, reason)
+#else
+#define STREAM_REF(refs, reason) grpc_stream_ref(refs)
+#define STREAM_UNREF(e, refs, reason) grpc_stream_unref(e, refs)
+#endif
+
+static void ref_stream(inproc_stream *s, const char *reason) {
+  INPROC_LOG(GPR_DEBUG, "ref_stream %p %s", s, reason);
+  STREAM_REF(s->refs, reason);
+}
+
+static void unref_stream(grpc_exec_ctx *exec_ctx, inproc_stream *s,
+                         const char *reason) {
+  INPROC_LOG(GPR_DEBUG, "unref_stream %p %s", s, reason);
+  STREAM_UNREF(exec_ctx, s->refs, reason);
+}
+
+static void really_destroy_stream(grpc_exec_ctx *exec_ctx, inproc_stream *s) {
+  INPROC_LOG(GPR_DEBUG, "really_destroy_stream %p", s);
+
+  slice_buffer_list_destroy(exec_ctx, &s->to_read_message);
+  slice_buffer_list_destroy(exec_ctx, &s->write_buffer_message);
+  GRPC_ERROR_UNREF(s->write_buffer_cancel_error);
+  GRPC_ERROR_UNREF(s->cancel_self_error);
+  GRPC_ERROR_UNREF(s->cancel_other_error);
+
+  unref_transport(exec_ctx, s->t);
+
+  if (s->closure_at_destroy) {
+    GRPC_CLOSURE_SCHED(exec_ctx, s->closure_at_destroy, GRPC_ERROR_NONE);
+  }
+}
+
+static void read_state_machine(grpc_exec_ctx *exec_ctx, void *arg,
+                               grpc_error *error);
+
+static void log_metadata(const grpc_metadata_batch *md_batch, bool is_client,
+                         bool is_initial) {
+  for (grpc_linked_mdelem *md = md_batch->list.head; md != NULL;
+       md = md->next) {
+    char *key = grpc_slice_to_c_string(GRPC_MDKEY(md->md));
+    char *value = grpc_slice_to_c_string(GRPC_MDVALUE(md->md));
+    gpr_log(GPR_INFO, "INPROC:%s:%s: %s: %s", is_initial ? "HDR" : "TRL",
+            is_client ? "CLI" : "SVR", key, value);
+    gpr_free(key);
+    gpr_free(value);
+  }
+}
+
+static grpc_error *fill_in_metadata(grpc_exec_ctx *exec_ctx, inproc_stream *s,
+                                    const grpc_metadata_batch *metadata,
+                                    uint32_t flags, grpc_metadata_batch *out_md,
+                                    uint32_t *outflags, bool *markfilled) {
+  if (GRPC_TRACER_ON(grpc_inproc_trace)) {
+    log_metadata(metadata, s->t->is_client, outflags != NULL);
+  }
+
+  if (outflags != NULL) {
+    *outflags = flags;
+  }
+  if (markfilled != NULL) {
+    *markfilled = true;
+  }
+  grpc_error *error = GRPC_ERROR_NONE;
+  for (grpc_linked_mdelem *elem = metadata->list.head;
+       (elem != NULL) && (error == GRPC_ERROR_NONE); elem = elem->next) {
+    grpc_linked_mdelem *nelem = gpr_arena_alloc(s->arena, sizeof(*nelem));
+    nelem->md = grpc_mdelem_from_slices(
+        exec_ctx, grpc_slice_intern(GRPC_MDKEY(elem->md)),
+        grpc_slice_intern(GRPC_MDVALUE(elem->md)));
+
+    error = grpc_metadata_batch_link_tail(exec_ctx, out_md, nelem);
+  }
+  return error;
+}
+
+static int init_stream(grpc_exec_ctx *exec_ctx, grpc_transport *gt,
+                       grpc_stream *gs, grpc_stream_refcount *refcount,
+                       const void *server_data, gpr_arena *arena) {
+  INPROC_LOG(GPR_DEBUG, "init_stream %p %p %p", gt, gs, server_data);
+  inproc_transport *t = (inproc_transport *)gt;
+  inproc_stream *s = (inproc_stream *)gs;
+  s->arena = arena;
+
+  s->refs = refcount;
+  // Ref this stream right now
+  ref_stream(s, "inproc_init_stream:init");
+
+  grpc_metadata_batch_init(&s->to_read_initial_md);
+  s->to_read_initial_md_flags = 0;
+  s->to_read_initial_md_filled = false;
+  grpc_metadata_batch_init(&s->to_read_trailing_md);
+  s->to_read_trailing_md_filled = false;
+  grpc_metadata_batch_init(&s->write_buffer_initial_md);
+  s->write_buffer_initial_md_flags = 0;
+  s->write_buffer_initial_md_filled = false;
+  grpc_metadata_batch_init(&s->write_buffer_trailing_md);
+  s->write_buffer_trailing_md_filled = false;
+  slice_buffer_list_init(&s->to_read_message);
+  slice_buffer_list_init(&s->write_buffer_message);
+  s->reads_needed = false;
+  s->read_closure_scheduled = false;
+  GRPC_CLOSURE_INIT(&s->read_closure, read_state_machine, s,
+                    grpc_schedule_on_exec_ctx);
+  s->t = t;
+  s->closure_at_destroy = NULL;
+  s->other_side_closed = false;
+
+  s->initial_md_sent = s->trailing_md_sent = s->initial_md_recvd =
+      s->trailing_md_recvd = false;
+
+  s->closed = false;
+
+  s->cancel_self_error = GRPC_ERROR_NONE;
+  s->cancel_other_error = GRPC_ERROR_NONE;
+  s->write_buffer_cancel_error = GRPC_ERROR_NONE;
+  s->deadline = gpr_inf_future(GPR_CLOCK_MONOTONIC);
+  s->write_buffer_deadline = gpr_inf_future(GPR_CLOCK_MONOTONIC);
+
+  s->stream_list_prev = NULL;
+  gpr_mu_lock(&t->mu->mu);
+  s->listed = true;
+  ref_stream(s, "inproc_init_stream:list");
+  s->stream_list_next = t->stream_list;
+  if (t->stream_list) {
+    t->stream_list->stream_list_prev = s;
+  }
+  t->stream_list = s;
+  gpr_mu_unlock(&t->mu->mu);
+
+  if (!server_data) {
+    ref_transport(t);
+    inproc_transport *st = t->other_side;
+    ref_transport(st);
+    s->other_side = NULL;  // will get filled in soon
+    // Pass the client-side stream address to the server-side for a ref
+    ref_stream(s, "inproc_init_stream:clt");  // ref it now on behalf of server
+                                              // side to avoid destruction
+    INPROC_LOG(GPR_DEBUG, "calling accept stream cb %p %p",
+               st->accept_stream_cb, st->accept_stream_data);
+    (*st->accept_stream_cb)(exec_ctx, st->accept_stream_data, &st->base,
+                            (void *)s);
+  } else {
+    // This is the server-side and is being called through accept_stream_cb
+    inproc_stream *cs = (inproc_stream *)server_data;
+    s->other_side = cs;
+    // Ref the server-side stream on behalf of the client now
+    ref_stream(s, "inproc_init_stream:srv");
+
+    // Now we are about to affect the other side, so lock the transport
+    // to make sure that it doesn't get destroyed
+    gpr_mu_lock(&s->t->mu->mu);
+    cs->other_side = s;
+    // Now transfer from the other side's write_buffer if any to the to_read
+    // buffer
+    if (cs->write_buffer_initial_md_filled) {
+      fill_in_metadata(exec_ctx, s, &cs->write_buffer_initial_md,
+                       cs->write_buffer_initial_md_flags,
+                       &s->to_read_initial_md, &s->to_read_initial_md_flags,
+                       &s->to_read_initial_md_filled);
+      s->deadline = gpr_time_min(s->deadline, cs->write_buffer_deadline);
+      grpc_metadata_batch_clear(exec_ctx, &cs->write_buffer_initial_md);
+      cs->write_buffer_initial_md_filled = false;
+    }
+    while (!slice_buffer_list_empty(&cs->write_buffer_message)) {
+      slice_buffer_list_append_entry(
+          &s->to_read_message,
+          slice_buffer_list_pophead(&cs->write_buffer_message));
+    }
+    if (cs->write_buffer_trailing_md_filled) {
+      fill_in_metadata(exec_ctx, s, &cs->write_buffer_trailing_md, 0,
+                       &s->to_read_trailing_md, NULL,
+                       &s->to_read_trailing_md_filled);
+      grpc_metadata_batch_clear(exec_ctx, &cs->write_buffer_trailing_md);
+      cs->write_buffer_trailing_md_filled = false;
+    }
+    if (cs->write_buffer_cancel_error != GRPC_ERROR_NONE) {
+      s->cancel_other_error = cs->write_buffer_cancel_error;
+      cs->write_buffer_cancel_error = GRPC_ERROR_NONE;
+    }
+
+    gpr_mu_unlock(&s->t->mu->mu);
+  }
+  return 0;  // return value is not important
+}
+
+static void close_stream_locked(grpc_exec_ctx *exec_ctx, inproc_stream *s) {
+  if (!s->closed) {
+    // Release the metadata that we would have written out
+    grpc_metadata_batch_destroy(exec_ctx, &s->write_buffer_initial_md);
+    grpc_metadata_batch_destroy(exec_ctx, &s->write_buffer_trailing_md);
+
+    if (s->listed) {
+      inproc_stream *p = s->stream_list_prev;
+      inproc_stream *n = s->stream_list_next;
+      if (p != NULL) {
+        p->stream_list_next = n;
+      } else {
+        s->t->stream_list = n;
+      }
+      if (n != NULL) {
+        n->stream_list_prev = p;
+      }
+      s->listed = false;
+      unref_stream(exec_ctx, s, "close_stream:list");
+    }
+    s->closed = true;
+    unref_stream(exec_ctx, s, "close_stream:closing");
+  }
+}
+
+// This function means that we are done talking/listening to the other side
+static void close_other_side_locked(grpc_exec_ctx *exec_ctx, inproc_stream *s,
+                                    const char *reason) {
+  if (s->other_side != NULL) {
+    // First release the metadata that came from the other side's arena
+    grpc_metadata_batch_destroy(exec_ctx, &s->to_read_initial_md);
+    grpc_metadata_batch_destroy(exec_ctx, &s->to_read_trailing_md);
+
+    unref_stream(exec_ctx, s->other_side, reason);
+    s->other_side_closed = true;
+    s->other_side = NULL;
+  } else if (!s->other_side_closed) {
+    s->write_buffer_other_side_closed = true;
+  }
+}
+
+static void fail_helper_locked(grpc_exec_ctx *exec_ctx, inproc_stream *s,
+                               grpc_error *error) {
+  INPROC_LOG(GPR_DEBUG, "read_state_machine %p fail_helper", s);
+  // If we're failing this side, we need to make sure that
+  // we also send or have already sent trailing metadata
+  if (!s->trailing_md_sent) {
+    // Send trailing md to the other side indicating cancellation
+    s->trailing_md_sent = true;
+
+    grpc_metadata_batch fake_md;
+    grpc_metadata_batch_init(&fake_md);
+
+    inproc_stream *other = s->other_side;
+    grpc_metadata_batch *dest = (other == NULL) ? &s->write_buffer_trailing_md
+                                                : &other->to_read_trailing_md;
+    bool *destfilled = (other == NULL) ? &s->write_buffer_trailing_md_filled
+                                       : &other->to_read_trailing_md_filled;
+    fill_in_metadata(exec_ctx, s, &fake_md, 0, dest, NULL, destfilled);
+    grpc_metadata_batch_destroy(exec_ctx, &fake_md);
+
+    if (other != NULL) {
+      if (other->cancel_other_error == GRPC_ERROR_NONE) {
+        other->cancel_other_error = GRPC_ERROR_REF(error);
+      }
+      if (other->reads_needed) {
+        if (!other->read_closure_scheduled) {
+          GRPC_CLOSURE_SCHED(exec_ctx, &other->read_closure,
+                             GRPC_ERROR_REF(error));
+          other->read_closure_scheduled = true;
+        }
+        other->reads_needed = false;
+      }
+    } else if (s->write_buffer_cancel_error == GRPC_ERROR_NONE) {
+      s->write_buffer_cancel_error = GRPC_ERROR_REF(error);
+    }
+  }
+  if (s->recv_initial_md_op) {
+    grpc_error *err;
+    if (!s->t->is_client) {
+      // If this is a server, provide initial metadata with a path and authority
+      // since it expects that as well as no error yet
+      grpc_metadata_batch fake_md;
+      grpc_metadata_batch_init(&fake_md);
+      grpc_linked_mdelem *path_md = gpr_arena_alloc(s->arena, sizeof(*path_md));
+      path_md->md =
+          grpc_mdelem_from_slices(exec_ctx, g_fake_path_key, g_fake_path_value);
+      GPR_ASSERT(grpc_metadata_batch_link_tail(exec_ctx, &fake_md, path_md) ==
+                 GRPC_ERROR_NONE);
+      grpc_linked_mdelem *auth_md = gpr_arena_alloc(s->arena, sizeof(*auth_md));
+      auth_md->md =
+          grpc_mdelem_from_slices(exec_ctx, g_fake_auth_key, g_fake_auth_value);
+      GPR_ASSERT(grpc_metadata_batch_link_tail(exec_ctx, &fake_md, auth_md) ==
+                 GRPC_ERROR_NONE);
+
+      fill_in_metadata(
+          exec_ctx, s, &fake_md, 0,
+          s->recv_initial_md_op->payload->recv_initial_metadata
+              .recv_initial_metadata,
+          s->recv_initial_md_op->payload->recv_initial_metadata.recv_flags,
+          NULL);
+      grpc_metadata_batch_destroy(exec_ctx, &fake_md);
+      err = GRPC_ERROR_NONE;
+    } else {
+      err = GRPC_ERROR_REF(error);
+    }
+    INPROC_LOG(GPR_DEBUG,
+               "fail_helper %p scheduling initial-metadata-ready %p %p", s,
+               error, err);
+    GRPC_CLOSURE_SCHED(exec_ctx,
+                       s->recv_initial_md_op->payload->recv_initial_metadata
+                           .recv_initial_metadata_ready,
+                       err);
+    // Last use of err so no need to REF and then UNREF it
+
+    if ((s->recv_initial_md_op != s->recv_message_op) &&
+        (s->recv_initial_md_op != s->recv_trailing_md_op)) {
+      INPROC_LOG(GPR_DEBUG,
+                 "fail_helper %p scheduling initial-metadata-on-complete %p",
+                 error, s);
+      GRPC_CLOSURE_SCHED(exec_ctx, s->recv_initial_md_op->on_complete,
+                         GRPC_ERROR_REF(error));
+    }
+    s->recv_initial_md_op = NULL;
+  }
+  if (s->recv_message_op) {
+    INPROC_LOG(GPR_DEBUG, "fail_helper %p scheduling message-ready %p", s,
+               error);
+    GRPC_CLOSURE_SCHED(
+        exec_ctx, s->recv_message_op->payload->recv_message.recv_message_ready,
+        GRPC_ERROR_REF(error));
+    if (s->recv_message_op != s->recv_trailing_md_op) {
+      INPROC_LOG(GPR_DEBUG, "fail_helper %p scheduling message-on-complete %p",
+                 s, error);
+      GRPC_CLOSURE_SCHED(exec_ctx, s->recv_message_op->on_complete,
+                         GRPC_ERROR_REF(error));
+    }
+    s->recv_message_op = NULL;
+  }
+  if (s->recv_trailing_md_op) {
+    INPROC_LOG(GPR_DEBUG,
+               "fail_helper %p scheduling trailing-md-on-complete %p", s,
+               error);
+    GRPC_CLOSURE_SCHED(exec_ctx, s->recv_trailing_md_op->on_complete,
+                       GRPC_ERROR_REF(error));
+    s->recv_trailing_md_op = NULL;
+  }
+  close_other_side_locked(exec_ctx, s, "fail_helper:other_side");
+  close_stream_locked(exec_ctx, s);
+
+  GRPC_ERROR_UNREF(error);
+}
+
+static void read_state_machine(grpc_exec_ctx *exec_ctx, void *arg,
+                               grpc_error *error) {
+  // This function gets called when we have contents in the unprocessed reads
+  // Get what we want based on our ops wanted
+  // Schedule our appropriate closures
+  // and then return to reads_needed state if still needed
+
+  // Since this is a closure directly invoked by the combiner, it should not
+  // unref the error parameter explicitly; the combiner will do that implicitly
+  grpc_error *new_err = GRPC_ERROR_NONE;
+
+  bool needs_close = false;
+
+  INPROC_LOG(GPR_DEBUG, "read_state_machine %p", arg);
+  inproc_stream *s = (inproc_stream *)arg;
+  gpr_mu *mu = &s->t->mu->mu;  // keep aside in case s gets closed
+  gpr_mu_lock(mu);
+  s->read_closure_scheduled = false;
+  // cancellation takes precedence
+  if (s->cancel_self_error != GRPC_ERROR_NONE) {
+    fail_helper_locked(exec_ctx, s, GRPC_ERROR_REF(s->cancel_self_error));
+    goto done;
+  } else if (s->cancel_other_error != GRPC_ERROR_NONE) {
+    fail_helper_locked(exec_ctx, s, GRPC_ERROR_REF(s->cancel_other_error));
+    goto done;
+  } else if (error != GRPC_ERROR_NONE) {
+    fail_helper_locked(exec_ctx, s, GRPC_ERROR_REF(error));
+    goto done;
+  }
+
+  if (s->recv_initial_md_op) {
+    if (!s->to_read_initial_md_filled) {
+      // We entered the state machine on some other kind of read even though
+      // we still haven't satisfied initial md . That's an error.
+      new_err =
+          GRPC_ERROR_CREATE_FROM_STATIC_STRING("Unexpected frame sequencing");
+      INPROC_LOG(GPR_DEBUG,
+                 "read_state_machine %p scheduling on_complete errors for no "
+                 "initial md %p",
+                 s, new_err);
+      fail_helper_locked(exec_ctx, s, GRPC_ERROR_REF(new_err));
+      goto done;
+    } else if (s->initial_md_recvd) {
+      new_err =
+          GRPC_ERROR_CREATE_FROM_STATIC_STRING("Already recvd initial md");
+      INPROC_LOG(
+          GPR_DEBUG,
+          "read_state_machine %p scheduling on_complete errors for already "
+          "recvd initial md %p",
+          s, new_err);
+      fail_helper_locked(exec_ctx, s, GRPC_ERROR_REF(new_err));
+      goto done;
+    }
+
+    s->initial_md_recvd = true;
+    new_err = fill_in_metadata(
+        exec_ctx, s, &s->to_read_initial_md, s->to_read_initial_md_flags,
+        s->recv_initial_md_op->payload->recv_initial_metadata
+            .recv_initial_metadata,
+        s->recv_initial_md_op->payload->recv_initial_metadata.recv_flags, NULL);
+    s->recv_initial_md_op->payload->recv_initial_metadata.recv_initial_metadata
+        ->deadline = s->deadline;
+    grpc_metadata_batch_clear(exec_ctx, &s->to_read_initial_md);
+    s->to_read_initial_md_filled = false;
+    INPROC_LOG(GPR_DEBUG,
+               "read_state_machine %p scheduling initial-metadata-ready %p", s,
+               new_err);
+    GRPC_CLOSURE_SCHED(exec_ctx,
+                       s->recv_initial_md_op->payload->recv_initial_metadata
+                           .recv_initial_metadata_ready,
+                       GRPC_ERROR_REF(new_err));
+    if ((s->recv_initial_md_op != s->recv_message_op) &&
+        (s->recv_initial_md_op != s->recv_trailing_md_op)) {
+      INPROC_LOG(
+          GPR_DEBUG,
+          "read_state_machine %p scheduling initial-metadata-on-complete %p", s,
+          new_err);
+      GRPC_CLOSURE_SCHED(exec_ctx, s->recv_initial_md_op->on_complete,
+                         GRPC_ERROR_REF(new_err));
+    }
+    s->recv_initial_md_op = NULL;
+
+    if (new_err != GRPC_ERROR_NONE) {
+      INPROC_LOG(GPR_DEBUG,
+                 "read_state_machine %p scheduling on_complete errors2 %p", s,
+                 new_err);
+      fail_helper_locked(exec_ctx, s, GRPC_ERROR_REF(new_err));
+      goto done;
+    }
+  }
+  if (s->to_read_initial_md_filled) {
+    new_err = GRPC_ERROR_CREATE_FROM_STATIC_STRING("Unexpected recv frame");
+    fail_helper_locked(exec_ctx, s, GRPC_ERROR_REF(new_err));
+    goto done;
+  }
+  if (!slice_buffer_list_empty(&s->to_read_message) && s->recv_message_op) {
+    inproc_slice_byte_stream_init(
+        &s->recv_message_stream,
+        slice_buffer_list_pophead(&s->to_read_message));
+    *s->recv_message_op->payload->recv_message.recv_message =
+        &s->recv_message_stream.base;
+    INPROC_LOG(GPR_DEBUG, "read_state_machine %p scheduling message-ready", s);
+    GRPC_CLOSURE_SCHED(
+        exec_ctx, s->recv_message_op->payload->recv_message.recv_message_ready,
+        GRPC_ERROR_NONE);
+    if (s->recv_message_op != s->recv_trailing_md_op) {
+      INPROC_LOG(GPR_DEBUG,
+                 "read_state_machine %p scheduling message-on-complete %p", s,
+                 new_err);
+      GRPC_CLOSURE_SCHED(exec_ctx, s->recv_message_op->on_complete,
+                         GRPC_ERROR_REF(new_err));
+    }
+    s->recv_message_op = NULL;
+  }
+  if (s->to_read_trailing_md_filled) {
+    if (s->trailing_md_recvd) {
+      new_err =
+          GRPC_ERROR_CREATE_FROM_STATIC_STRING("Already recvd trailing md");
+      INPROC_LOG(
+          GPR_DEBUG,
+          "read_state_machine %p scheduling on_complete errors for already "
+          "recvd trailing md %p",
+          s, new_err);
+      fail_helper_locked(exec_ctx, s, GRPC_ERROR_REF(new_err));
+      goto done;
+    }
+    if (s->recv_message_op != NULL) {
+      // This message needs to be wrapped up because it will never be
+      // satisfied
+      INPROC_LOG(GPR_DEBUG, "read_state_machine %p scheduling message-ready",
+                 s);
+      GRPC_CLOSURE_SCHED(
+          exec_ctx,
+          s->recv_message_op->payload->recv_message.recv_message_ready,
+          GRPC_ERROR_NONE);
+      if (s->recv_message_op != s->recv_trailing_md_op) {
+        INPROC_LOG(GPR_DEBUG,
+                   "read_state_machine %p scheduling message-on-complete %p", s,
+                   new_err);
+        GRPC_CLOSURE_SCHED(exec_ctx, s->recv_message_op->on_complete,
+                           GRPC_ERROR_REF(new_err));
+      }
+      s->recv_message_op = NULL;
+    }
+    if (s->recv_trailing_md_op != NULL) {
+      // We wanted trailing metadata and we got it
+      s->trailing_md_recvd = true;
+      new_err =
+          fill_in_metadata(exec_ctx, s, &s->to_read_trailing_md, 0,
+                           s->recv_trailing_md_op->payload
+                               ->recv_trailing_metadata.recv_trailing_metadata,
+                           NULL, NULL);
+      grpc_metadata_batch_clear(exec_ctx, &s->to_read_trailing_md);
+      s->to_read_trailing_md_filled = false;
+
+      // We should schedule the recv_trailing_md_op completion if
+      // 1. this stream is the client-side
+      // 2. this stream is the server-side AND has already sent its trailing md
+      //    (If the server hasn't already sent its trailing md, it doesn't have
+      //     a final status, so don't mark this op complete)
+      if (s->t->is_client || s->trailing_md_sent) {
+        INPROC_LOG(
+            GPR_DEBUG,
+            "read_state_machine %p scheduling trailing-md-on-complete %p", s,
+            new_err);
+        GRPC_CLOSURE_SCHED(exec_ctx, s->recv_trailing_md_op->on_complete,
+                           GRPC_ERROR_REF(new_err));
+        s->recv_trailing_md_op = NULL;
+        needs_close = true;
+      } else {
+        INPROC_LOG(GPR_DEBUG,
+                   "read_state_machine %p server needs to delay handling "
+                   "trailing-md-on-complete %p",
+                   s, new_err);
+      }
+    } else {
+      INPROC_LOG(
+          GPR_DEBUG,
+          "read_state_machine %p has trailing md but not yet waiting for it",
+          s);
+    }
+  }
+  if (s->trailing_md_recvd && s->recv_message_op) {
+    // No further message will come on this stream, so finish off the
+    // recv_message_op
+    INPROC_LOG(GPR_DEBUG, "read_state_machine %p scheduling message-ready", s);
+    GRPC_CLOSURE_SCHED(
+        exec_ctx, s->recv_message_op->payload->recv_message.recv_message_ready,
+        GRPC_ERROR_NONE);
+    if (s->recv_message_op != s->recv_trailing_md_op) {
+      INPROC_LOG(GPR_DEBUG,
+                 "read_state_machine %p scheduling message-on-complete %p", s,
+                 new_err);
+      GRPC_CLOSURE_SCHED(exec_ctx, s->recv_message_op->on_complete,
+                         GRPC_ERROR_REF(new_err));
+    }
+    s->recv_message_op = NULL;
+  }
+  if (s->recv_message_op || s->recv_trailing_md_op) {
+    // Didn't get the item we wanted so we still need to get
+    // rescheduled
+    INPROC_LOG(GPR_DEBUG, "read_state_machine %p still needs closure %p %p", s,
+               s->recv_message_op, s->recv_trailing_md_op);
+    s->reads_needed = true;
+  }
+done:
+  if (needs_close) {
+    close_other_side_locked(exec_ctx, s, "read_state_machine");
+    close_stream_locked(exec_ctx, s);
+  }
+  gpr_mu_unlock(mu);
+  GRPC_ERROR_UNREF(new_err);
+}
+
+static grpc_closure do_nothing_closure;
+
+static bool cancel_stream_locked(grpc_exec_ctx *exec_ctx, inproc_stream *s,
+                                 grpc_error *error) {
+  bool ret = false;  // was the cancel accepted
+  INPROC_LOG(GPR_DEBUG, "cancel_stream %p with %s", s,
+             grpc_error_string(error));
+  if (s->cancel_self_error == GRPC_ERROR_NONE) {
+    ret = true;
+    s->cancel_self_error = GRPC_ERROR_REF(error);
+    if (s->reads_needed) {
+      if (!s->read_closure_scheduled) {
+        GRPC_CLOSURE_SCHED(exec_ctx, &s->read_closure,
+                           GRPC_ERROR_REF(s->cancel_self_error));
+        s->read_closure_scheduled = true;
+      }
+      s->reads_needed = false;
+    }
+    // Send trailing md to the other side indicating cancellation, even if we
+    // already have
+    s->trailing_md_sent = true;
+
+    grpc_metadata_batch cancel_md;
+    grpc_metadata_batch_init(&cancel_md);
+
+    inproc_stream *other = s->other_side;
+    grpc_metadata_batch *dest = (other == NULL) ? &s->write_buffer_trailing_md
+                                                : &other->to_read_trailing_md;
+    bool *destfilled = (other == NULL) ? &s->write_buffer_trailing_md_filled
+                                       : &other->to_read_trailing_md_filled;
+    fill_in_metadata(exec_ctx, s, &cancel_md, 0, dest, NULL, destfilled);
+    grpc_metadata_batch_destroy(exec_ctx, &cancel_md);
+
+    if (other != NULL) {
+      if (other->cancel_other_error == GRPC_ERROR_NONE) {
+        other->cancel_other_error = GRPC_ERROR_REF(s->cancel_self_error);
+      }
+      if (other->reads_needed) {
+        if (!other->read_closure_scheduled) {
+          GRPC_CLOSURE_SCHED(exec_ctx, &other->read_closure,
+                             GRPC_ERROR_REF(other->cancel_other_error));
+          other->read_closure_scheduled = true;
+        }
+        other->reads_needed = false;
+      }
+    } else if (s->write_buffer_cancel_error == GRPC_ERROR_NONE) {
+      s->write_buffer_cancel_error = GRPC_ERROR_REF(s->cancel_self_error);
+    }
+
+    // if we are a server and already received trailing md but
+    // couldn't complete that because we hadn't yet sent out trailing
+    // md, now's the chance
+    if (!s->t->is_client && s->trailing_md_recvd && s->recv_trailing_md_op) {
+      INPROC_LOG(GPR_DEBUG,
+                 "cancel_stream %p scheduling trailing-md-on-complete %p", s,
+                 s->cancel_self_error);
+      GRPC_CLOSURE_SCHED(exec_ctx, s->recv_trailing_md_op->on_complete,
+                         GRPC_ERROR_REF(s->cancel_self_error));
+      s->recv_trailing_md_op = NULL;
+    }
+  }
+
+  close_other_side_locked(exec_ctx, s, "cancel_stream:other_side");
+  close_stream_locked(exec_ctx, s);
+
+  GRPC_ERROR_UNREF(error);
+  return ret;
+}
+
+static void perform_stream_op(grpc_exec_ctx *exec_ctx, grpc_transport *gt,
+                              grpc_stream *gs,
+                              grpc_transport_stream_op_batch *op) {
+  INPROC_LOG(GPR_DEBUG, "perform_stream_op %p %p %p", gt, gs, op);
+  inproc_stream *s = (inproc_stream *)gs;
+  gpr_mu *mu = &s->t->mu->mu;  // save aside in case s gets closed
+  gpr_mu_lock(mu);
+
+  if (GRPC_TRACER_ON(grpc_inproc_trace)) {
+    if (op->send_initial_metadata) {
+      log_metadata(op->payload->send_initial_metadata.send_initial_metadata,
+                   s->t->is_client, true);
+    }
+    if (op->send_trailing_metadata) {
+      log_metadata(op->payload->send_trailing_metadata.send_trailing_metadata,
+                   s->t->is_client, false);
+    }
+  }
+  grpc_error *error = GRPC_ERROR_NONE;
+  grpc_closure *on_complete = op->on_complete;
+  if (on_complete == NULL) {
+    on_complete = &do_nothing_closure;
+  }
+
+  if (op->cancel_stream) {
+    // Call cancel_stream_locked without ref'ing the cancel_error because
+    // this function is responsible to make sure that that field gets unref'ed
+    cancel_stream_locked(exec_ctx, s, op->payload->cancel_stream.cancel_error);
+    // this op can complete without an error
+  } else if (s->cancel_self_error != GRPC_ERROR_NONE) {
+    // already self-canceled so still give it an error
+    error = GRPC_ERROR_REF(s->cancel_self_error);
+  } else {
+    INPROC_LOG(GPR_DEBUG, "perform_stream_op %p%s%s%s%s%s%s", s,
+               op->send_initial_metadata ? " send_initial_metadata" : "",
+               op->send_message ? " send_message" : "",
+               op->send_trailing_metadata ? " send_trailing_metadata" : "",
+               op->recv_initial_metadata ? " recv_initial_metadata" : "",
+               op->recv_message ? " recv_message" : "",
+               op->recv_trailing_metadata ? " recv_trailing_metadata" : "");
+  }
+
+  bool needs_close = false;
+
+  if (error == GRPC_ERROR_NONE &&
+      (op->send_initial_metadata || op->send_message ||
+       op->send_trailing_metadata)) {
+    inproc_stream *other = s->other_side;
+    if (s->t->is_closed) {
+      error = GRPC_ERROR_CREATE_FROM_STATIC_STRING("Endpoint already shutdown");
+    }
+    if (error == GRPC_ERROR_NONE && op->send_initial_metadata) {
+      grpc_metadata_batch *dest = (other == NULL) ? &s->write_buffer_initial_md
+                                                  : &other->to_read_initial_md;
+      uint32_t *destflags = (other == NULL) ? &s->write_buffer_initial_md_flags
+                                            : &other->to_read_initial_md_flags;
+      bool *destfilled = (other == NULL) ? &s->write_buffer_initial_md_filled
+                                         : &other->to_read_initial_md_filled;
+      if (*destfilled || s->initial_md_sent) {
+        // The buffer is already in use; that's an error!
+        INPROC_LOG(GPR_DEBUG, "Extra initial metadata %p", s);
+        error = GRPC_ERROR_CREATE_FROM_STATIC_STRING("Extra initial metadata");
+      } else {
+        if (!other->closed) {
+          fill_in_metadata(
+              exec_ctx, s,
+              op->payload->send_initial_metadata.send_initial_metadata,
+              op->payload->send_initial_metadata.send_initial_metadata_flags,
+              dest, destflags, destfilled);
+        }
+        if (s->t->is_client) {
+          gpr_timespec *dl =
+              (other == NULL) ? &s->write_buffer_deadline : &other->deadline;
+          *dl = gpr_time_min(*dl, op->payload->send_initial_metadata
+                                      .send_initial_metadata->deadline);
+          s->initial_md_sent = true;
+        }
+      }
+    }
+    if (error == GRPC_ERROR_NONE && op->send_message) {
+      size_t remaining = op->payload->send_message.send_message->length;
+      grpc_slice_buffer *dest = slice_buffer_list_append(
+          (other == NULL) ? &s->write_buffer_message : &other->to_read_message);
+      do {
+        grpc_slice message_slice;
+        grpc_closure unused;
+        GPR_ASSERT(grpc_byte_stream_next(exec_ctx,
+                                         op->payload->send_message.send_message,
+                                         SIZE_MAX, &unused));
+        grpc_byte_stream_pull(exec_ctx, op->payload->send_message.send_message,
+                              &message_slice);
+        remaining -= GRPC_SLICE_LENGTH(message_slice);
+        grpc_slice_buffer_add(dest, message_slice);
+      } while (remaining != 0);
+    }
+    if (error == GRPC_ERROR_NONE && op->send_trailing_metadata) {
+      grpc_metadata_batch *dest = (other == NULL) ? &s->write_buffer_trailing_md
+                                                  : &other->to_read_trailing_md;
+      bool *destfilled = (other == NULL) ? &s->write_buffer_trailing_md_filled
+                                         : &other->to_read_trailing_md_filled;
+      if (*destfilled || s->trailing_md_sent) {
+        // The buffer is already in use; that's an error!
+        INPROC_LOG(GPR_DEBUG, "Extra trailing metadata %p", s);
+        error = GRPC_ERROR_CREATE_FROM_STATIC_STRING("Extra trailing metadata");
+      } else {
+        if (!other->closed) {
+          fill_in_metadata(
+              exec_ctx, s,
+              op->payload->send_trailing_metadata.send_trailing_metadata, 0,
+              dest, NULL, destfilled);
+        }
+        s->trailing_md_sent = true;
+        if (!s->t->is_client && s->trailing_md_recvd &&
+            s->recv_trailing_md_op) {
+          INPROC_LOG(GPR_DEBUG,
+                     "perform_stream_op %p scheduling trailing-md-on-complete",
+                     s);
+          GRPC_CLOSURE_SCHED(exec_ctx, s->recv_trailing_md_op->on_complete,
+                             GRPC_ERROR_NONE);
+          s->recv_trailing_md_op = NULL;
+          needs_close = true;
+        }
+      }
+    }
+    if (other != NULL && other->reads_needed) {
+      if (!other->read_closure_scheduled) {
+        GRPC_CLOSURE_SCHED(exec_ctx, &other->read_closure, error);
+        other->read_closure_scheduled = true;
+      }
+      other->reads_needed = false;
+    }
+  }
+  if (error == GRPC_ERROR_NONE &&
+      (op->recv_initial_metadata || op->recv_message ||
+       op->recv_trailing_metadata)) {
+    // If there are any reads, mark it so that the read closure will react to
+    // them
+    if (op->recv_initial_metadata) {
+      s->recv_initial_md_op = op;
+    }
+    if (op->recv_message) {
+      s->recv_message_op = op;
+    }
+    if (op->recv_trailing_metadata) {
+      s->recv_trailing_md_op = op;
+    }
+
+    // We want to initiate the closure if:
+    // 1. There is initial metadata and something ready to take that
+    // 2. There is a message and something ready to take it
+    // 3. There is trailing metadata, even if nothing specifically wants
+    //    that because that can shut down the message as well
+    if ((s->to_read_initial_md_filled && op->recv_initial_metadata) ||
+        ((!slice_buffer_list_empty(&s->to_read_message) ||
+          s->trailing_md_recvd) &&
+         op->recv_message) ||
+        (s->to_read_trailing_md_filled)) {
+      if (!s->read_closure_scheduled) {
+        GRPC_CLOSURE_SCHED(exec_ctx, &s->read_closure, GRPC_ERROR_NONE);
+        s->read_closure_scheduled = true;
+      }
+    } else {
+      s->reads_needed = true;
+    }
+  } else {
+    if (error != GRPC_ERROR_NONE) {
+      // Schedule op's read closures that we didn't push to read state machine
+      if (op->recv_initial_metadata) {
+        INPROC_LOG(
+            GPR_DEBUG,
+            "perform_stream_op error %p scheduling initial-metadata-ready %p",
+            s, error);
+        GRPC_CLOSURE_SCHED(
+            exec_ctx,
+            op->payload->recv_initial_metadata.recv_initial_metadata_ready,
+            GRPC_ERROR_REF(error));
+      }
+      if (op->recv_message) {
+        INPROC_LOG(
+            GPR_DEBUG,
+            "perform_stream_op error %p scheduling recv message-ready %p", s,
+            error);
+        GRPC_CLOSURE_SCHED(exec_ctx,
+                           op->payload->recv_message.recv_message_ready,
+                           GRPC_ERROR_REF(error));
+      }
+    }
+    INPROC_LOG(GPR_DEBUG, "perform_stream_op %p scheduling on_complete %p", s,
+               error);
+    GRPC_CLOSURE_SCHED(exec_ctx, on_complete, GRPC_ERROR_REF(error));
+  }
+  if (needs_close) {
+    close_other_side_locked(exec_ctx, s, "perform_stream_op:other_side");
+    close_stream_locked(exec_ctx, s);
+  }
+  gpr_mu_unlock(mu);
+  GRPC_ERROR_UNREF(error);
+}
+
+static void close_transport_locked(grpc_exec_ctx *exec_ctx,
+                                   inproc_transport *t) {
+  INPROC_LOG(GPR_DEBUG, "close_transport %p %d", t, t->is_closed);
+  grpc_connectivity_state_set(
+      exec_ctx, &t->connectivity, GRPC_CHANNEL_SHUTDOWN,
+      GRPC_ERROR_CREATE_FROM_STATIC_STRING("Closing transport."),
+      "close transport");
+  if (!t->is_closed) {
+    t->is_closed = true;
+    /* Also end all streams on this transport */
+    while (t->stream_list != NULL) {
+      // cancel_stream_locked also adjusts stream list
+      cancel_stream_locked(
+          exec_ctx, t->stream_list,
+          grpc_error_set_int(
+              GRPC_ERROR_CREATE_FROM_STATIC_STRING("Transport closed"),
+              GRPC_ERROR_INT_GRPC_STATUS, GRPC_STATUS_UNAVAILABLE));
+    }
+  }
+}
+
+static void perform_transport_op(grpc_exec_ctx *exec_ctx, grpc_transport *gt,
+                                 grpc_transport_op *op) {
+  inproc_transport *t = (inproc_transport *)gt;
+  INPROC_LOG(GPR_DEBUG, "perform_transport_op %p %p", t, op);
+  gpr_mu_lock(&t->mu->mu);
+  if (op->on_connectivity_state_change) {
+    grpc_connectivity_state_notify_on_state_change(
+        exec_ctx, &t->connectivity, op->connectivity_state,
+        op->on_connectivity_state_change);
+  }
+  if (op->set_accept_stream) {
+    t->accept_stream_cb = op->set_accept_stream_fn;
+    t->accept_stream_data = op->set_accept_stream_user_data;
+  }
+  if (op->on_consumed) {
+    GRPC_CLOSURE_SCHED(exec_ctx, op->on_consumed, GRPC_ERROR_NONE);
+  }
+
+  bool do_close = false;
+  if (op->goaway_error != GRPC_ERROR_NONE) {
+    do_close = true;
+    GRPC_ERROR_UNREF(op->goaway_error);
+  }
+  if (op->disconnect_with_error != GRPC_ERROR_NONE) {
+    do_close = true;
+    GRPC_ERROR_UNREF(op->disconnect_with_error);
+  }
+
+  if (do_close) {
+    close_transport_locked(exec_ctx, t);
+  }
+  gpr_mu_unlock(&t->mu->mu);
+}
+
+static void destroy_stream(grpc_exec_ctx *exec_ctx, grpc_transport *gt,
+                           grpc_stream *gs,
+                           grpc_closure *then_schedule_closure) {
+  INPROC_LOG(GPR_DEBUG, "destroy_stream %p %p", gs, then_schedule_closure);
+  inproc_stream *s = (inproc_stream *)gs;
+  s->closure_at_destroy = then_schedule_closure;
+  really_destroy_stream(exec_ctx, s);
+}
+
+static void destroy_transport(grpc_exec_ctx *exec_ctx, grpc_transport *gt) {
+  inproc_transport *t = (inproc_transport *)gt;
+  INPROC_LOG(GPR_DEBUG, "destroy_transport %p", t);
+  gpr_mu_lock(&t->mu->mu);
+  close_transport_locked(exec_ctx, t);
+  gpr_mu_unlock(&t->mu->mu);
+  unref_transport(exec_ctx, t->other_side);
+  unref_transport(exec_ctx, t);
+}
+
+/*******************************************************************************
+ * Main inproc transport functions
+ */
+static void inproc_transports_create(grpc_exec_ctx *exec_ctx,
+                                     grpc_transport **server_transport,
+                                     const grpc_channel_args *server_args,
+                                     grpc_transport **client_transport,
+                                     const grpc_channel_args *client_args) {
+  INPROC_LOG(GPR_DEBUG, "inproc_transports_create");
+  inproc_transport *st = gpr_zalloc(sizeof(*st));
+  inproc_transport *ct = gpr_zalloc(sizeof(*ct));
+  // Share one lock between both sides since both sides get affected
+  st->mu = ct->mu = gpr_malloc(sizeof(*st->mu));
+  gpr_mu_init(&st->mu->mu);
+  gpr_ref_init(&st->mu->refs, 2);
+  st->base.vtable = &inproc_vtable;
+  ct->base.vtable = &inproc_vtable;
+  // Start each side of transport with 2 refs since they each have a ref
+  // to the other
+  gpr_ref_init(&st->refs, 2);
+  gpr_ref_init(&ct->refs, 2);
+  st->is_client = false;
+  ct->is_client = true;
+  grpc_connectivity_state_init(&st->connectivity, GRPC_CHANNEL_READY,
+                               "inproc_server");
+  grpc_connectivity_state_init(&ct->connectivity, GRPC_CHANNEL_READY,
+                               "inproc_client");
+  st->other_side = ct;
+  ct->other_side = st;
+  st->stream_list = NULL;
+  ct->stream_list = NULL;
+  *server_transport = (grpc_transport *)st;
+  *client_transport = (grpc_transport *)ct;
+}
+
+grpc_channel *grpc_inproc_channel_create(grpc_server *server,
+                                         grpc_channel_args *args,
+                                         void *reserved) {
+  GRPC_API_TRACE("grpc_inproc_channel_create(server=%p, args=%p)", 2,
+                 (server, args));
+
+  grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
+
+  const grpc_channel_args *server_args = grpc_server_get_channel_args(server);
+
+  // Add a default authority channel argument for the client
+
+  grpc_arg default_authority_arg;
+  default_authority_arg.type = GRPC_ARG_STRING;
+  default_authority_arg.key = GRPC_ARG_DEFAULT_AUTHORITY;
+  default_authority_arg.value.string = "inproc.authority";
+  grpc_channel_args *client_args =
+      grpc_channel_args_copy_and_add(args, &default_authority_arg, 1);
+
+  grpc_transport *server_transport;
+  grpc_transport *client_transport;
+  inproc_transports_create(&exec_ctx, &server_transport, server_args,
+                           &client_transport, client_args);
+
+  grpc_server_setup_transport(&exec_ctx, server, server_transport, NULL,
+                              server_args);
+  grpc_channel *channel =
+      grpc_channel_create(&exec_ctx, "inproc", client_args,
+                          GRPC_CLIENT_DIRECT_CHANNEL, client_transport);
+
+  // Free up created channel args
+  grpc_channel_args_destroy(&exec_ctx, client_args);
+
+  // Now finish scheduled operations
+  grpc_exec_ctx_finish(&exec_ctx);
+
+  return channel;
+}
+
+/*******************************************************************************
+ * INTEGRATION GLUE
+ */
+
+static void set_pollset(grpc_exec_ctx *exec_ctx, grpc_transport *gt,
+                        grpc_stream *gs, grpc_pollset *pollset) {
+  // Nothing to do here
+}
+
+static void set_pollset_set(grpc_exec_ctx *exec_ctx, grpc_transport *gt,
+                            grpc_stream *gs, grpc_pollset_set *pollset_set) {
+  // Nothing to do here
+}
+
+static char *get_peer(grpc_exec_ctx *exec_ctx, grpc_transport *t) {
+  return gpr_strdup("inproc");
+}
+
+static grpc_endpoint *get_endpoint(grpc_exec_ctx *exec_ctx, grpc_transport *t) {
+  return NULL;
+}
+
+static const grpc_transport_vtable inproc_vtable = {
+    sizeof(inproc_stream), "inproc",
+    init_stream,           set_pollset,
+    set_pollset_set,       perform_stream_op,
+    perform_transport_op,  destroy_stream,
+    destroy_transport,     get_peer,
+    get_endpoint};
+
+/*******************************************************************************
+ * GLOBAL INIT AND DESTROY
+ */
+static void do_nothing(grpc_exec_ctx *exec_ctx, void *arg, grpc_error *error) {}
+
+void grpc_inproc_transport_init(void) {
+  grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
+  GRPC_CLOSURE_INIT(&do_nothing_closure, do_nothing, NULL,
+                    grpc_schedule_on_exec_ctx);
+  g_empty_slice = grpc_slice_from_static_buffer(NULL, 0);
+
+  grpc_slice key_tmp = grpc_slice_from_static_string(":path");
+  g_fake_path_key = grpc_slice_intern(key_tmp);
+  grpc_slice_unref_internal(&exec_ctx, key_tmp);
+
+  g_fake_path_value = grpc_slice_from_static_string("/");
+
+  grpc_slice auth_tmp = grpc_slice_from_static_string(":authority");
+  g_fake_auth_key = grpc_slice_intern(auth_tmp);
+  grpc_slice_unref_internal(&exec_ctx, auth_tmp);
+
+  g_fake_auth_value = grpc_slice_from_static_string("inproc-fail");
+  grpc_exec_ctx_finish(&exec_ctx);
+}
+
+void grpc_inproc_transport_shutdown(void) {
+  grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
+  grpc_slice_unref_internal(&exec_ctx, g_empty_slice);
+  grpc_slice_unref_internal(&exec_ctx, g_fake_path_key);
+  grpc_slice_unref_internal(&exec_ctx, g_fake_path_value);
+  grpc_slice_unref_internal(&exec_ctx, g_fake_auth_key);
+  grpc_slice_unref_internal(&exec_ctx, g_fake_auth_value);
+  grpc_exec_ctx_finish(&exec_ctx);
+}
diff --git a/src/core/ext/transport/inproc/inproc_transport.h b/src/core/ext/transport/inproc/inproc_transport.h
new file mode 100644
index 0000000000..37e6d99e99
--- /dev/null
+++ b/src/core/ext/transport/inproc/inproc_transport.h
@@ -0,0 +1,41 @@
+/*
+ *
+ * Copyright 2017 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_TRANSPORT_INPROC_INPROC_TRANSPORT_H
+#define GRPC_CORE_EXT_TRANSPORT_INPROC_INPROC_TRANSPORT_H
+
+#include "src/core/lib/transport/transport_impl.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+grpc_channel *grpc_inproc_channel_create(grpc_server *server,
+                                         grpc_channel_args *args,
+                                         void *reserved);
+
+extern grpc_tracer_flag grpc_inproc_trace;
+
+void grpc_inproc_transport_init(void);
+void grpc_inproc_transport_shutdown(void);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* GRPC_CORE_EXT_TRANSPORT_INPROC_INPROC_TRANSPORT_H */
diff --git a/src/core/plugin_registry/grpc_plugin_registry.c b/src/core/plugin_registry/grpc_plugin_registry.c
index a816186c39..b0d06a3f43 100644
--- a/src/core/plugin_registry/grpc_plugin_registry.c
+++ b/src/core/plugin_registry/grpc_plugin_registry.c
@@ -26,6 +26,8 @@ extern void grpc_deadline_filter_init(void);
 extern void grpc_deadline_filter_shutdown(void);
 extern void grpc_client_channel_init(void);
 extern void grpc_client_channel_shutdown(void);
+extern void grpc_inproc_plugin_init(void);
+extern void grpc_inproc_plugin_shutdown(void);
 extern void grpc_resolver_fake_init(void);
 extern void grpc_resolver_fake_shutdown(void);
 extern void grpc_lb_policy_grpclb_init(void);
@@ -60,6 +62,8 @@ void grpc_register_built_in_plugins(void) {
                        grpc_deadline_filter_shutdown);
   grpc_register_plugin(grpc_client_channel_init,
                        grpc_client_channel_shutdown);
+  grpc_register_plugin(grpc_inproc_plugin_init,
+                       grpc_inproc_plugin_shutdown);
   grpc_register_plugin(grpc_resolver_fake_init,
                        grpc_resolver_fake_shutdown);
   grpc_register_plugin(grpc_lb_policy_grpclb_init,
diff --git a/src/core/plugin_registry/grpc_unsecure_plugin_registry.c b/src/core/plugin_registry/grpc_unsecure_plugin_registry.c
index 809d444bf7..7eb599d81a 100644
--- a/src/core/plugin_registry/grpc_unsecure_plugin_registry.c
+++ b/src/core/plugin_registry/grpc_unsecure_plugin_registry.c
@@ -26,6 +26,8 @@ extern void grpc_deadline_filter_init(void);
 extern void grpc_deadline_filter_shutdown(void);
 extern void grpc_client_channel_init(void);
 extern void grpc_client_channel_shutdown(void);
+extern void grpc_inproc_plugin_init(void);
+extern void grpc_inproc_plugin_shutdown(void);
 extern void grpc_resolver_dns_ares_init(void);
 extern void grpc_resolver_dns_ares_shutdown(void);
 extern void grpc_resolver_dns_native_init(void);
@@ -60,6 +62,8 @@ void grpc_register_built_in_plugins(void) {
                        grpc_deadline_filter_shutdown);
   grpc_register_plugin(grpc_client_channel_init,
                        grpc_client_channel_shutdown);
+  grpc_register_plugin(grpc_inproc_plugin_init,
+                       grpc_inproc_plugin_shutdown);
   grpc_register_plugin(grpc_resolver_dns_ares_init,
                        grpc_resolver_dns_ares_shutdown);
   grpc_register_plugin(grpc_resolver_dns_native_init,
diff --git a/src/cpp/server/server_cc.cc b/src/cpp/server/server_cc.cc
index 3bff9999b9..60e067d89d 100644
--- a/src/cpp/server/server_cc.cc
+++ b/src/cpp/server/server_cc.cc
@@ -36,7 +36,9 @@
 #include <grpc/support/alloc.h>
 #include <grpc/support/log.h>
 
+#include "src/core/ext/transport/inproc/inproc_transport.h"
 #include "src/core/lib/profiling/timers.h"
+#include "src/cpp/client/create_channel_internal.h"
 #include "src/cpp/server/health/default_health_check_service.h"
 #include "src/cpp/thread_manager/thread_manager.h"
 
@@ -422,6 +424,13 @@ void Server::SetGlobalCallbacks(GlobalCallbacks* callbacks) {
 
 grpc_server* Server::c_server() { return server_; }
 
+std::shared_ptr<Channel> Server::InProcessChannel(
+    const ChannelArguments& args) {
+  grpc_channel_args channel_args = args.c_channel_args();
+  return CreateChannelInternal(
+      "inproc", grpc_inproc_channel_create(server_, &channel_args, nullptr));
+}
+
 static grpc_server_register_method_payload_handling PayloadHandlingForMethod(
     internal::RpcServiceMethod* method) {
   switch (method->method_type()) {
diff --git a/src/python/grpcio/grpc_core_dependencies.py b/src/python/grpcio/grpc_core_dependencies.py
index ea5bdbae58..b30d340ce5 100644
--- a/src/python/grpcio/grpc_core_dependencies.py
+++ b/src/python/grpcio/grpc_core_dependencies.py
@@ -270,6 +270,8 @@ CORE_SOURCE_FILES = [
   'src/core/ext/transport/chttp2/server/insecure/server_chttp2_posix.c',
   'src/core/ext/transport/chttp2/client/insecure/channel_create.c',
   'src/core/ext/transport/chttp2/client/insecure/channel_create_posix.c',
+  'src/core/ext/transport/inproc/inproc_plugin.c',
+  'src/core/ext/transport/inproc/inproc_transport.c',
   'src/core/ext/filters/client_channel/lb_policy/grpclb/client_load_reporting_filter.c',
   'src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb.c',
   'src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb_channel_secure.c',