Merge branch 'master' of https://github.com/grpc/grpc into cpp_bazelness

62 files changed, 2181 insertions, 193 deletions

diff --git a/examples/ruby/errors_and_cancellation/README.md b/examples/ruby/errors_and_cancellation/README.md
new file mode 100644
index 0000000000..126518c4aa
--- /dev/null
+++ b/examples/ruby/errors_and_cancellation/README.md
@@ -0,0 +1,25 @@
+#Errors and Cancelletion code samples for grpc-ruby
+
+The examples in this directory show use of grpc errors.
+
+On the server side, errors are returned from service
+implementations by raising a certain `GRPC::BadStatus` exception.
+
+On the client side, GRPC errors get raised when either:
+ * the call completes (unary and client-streaming call types)
+ * the response `Enumerable` is iterated through (server-streaming and
+   bidi call types).
+
+## To run the examples here:
+
+Start the server:
+
+```
+> ruby error_examples_server.rb
+```
+
+Then run the client:
+
+```
+> ruby error_examples_client.rb
+```
diff --git a/examples/ruby/errors_and_cancellation/error_examples_client.rb b/examples/ruby/errors_and_cancellation/error_examples_client.rb
new file mode 100755
index 0000000000..90456d066d
--- /dev/null
+++ b/examples/ruby/errors_and_cancellation/error_examples_client.rb
@@ -0,0 +1,117 @@
+#!/usr/bin/env ruby
+
+# Copyright 2015, Google Inc.
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met:
+#
+#     * Redistributions of source code must retain the above copyright
+# notice, this list of conditions and the following disclaimer.
+#     * Redistributions in binary form must reproduce the above
+# copyright notice, this list of conditions and the following disclaimer
+# in the documentation and/or other materials provided with the
+# distribution.
+#     * Neither the name of Google Inc. nor the names of its
+# contributors may be used to endorse or promote products derived from
+# this software without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+# Sample app that connects to an error-throwing implementation of
+# Route Guide service.
+#
+# Usage: $ path/to/route_guide_client.rb
+
+this_dir = File.expand_path(File.dirname(__FILE__))
+lib_dir = File.join(File.dirname(this_dir), 'lib')
+$LOAD_PATH.unshift(lib_dir) unless $LOAD_PATH.include?(lib_dir)
+
+require 'grpc'
+require 'route_guide_services_pb'
+
+include Routeguide
+
+def run_get_feature_expect_error(stub)
+  resp = stub.get_feature(Point.new)
+end
+
+def run_list_features_expect_error(stub)
+  resps = stub.list_features(Rectangle.new)
+
+  # NOOP iteration to pick up error
+  resps.each { }
+end
+
+def run_record_route_expect_error(stub)
+  stub.record_route([])
+end
+
+def run_route_chat_expect_error(stub)
+  resps = stub.route_chat([])
+
+  # NOOP iteration to pick up error
+  resps.each { }
+end
+
+def main
+  stub = RouteGuide::Stub.new('localhost:50051', :this_channel_is_insecure)
+
+  begin
+    run_get_feature_expect_error(stub)
+  rescue GRPC::BadStatus => e
+    puts "===== GetFeature exception: ====="
+    puts e.inspect
+    puts "e.code: #{e.code}"
+    puts "e.details: #{e.details}"
+    puts "e.metadata: #{e.metadata}"
+    puts "================================="
+  end
+
+  begin
+    run_list_features_expect_error(stub)
+  rescue GRPC::BadStatus => e
+    error = true
+    puts "===== ListFeatures exception: ====="
+    puts e.inspect
+    puts "e.code: #{e.code}"
+    puts "e.details: #{e.details}"
+    puts "e.metadata: #{e.metadata}"
+    puts "================================="
+  end
+
+  begin
+    run_route_chat_expect_error(stub)
+  rescue GRPC::BadStatus => e
+    puts "==== RouteChat exception: ===="
+    puts e.inspect
+    puts "e.code: #{e.code}"
+    puts "e.details: #{e.details}"
+    puts "e.metadata: #{e.metadata}"
+    puts "================================="
+  end
+
+  begin
+    run_record_route_expect_error(stub)
+  rescue GRPC::BadStatus => e
+    puts "==== RecordRoute exception: ===="
+    puts e.inspect
+    puts "e.code: #{e.code}"
+    puts "e.details: #{e.details}"
+    puts "e.metadata: #{e.metadata}"
+    puts "================================="
+  end
+end
+
+main
diff --git a/examples/ruby/errors_and_cancellation/error_examples_server.rb b/examples/ruby/errors_and_cancellation/error_examples_server.rb
new file mode 100755
index 0000000000..66751882d9
--- /dev/null
+++ b/examples/ruby/errors_and_cancellation/error_examples_server.rb
@@ -0,0 +1,76 @@
+#!/usr/bin/env ruby
+# -*- coding: utf-8 -*-
+
+# Copyright 2015, Google Inc.
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met:
+#
+#     * Redistributions of source code must retain the above copyright
+# notice, this list of conditions and the following disclaimer.
+#     * Redistributions in binary form must reproduce the above
+# copyright notice, this list of conditions and the following disclaimer
+# in the documentation and/or other materials provided with the
+# distribution.
+#     * Neither the name of Google Inc. nor the names of its
+# contributors may be used to endorse or promote products derived from
+# this software without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+# Error-throwing implementation of Route Guide service.
+#
+# Usage: $ path/to/route_guide_server.rb
+
+this_dir = File.expand_path(File.dirname(__FILE__))
+lib_dir = File.join(File.dirname(this_dir), 'lib')
+$LOAD_PATH.unshift(lib_dir) unless $LOAD_PATH.include?(lib_dir)
+
+require 'grpc'
+require 'route_guide_services_pb'
+
+include Routeguide
+
+include GRPC::Core::StatusCodes
+
+# CanellingandErrorReturningServiceImpl provides an implementation of the RouteGuide service.
+class CancellingAndErrorReturningServerImpl < RouteGuide::Service
+  # def get_feature
+  #   Note get_feature isn't implemented in this subclass, so the server
+  #   will get a gRPC UNIMPLEMENTED error when it's called.
+
+  def list_features(rectangle, _call)
+    raise "string appears on the client in the 'details' field of a 'GRPC::Unknown' exception"
+  end
+
+  def record_route(call)
+    raise GRPC::BadStatus.new_status_exception(CANCELLED)
+  end
+
+  def route_chat(notes)
+    raise GRPC::BadStatus.new_status_exception(ABORTED, details = 'arbitrary', metadata = {somekey: 'val'})
+  end
+end
+
+def main
+  port = '0.0.0.0:50051'
+  s = GRPC::RpcServer.new
+  s.add_http2_port(port, :this_port_is_insecure)
+  GRPC.logger.info("... running insecurely on #{port}")
+  s.handle(CancellingAndErrorReturningServerImpl.new)
+  s.run_till_terminated
+end
+
+main
diff --git a/include/grpc++/impl/codegen/async_stream.h b/include/grpc++/impl/codegen/async_stream.h
index 1a5cbbd45d..8f529895ca 100644
--- a/include/grpc++/impl/codegen/async_stream.h
+++ b/include/grpc++/impl/codegen/async_stream.h
@@ -101,6 +101,39 @@ class AsyncWriterInterface {
   /// \param[in] msg The message to be written.
   /// \param[in] tag The tag identifying the operation.
   virtual void Write(const W& msg, void* tag) = 0;
+
+  /// Request the writing of \a msg using WriteOptions \a options with
+  /// identifying tag \a tag.
+  ///
+  /// Only one write may be outstanding at any given time. This means that
+  /// after calling Write, one must wait to receive \a tag from the completion
+  /// queue BEFORE calling Write again.
+  /// WriteOptions \a options is used to set the write options of this message.
+  /// This is thread-safe with respect to \a Read
+  ///
+  /// \param[in] msg The message to be written.
+  /// \param[in] options The WriteOptions to be used to write this message.
+  /// \param[in] tag The tag identifying the operation.
+  virtual void Write(const W& msg, WriteOptions options, void* tag) = 0;
+
+  /// Request the writing of \a msg and coalesce it with the writing
+  /// of trailing metadata, using WriteOptions \a options with identifying tag
+  /// \a tag.
+  ///
+  /// For client, WriteLast is equivalent of performing Write and WritesDone in
+  /// a single step.
+  /// For server, WriteLast buffers the \a msg. The writing of \a msg is held
+  /// until Finish is called, where \a msg and trailing metadata are coalesced
+  /// and write is initiated. Note that WriteLast can only buffer \a msg up to
+  /// the flow control window size. If \a msg size is larger than the window
+  /// size, it will be sent on wire without buffering.
+  ///
+  /// \param[in] msg The message to be written.
+  /// \param[in] options The WriteOptions to be used to write this message.
+  /// \param[in] tag The tag identifying the operation.
+  void WriteLast(const W& msg, WriteOptions options, void* tag) {
+    Write(msg, options.set_last_message(), tag);
+  }
 };
 
 template <class R>
@@ -183,11 +216,17 @@ class ClientAsyncWriter final : public ClientAsyncWriterInterface<W> {
       : context_(context), call_(channel->CreateCall(method, context, cq)) {
     finish_ops_.RecvMessage(response);
     finish_ops_.AllowNoMessage();
-
-    init_ops_.set_output_tag(tag);
-    init_ops_.SendInitialMetadata(context->send_initial_metadata_,
-                                  context->initial_metadata_flags());
-    call_.PerformOps(&init_ops_);
+    // if corked bit is set in context, we buffer up the initial metadata to
+    // coalesce with later message to be sent. No op is performed.
+    if (context_->initial_metadata_corked_) {
+      write_ops_.SendInitialMetadata(context->send_initial_metadata_,
+                                     context->initial_metadata_flags());
+    } else {
+      write_ops_.set_output_tag(tag);
+      write_ops_.SendInitialMetadata(context->send_initial_metadata_,
+                                     context->initial_metadata_flags());
+      call_.PerformOps(&write_ops_);
+    }
   }
 
   void ReadInitialMetadata(void* tag) override {
@@ -205,10 +244,21 @@ class ClientAsyncWriter final : public ClientAsyncWriterInterface<W> {
     call_.PerformOps(&write_ops_);
   }
 
+  void Write(const W& msg, WriteOptions options, void* tag) override {
+    write_ops_.set_output_tag(tag);
+    if (options.is_last_message()) {
+      options.set_buffer_hint();
+      write_ops_.ClientSendClose();
+    }
+    // TODO(ctiller): don't assert
+    GPR_CODEGEN_ASSERT(write_ops_.SendMessage(msg, options).ok());
+    call_.PerformOps(&write_ops_);
+  }
+
   void WritesDone(void* tag) override {
-    writes_done_ops_.set_output_tag(tag);
-    writes_done_ops_.ClientSendClose();
-    call_.PerformOps(&writes_done_ops_);
+    write_ops_.set_output_tag(tag);
+    write_ops_.ClientSendClose();
+    call_.PerformOps(&write_ops_);
   }
 
   void Finish(Status* status, void* tag) override {
@@ -223,10 +273,9 @@ class ClientAsyncWriter final : public ClientAsyncWriterInterface<W> {
  private:
   ClientContext* context_;
   Call call_;
-  CallOpSet<CallOpSendInitialMetadata> init_ops_;
   CallOpSet<CallOpRecvInitialMetadata> meta_ops_;
-  CallOpSet<CallOpSendMessage> write_ops_;
-  CallOpSet<CallOpClientSendClose> writes_done_ops_;
+  CallOpSet<CallOpSendInitialMetadata, CallOpSendMessage, CallOpClientSendClose>
+      write_ops_;
   CallOpSet<CallOpRecvInitialMetadata, CallOpGenericRecvMessage,
             CallOpClientRecvStatus>
       finish_ops_;
@@ -253,10 +302,17 @@ class ClientAsyncReaderWriter final
                           const RpcMethod& method, ClientContext* context,
                           void* tag)
       : context_(context), call_(channel->CreateCall(method, context, cq)) {
-    init_ops_.set_output_tag(tag);
-    init_ops_.SendInitialMetadata(context->send_initial_metadata_,
-                                  context->initial_metadata_flags());
-    call_.PerformOps(&init_ops_);
+    if (context_->initial_metadata_corked_) {
+      // if corked bit is set in context, we buffer up the initial metadata to
+      // coalesce with later message to be sent. No op is performed.
+      write_ops_.SendInitialMetadata(context->send_initial_metadata_,
+                                     context->initial_metadata_flags());
+    } else {
+      write_ops_.set_output_tag(tag);
+      write_ops_.SendInitialMetadata(context->send_initial_metadata_,
+                                     context->initial_metadata_flags());
+      call_.PerformOps(&write_ops_);
+    }
   }
 
   void ReadInitialMetadata(void* tag) override {
@@ -283,10 +339,21 @@ class ClientAsyncReaderWriter final
     call_.PerformOps(&write_ops_);
   }
 
+  void Write(const W& msg, WriteOptions options, void* tag) override {
+    write_ops_.set_output_tag(tag);
+    if (options.is_last_message()) {
+      options.set_buffer_hint();
+      write_ops_.ClientSendClose();
+    }
+    // TODO(ctiller): don't assert
+    GPR_CODEGEN_ASSERT(write_ops_.SendMessage(msg, options).ok());
+    call_.PerformOps(&write_ops_);
+  }
+
   void WritesDone(void* tag) override {
-    writes_done_ops_.set_output_tag(tag);
-    writes_done_ops_.ClientSendClose();
-    call_.PerformOps(&writes_done_ops_);
+    write_ops_.set_output_tag(tag);
+    write_ops_.ClientSendClose();
+    call_.PerformOps(&write_ops_);
   }
 
   void Finish(Status* status, void* tag) override {
@@ -301,11 +368,10 @@ class ClientAsyncReaderWriter final
  private:
   ClientContext* context_;
   Call call_;
-  CallOpSet<CallOpSendInitialMetadata> init_ops_;
   CallOpSet<CallOpRecvInitialMetadata> meta_ops_;
   CallOpSet<CallOpRecvInitialMetadata, CallOpRecvMessage<R>> read_ops_;
-  CallOpSet<CallOpSendMessage> write_ops_;
-  CallOpSet<CallOpClientSendClose> writes_done_ops_;
+  CallOpSet<CallOpSendInitialMetadata, CallOpSendMessage, CallOpClientSendClose>
+      write_ops_;
   CallOpSet<CallOpRecvInitialMetadata, CallOpClientRecvStatus> finish_ops_;
 };
 
@@ -395,6 +461,20 @@ class ServerAsyncWriterInterface : public ServerAsyncStreamingInterface,
                                    public AsyncWriterInterface<W> {
  public:
   virtual void Finish(const Status& status, void* tag) = 0;
+
+  /// Request the writing of \a msg and coalesce it with trailing metadata which
+  /// contains \a status, using WriteOptions options with identifying tag \a
+  /// tag.
+  ///
+  /// WriteAndFinish is equivalent of performing WriteLast and Finish in a
+  /// single step.
+  ///
+  /// \param[in] msg The message to be written.
+  /// \param[in] options The WriteOptions to be used to write this message.
+  /// \param[in] status The Status that server returns to client.
+  /// \param[in] tag The tag identifying the operation.
+  virtual void WriteAndFinish(const W& msg, WriteOptions options,
+                              const Status& status, void* tag) = 0;
 };
 
 template <class W>
@@ -418,29 +498,37 @@ class ServerAsyncWriter final : public ServerAsyncWriterInterface<W> {
 
   void Write(const W& msg, void* tag) override {
     write_ops_.set_output_tag(tag);
-    if (!ctx_->sent_initial_metadata_) {
-      write_ops_.SendInitialMetadata(ctx_->initial_metadata_,
-                                     ctx_->initial_metadata_flags());
-      if (ctx_->compression_level_set()) {
-        write_ops_.set_compression_level(ctx_->compression_level());
-      }
-      ctx_->sent_initial_metadata_ = true;
-    }
+    EnsureInitialMetadataSent(&write_ops_);
     // TODO(ctiller): don't assert
     GPR_CODEGEN_ASSERT(write_ops_.SendMessage(msg).ok());
     call_.PerformOps(&write_ops_);
   }
 
+  void Write(const W& msg, WriteOptions options, void* tag) override {
+    write_ops_.set_output_tag(tag);
+    if (options.is_last_message()) {
+      options.set_buffer_hint();
+    }
+
+    EnsureInitialMetadataSent(&write_ops_);
+    // TODO(ctiller): don't assert
+    GPR_CODEGEN_ASSERT(write_ops_.SendMessage(msg, options).ok());
+    call_.PerformOps(&write_ops_);
+  }
+
+  void WriteAndFinish(const W& msg, WriteOptions options, const Status& status,
+                      void* tag) override {
+    write_ops_.set_output_tag(tag);
+    EnsureInitialMetadataSent(&write_ops_);
+    options.set_buffer_hint();
+    GPR_CODEGEN_ASSERT(write_ops_.SendMessage(msg, options).ok());
+    write_ops_.ServerSendStatus(ctx_->trailing_metadata_, status);
+    call_.PerformOps(&write_ops_);
+  }
+
   void Finish(const Status& status, void* tag) override {
     finish_ops_.set_output_tag(tag);
-    if (!ctx_->sent_initial_metadata_) {
-      finish_ops_.SendInitialMetadata(ctx_->initial_metadata_,
-                                      ctx_->initial_metadata_flags());
-      if (ctx_->compression_level_set()) {
-        finish_ops_.set_compression_level(ctx_->compression_level());
-      }
-      ctx_->sent_initial_metadata_ = true;
-    }
+    EnsureInitialMetadataSent(&finish_ops_);
     finish_ops_.ServerSendStatus(ctx_->trailing_metadata_, status);
     call_.PerformOps(&finish_ops_);
   }
@@ -448,10 +536,24 @@ class ServerAsyncWriter final : public ServerAsyncWriterInterface<W> {
  private:
   void BindCall(Call* call) override { call_ = *call; }
 
+  template <class T>
+  void EnsureInitialMetadataSent(T* ops) {
+    if (!ctx_->sent_initial_metadata_) {
+      ops->SendInitialMetadata(ctx_->initial_metadata_,
+                               ctx_->initial_metadata_flags());
+      if (ctx_->compression_level_set()) {
+        ops->set_compression_level(ctx_->compression_level());
+      }
+      ctx_->sent_initial_metadata_ = true;
+    }
+  }
+
   Call call_;
   ServerContext* ctx_;
   CallOpSet<CallOpSendInitialMetadata> meta_ops_;
-  CallOpSet<CallOpSendInitialMetadata, CallOpSendMessage> write_ops_;
+  CallOpSet<CallOpSendInitialMetadata, CallOpSendMessage,
+            CallOpServerSendStatus>
+      write_ops_;
   CallOpSet<CallOpSendInitialMetadata, CallOpServerSendStatus> finish_ops_;
 };
 
@@ -462,6 +564,20 @@ class ServerAsyncReaderWriterInterface : public ServerAsyncStreamingInterface,
                                          public AsyncReaderInterface<R> {
  public:
   virtual void Finish(const Status& status, void* tag) = 0;
+
+  /// Request the writing of \a msg and coalesce it with trailing metadata which
+  /// contains \a status, using WriteOptions options with identifying tag \a
+  /// tag.
+  ///
+  /// WriteAndFinish is equivalent of performing WriteLast and Finish in a
+  /// single step.
+  ///
+  /// \param[in] msg The message to be written.
+  /// \param[in] options The WriteOptions to be used to write this message.
+  /// \param[in] status The Status that server returns to client.
+  /// \param[in] tag The tag identifying the operation.
+  virtual void WriteAndFinish(const W& msg, WriteOptions options,
+                              const Status& status, void* tag) = 0;
 };
 
 template <class W, class R>
@@ -492,29 +608,36 @@ class ServerAsyncReaderWriter final
 
   void Write(const W& msg, void* tag) override {
     write_ops_.set_output_tag(tag);
-    if (!ctx_->sent_initial_metadata_) {
-      write_ops_.SendInitialMetadata(ctx_->initial_metadata_,
-                                     ctx_->initial_metadata_flags());
-      if (ctx_->compression_level_set()) {
-        write_ops_.set_compression_level(ctx_->compression_level());
-      }
-      ctx_->sent_initial_metadata_ = true;
-    }
+    EnsureInitialMetadataSent(&write_ops_);
     // TODO(ctiller): don't assert
     GPR_CODEGEN_ASSERT(write_ops_.SendMessage(msg).ok());
     call_.PerformOps(&write_ops_);
   }
 
+  void Write(const W& msg, WriteOptions options, void* tag) override {
+    write_ops_.set_output_tag(tag);
+    if (options.is_last_message()) {
+      options.set_buffer_hint();
+    }
+    EnsureInitialMetadataSent(&write_ops_);
+    GPR_CODEGEN_ASSERT(write_ops_.SendMessage(msg, options).ok());
+    call_.PerformOps(&write_ops_);
+  }
+
+  void WriteAndFinish(const W& msg, WriteOptions options, const Status& status,
+                      void* tag) override {
+    write_ops_.set_output_tag(tag);
+    EnsureInitialMetadataSent(&write_ops_);
+    options.set_buffer_hint();
+    GPR_CODEGEN_ASSERT(write_ops_.SendMessage(msg, options).ok());
+    write_ops_.ServerSendStatus(ctx_->trailing_metadata_, status);
+    call_.PerformOps(&write_ops_);
+  }
+
   void Finish(const Status& status, void* tag) override {
     finish_ops_.set_output_tag(tag);
-    if (!ctx_->sent_initial_metadata_) {
-      finish_ops_.SendInitialMetadata(ctx_->initial_metadata_,
-                                      ctx_->initial_metadata_flags());
-      if (ctx_->compression_level_set()) {
-        finish_ops_.set_compression_level(ctx_->compression_level());
-      }
-      ctx_->sent_initial_metadata_ = true;
-    }
+    EnsureInitialMetadataSent(&finish_ops_);
+
     finish_ops_.ServerSendStatus(ctx_->trailing_metadata_, status);
     call_.PerformOps(&finish_ops_);
   }
@@ -524,11 +647,25 @@ class ServerAsyncReaderWriter final
 
   void BindCall(Call* call) override { call_ = *call; }
 
+  template <class T>
+  void EnsureInitialMetadataSent(T* ops) {
+    if (!ctx_->sent_initial_metadata_) {
+      ops->SendInitialMetadata(ctx_->initial_metadata_,
+                               ctx_->initial_metadata_flags());
+      if (ctx_->compression_level_set()) {
+        ops->set_compression_level(ctx_->compression_level());
+      }
+      ctx_->sent_initial_metadata_ = true;
+    }
+  }
+
   Call call_;
   ServerContext* ctx_;
   CallOpSet<CallOpSendInitialMetadata> meta_ops_;
   CallOpSet<CallOpRecvMessage<R>> read_ops_;
-  CallOpSet<CallOpSendInitialMetadata, CallOpSendMessage> write_ops_;
+  CallOpSet<CallOpSendInitialMetadata, CallOpSendMessage,
+            CallOpServerSendStatus>
+      write_ops_;
   CallOpSet<CallOpSendInitialMetadata, CallOpServerSendStatus> finish_ops_;
 };
 
diff --git a/include/grpc++/impl/codegen/call.h b/include/grpc++/impl/codegen/call.h
index 19a5ca2b2e..a3f2be6bb1 100644
--- a/include/grpc++/impl/codegen/call.h
+++ b/include/grpc++/impl/codegen/call.h
@@ -84,8 +84,9 @@ inline grpc_metadata* FillMetadataArray(
 /// Per-message write options.
 class WriteOptions {
  public:
-  WriteOptions() : flags_(0) {}
-  WriteOptions(const WriteOptions& other) : flags_(other.flags_) {}
+  WriteOptions() : flags_(0), last_message_(false) {}
+  WriteOptions(const WriteOptions& other)
+      : flags_(other.flags_), last_message_(other.last_message_) {}
 
   /// Clear all flags.
   inline void Clear() { flags_ = 0; }
@@ -141,6 +142,43 @@ class WriteOptions {
   /// \sa GRPC_WRITE_BUFFER_HINT
   inline bool get_buffer_hint() const { return GetBit(GRPC_WRITE_BUFFER_HINT); }
 
+  /// corked bit: aliases set_buffer_hint currently, with the intent that
+  /// set_buffer_hint will be removed in the future
+  inline WriteOptions& set_corked() {
+    SetBit(GRPC_WRITE_BUFFER_HINT);
+    return *this;
+  }
+
+  inline WriteOptions& clear_corked() {
+    ClearBit(GRPC_WRITE_BUFFER_HINT);
+    return *this;
+  }
+
+  inline bool is_corked() const { return GetBit(GRPC_WRITE_BUFFER_HINT); }
+
+  /// last-message bit: indicates this is the last message in a stream
+  /// client-side:  makes Write the equivalent of performing Write, WritesDone
+  /// in a single step
+  /// server-side:  hold the Write until the service handler returns (sync api)
+  /// or until Finish is called (async api)
+  inline WriteOptions& set_last_message() {
+    last_message_ = true;
+    return *this;
+  }
+
+  /// Clears flag indicating that this is the last message in a stream,
+  /// disabling coalescing.
+  inline WriteOptions& clear_last_messsage() {
+    last_message_ = false;
+    return *this;
+  }
+
+  /// Get value for the flag indicating that this is the last message, and
+  /// should be coalesced with trailing metadata.
+  ///
+  /// \sa GRPC_WRITE_LAST_MESSAGE
+  bool is_last_message() const { return last_message_; }
+
   WriteOptions& operator=(const WriteOptions& rhs) {
     flags_ = rhs.flags_;
     return *this;
@@ -154,6 +192,7 @@ class WriteOptions {
   bool GetBit(const uint32_t mask) const { return (flags_ & mask) != 0; }
 
   uint32_t flags_;
+  bool last_message_;
 };
 
 /// Default argument for CallOpSet. I is unused by the class, but can be
@@ -224,7 +263,7 @@ class CallOpSendMessage {
   /// after use.
   template <class M>
   Status SendMessage(const M& message,
-                     const WriteOptions& options) GRPC_MUST_USE_RESULT;
+                     WriteOptions options) GRPC_MUST_USE_RESULT;
 
   template <class M>
   Status SendMessage(const M& message) GRPC_MUST_USE_RESULT;
@@ -252,8 +291,7 @@ class CallOpSendMessage {
 };
 
 template <class M>
-Status CallOpSendMessage::SendMessage(const M& message,
-                                      const WriteOptions& options) {
+Status CallOpSendMessage::SendMessage(const M& message, WriteOptions options) {
   write_options_ = options;
   return SerializationTraits<M>::Serialize(message, &send_buf_, &own_buf_);
 }
diff --git a/include/grpc++/impl/codegen/client_context.h b/include/grpc++/impl/codegen/client_context.h
index b91c7f65d4..3c50e6ba9d 100644
--- a/include/grpc++/impl/codegen/client_context.h
+++ b/include/grpc++/impl/codegen/client_context.h
@@ -281,6 +281,17 @@ class ClientContext {
   /// \param algorithm The compression algorithm used for the client call.
   void set_compression_algorithm(grpc_compression_algorithm algorithm);
 
+  /// Flag whether the initial metadata should be \a corked
+  ///
+  /// If \a corked is true, then the initial metadata will be colasced with the
+  /// write of first message in the stream.
+  ///
+  /// \param corked The flag indicating whether the initial metadata is to be
+  /// corked or not.
+  void set_initial_metadata_corked(bool corked) {
+    initial_metadata_corked_ = corked;
+  }
+
   /// Return the peer uri in a string.
   ///
   /// \warning This value is never authenticated or subject to any security
@@ -357,7 +368,8 @@ class ClientContext {
            (cacheable_ ? GRPC_INITIAL_METADATA_CACHEABLE_REQUEST : 0) |
            (wait_for_ready_explicitly_set_
                 ? GRPC_INITIAL_METADATA_WAIT_FOR_READY_EXPLICITLY_SET
-                : 0);
+                : 0) |
+           (initial_metadata_corked_ ? GRPC_INITIAL_METADATA_CORKED : 0);
   }
 
   grpc::string authority() { return authority_; }
@@ -384,6 +396,7 @@ class ClientContext {
   PropagationOptions propagation_options_;
 
   grpc_compression_algorithm compression_algorithm_;
+  bool initial_metadata_corked_;
 };
 
 }  // namespace grpc
diff --git a/include/grpc++/impl/codegen/sync_stream.h b/include/grpc++/impl/codegen/sync_stream.h
index 4d9b074e95..ae3b8e441d 100644
--- a/include/grpc++/impl/codegen/sync_stream.h
+++ b/include/grpc++/impl/codegen/sync_stream.h
@@ -100,22 +100,40 @@ class WriterInterface {
  public:
   virtual ~WriterInterface() {}
 
-  /// Blocking write \a msg to the stream with options.
+  /// Blocking write \a msg to the stream with WriteOptions \a options.
   /// This is thread-safe with respect to \a Read
   ///
   /// \param msg The message to be written to the stream.
-  /// \param options Options affecting the write operation.
+  /// \param options The WriteOptions affecting the write operation.
   ///
   /// \return \a true on success, \a false when the stream has been closed.
-  virtual bool Write(const W& msg, const WriteOptions& options) = 0;
+  virtual bool Write(const W& msg, WriteOptions options) = 0;
 
-  /// Blocking write \a msg to the stream with default options.
+  /// Blocking write \a msg to the stream with default write options.
   /// This is thread-safe with respect to \a Read
   ///
   /// \param msg The message to be written to the stream.
   ///
   /// \return \a true on success, \a false when the stream has been closed.
   inline bool Write(const W& msg) { return Write(msg, WriteOptions()); }
+
+  /// Write \a msg and coalesce it with the writing of trailing metadata, using
+  /// WriteOptions \a options.
+  ///
+  /// For client, WriteLast is equivalent of performing Write and WritesDone in
+  /// a single step. \a msg and trailing metadata are coalesced and sent on wire
+  /// by calling this function.
+  /// For server, WriteLast buffers the \a msg. The writing of \a msg is held
+  /// until the service handler returns, where \a msg and trailing metadata are
+  /// coalesced and sent on wire. Note that WriteLast can only buffer \a msg up
+  /// to the flow control window size. If \a msg size is larger than the window
+  /// size, it will be sent on wire without buffering.
+  ///
+  /// \param[in] msg The message to be written to the stream.
+  /// \param[in] options The WriteOptions to be used to write this message.
+  void WriteLast(const W& msg, WriteOptions options) {
+    Write(msg, options.set_last_message());
+  }
 };
 
 /// Client-side interface for streaming reads of message of type \a R.
@@ -213,11 +231,13 @@ class ClientWriter : public ClientWriterInterface<W> {
     finish_ops_.RecvMessage(response);
     finish_ops_.AllowNoMessage();
 
-    CallOpSet<CallOpSendInitialMetadata> ops;
-    ops.SendInitialMetadata(context->send_initial_metadata_,
-                            context->initial_metadata_flags());
-    call_.PerformOps(&ops);
-    cq_.Pluck(&ops);
+    if (!context_->initial_metadata_corked_) {
+      CallOpSet<CallOpSendInitialMetadata> ops;
+      ops.SendInitialMetadata(context->send_initial_metadata_,
+                              context->initial_metadata_flags());
+      call_.PerformOps(&ops);
+      cq_.Pluck(&ops);
+    }
   }
 
   void WaitForInitialMetadata() {
@@ -230,11 +250,24 @@ class ClientWriter : public ClientWriterInterface<W> {
   }
 
   using WriterInterface<W>::Write;
-  bool Write(const W& msg, const WriteOptions& options) override {
-    CallOpSet<CallOpSendMessage> ops;
+  bool Write(const W& msg, WriteOptions options) override {
+    CallOpSet<CallOpSendInitialMetadata, CallOpSendMessage,
+              CallOpClientSendClose>
+        ops;
+
+    if (options.is_last_message()) {
+      options.set_buffer_hint();
+      ops.ClientSendClose();
+    }
+    if (context_->initial_metadata_corked_) {
+      ops.SendInitialMetadata(context_->send_initial_metadata_,
+                              context_->initial_metadata_flags());
+      context_->set_initial_metadata_corked(false);
+    }
     if (!ops.SendMessage(msg, options).ok()) {
       return false;
     }
+
     call_.PerformOps(&ops);
     return cq_.Pluck(&ops);
   }
@@ -293,11 +326,13 @@ class ClientReaderWriter final : public ClientReaderWriterInterface<W, R> {
   ClientReaderWriter(ChannelInterface* channel, const RpcMethod& method,
                      ClientContext* context)
       : context_(context), call_(channel->CreateCall(method, context, &cq_)) {
-    CallOpSet<CallOpSendInitialMetadata> ops;
-    ops.SendInitialMetadata(context->send_initial_metadata_,
-                            context->initial_metadata_flags());
-    call_.PerformOps(&ops);
-    cq_.Pluck(&ops);
+    if (!context_->initial_metadata_corked_) {
+      CallOpSet<CallOpSendInitialMetadata> ops;
+      ops.SendInitialMetadata(context->send_initial_metadata_,
+                              context->initial_metadata_flags());
+      call_.PerformOps(&ops);
+      cq_.Pluck(&ops);
+    }
   }
 
   void WaitForInitialMetadata() override {
@@ -325,9 +360,24 @@ class ClientReaderWriter final : public ClientReaderWriterInterface<W, R> {
   }
 
   using WriterInterface<W>::Write;
-  bool Write(const W& msg, const WriteOptions& options) override {
-    CallOpSet<CallOpSendMessage> ops;
-    if (!ops.SendMessage(msg, options).ok()) return false;
+  bool Write(const W& msg, WriteOptions options) override {
+    CallOpSet<CallOpSendInitialMetadata, CallOpSendMessage,
+              CallOpClientSendClose>
+        ops;
+
+    if (options.is_last_message()) {
+      options.set_buffer_hint();
+      ops.ClientSendClose();
+    }
+    if (context_->initial_metadata_corked_) {
+      ops.SendInitialMetadata(context_->send_initial_metadata_,
+                              context_->initial_metadata_flags());
+      context_->set_initial_metadata_corked(false);
+    }
+    if (!ops.SendMessage(msg, options).ok()) {
+      return false;
+    }
+
     call_.PerformOps(&ops);
     return cq_.Pluck(&ops);
   }
@@ -423,7 +473,10 @@ class ServerWriter final : public ServerWriterInterface<W> {
   }
 
   using WriterInterface<W>::Write;
-  bool Write(const W& msg, const WriteOptions& options) override {
+  bool Write(const W& msg, WriteOptions options) override {
+    if (options.is_last_message()) {
+      options.set_buffer_hint();
+    }
     CallOpSet<CallOpSendInitialMetadata, CallOpSendMessage> ops;
     if (!ops.SendMessage(msg, options).ok()) {
       return false;
@@ -485,7 +538,10 @@ class ServerReaderWriterBody final {
     return call_->cq()->Pluck(&ops) && ops.got_message;
   }
 
-  bool Write(const W& msg, const WriteOptions& options) {
+  bool Write(const W& msg, WriteOptions options) {
+    if (options.is_last_message()) {
+      options.set_buffer_hint();
+    }
     CallOpSet<CallOpSendInitialMetadata, CallOpSendMessage> ops;
     if (!ops.SendMessage(msg, options).ok()) {
       return false;
@@ -523,7 +579,7 @@ class ServerReaderWriter final : public ServerReaderWriterInterface<W, R> {
   bool Read(R* msg) override { return body_.Read(msg); }
 
   using WriterInterface<W>::Write;
-  bool Write(const W& msg, const WriteOptions& options) override {
+  bool Write(const W& msg, WriteOptions options) override {
     return body_.Write(msg, options);
   }
 
@@ -562,8 +618,7 @@ class ServerUnaryStreamer final
   }
 
   using WriterInterface<ResponseType>::Write;
-  bool Write(const ResponseType& response,
-             const WriteOptions& options) override {
+  bool Write(const ResponseType& response, WriteOptions options) override {
     if (write_done_ || !read_done_) {
       return false;
     }
@@ -604,8 +659,7 @@ class ServerSplitStreamer final
   }
 
   using WriterInterface<ResponseType>::Write;
-  bool Write(const ResponseType& response,
-             const WriteOptions& options) override {
+  bool Write(const ResponseType& response, WriteOptions options) override {
     return read_done_ && body_.Write(response, options);
   }
 
diff --git a/include/grpc/impl/codegen/grpc_types.h b/include/grpc/impl/codegen/grpc_types.h
index 887c176f1a..833ccf3bfe 100644
--- a/include/grpc/impl/codegen/grpc_types.h
+++ b/include/grpc/impl/codegen/grpc_types.h
@@ -198,14 +198,14 @@ typedef struct {
 #define GRPC_ARG_HTTP2_WRITE_BUFFER_SIZE "grpc.http2.write_buffer_size"
 /** After a duration of this time the client pings the server to see if the
     transport is still alive. Int valued, seconds. */
-#define GRPC_ARG_HTTP2_KEEPALIVE_TIME "grpc.http2.keepalive_time"
+#define GRPC_ARG_CLIENT_KEEPALIVE_TIME_S "grpc.client_keepalive_time"
 /** After waiting for a duration of this time, if the client does not receive
     the ping ack, it will close the transport. Int valued, seconds. */
-#define GRPC_ARG_HTTP2_KEEPALIVE_TIMEOUT "grpc.http2.keepalive_timeout"
+#define GRPC_ARG_CLIENT_KEEPALIVE_TIMEOUT_S "grpc.client_keepalive_timeout"
 /** Is it permissible to send keepalive pings without any outstanding streams.
     Int valued, 0(false)/1(true). */
-#define GRPC_ARG_HTTP2_KEEPALIVE_PERMIT_WITHOUT_CALLS \
-  "grpc.http2.keepalive_permit_without_calls"
+#define GRPC_ARG_KEEPALIVE_PERMIT_WITHOUT_CALLS \
+  "grpc.keepalive_permit_without_calls"
 /** Default authority to pass if none specified on call construction. A string.
  * */
 #define GRPC_ARG_DEFAULT_AUTHORITY "grpc.default_authority"
@@ -316,13 +316,16 @@ typedef enum grpc_call_error {
 /** Signal that GRPC_INITIAL_METADATA_WAIT_FOR_READY was explicitly set
     by the calling application. */
 #define GRPC_INITIAL_METADATA_WAIT_FOR_READY_EXPLICITLY_SET (0x00000080u)
+/** Signal that the initial metadata should be corked */
+#define GRPC_INITIAL_METADATA_CORKED (0x00000100u)
 
 /** Mask of all valid flags */
-#define GRPC_INITIAL_METADATA_USED_MASK       \
-  (GRPC_INITIAL_METADATA_IDEMPOTENT_REQUEST | \
-   GRPC_INITIAL_METADATA_WAIT_FOR_READY |     \
-   GRPC_INITIAL_METADATA_CACHEABLE_REQUEST |  \
-   GRPC_INITIAL_METADATA_WAIT_FOR_READY_EXPLICITLY_SET)
+#define GRPC_INITIAL_METADATA_USED_MASK                  \
+  (GRPC_INITIAL_METADATA_IDEMPOTENT_REQUEST |            \
+   GRPC_INITIAL_METADATA_WAIT_FOR_READY |                \
+   GRPC_INITIAL_METADATA_CACHEABLE_REQUEST |             \
+   GRPC_INITIAL_METADATA_WAIT_FOR_READY_EXPLICITLY_SET | \
+   GRPC_INITIAL_METADATA_CORKED)
 
 /** A single metadata element */
 typedef struct grpc_metadata {
diff --git a/src/compiler/README.md b/src/compiler/README.md
index a2f49b3cd5..d5684af7ff 100644
--- a/src/compiler/README.md
+++ b/src/compiler/README.md
@@ -1,4 +1,4 @@
-#Overview
+# Overview
 
 This directory contains source code for gRPC protocol buffer compiler (*protoc*) plugins. Along with `protoc`,
 these plugins are used to generate gRPC client and server stubs from `.proto` files.
diff --git a/src/core/README.md b/src/core/README.md
index 44c6f24772..130d2652b3 100644
--- a/src/core/README.md
+++ b/src/core/README.md
@@ -1,4 +1,4 @@
-#Overview
+# Overview
 
 This directory contains source code for C library (a.k.a the *gRPC C core*) that provides all gRPC's core functionality through a low level API. Libraries in other languages in this repository (C++, Ruby,
 Python, PHP, NodeJS, Objective-C) are layered on top of this library.
diff --git a/src/core/ext/census/gen/README.md b/src/core/ext/census/gen/README.md
index fdbac1084c..d4612bc7c8 100644
--- a/src/core/ext/census/gen/README.md
+++ b/src/core/ext/census/gen/README.md
@@ -1,6 +1,6 @@
 Files generated for use by Census stats and trace recording subsystem.
 
-#Files
+# Files
 * census.pb.{h,c} - Generated from src/core/ext/census/census.proto, using the
   script `tools/codegen/core/gen_nano_proto.sh src/proto/census/census.proto
   $PWD/src/core/ext/census/gen src/core/ext/census/gen`
diff --git a/src/core/ext/transport/chttp2/transport/chttp2_transport.c b/src/core/ext/transport/chttp2/transport/chttp2_transport.c
index 8676a3752e..73f9454f7a 100644
--- a/src/core/ext/transport/chttp2/transport/chttp2_transport.c
+++ b/src/core/ext/transport/chttp2/transport/chttp2_transport.c
@@ -69,10 +69,16 @@
 #define MAX_WRITE_BUFFER_SIZE (64 * 1024 * 1024)
 #define DEFAULT_MAX_HEADER_LIST_SIZE (16 * 1024)
 
-#define DEFAULT_KEEPALIVE_TIME_SECOND INT_MAX
-#define DEFAULT_KEEPALIVE_TIMEOUT_SECOND 20
+#define DEFAULT_CLIENT_KEEPALIVE_TIME_S INT_MAX
+#define DEFAULT_CLIENT_KEEPALIVE_TIMEOUT_S 20
 #define DEFAULT_KEEPALIVE_PERMIT_WITHOUT_CALLS false
 
+static int g_default_client_keepalive_time_s = DEFAULT_CLIENT_KEEPALIVE_TIME_S;
+static int g_default_client_keepalive_timeout_s =
+    DEFAULT_CLIENT_KEEPALIVE_TIMEOUT_S;
+static bool g_default_keepalive_permit_without_calls =
+    DEFAULT_KEEPALIVE_PERMIT_WITHOUT_CALLS;
+
 #define MAX_CLIENT_STREAM_ID 0x7fffffffu
 int grpc_http_trace = 0;
 int grpc_flowctl_trace = 0;
@@ -142,6 +148,8 @@ static void send_ping_locked(grpc_exec_ctx *exec_ctx, grpc_chttp2_transport *t,
                              grpc_chttp2_ping_type ping_type,
                              grpc_closure *on_initiate,
                              grpc_closure *on_complete);
+static void retry_initiate_ping_locked(grpc_exec_ctx *exec_ctx, void *tp,
+                                       grpc_error *error);
 
 #define DEFAULT_MIN_TIME_BETWEEN_PINGS_MS 0
 #define DEFAULT_MAX_PINGS_BETWEEN_DATA 3
@@ -267,6 +275,8 @@ static void init_transport(grpc_exec_ctx *exec_ctx, grpc_chttp2_transport *t,
   grpc_closure_init(&t->destructive_reclaimer_locked,
                     destructive_reclaimer_locked, t,
                     grpc_combiner_scheduler(t->combiner, false));
+  grpc_closure_init(&t->retry_initiate_ping_locked, retry_initiate_ping_locked,
+                    t, grpc_combiner_scheduler(t->combiner, false));
   grpc_closure_init(&t->start_bdp_ping_locked, start_bdp_ping_locked, t,
                     grpc_combiner_scheduler(t->combiner, false));
   grpc_closure_init(&t->finish_bdp_ping_locked, finish_bdp_ping_locked, t,
@@ -345,15 +355,16 @@ static void init_transport(grpc_exec_ctx *exec_ctx, grpc_chttp2_transport *t,
 
   /* client-side keepalive setting */
   t->keepalive_time =
-      DEFAULT_KEEPALIVE_TIME_SECOND == INT_MAX
+      g_default_client_keepalive_time_s == INT_MAX
           ? gpr_inf_future(GPR_TIMESPAN)
-          : gpr_time_from_seconds(DEFAULT_KEEPALIVE_TIME_SECOND, GPR_TIMESPAN);
+          : gpr_time_from_seconds(g_default_client_keepalive_time_s,
+                                  GPR_TIMESPAN);
   t->keepalive_timeout =
-      DEFAULT_KEEPALIVE_TIMEOUT_SECOND == INT_MAX
+      g_default_client_keepalive_timeout_s == INT_MAX
           ? gpr_inf_future(GPR_TIMESPAN)
-          : gpr_time_from_seconds(DEFAULT_KEEPALIVE_TIMEOUT_SECOND,
+          : gpr_time_from_seconds(g_default_client_keepalive_timeout_s,
                                   GPR_TIMESPAN);
-  t->keepalive_permit_without_calls = DEFAULT_KEEPALIVE_PERMIT_WITHOUT_CALLS;
+  t->keepalive_permit_without_calls = g_default_keepalive_permit_without_calls;
 
   if (channel_args) {
     for (i = 0; i < channel_args->num_args; i++) {
@@ -403,24 +414,25 @@ static void init_transport(grpc_exec_ctx *exec_ctx, grpc_chttp2_transport *t,
         t->enable_bdp_probe = grpc_channel_arg_get_integer(
             &channel_args->args[i], (grpc_integer_options){1, 0, 1});
       } else if (0 == strcmp(channel_args->args[i].key,
-                             GRPC_ARG_HTTP2_KEEPALIVE_TIME)) {
+                             GRPC_ARG_CLIENT_KEEPALIVE_TIME_S)) {
         const int value = grpc_channel_arg_get_integer(
             &channel_args->args[i],
-            (grpc_integer_options){DEFAULT_KEEPALIVE_TIME_SECOND, 1, INT_MAX});
+            (grpc_integer_options){g_default_client_keepalive_time_s, 1,
+                                   INT_MAX});
         t->keepalive_time = value == INT_MAX
                                 ? gpr_inf_future(GPR_TIMESPAN)
                                 : gpr_time_from_seconds(value, GPR_TIMESPAN);
       } else if (0 == strcmp(channel_args->args[i].key,
-                             GRPC_ARG_HTTP2_KEEPALIVE_TIMEOUT)) {
+                             GRPC_ARG_CLIENT_KEEPALIVE_TIMEOUT_S)) {
         const int value = grpc_channel_arg_get_integer(
             &channel_args->args[i],
-            (grpc_integer_options){DEFAULT_KEEPALIVE_TIMEOUT_SECOND, 0,
+            (grpc_integer_options){g_default_client_keepalive_timeout_s, 0,
                                    INT_MAX});
         t->keepalive_timeout = value == INT_MAX
                                    ? gpr_inf_future(GPR_TIMESPAN)
                                    : gpr_time_from_seconds(value, GPR_TIMESPAN);
       } else if (0 == strcmp(channel_args->args[i].key,
-                             GRPC_ARG_HTTP2_KEEPALIVE_PERMIT_WITHOUT_CALLS)) {
+                             GRPC_ARG_KEEPALIVE_PERMIT_WITHOUT_CALLS)) {
         t->keepalive_permit_without_calls =
             (uint32_t)grpc_channel_arg_get_integer(
                 &channel_args->args[i], (grpc_integer_options){0, 0, 1});
@@ -474,6 +486,7 @@ static void init_transport(grpc_exec_ctx *exec_ctx, grpc_chttp2_transport *t,
 
   t->ping_state.pings_before_data_required =
       t->ping_policy.max_pings_without_data;
+  t->ping_state.is_delayed_ping_timer_set = false;
 
   /** Start client-side keepalive pings */
   if (t->is_client) {
@@ -1210,8 +1223,13 @@ static void perform_stream_op_locked(grpc_exec_ctx *exec_ctx, void *stream_op,
           }
         } else {
           GPR_ASSERT(s->id != 0);
-          grpc_chttp2_become_writable(exec_ctx, t, s,
-                                      GRPC_CHTTP2_STREAM_WRITE_INITIATE_COVERED,
+          grpc_chttp2_stream_write_type write_type =
+              GRPC_CHTTP2_STREAM_WRITE_INITIATE_COVERED;
+          if (op->send_message != NULL &&
+              (op->send_message->flags & GRPC_WRITE_BUFFER_HINT)) {
+            write_type = GRPC_CHTTP2_STREAM_WRITE_PIGGYBACK;
+          }
+          grpc_chttp2_become_writable(exec_ctx, t, s, write_type,
                                       "op.send_initial_metadata");
         }
       } else {
@@ -1394,6 +1412,13 @@ static void send_ping_locked(grpc_exec_ctx *exec_ctx, grpc_chttp2_transport *t,
   }
 }
 
+static void retry_initiate_ping_locked(grpc_exec_ctx *exec_ctx, void *tp,
+                                       grpc_error *error) {
+  grpc_chttp2_transport *t = tp;
+  t->ping_state.is_delayed_ping_timer_set = false;
+  grpc_chttp2_initiate_write(exec_ctx, t, false, "retry_send_ping");
+}
+
 void grpc_chttp2_ack_ping(grpc_exec_ctx *exec_ctx, grpc_chttp2_transport *t,
                           uint64_t id) {
   grpc_chttp2_ping_queue *pq =
@@ -2103,6 +2128,32 @@ static void finish_bdp_ping_locked(grpc_exec_ctx *exec_ctx, void *tp,
   GRPC_CHTTP2_UNREF_TRANSPORT(exec_ctx, t, "bdp_ping");
 }
 
+void grpc_chttp2_config_default_keepalive_args(grpc_channel_args *args) {
+  size_t i;
+  if (args) {
+    for (i = 0; i < args->num_args; i++) {
+      if (0 == strcmp(args->args[i].key, GRPC_ARG_CLIENT_KEEPALIVE_TIME_S)) {
+        g_default_client_keepalive_time_s = grpc_channel_arg_get_integer(
+            &args->args[i], (grpc_integer_options){
+                                g_default_client_keepalive_time_s, 1, INT_MAX});
+      } else if (0 == strcmp(args->args[i].key,
+                             GRPC_ARG_CLIENT_KEEPALIVE_TIMEOUT_S)) {
+        g_default_client_keepalive_timeout_s = grpc_channel_arg_get_integer(
+            &args->args[i],
+            (grpc_integer_options){g_default_client_keepalive_timeout_s, 0,
+                                   INT_MAX});
+      } else if (0 == strcmp(args->args[i].key,
+                             GRPC_ARG_KEEPALIVE_PERMIT_WITHOUT_CALLS)) {
+        g_default_keepalive_permit_without_calls =
+            (uint32_t)grpc_channel_arg_get_integer(
+                &args->args[i],
+                (grpc_integer_options){g_default_keepalive_permit_without_calls,
+                                       0, 1});
+      }
+    }
+  }
+}
+
 static void init_keepalive_ping_locked(grpc_exec_ctx *exec_ctx, void *arg,
                                        grpc_error *error) {
   grpc_chttp2_transport *t = arg;
@@ -2146,9 +2197,7 @@ static void finish_keepalive_ping_locked(grpc_exec_ctx *exec_ctx, void *arg,
       grpc_timer_init(
           exec_ctx, &t->keepalive_ping_timer,
           gpr_time_add(gpr_now(GPR_CLOCK_MONOTONIC), t->keepalive_time),
-          grpc_closure_create(init_keepalive_ping_locked, t,
-                              grpc_combiner_scheduler(t->combiner, false)),
-          gpr_now(GPR_CLOCK_MONOTONIC));
+          &t->init_keepalive_ping_locked, gpr_now(GPR_CLOCK_MONOTONIC));
     }
   }
   GRPC_CHTTP2_UNREF_TRANSPORT(exec_ctx, t, "keepalive ping end");
diff --git a/src/core/ext/transport/chttp2/transport/frame_ping.c b/src/core/ext/transport/chttp2/transport/frame_ping.c
index de8462a17e..46dafdb62f 100644
--- a/src/core/ext/transport/chttp2/transport/frame_ping.c
+++ b/src/core/ext/transport/chttp2/transport/frame_ping.c
@@ -40,6 +40,8 @@
 #include <grpc/support/log.h>
 #include <grpc/support/string_util.h>
 
+static bool g_disable_ping_ack = false;
+
 grpc_slice grpc_chttp2_ping_create(uint8_t ack, uint64_t opaque_8bytes) {
   grpc_slice slice = grpc_slice_malloc(9 + 8);
   uint8_t *p = GRPC_SLICE_START_PTR(slice);
@@ -101,15 +103,21 @@ grpc_error *grpc_chttp2_ping_parser_parse(grpc_exec_ctx *exec_ctx, void *parser,
     if (p->is_ack) {
       grpc_chttp2_ack_ping(exec_ctx, t, p->opaque_8bytes);
     } else {
-      if (t->ping_ack_count == t->ping_ack_capacity) {
-        t->ping_ack_capacity = GPR_MAX(t->ping_ack_capacity * 3 / 2, 3);
-        t->ping_acks = gpr_realloc(
-            t->ping_acks, t->ping_ack_capacity * sizeof(*t->ping_acks));
+      if (!g_disable_ping_ack) {
+        if (t->ping_ack_count == t->ping_ack_capacity) {
+          t->ping_ack_capacity = GPR_MAX(t->ping_ack_capacity * 3 / 2, 3);
+          t->ping_acks = gpr_realloc(
+              t->ping_acks, t->ping_ack_capacity * sizeof(*t->ping_acks));
+        }
+        t->ping_acks[t->ping_ack_count++] = p->opaque_8bytes;
+        grpc_chttp2_initiate_write(exec_ctx, t, false, "ping response");
       }
-      t->ping_acks[t->ping_ack_count++] = p->opaque_8bytes;
-      grpc_chttp2_initiate_write(exec_ctx, t, false, "ping response");
     }
   }
 
   return GRPC_ERROR_NONE;
 }
+
+void grpc_set_disable_ping_ack(bool disable_ping_ack) {
+  g_disable_ping_ack = disable_ping_ack;
+}
diff --git a/src/core/ext/transport/chttp2/transport/frame_ping.h b/src/core/ext/transport/chttp2/transport/frame_ping.h
index ef642465d7..01983d2b12 100644
--- a/src/core/ext/transport/chttp2/transport/frame_ping.h
+++ b/src/core/ext/transport/chttp2/transport/frame_ping.h
@@ -53,4 +53,7 @@ grpc_error *grpc_chttp2_ping_parser_parse(grpc_exec_ctx *exec_ctx, void *parser,
                                           grpc_chttp2_stream *s,
                                           grpc_slice slice, int is_last);
 
+/* Test-only function for disabling ping ack */
+void grpc_set_disable_ping_ack(bool disable_ping_ack);
+
 #endif /* GRPC_CORE_EXT_TRANSPORT_CHTTP2_TRANSPORT_FRAME_PING_H */
diff --git a/src/core/ext/transport/chttp2/transport/internal.h b/src/core/ext/transport/chttp2/transport/internal.h
index 3c56c21599..8b718e963c 100644
--- a/src/core/ext/transport/chttp2/transport/internal.h
+++ b/src/core/ext/transport/chttp2/transport/internal.h
@@ -102,6 +102,8 @@ typedef struct {
 typedef struct {
   gpr_timespec last_ping_sent_time;
   int pings_before_data_required;
+  grpc_timer delayed_ping_timer;
+  bool is_delayed_ping_timer_set;
 } grpc_chttp2_repeated_ping_state;
 
 /* deframer state for the overall http2 stream of bytes */
@@ -308,6 +310,7 @@ struct grpc_chttp2_transport {
   grpc_chttp2_repeated_ping_policy ping_policy;
   grpc_chttp2_repeated_ping_state ping_state;
   uint64_t ping_ctr; /* unique id for pings */
+  grpc_closure retry_initiate_ping_locked;
 
   /** ping acks */
   size_t ping_ack_count;
@@ -827,4 +830,8 @@ void grpc_chttp2_fail_pending_writes(grpc_exec_ctx *exec_ctx,
 
 uint32_t grpc_chttp2_target_incoming_window(grpc_chttp2_transport *t);
 
+/** Set the default keepalive configurations, must only be called at
+    initialization */
+void grpc_chttp2_config_default_keepalive_args(grpc_channel_args *args);
+
 #endif /* GRPC_CORE_EXT_TRANSPORT_CHTTP2_TRANSPORT_INTERNAL_H */
diff --git a/src/core/ext/transport/chttp2/transport/writing.c b/src/core/ext/transport/chttp2/transport/writing.c
index 2b9d93cae7..0869056f56 100644
--- a/src/core/ext/transport/chttp2/transport/writing.c
+++ b/src/core/ext/transport/chttp2/transport/writing.c
@@ -101,6 +101,14 @@ static void maybe_initiate_ping(grpc_exec_ctx *exec_ctx,
               "Ping delayed [%p]: not enough time elapsed since last ping",
               t->peer_string);
     }
+    if (!t->ping_state.is_delayed_ping_timer_set) {
+      t->ping_state.is_delayed_ping_timer_set = true;
+      grpc_timer_init(exec_ctx, &t->ping_state.delayed_ping_timer,
+                      gpr_time_add(t->ping_state.last_ping_sent_time,
+                                   t->ping_policy.min_time_between_pings),
+                      &t->retry_initiate_ping_locked,
+                      gpr_now(GPR_CLOCK_MONOTONIC));
+    }
     return;
   }
   /* coalesce equivalent pings into this one */
diff --git a/src/core/lib/iomgr/resource_quota.c b/src/core/lib/iomgr/resource_quota.c
index 511ffdcdf1..8dcd80d001 100644
--- a/src/core/lib/iomgr/resource_quota.c
+++ b/src/core/lib/iomgr/resource_quota.c
@@ -279,11 +279,17 @@ static void rq_step_sched(grpc_exec_ctx *exec_ctx,
 /* update the atomically available resource estimate - use no barriers since
    timeliness of delivery really doesn't matter much */
 static void rq_update_estimate(grpc_resource_quota *resource_quota) {
+  gpr_atm memory_usage_estimation = MEMORY_USAGE_ESTIMATION_MAX;
+  if (resource_quota->size != 0) {
+    memory_usage_estimation =
+        GPR_CLAMP((gpr_atm)((1.0 -
+                             ((double)resource_quota->free_pool) /
+                                 ((double)resource_quota->size)) *
+                            MEMORY_USAGE_ESTIMATION_MAX),
+                  0, MEMORY_USAGE_ESTIMATION_MAX);
+  }
   gpr_atm_no_barrier_store(&resource_quota->memory_usage_estimation,
-                           (gpr_atm)((1.0 -
-                                      ((double)resource_quota->free_pool) /
-                                          ((double)resource_quota->size)) *
-                                     MEMORY_USAGE_ESTIMATION_MAX));
+                           memory_usage_estimation);
 }
 
 /* returns true if all allocations are completed */
diff --git a/src/core/lib/surface/call.c b/src/core/lib/surface/call.c
index 895a8a3b06..9342c5f8e9 100644
--- a/src/core/lib/surface/call.c
+++ b/src/core/lib/surface/call.c
@@ -625,7 +625,7 @@ static bool get_final_status_from(
     void (*set_value)(grpc_status_code code, void *user_data),
     void *set_value_user_data, grpc_slice *details) {
   grpc_status_code code;
-  grpc_slice slice;
+  grpc_slice slice = grpc_empty_slice();
   grpc_error_get_status(error, call->send_deadline, &code, &slice, NULL);
   if (code == GRPC_STATUS_OK && !allow_ok_status) {
     return false;
diff --git a/src/cpp/README.md b/src/cpp/README.md
index d9b521317a..e9ef489a7c 100644
--- a/src/cpp/README.md
+++ b/src/cpp/README.md
@@ -1,17 +1,17 @@
 
-#Overview
+# Overview
 
 This directory contains source code for C++ implementation of gRPC.
 
-#Pre-requisites
+# Pre-requisites
 
-##Linux
+## Linux
 
 ```sh
  $ [sudo] apt-get install build-essential autoconf libtool
 ```
 
-##Mac OSX
+## Mac OSX
 
 For a Mac system, git is not available by default. You will first need to
 install Xcode from the Mac AppStore and then run the following command from a
@@ -21,7 +21,7 @@ terminal:
  $ [sudo] xcode-select --install
 ```
 
-##Protoc
+## Protoc
 
 By default gRPC uses [protocol buffers](https://github.com/google/protobuf),
 you will need the `protoc` compiler to generate stub server and client code.
@@ -39,12 +39,12 @@ $ sudo make install   # 'make' should have been run by core grpc
 Alternatively, you can download `protoc` binaries from
 [the protocol buffers Github repository](https://github.com/google/protobuf/releases).
 
-#Installation
+# Installation
 
 Currently to install gRPC for C++, you need to build from source as described
 below.
 
-#Build from Source
+# Build from Source
 
 ```sh
  $ git clone -b $(curl -L http://grpc.io/release) https://github.com/grpc/grpc
@@ -54,7 +54,7 @@ below.
  $ [sudo] make install
 ```
 
-#Documentation
+# Documentation
 
 You can find out how to build and run our simplest gRPC C++ example in our
 [C++ quick start](../../examples/cpp).
diff --git a/src/cpp/client/client_context.cc b/src/cpp/client/client_context.cc
index c073741dac..3d884cf62e 100644
--- a/src/cpp/client/client_context.cc
+++ b/src/cpp/client/client_context.cc
@@ -67,7 +67,8 @@ ClientContext::ClientContext()
       call_canceled_(false),
       deadline_(gpr_inf_future(GPR_CLOCK_REALTIME)),
       census_context_(nullptr),
-      propagate_from_call_(nullptr) {
+      propagate_from_call_(nullptr),
+      initial_metadata_corked_(false) {
   g_client_callbacks->DefaultConstructor(this);
 }
 
diff --git a/src/objective-c/GRPCClient/GRPCCall.m b/src/objective-c/GRPCClient/GRPCCall.m
index 44393f6b99..051138ea4d 100644
--- a/src/objective-c/GRPCClient/GRPCCall.m
+++ b/src/objective-c/GRPCClient/GRPCCall.m
@@ -36,6 +36,7 @@
 #include <grpc/grpc.h>
 #include <grpc/support/time.h>
 #import <RxLibrary/GRXConcurrentWriteable.h>
+#import <RxLibrary/GRXImmediateSingleWriter.h>
 
 #import "private/GRPCConnectivityMonitor.h"
 #import "private/GRPCHost.h"
@@ -45,6 +46,11 @@
 #import "private/NSDictionary+GRPC.h"
 #import "private/NSError+GRPC.h"
 
+// At most 6 ops can be in an op batch for a client: SEND_INITIAL_METADATA,
+// SEND_MESSAGE, SEND_CLOSE_FROM_CLIENT, RECV_INITIAL_METADATA, RECV_MESSAGE,
+// and RECV_STATUS_ON_CLIENT.
+NSInteger kMaxClientBatch = 6;
+
 NSString * const kGRPCHeadersKey = @"io.grpc.HeadersKey";
 NSString * const kGRPCTrailersKey = @"io.grpc.TrailersKey";
 static NSMutableDictionary *callFlags;
@@ -100,6 +106,13 @@ static NSMutableDictionary *callFlags;
   GRPCCall *_retainSelf;
 
   GRPCRequestHeaders *_requestHeaders;
+
+  // In the case that the call is a unary call (i.e. the writer to GRPCCall is of type
+  // GRXImmediateSingleWriter), GRPCCall will delay sending ops (not send them to C core
+  // immediately) and buffer them into a batch _unaryOpBatch. The batch is sent to C core when
+  // the SendClose op is added.
+  BOOL _unaryCall;
+  NSMutableArray *_unaryOpBatch;
 }
 
 @synthesize state = _state;
@@ -157,6 +170,11 @@ static NSMutableDictionary *callFlags;
     _requestWriter = requestWriter;
 
     _requestHeaders = [[GRPCRequestHeaders alloc] initWithCall:self];
+
+    if ([requestWriter isKindOfClass:[GRXImmediateSingleWriter class]]) {
+      _unaryCall = YES;
+      _unaryOpBatch = [NSMutableArray arrayWithCapacity:kMaxClientBatch];
+    }
   }
   return self;
 }
@@ -165,6 +183,9 @@ static NSMutableDictionary *callFlags;
 
 - (void)finishWithError:(NSError *)errorOrNil {
   @synchronized(self) {
+    if (_state == GRXWriterStateFinished) {
+      return;
+    }
     _state = GRXWriterStateFinished;
   }
 
@@ -254,15 +275,22 @@ static NSMutableDictionary *callFlags;
 
 - (void)sendHeaders:(NSDictionary *)headers {
   // TODO(jcanizales): Add error handlers for async failures
-  [_wrappedCall startBatchWithOperations:@[[[GRPCOpSendMetadata alloc] initWithMetadata:headers
-                                                                                  flags:[GRPCCall callFlagsForHost:_host path:_path]
-                                                                                handler:nil]]];
+  GRPCOpSendMetadata *op = [[GRPCOpSendMetadata alloc] initWithMetadata:headers
+                                                                  flags:[GRPCCall callFlagsForHost:_host path:_path]
+                                                                handler:nil];  // No clean-up needed after SEND_INITIAL_METADATA
+  if (!_unaryCall) {
+    [_wrappedCall startBatchWithOperations:@[op]];
+  } else {
+    [_unaryOpBatch addObject:op];
+  }
 }
 
 #pragma mark GRXWriteable implementation
 
 // Only called from the call queue. The error handler will be called from the
 // network queue if the write didn't succeed.
+// If the call is a unary call, parameter \a errorHandler will be ignored and
+// the error handler of GRPCOpSendClose will be executed in case of error.
 - (void)writeMessage:(NSData *)message withErrorHandler:(void (^)())errorHandler {
 
   __weak GRPCCall *weakSelf = self;
@@ -275,9 +303,17 @@ static NSMutableDictionary *callFlags;
       }
     }
   };
-  [_wrappedCall startBatchWithOperations:@[[[GRPCOpSendMessage alloc] initWithMessage:message
-                                                                              handler:resumingHandler]]
-                            errorHandler:errorHandler];
+
+  GRPCOpSendMessage *op = [[GRPCOpSendMessage alloc] initWithMessage:message
+                                                             handler:resumingHandler];
+  if (!_unaryCall) {
+    [_wrappedCall startBatchWithOperations:@[op]
+                              errorHandler:errorHandler];
+  } else {
+    // Ignored errorHandler since it is the same as the one for GRPCOpSendClose.
+    // TODO (mxyan): unify the error handlers of all Ops into a single closure.
+    [_unaryOpBatch addObject:op];
+  }
 }
 
 - (void)writeValue:(id)value {
@@ -302,8 +338,14 @@ static NSMutableDictionary *callFlags;
 // Only called from the call queue. The error handler will be called from the
 // network queue if the requests stream couldn't be closed successfully.
 - (void)finishRequestWithErrorHandler:(void (^)())errorHandler {
-  [_wrappedCall startBatchWithOperations:@[[[GRPCOpSendClose alloc] init]]
-                            errorHandler:errorHandler];
+  if (!_unaryCall) {
+    [_wrappedCall startBatchWithOperations:@[[[GRPCOpSendClose alloc] init]]
+                              errorHandler:errorHandler];
+  } else {
+    [_unaryOpBatch addObject:[[GRPCOpSendClose alloc] init]];
+    [_wrappedCall startBatchWithOperations:_unaryOpBatch
+                              errorHandler:errorHandler];
+  }
 }
 
 - (void)writesFinishedWithError:(NSError *)errorOrNil {
diff --git a/src/objective-c/GRPCClient/internal_testing/GRPCCall+InternalTests.h b/src/objective-c/GRPCClient/internal_testing/GRPCCall+InternalTests.h
new file mode 100644
index 0000000000..29bd12f0cf
--- /dev/null
+++ b/src/objective-c/GRPCClient/internal_testing/GRPCCall+InternalTests.h
@@ -0,0 +1,61 @@
+/*
+ *
+ * Copyright 2017, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#ifdef GRPC_TEST_OBJC
+
+#import "../GRPCCall.h"
+
+/**
+ * Methods used for gRPC internal tests. DO NOT USE.
+ */
+@interface GRPCCall (InternalTests)
+
+/**
+ * Enables logging of op batches. Memory consumption increases as more ops are logged.
+ *
+ * This function is for internal testing of gRPC only. It is not part of gRPC's public interface.
+ * Do not use in production. To enable, set the preprocessor flag GRPC_TEST_OBJC.
+ */
++ (void)enableOpBatchLog:(BOOL)enabled;
+
+/**
+ * Obtain the logged op batches. Invoking this method will clean the log.
+ *
+ * This function is for internal testing of gRPC only. It is not part of gRPC's public interface.
+ * Do not use in production. To enable, set the preprocessor flag GRPC_TEST_OBJC.
+ */
++ (NSArray *)obtainAndCleanOpBatchLog;
+
+@end
+
+#endif
diff --git a/src/objective-c/GRPCClient/internal_testing/GRPCCall+InternalTests.m b/src/objective-c/GRPCClient/internal_testing/GRPCCall+InternalTests.m
new file mode 100644
index 0000000000..6371df6739
--- /dev/null
+++ b/src/objective-c/GRPCClient/internal_testing/GRPCCall+InternalTests.m
@@ -0,0 +1,52 @@
+/*
+ *
+ * Copyright 2017, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#ifdef GRPC_TEST_OBJC
+
+#import "GRPCCall+InternalTests.h"
+
+#import "../private/GRPCOpBatchLog.h"
+
+@implementation GRPCCall (InternalTests)
+
++ (void)enableOpBatchLog:(BOOL)enabled {
+  [GRPCOpBatchLog enableOpBatchLog:enabled];
+}
+
++ (NSArray *)obtainAndCleanOpBatchLog {
+  return [GRPCOpBatchLog obtainAndCleanOpBatchLog];
+}
+
+@end
+
+#endif
diff --git a/src/objective-c/GRPCClient/private/GRPCOpBatchLog.h b/src/objective-c/GRPCClient/private/GRPCOpBatchLog.h
new file mode 100644
index 0000000000..753c4cfee6
--- /dev/null
+++ b/src/objective-c/GRPCClient/private/GRPCOpBatchLog.h
@@ -0,0 +1,59 @@
+/*
+ *
+ * Copyright 2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+
+#ifdef GRPC_TEST_OBJC
+
+/**
+ * Logs the op batches of a client. Used for testing.
+ */
+@interface GRPCOpBatchLog : NSObject
+
+/**
+ * Enables logging of op batches. Memory consumption increases as more ops are logged.
+ */
++ (void)enableOpBatchLog:(BOOL)enabled;
+
+/**
+ * Add an op batch to log.
+ */
++ (void)addOpBatchToLog:(NSArray *)batch;
+
+/**
+ * Obtain the logged op batches. Invoking this method will clean the log.
+ */
++ (NSArray *)obtainAndCleanOpBatchLog;
+
+@end
+
+#endif
diff --git a/src/objective-c/GRPCClient/private/GRPCOpBatchLog.m b/src/objective-c/GRPCClient/private/GRPCOpBatchLog.m
new file mode 100644
index 0000000000..4b40baf122
--- /dev/null
+++ b/src/objective-c/GRPCClient/private/GRPCOpBatchLog.m
@@ -0,0 +1,72 @@
+/*
+ *
+ * Copyright 2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#ifdef GRPC_TEST_OBJC
+
+#import "GRPCOpBatchLog.h"
+
+static NSMutableArray *opBatchLog = nil;
+
+@implementation GRPCOpBatchLog
+
++ (void)enableOpBatchLog:(BOOL)enabled {
+  @synchronized (opBatchLog) {
+    if (enabled) {
+      if (!opBatchLog) {
+        opBatchLog = [NSMutableArray array];
+      }
+    } else {
+      if (opBatchLog) {
+        opBatchLog = nil;
+      }
+    }
+  }
+}
+
++ (void)addOpBatchToLog:(NSArray *)batch {
+  @synchronized (opBatchLog) {
+    [opBatchLog addObject:batch];
+  }
+}
+
++ (NSArray *)obtainAndCleanOpBatchLog {
+  @synchronized (opBatchLog) {
+    NSArray *out = opBatchLog;
+    opBatchLog = [NSMutableArray array];
+    return out;
+  }
+}
+
+@end
+
+#endif
diff --git a/src/objective-c/GRPCClient/private/GRPCWrappedCall.m b/src/objective-c/GRPCClient/private/GRPCWrappedCall.m
index 9f1901ab30..46e9fee7e1 100644
--- a/src/objective-c/GRPCClient/private/GRPCWrappedCall.m
+++ b/src/objective-c/GRPCClient/private/GRPCWrappedCall.m
@@ -44,6 +44,8 @@
 #import "NSData+GRPC.h"
 #import "NSError+GRPC.h"
 
+#import "GRPCOpBatchLog.h"
+
 @implementation GRPCOperation {
 @protected
   // Most operation subclasses don't set any flags in the grpc_op, and rely on the flag member being
@@ -274,6 +276,12 @@
 }
 
 - (void)startBatchWithOperations:(NSArray *)operations errorHandler:(void (^)())errorHandler {
+  // Keep logs of op batches when we are running tests. Disabled when in production for improved
+  // performance.
+#ifdef GRPC_TEST_OBJC
+  [GRPCOpBatchLog addOpBatchToLog:operations];
+#endif
+
   size_t nops = operations.count;
   grpc_op *ops_array = gpr_malloc(nops * sizeof(grpc_op));
   size_t i = 0;
diff --git a/src/objective-c/RxLibrary/GRXImmediateSingleWriter.h b/src/objective-c/RxLibrary/GRXImmediateSingleWriter.h
new file mode 100644
index 0000000000..0ec788f756
--- /dev/null
+++ b/src/objective-c/RxLibrary/GRXImmediateSingleWriter.h
@@ -0,0 +1,50 @@
+/*
+ *
+ * Copyright 2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#import <Foundation/Foundation.h>
+
+#import "GRXImmediateWriter.h"
+
+/**
+ * Utility to construct GRXWriter instances from values that are immediately available when
+ * required.
+ */
+@interface GRXImmediateSingleWriter : GRXImmediateWriter
+
+/**
+ * Returns a writer that sends the passed value to its writeable and then finishes (releasing the
+ * value).
+ */
++ (GRXWriter *)writerWithValue:(id)value;
+
+@end
diff --git a/src/objective-c/RxLibrary/GRXImmediateSingleWriter.m b/src/objective-c/RxLibrary/GRXImmediateSingleWriter.m
new file mode 100644
index 0000000000..0096c996d4
--- /dev/null
+++ b/src/objective-c/RxLibrary/GRXImmediateSingleWriter.m
@@ -0,0 +1,89 @@
+/*
+ *
+ * Copyright 2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#import "GRXImmediateSingleWriter.h"
+
+@implementation GRXImmediateSingleWriter {
+  id _value;
+  id<GRXWriteable> _writeable;
+}
+
+@synthesize state = _state;
+
+- (instancetype)initWithValue:(id)value {
+  if (self = [super init]) {
+    _value = value;
+    _state = GRXWriterStateNotStarted;
+  }
+  return self;
+}
+
++ (GRXWriter *)writerWithValue:(id)value {
+  return [[self alloc] initWithValue:value];
+}
+
+- (void)startWithWriteable:(id<GRXWriteable>)writeable {
+  _state = GRXWriterStateStarted;
+  _writeable = writeable;
+  [writeable writeValue:_value];
+  [self finish];
+}
+
+- (void)finish {
+  _state = GRXWriterStateFinished;
+  _value = nil;
+  id<GRXWriteable> writeable = _writeable;
+  _writeable = nil;
+  [writeable writesFinishedWithError:nil];
+}
+
+// Overwrite the setter to disallow manual state transition. The getter
+// of _state is synthesized.
+- (void)setState:(GRXWriterState)newState {
+  // Manual state transition is not allowed
+  return;
+}
+
+// Overrides [requestWriter(Transformations):map:] for Protocol Buffers
+// encoding.
+// We need the return value of this map to be a GRXImmediateSingleWriter but
+// the original \a map function returns a new Writer of another type. So we
+// need to override this function here.
+- (GRXWriter *)map:(id (^)(id))map {
+  // Since _value is available when creating the object, we can simply
+  // apply the map and store the output.
+  _value = map(_value);
+  return self;
+}
+
+@end
diff --git a/src/objective-c/RxLibrary/GRXWriter+Immediate.m b/src/objective-c/RxLibrary/GRXWriter+Immediate.m
index 1d55eb3529..ea6e681406 100644
--- a/src/objective-c/RxLibrary/GRXWriter+Immediate.m
+++ b/src/objective-c/RxLibrary/GRXWriter+Immediate.m
@@ -34,6 +34,7 @@
 #import "GRXWriter+Immediate.h"
 
 #import "GRXImmediateWriter.h"
+#import "GRXImmediateSingleWriter.h"
 
 @implementation GRXWriter (Immediate)
 
@@ -50,7 +51,7 @@
 }
 
 + (instancetype)writerWithValue:(id)value {
-  return [GRXImmediateWriter writerWithValue:value];
+  return [GRXImmediateSingleWriter writerWithValue:value];
 }
 
 + (instancetype)writerWithError:(NSError *)error {
diff --git a/src/objective-c/tests/GRPCClientTests.m b/src/objective-c/tests/GRPCClientTests.m
index 0b72a75f3d..76c15003f6 100644
--- a/src/objective-c/tests/GRPCClientTests.m
+++ b/src/objective-c/tests/GRPCClientTests.m
@@ -38,6 +38,7 @@
 #import <GRPCClient/GRPCCall+ChannelArg.h>
 #import <GRPCClient/GRPCCall+OAuth2.h>
 #import <GRPCClient/GRPCCall+Tests.h>
+#import <GRPCClient/internal_testing/GRPCCall+InternalTests.h>
 #import <ProtoRPC/ProtoMethod.h>
 #import <RemoteTest/Messages.pbobjc.h>
 #import <RxLibrary/GRXWriteable.h>
diff --git a/src/objective-c/tests/InteropTests.m b/src/objective-c/tests/InteropTests.m
index d964f53e8e..9105356869 100644
--- a/src/objective-c/tests/InteropTests.m
+++ b/src/objective-c/tests/InteropTests.m
@@ -38,6 +38,7 @@
 #import <Cronet/Cronet.h>
 #import <GRPCClient/GRPCCall+ChannelArg.h>
 #import <GRPCClient/GRPCCall+Tests.h>
+#import <GRPCClient/internal_testing/GRPCCall+InternalTests.h>
 #import <GRPCClient/GRPCCall+Cronet.h>
 #import <ProtoRPC/ProtoRPC.h>
 #import <RemoteTest/Messages.pbobjc.h>
@@ -45,6 +46,8 @@
 #import <RemoteTest/Test.pbrpc.h>
 #import <RxLibrary/GRXBufferedPipe.h>
 #import <RxLibrary/GRXWriter+Immediate.h>
+#import <grpc/support/log.h>
+#import <grpc/grpc.h>
 
 #define TEST_TIMEOUT 32
 
@@ -97,15 +100,6 @@
   return 0;
 }
 
-+ (void)setUp {
-#ifdef GRPC_COMPILE_WITH_CRONET
-  // Cronet setup
-  [Cronet setHttp2Enabled:YES];
-  [Cronet start];
-  [GRPCCall useCronetWithEngine:[Cronet getGlobalEngine]];
-#endif
-}
-
 - (void)setUp {
   self.continueAfterFailure = NO;
 
@@ -155,6 +149,44 @@
   [self waitForExpectationsWithTimeout:TEST_TIMEOUT handler:nil];
 }
 
+- (void)testPacketCoalescing {
+  XCTAssertNotNil(self.class.host);
+  __weak XCTestExpectation *expectation = [self expectationWithDescription:@"LargeUnary"];
+
+  RMTSimpleRequest *request = [RMTSimpleRequest message];
+  request.responseType = RMTPayloadType_Compressable;
+  request.responseSize = 10;
+  request.payload.body = [NSMutableData dataWithLength:10];
+
+  [GRPCCall enableOpBatchLog:YES];
+  [_service unaryCallWithRequest:request handler:^(RMTSimpleResponse *response, NSError *error) {
+    XCTAssertNil(error, @"Finished with unexpected error: %@", error);
+
+    RMTSimpleResponse *expectedResponse = [RMTSimpleResponse message];
+    expectedResponse.payload.type = RMTPayloadType_Compressable;
+    expectedResponse.payload.body = [NSMutableData dataWithLength:10];
+    XCTAssertEqualObjects(response, expectedResponse);
+
+    // The test is a success if there is a batch of exactly 3 ops (SEND_INITIAL_METADATA,
+    // SEND_MESSAGE, SEND_CLOSE_FROM_CLIENT). Without packet coalescing each batch of ops contains
+    // only one op.
+    NSArray *opBatches = [GRPCCall obtainAndCleanOpBatchLog];
+    const NSInteger kExpectedOpBatchSize = 3;
+    for (NSObject *o in opBatches) {
+      if ([o isKindOfClass:[NSArray class]]) {
+        NSArray *batch = (NSArray *)o;
+        if ([batch count] == kExpectedOpBatchSize) {
+          [expectation fulfill];
+          break;
+        }
+      }
+    }
+  }];
+
+  [self waitForExpectationsWithTimeout:16 handler:nil];
+  [GRPCCall enableOpBatchLog:NO];
+}
+
 - (void)test4MBResponsesAreAccepted {
   XCTAssertNotNil(self.class.host);
   __weak XCTestExpectation *expectation = [self expectationWithDescription:@"MaxResponseSize"];
diff --git a/src/objective-c/tests/InteropTestsLocalCleartext.m b/src/objective-c/tests/InteropTestsLocalCleartext.m
index 4987660808..94cdf85965 100644
--- a/src/objective-c/tests/InteropTestsLocalCleartext.m
+++ b/src/objective-c/tests/InteropTestsLocalCleartext.m
@@ -32,6 +32,7 @@
  */
 
 #import <GRPCClient/GRPCCall+Tests.h>
+#import <GRPCClient/internal_testing/GRPCCall+InternalTests.h>
 
 #import "InteropTests.h"
 
diff --git a/src/objective-c/tests/InteropTestsLocalSSL.m b/src/objective-c/tests/InteropTestsLocalSSL.m
index 934d500abc..3c78b65ede 100644
--- a/src/objective-c/tests/InteropTestsLocalSSL.m
+++ b/src/objective-c/tests/InteropTestsLocalSSL.m
@@ -32,6 +32,7 @@
  */
 
 #import <GRPCClient/GRPCCall+Tests.h>
+#import <GRPCClient/internal_testing/GRPCCall+InternalTests.h>
 
 #import "InteropTests.h"
 
diff --git a/src/objective-c/tests/InteropTestsRemote.m b/src/objective-c/tests/InteropTestsRemote.m
index 9fb30aa43d..ff1193302b 100644
--- a/src/objective-c/tests/InteropTestsRemote.m
+++ b/src/objective-c/tests/InteropTestsRemote.m
@@ -32,6 +32,7 @@
  */
 
 #import <GRPCClient/GRPCCall+Tests.h>
+#import <GRPCClient/internal_testing/GRPCCall+InternalTests.h>
 
 #import "InteropTests.h"
 
diff --git a/src/objective-c/tests/InteropTestsRemoteWithCronet/InteropTestsRemoteWithCronet.m b/src/objective-c/tests/InteropTestsRemoteWithCronet/InteropTestsRemoteWithCronet.m
index 005bac0a0d..9edfbc2639 100644
--- a/src/objective-c/tests/InteropTestsRemoteWithCronet/InteropTestsRemoteWithCronet.m
+++ b/src/objective-c/tests/InteropTestsRemoteWithCronet/InteropTestsRemoteWithCronet.m
@@ -32,6 +32,10 @@
  */
 
 #import <GRPCClient/GRPCCall+Tests.h>
+#import <GRPCClient/internal_testing/GRPCCall+InternalTests.h>
+
+#import <Cronet/Cronet.h>
+#import <GRPCClient/GRPCCall+Cronet.h>
 
 #import "InteropTests.h"
 
diff --git a/src/objective-c/tests/Podfile b/src/objective-c/tests/Podfile
index 3760330be9..8f1cb041d8 100644
--- a/src/objective-c/tests/Podfile
+++ b/src/objective-c/tests/Podfile
@@ -97,15 +97,20 @@ post_install do |installer|
         # GPR_UNREACHABLE_CODE causes "Control may reach end of non-void
         # function" warning
         config.build_settings['GCC_WARN_ABOUT_RETURN_TYPE'] = 'NO'
+        config.build_settings['GCC_PREPROCESSOR_DEFINITIONS'] = '$(inherited) COCOAPODS=1 GRPC_CRONET_WITH_PACKET_COALESCING=1'
       end
     end
 
     # Activate Cronet for the dedicated build configuration 'Cronet', which will be used solely by
     # the test target 'InteropTestsRemoteWithCronet'
+    # Activate GRPCCall+InternalTests functions for the dedicated build configuration 'Test', which will
+    # be used by all test targets using it.
     if target.name == 'gRPC'
       target.build_configurations.each do |config|
         if config.name == 'Cronet'
-          config.build_settings['GCC_PREPROCESSOR_DEFINITIONS'] = '$(inherited) COCOAPODS=1 GRPC_COMPILE_WITH_CRONET=1'
+          config.build_settings['GCC_PREPROCESSOR_DEFINITIONS'] = '$(inherited) COCOAPODS=1 GRPC_COMPILE_WITH_CRONET=1 GRPC_TEST_OBJC=1'
+        elsif config.name == 'Test'
+          config.build_settings['GCC_PREPROCESSOR_DEFINITIONS'] = '$(inherited) COCOAPODS=1 GRPC_TEST_OBJC=1'
         end
       end
     end
diff --git a/src/objective-c/tests/Tests.xcodeproj/project.pbxproj b/src/objective-c/tests/Tests.xcodeproj/project.pbxproj
index 32b35ef333..97de723a22 100644
--- a/src/objective-c/tests/Tests.xcodeproj/project.pbxproj
+++ b/src/objective-c/tests/Tests.xcodeproj/project.pbxproj
@@ -125,8 +125,10 @@
 		0A4F89D9C90E9C30990218F0 /* Pods.release.xcconfig */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = text.xcconfig; name = Pods.release.xcconfig; path = "Pods/Target Support Files/Pods/Pods.release.xcconfig"; sourceTree = "<group>"; };
 		0D2284C3DF7E57F0ED504E39 /* Pods-CoreCronetEnd2EndTests.debug.xcconfig */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = text.xcconfig; name = "Pods-CoreCronetEnd2EndTests.debug.xcconfig"; path = "Pods/Target Support Files/Pods-CoreCronetEnd2EndTests/Pods-CoreCronetEnd2EndTests.debug.xcconfig"; sourceTree = "<group>"; };
 		14B09A58FEE53A7A6B838920 /* Pods-InteropTestsLocalSSL.cronet.xcconfig */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = text.xcconfig; name = "Pods-InteropTestsLocalSSL.cronet.xcconfig"; path = "Pods/Target Support Files/Pods-InteropTestsLocalSSL/Pods-InteropTestsLocalSSL.cronet.xcconfig"; sourceTree = "<group>"; };
+		1588C85DEAF7FC0ACDEA4C02 /* Pods-InteropTestsLocalCleartext.test.xcconfig */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = text.xcconfig; name = "Pods-InteropTestsLocalCleartext.test.xcconfig"; path = "Pods/Target Support Files/Pods-InteropTestsLocalCleartext/Pods-InteropTestsLocalCleartext.test.xcconfig"; sourceTree = "<group>"; };
 		17F60BF2871F6AF85FB3FA12 /* Pods-InteropTestsRemoteWithCronet.debug.xcconfig */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = text.xcconfig; name = "Pods-InteropTestsRemoteWithCronet.debug.xcconfig"; path = "Pods/Target Support Files/Pods-InteropTestsRemoteWithCronet/Pods-InteropTestsRemoteWithCronet.debug.xcconfig"; sourceTree = "<group>"; };
 		20DFF2F3C97EF098FE5A3171 /* libPods-Tests.a */ = {isa = PBXFileReference; explicitFileType = archive.ar; includeInIndex = 0; path = "libPods-Tests.a"; sourceTree = BUILT_PRODUCTS_DIR; };
+		2B89F3037963E6EDDD48D8C3 /* Pods-InteropTestsRemoteWithCronet.test.xcconfig */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = text.xcconfig; name = "Pods-InteropTestsRemoteWithCronet.test.xcconfig"; path = "Pods/Target Support Files/Pods-InteropTestsRemoteWithCronet/Pods-InteropTestsRemoteWithCronet.test.xcconfig"; sourceTree = "<group>"; };
 		35F2B6BF3BAE8F0DC4AFD76E /* libPods.a */ = {isa = PBXFileReference; explicitFileType = archive.ar; includeInIndex = 0; path = libPods.a; sourceTree = BUILT_PRODUCTS_DIR; };
 		386712AEACF7C2190C4B8B3F /* Pods-CronetUnitTests.cronet.xcconfig */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = text.xcconfig; name = "Pods-CronetUnitTests.cronet.xcconfig"; path = "Pods/Target Support Files/Pods-CronetUnitTests/Pods-CronetUnitTests.cronet.xcconfig"; sourceTree = "<group>"; };
 		3B0861FC805389C52DB260D4 /* Pods-RxLibraryUnitTests.release.xcconfig */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = text.xcconfig; name = "Pods-RxLibraryUnitTests.release.xcconfig"; path = "Pods/Target Support Files/Pods-RxLibraryUnitTests/Pods-RxLibraryUnitTests.release.xcconfig"; sourceTree = "<group>"; };
@@ -162,15 +164,22 @@
 		63E240CD1B6C4E2B005F3B0E /* InteropTestsLocalSSL.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = InteropTestsLocalSSL.m; sourceTree = "<group>"; };
 		63E240CF1B6C63DC005F3B0E /* TestCertificates.bundle */ = {isa = PBXFileReference; lastKnownFileType = "wrapper.plug-in"; path = TestCertificates.bundle; sourceTree = "<group>"; };
 		64F68A9A6A63CC930DD30A6E /* Pods-CronetUnitTests.debug.xcconfig */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = text.xcconfig; name = "Pods-CronetUnitTests.debug.xcconfig"; path = "Pods/Target Support Files/Pods-CronetUnitTests/Pods-CronetUnitTests.debug.xcconfig"; sourceTree = "<group>"; };
+		6793C9D019CB268C5BB491A2 /* Pods-CoreCronetEnd2EndTests.test.xcconfig */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = text.xcconfig; name = "Pods-CoreCronetEnd2EndTests.test.xcconfig"; path = "Pods/Target Support Files/Pods-CoreCronetEnd2EndTests/Pods-CoreCronetEnd2EndTests.test.xcconfig"; sourceTree = "<group>"; };
+		781089FAE980F51F88A3BE0B /* Pods-RxLibraryUnitTests.test.xcconfig */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = text.xcconfig; name = "Pods-RxLibraryUnitTests.test.xcconfig"; path = "Pods/Target Support Files/Pods-RxLibraryUnitTests/Pods-RxLibraryUnitTests.test.xcconfig"; sourceTree = "<group>"; };
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 		5E8A5DAC1D3840B4000F8BC4 /* Debug */ = {
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 					"GRPC_COMPILE_WITH_CRONET=1",
 					"GRPC_CRONET_WITH_PACKET_COALESCING=1",
+					"GRPC_TEST_OBJC=1",
 				);
 				INFOPLIST_FILE = InteropTestsRemoteWithCronet/Info.plist;
 				IPHONEOS_DEPLOYMENT_TARGET = 9.3;
@@ -1495,7 +1723,6 @@
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-					"$(inherited)",
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diff --git a/src/objective-c/tests/Tests.xcodeproj/xcshareddata/xcschemes/AllTests.xcscheme b/src/objective-c/tests/Tests.xcodeproj/xcshareddata/xcschemes/AllTests.xcscheme
index d1d616c4cf..a2560fee02 100644
--- a/src/objective-c/tests/Tests.xcodeproj/xcshareddata/xcschemes/AllTests.xcscheme
+++ b/src/objective-c/tests/Tests.xcodeproj/xcshareddata/xcschemes/AllTests.xcscheme
@@ -23,7 +23,7 @@
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       shouldUseLaunchSchemeArgsEnv = "YES">
@@ -63,7 +63,7 @@
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-      buildConfiguration = "Debug"
+      buildConfiguration = "Test"
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@@ -101,7 +101,7 @@
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-      buildConfiguration = "Debug">
+      buildConfiguration = "Test">
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diff --git a/src/objective-c/tests/Tests.xcodeproj/xcshareddata/xcschemes/InteropTestsLocalCleartext.xcscheme b/src/objective-c/tests/Tests.xcodeproj/xcshareddata/xcschemes/InteropTestsLocalCleartext.xcscheme
index ce358bf69f..6d85b62fab 100644
--- a/src/objective-c/tests/Tests.xcodeproj/xcshareddata/xcschemes/InteropTestsLocalCleartext.xcscheme
+++ b/src/objective-c/tests/Tests.xcodeproj/xcshareddata/xcschemes/InteropTestsLocalCleartext.xcscheme
@@ -23,7 +23,7 @@
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    <TestAction
-      buildConfiguration = "Debug"
+      buildConfiguration = "Test"
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@@ -54,7 +54,7 @@
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    <LaunchAction
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+      buildConfiguration = "Test"
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@@ -92,7 +92,7 @@
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-      buildConfiguration = "Debug">
+      buildConfiguration = "Test">
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diff --git a/src/objective-c/tests/Tests.xcodeproj/xcshareddata/xcschemes/InteropTestsLocalSSL.xcscheme b/src/objective-c/tests/Tests.xcodeproj/xcshareddata/xcschemes/InteropTestsLocalSSL.xcscheme
index f268da1fb0..37135b3ad3 100644
--- a/src/objective-c/tests/Tests.xcodeproj/xcshareddata/xcschemes/InteropTestsLocalSSL.xcscheme
+++ b/src/objective-c/tests/Tests.xcodeproj/xcshareddata/xcschemes/InteropTestsLocalSSL.xcscheme
@@ -23,7 +23,7 @@
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+      buildConfiguration = "Test"
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       selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
       shouldUseLaunchSchemeArgsEnv = "YES">
@@ -57,7 +57,7 @@
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+      buildConfiguration = "Test"
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       launchStyle = "0"
@@ -86,7 +86,7 @@
       debugDocumentVersioning = "YES">
    </ProfileAction>
    <AnalyzeAction
-      buildConfiguration = "Debug">
+      buildConfiguration = "Test">
    </AnalyzeAction>
    <ArchiveAction
       buildConfiguration = "Release"
diff --git a/src/objective-c/tests/Tests.xcodeproj/xcshareddata/xcschemes/InteropTestsRemote.xcscheme b/src/objective-c/tests/Tests.xcodeproj/xcshareddata/xcschemes/InteropTestsRemote.xcscheme
index 186d7208e0..412bf6a014 100644
--- a/src/objective-c/tests/Tests.xcodeproj/xcshareddata/xcschemes/InteropTestsRemote.xcscheme
+++ b/src/objective-c/tests/Tests.xcodeproj/xcshareddata/xcschemes/InteropTestsRemote.xcscheme
@@ -23,7 +23,7 @@
       </BuildActionEntries>
    </BuildAction>
    <TestAction
-      buildConfiguration = "Debug"
+      buildConfiguration = "Test"
       selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
       selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
       shouldUseLaunchSchemeArgsEnv = "YES">
@@ -57,7 +57,7 @@
       </AdditionalOptions>
    </TestAction>
    <LaunchAction
-      buildConfiguration = "Debug"
+      buildConfiguration = "Test"
       selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
       selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
       launchStyle = "0"
@@ -86,7 +86,7 @@
       debugDocumentVersioning = "YES">
    </ProfileAction>
    <AnalyzeAction
-      buildConfiguration = "Debug">
+      buildConfiguration = "Test">
    </AnalyzeAction>
    <ArchiveAction
       buildConfiguration = "Release"
diff --git a/src/php/README.md b/src/php/README.md
index f08541f16c..f9f93ba815 100644
--- a/src/php/README.md
+++ b/src/php/README.md
@@ -1,5 +1,5 @@
 
-#Overview
+# Overview
 
 This directory contains source code for PHP implementation of gRPC layered on
 shared C library.
diff --git a/src/php/lib/Grpc/AbstractCall.php b/src/php/lib/Grpc/AbstractCall.php
index 4833fdc7b6..a59bfa3ba3 100644
--- a/src/php/lib/Grpc/AbstractCall.php
+++ b/src/php/lib/Grpc/AbstractCall.php
@@ -131,7 +131,7 @@ abstract class AbstractCall
         // Proto3 implementation
         if (method_exists($data, 'encode')) {
             return $data->encode();
-        } else if (method_exists($data, 'serializeToString')) {
+        } elseif (method_exists($data, 'serializeToString')) {
             return $data->serializeToString();
         }
 
diff --git a/src/php/tests/unit_tests/ServerTest.php b/src/php/tests/unit_tests/ServerTest.php
index 5f40202f18..3e7c01f20e 100644
--- a/src/php/tests/unit_tests/ServerTest.php
+++ b/src/php/tests/unit_tests/ServerTest.php
@@ -69,7 +69,7 @@ class ServerTest extends PHPUnit_Framework_TestCase
         $this->server = new Grpc\Server();
         $port = $this->server->addHttp2Port('0.0.0.0:0');
         $this->server->start();
-        $channel = new Grpc\Channel('localhost:' . $port,
+        $channel = new Grpc\Channel('localhost:'.$port,
              ['credentials' => Grpc\ChannelCredentials::createInsecure()]);
 
         $deadline = Grpc\Timeval::infFuture();
diff --git a/templates/tools/dockerfile/interoptest/grpc_interop_go/Dockerfile.template b/templates/tools/dockerfile/interoptest/grpc_interop_go/Dockerfile.template
index 38a5ca725d..bf025d8037 100644
--- a/templates/tools/dockerfile/interoptest/grpc_interop_go/Dockerfile.template
+++ b/templates/tools/dockerfile/interoptest/grpc_interop_go/Dockerfile.template
@@ -29,7 +29,7 @@
   # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
   # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   
-  FROM golang:1.5
+  FROM golang:latest
   
   <%include file="../../go_path.include"/>
   <%include file="../../python_deps.include"/>
diff --git a/templates/tools/dockerfile/interoptest/grpc_interop_http2/Dockerfile.template b/templates/tools/dockerfile/interoptest/grpc_interop_http2/Dockerfile.template
index 12b9984425..a49e951289 100644
--- a/templates/tools/dockerfile/interoptest/grpc_interop_http2/Dockerfile.template
+++ b/templates/tools/dockerfile/interoptest/grpc_interop_http2/Dockerfile.template
@@ -29,7 +29,7 @@
   # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
   # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   
-  FROM golang:1.5
+  FROM golang:latest
   
   <%include file="../../go_path.include"/>
   <%include file="../../python_deps.include"/>
diff --git a/templates/tools/dockerfile/stress_test/grpc_interop_stress_go/Dockerfile.template b/templates/tools/dockerfile/stress_test/grpc_interop_stress_go/Dockerfile.template
index e02254cd53..ad8ad71b5f 100644
--- a/templates/tools/dockerfile/stress_test/grpc_interop_stress_go/Dockerfile.template
+++ b/templates/tools/dockerfile/stress_test/grpc_interop_stress_go/Dockerfile.template
@@ -29,7 +29,7 @@
   # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
   # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   
-  FROM golang:1.5
+  FROM golang:latest
   
   <%include file="../../gcp_api_libraries.include"/>
   <%include file="../../python_deps.include"/>
diff --git a/test/core/end2end/fuzzers/api_fuzzer_corpus/crash-59a56fa18034a104fb9f16cd58071b6ff93b8756 b/test/core/end2end/fuzzers/api_fuzzer_corpus/crash-59a56fa18034a104fb9f16cd58071b6ff93b8756
new file mode 100644
index 0000000000..1460bc9fbf
--- /dev/null
+++ b/test/core/end2end/fuzzers/api_fuzzer_corpus/crash-59a56fa18034a104fb9f16cd58071b6ff93b8756
diff --git a/test/core/end2end/fuzzers/api_fuzzer_corpus/poc-c726ee220e980ed6ad17809fd9efe2844ee61555ac08e4f88afd8901cc2dd53a b/test/core/end2end/fuzzers/api_fuzzer_corpus/poc-c726ee220e980ed6ad17809fd9efe2844ee61555ac08e4f88afd8901cc2dd53a
new file mode 100644
index 0000000000..01428693cf
--- /dev/null
+++ b/test/core/end2end/fuzzers/api_fuzzer_corpus/poc-c726ee220e980ed6ad17809fd9efe2844ee61555ac08e4f88afd8901cc2dd53a
diff --git a/test/core/end2end/tests/keepalive_timeout.c b/test/core/end2end/tests/keepalive_timeout.c
index 4296be3619..44b6e12abc 100644
--- a/test/core/end2end/tests/keepalive_timeout.c
+++ b/test/core/end2end/tests/keepalive_timeout.c
@@ -41,6 +41,7 @@
 #include <grpc/support/log.h>
 #include <grpc/support/time.h>
 #include <grpc/support/useful.h>
+#include "src/core/ext/transport/chttp2/transport/frame_ping.h"
 #include "src/core/lib/channel/channel_args.h"
 #include "src/core/lib/iomgr/exec_ctx.h"
 #include "src/core/lib/support/env.h"
@@ -109,13 +110,15 @@ static void test_keepalive_timeout(grpc_end2end_test_config config) {
       grpc_raw_byte_buffer_create(&response_payload_slice, 1);
   gpr_timespec deadline = five_seconds_time();
 
-  grpc_arg keepalive_args[2];
-  keepalive_args[0].type = GRPC_ARG_INTEGER;
-  keepalive_args[0].key = GRPC_ARG_HTTP2_KEEPALIVE_TIME;
-  keepalive_args[0].value.integer = 2;
-  keepalive_args[1].type = GRPC_ARG_INTEGER;
-  keepalive_args[1].key = GRPC_ARG_HTTP2_KEEPALIVE_TIMEOUT;
-  keepalive_args[1].value.integer = 0;
+  grpc_arg keepalive_args[] = {{.type = GRPC_ARG_INTEGER,
+                                .key = GRPC_ARG_CLIENT_KEEPALIVE_TIME_S,
+                                .value.integer = 2},
+                               {.type = GRPC_ARG_INTEGER,
+                                .key = GRPC_ARG_CLIENT_KEEPALIVE_TIMEOUT_S,
+                                .value.integer = 0},
+                               {.type = GRPC_ARG_INTEGER,
+                                .key = GRPC_ARG_HTTP2_BDP_PROBE,
+                                .value.integer = 1}};
 
   grpc_channel_args *client_args = NULL;
   client_args = grpc_channel_args_copy_and_add(client_args, keepalive_args, 2);
@@ -134,6 +137,9 @@ static void test_keepalive_timeout(grpc_end2end_test_config config) {
   grpc_call_error error;
   grpc_slice details;
 
+  /* Disable ping ack to trigger the keepalive timeout */
+  grpc_set_disable_ping_ack(true);
+
   c = grpc_channel_create_call(
       f.client, NULL, GRPC_PROPAGATE_DEFAULTS, f.cq,
       grpc_slice_from_static_string("/foo"),
diff --git a/test/core/end2end/tests/ping.c b/test/core/end2end/tests/ping.c
index f5bfac2255..082ac641f0 100644
--- a/test/core/end2end/tests/ping.c
+++ b/test/core/end2end/tests/ping.c
@@ -41,9 +41,12 @@
 
 #include "test/core/end2end/cq_verifier.h"
 
+#define PING_NUM 5
+
 static void *tag(intptr_t t) { return (void *)t; }
 
-static void test_ping(grpc_end2end_test_config config) {
+static void test_ping(grpc_end2end_test_config config,
+                      int min_time_between_pings_ms) {
   grpc_end2end_test_fixture f = config.create_fixture(NULL, NULL);
   cq_verifier *cqv = cq_verifier_create(f.cq);
   grpc_connectivity_state state = GRPC_CHANNEL_IDLE;
@@ -51,7 +54,7 @@ static void test_ping(grpc_end2end_test_config config) {
 
   grpc_arg a[] = {{.type = GRPC_ARG_INTEGER,
                    .key = GRPC_ARG_HTTP2_MIN_TIME_BETWEEN_PINGS_MS,
-                   .value.integer = 0},
+                   .value.integer = min_time_between_pings_ms},
                   {.type = GRPC_ARG_INTEGER,
                    .key = GRPC_ARG_HTTP2_MAX_PINGS_WITHOUT_DATA,
                    .value.integer = 20}};
@@ -70,7 +73,11 @@ static void test_ping(grpc_end2end_test_config config) {
      READY is reached */
   while (state != GRPC_CHANNEL_READY) {
     grpc_channel_watch_connectivity_state(
-        f.client, state, grpc_timeout_seconds_to_deadline(3), f.cq, tag(99));
+        f.client, state,
+        gpr_time_add(grpc_timeout_seconds_to_deadline(3),
+                     gpr_time_from_millis(min_time_between_pings_ms * PING_NUM,
+                                          GPR_TIMESPAN)),
+        f.cq, tag(99));
     CQ_EXPECT_COMPLETION(cqv, tag(99), 1);
     cq_verify(cqv);
     state = grpc_channel_check_connectivity_state(f.client, 0);
@@ -79,7 +86,7 @@ static void test_ping(grpc_end2end_test_config config) {
                state == GRPC_CHANNEL_TRANSIENT_FAILURE);
   }
 
-  for (i = 1; i <= 5; i++) {
+  for (i = 1; i <= PING_NUM; i++) {
     grpc_channel_ping(f.client, f.cq, tag(i), NULL);
     CQ_EXPECT_COMPLETION(cqv, tag(i), 1);
     cq_verify(cqv);
@@ -102,7 +109,8 @@ static void test_ping(grpc_end2end_test_config config) {
 
 void ping(grpc_end2end_test_config config) {
   GPR_ASSERT(config.feature_mask & FEATURE_MASK_SUPPORTS_DELAYED_CONNECTION);
-  test_ping(config);
+  test_ping(config, 0);
+  test_ping(config, 100);
 }
 
 void ping_pre_init(void) {}
diff --git a/test/core/iomgr/resource_quota_test.c b/test/core/iomgr/resource_quota_test.c
index a5b28f210d..ebce8b9da6 100644
--- a/test/core/iomgr/resource_quota_test.c
+++ b/test/core/iomgr/resource_quota_test.c
@@ -682,6 +682,56 @@ static void test_one_slice_deleted_late(void) {
   }
 }
 
+static void test_resize_to_zero(void) {
+  gpr_log(GPR_INFO, "** test_resize_to_zero **");
+  grpc_resource_quota *q = grpc_resource_quota_create("test_resize_to_zero");
+  grpc_resource_quota_resize(q, 0);
+  grpc_resource_quota_unref(q);
+}
+
+static void test_negative_rq_free_pool(void) {
+  gpr_log(GPR_INFO, "** test_negative_rq_free_pool **");
+  grpc_resource_quota *q =
+      grpc_resource_quota_create("test_negative_rq_free_pool");
+  grpc_resource_quota_resize(q, 1024);
+
+  grpc_resource_user *usr = grpc_resource_user_create(q, "usr");
+
+  grpc_resource_user_slice_allocator alloc;
+  int num_allocs = 0;
+  grpc_resource_user_slice_allocator_init(&alloc, usr, inc_int_cb, &num_allocs);
+
+  grpc_slice_buffer buffer;
+  grpc_slice_buffer_init(&buffer);
+
+  {
+    const int start_allocs = num_allocs;
+    grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
+    grpc_resource_user_alloc_slices(&exec_ctx, &alloc, 1024, 1, &buffer);
+    grpc_exec_ctx_finish(&exec_ctx);
+    GPR_ASSERT(num_allocs == start_allocs + 1);
+  }
+
+  grpc_resource_quota_resize(q, 512);
+
+  double eps = 0.0001;
+  GPR_ASSERT(grpc_resource_quota_get_memory_pressure(q) < 1 + eps);
+  GPR_ASSERT(grpc_resource_quota_get_memory_pressure(q) > 1 - eps);
+
+  {
+    grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
+    grpc_resource_user_unref(&exec_ctx, usr);
+    grpc_exec_ctx_finish(&exec_ctx);
+  }
+
+  grpc_resource_quota_unref(q);
+  {
+    grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
+    grpc_slice_buffer_destroy_internal(&exec_ctx, &buffer);
+    grpc_exec_ctx_finish(&exec_ctx);
+  }
+}
+
 int main(int argc, char **argv) {
   grpc_test_init(argc, argv);
   grpc_init();
@@ -705,6 +755,8 @@ int main(int argc, char **argv) {
   test_reclaimers_can_be_posted_repeatedly();
   test_one_slice();
   test_one_slice_deleted_late();
+  test_resize_to_zero();
+  test_negative_rq_free_pool();
   grpc_shutdown();
   return 0;
 }
diff --git a/test/cpp/end2end/async_end2end_test.cc b/test/cpp/end2end/async_end2end_test.cc
index 32e8a41795..0b5215ef8e 100644
--- a/test/cpp/end2end/async_end2end_test.cc
+++ b/test/cpp/end2end/async_end2end_test.cc
@@ -484,6 +484,81 @@ TEST_P(AsyncEnd2endTest, SimpleClientStreaming) {
   EXPECT_TRUE(recv_status.ok());
 }
 
+// Two pings and a final pong.
+TEST_P(AsyncEnd2endTest, SimpleClientStreamingWithCoalescingApi) {
+  ResetStub();
+
+  EchoRequest send_request;
+  EchoRequest recv_request;
+  EchoResponse send_response;
+  EchoResponse recv_response;
+  Status recv_status;
+  ClientContext cli_ctx;
+  ServerContext srv_ctx;
+  ServerAsyncReader<EchoResponse, EchoRequest> srv_stream(&srv_ctx);
+
+  send_request.set_message(GetParam().message_content);
+  cli_ctx.set_initial_metadata_corked(true);
+  // tag:1 never comes up since no op is performed
+  std::unique_ptr<ClientAsyncWriter<EchoRequest>> cli_stream(
+      stub_->AsyncRequestStream(&cli_ctx, &recv_response, cq_.get(), tag(1)));
+
+  service_.RequestRequestStream(&srv_ctx, &srv_stream, cq_.get(), cq_.get(),
+                                tag(2));
+
+  cli_stream->Write(send_request, tag(3));
+
+  // 65536(64KB) is the default flow control window size. Should change this
+  // number when default flow control window size changes. For the write of
+  // send_request larger than the flow control window size, tag:3 will not come
+  // up until server read is initiated. For write of send_request smaller than
+  // the flow control window size, the request can take the free ride with
+  // initial metadata due to coalescing, thus write tag:3 will come up here.
+  if (GetParam().message_content.length() < 65536) {
+    Verifier(GetParam().disable_blocking)
+        .Expect(2, true)
+        .Expect(3, true)
+        .Verify(cq_.get());
+  } else {
+    Verifier(GetParam().disable_blocking).Expect(2, true).Verify(cq_.get());
+  }
+
+  srv_stream.Read(&recv_request, tag(4));
+
+  if (GetParam().message_content.length() < 65536) {
+    Verifier(GetParam().disable_blocking).Expect(4, true).Verify(cq_.get());
+  } else {
+    Verifier(GetParam().disable_blocking)
+        .Expect(3, true)
+        .Expect(4, true)
+        .Verify(cq_.get());
+  }
+
+  EXPECT_EQ(send_request.message(), recv_request.message());
+
+  cli_stream->WriteLast(send_request, WriteOptions(), tag(5));
+  srv_stream.Read(&recv_request, tag(6));
+  Verifier(GetParam().disable_blocking)
+      .Expect(5, true)
+      .Expect(6, true)
+      .Verify(cq_.get());
+  EXPECT_EQ(send_request.message(), recv_request.message());
+
+  srv_stream.Read(&recv_request, tag(7));
+  Verifier(GetParam().disable_blocking).Expect(7, false).Verify(cq_.get());
+
+  send_response.set_message(recv_request.message());
+  srv_stream.Finish(send_response, Status::OK, tag(8));
+  cli_stream->Finish(&recv_status, tag(9));
+  Verifier(GetParam().disable_blocking)
+      .Expect(8, true)
+      .Expect(9, true)
+      .Verify(cq_.get());
+
+  EXPECT_EQ(send_response.message(), recv_response.message());
+  EXPECT_TRUE(recv_status.ok());
+}
+
 // One ping, two pongs.
 TEST_P(AsyncEnd2endTest, SimpleServerStreaming) {
   ResetStub();
@@ -540,6 +615,112 @@ TEST_P(AsyncEnd2endTest, SimpleServerStreaming) {
   EXPECT_TRUE(recv_status.ok());
 }
 
+// One ping, two pongs. Using WriteAndFinish API
+TEST_P(AsyncEnd2endTest, SimpleServerStreamingWithCoalescingApiWAF) {
+  ResetStub();
+
+  EchoRequest send_request;
+  EchoRequest recv_request;
+  EchoResponse send_response;
+  EchoResponse recv_response;
+  Status recv_status;
+  ClientContext cli_ctx;
+  ServerContext srv_ctx;
+  ServerAsyncWriter<EchoResponse> srv_stream(&srv_ctx);
+
+  send_request.set_message(GetParam().message_content);
+  std::unique_ptr<ClientAsyncReader<EchoResponse>> cli_stream(
+      stub_->AsyncResponseStream(&cli_ctx, send_request, cq_.get(), tag(1)));
+
+  service_.RequestResponseStream(&srv_ctx, &recv_request, &srv_stream,
+                                 cq_.get(), cq_.get(), tag(2));
+
+  Verifier(GetParam().disable_blocking)
+      .Expect(1, true)
+      .Expect(2, true)
+      .Verify(cq_.get());
+  EXPECT_EQ(send_request.message(), recv_request.message());
+
+  send_response.set_message(recv_request.message());
+  srv_stream.Write(send_response, tag(3));
+  cli_stream->Read(&recv_response, tag(4));
+  Verifier(GetParam().disable_blocking)
+      .Expect(3, true)
+      .Expect(4, true)
+      .Verify(cq_.get());
+  EXPECT_EQ(send_response.message(), recv_response.message());
+
+  srv_stream.WriteAndFinish(send_response, WriteOptions(), Status::OK, tag(5));
+  cli_stream->Read(&recv_response, tag(6));
+  Verifier(GetParam().disable_blocking)
+      .Expect(5, true)
+      .Expect(6, true)
+      .Verify(cq_.get());
+  EXPECT_EQ(send_response.message(), recv_response.message());
+
+  cli_stream->Read(&recv_response, tag(7));
+  Verifier(GetParam().disable_blocking).Expect(7, false).Verify(cq_.get());
+
+  cli_stream->Finish(&recv_status, tag(8));
+  Verifier(GetParam().disable_blocking).Expect(8, true).Verify(cq_.get());
+
+  EXPECT_TRUE(recv_status.ok());
+}
+
+// One ping, two pongs. Using WriteLast API
+TEST_P(AsyncEnd2endTest, SimpleServerStreamingWithCoalescingApiWL) {
+  ResetStub();
+
+  EchoRequest send_request;
+  EchoRequest recv_request;
+  EchoResponse send_response;
+  EchoResponse recv_response;
+  Status recv_status;
+  ClientContext cli_ctx;
+  ServerContext srv_ctx;
+  ServerAsyncWriter<EchoResponse> srv_stream(&srv_ctx);
+
+  send_request.set_message(GetParam().message_content);
+  std::unique_ptr<ClientAsyncReader<EchoResponse>> cli_stream(
+      stub_->AsyncResponseStream(&cli_ctx, send_request, cq_.get(), tag(1)));
+
+  service_.RequestResponseStream(&srv_ctx, &recv_request, &srv_stream,
+                                 cq_.get(), cq_.get(), tag(2));
+
+  Verifier(GetParam().disable_blocking)
+      .Expect(1, true)
+      .Expect(2, true)
+      .Verify(cq_.get());
+  EXPECT_EQ(send_request.message(), recv_request.message());
+
+  send_response.set_message(recv_request.message());
+  srv_stream.Write(send_response, tag(3));
+  cli_stream->Read(&recv_response, tag(4));
+  Verifier(GetParam().disable_blocking)
+      .Expect(3, true)
+      .Expect(4, true)
+      .Verify(cq_.get());
+  EXPECT_EQ(send_response.message(), recv_response.message());
+
+  srv_stream.WriteLast(send_response, WriteOptions(), tag(5));
+  cli_stream->Read(&recv_response, tag(6));
+  srv_stream.Finish(Status::OK, tag(7));
+  Verifier(GetParam().disable_blocking)
+      .Expect(5, true)
+      .Expect(6, true)
+      .Expect(7, true)
+      .Verify(cq_.get());
+  EXPECT_EQ(send_response.message(), recv_response.message());
+
+  cli_stream->Read(&recv_response, tag(8));
+  Verifier(GetParam().disable_blocking).Expect(8, false).Verify(cq_.get());
+
+  cli_stream->Finish(&recv_status, tag(9));
+  Verifier(GetParam().disable_blocking).Expect(9, true).Verify(cq_.get());
+
+  EXPECT_TRUE(recv_status.ok());
+}
+
 // One ping, one pong.
 TEST_P(AsyncEnd2endTest, SimpleBidiStreaming) {
   ResetStub();
@@ -599,6 +780,144 @@ TEST_P(AsyncEnd2endTest, SimpleBidiStreaming) {
   EXPECT_TRUE(recv_status.ok());
 }
 
+// One ping, one pong. Using server:WriteAndFinish api
+TEST_P(AsyncEnd2endTest, SimpleBidiStreamingWithCoalescingApiWAF) {
+  ResetStub();
+
+  EchoRequest send_request;
+  EchoRequest recv_request;
+  EchoResponse send_response;
+  EchoResponse recv_response;
+  Status recv_status;
+  ClientContext cli_ctx;
+  ServerContext srv_ctx;
+  ServerAsyncReaderWriter<EchoResponse, EchoRequest> srv_stream(&srv_ctx);
+
+  send_request.set_message(GetParam().message_content);
+  cli_ctx.set_initial_metadata_corked(true);
+  std::unique_ptr<ClientAsyncReaderWriter<EchoRequest, EchoResponse>>
+      cli_stream(stub_->AsyncBidiStream(&cli_ctx, cq_.get(), tag(1)));
+
+  service_.RequestBidiStream(&srv_ctx, &srv_stream, cq_.get(), cq_.get(),
+                             tag(2));
+
+  cli_stream->WriteLast(send_request, WriteOptions(), tag(3));
+
+  // 65536(64KB) is the default flow control window size. Should change this
+  // number when default flow control window size changes. For the write of
+  // send_request larger than the flow control window size, tag:3 will not come
+  // up until server read is initiated. For write of send_request smaller than
+  // the flow control window size, the request can take the free ride with
+  // initial metadata due to coalescing, thus write tag:3 will come up here.
+  if (GetParam().message_content.length() < 65536) {
+    Verifier(GetParam().disable_blocking)
+        .Expect(2, true)
+        .Expect(3, true)
+        .Verify(cq_.get());
+  } else {
+    Verifier(GetParam().disable_blocking).Expect(2, true).Verify(cq_.get());
+  }
+
+  srv_stream.Read(&recv_request, tag(4));
+
+  if (GetParam().message_content.length() < 65536) {
+    Verifier(GetParam().disable_blocking).Expect(4, true).Verify(cq_.get());
+  } else {
+    Verifier(GetParam().disable_blocking)
+        .Expect(3, true)
+        .Expect(4, true)
+        .Verify(cq_.get());
+  }
+  EXPECT_EQ(send_request.message(), recv_request.message());
+
+  srv_stream.Read(&recv_request, tag(5));
+  Verifier(GetParam().disable_blocking).Expect(5, false).Verify(cq_.get());
+
+  send_response.set_message(recv_request.message());
+  srv_stream.WriteAndFinish(send_response, WriteOptions(), Status::OK, tag(6));
+  cli_stream->Read(&recv_response, tag(7));
+  Verifier(GetParam().disable_blocking)
+      .Expect(6, true)
+      .Expect(7, true)
+      .Verify(cq_.get());
+  EXPECT_EQ(send_response.message(), recv_response.message());
+
+  cli_stream->Finish(&recv_status, tag(8));
+  Verifier(GetParam().disable_blocking).Expect(8, true).Verify(cq_.get());
+
+  EXPECT_TRUE(recv_status.ok());
+}
+
+// One ping, one pong. Using server:WriteLast api
+TEST_P(AsyncEnd2endTest, SimpleBidiStreamingWithCoalescingApiWL) {
+  ResetStub();
+
+  EchoRequest send_request;
+  EchoRequest recv_request;
+  EchoResponse send_response;
+  EchoResponse recv_response;
+  Status recv_status;
+  ClientContext cli_ctx;
+  ServerContext srv_ctx;
+  ServerAsyncReaderWriter<EchoResponse, EchoRequest> srv_stream(&srv_ctx);
+
+  send_request.set_message(GetParam().message_content);
+  cli_ctx.set_initial_metadata_corked(true);
+  std::unique_ptr<ClientAsyncReaderWriter<EchoRequest, EchoResponse>>
+      cli_stream(stub_->AsyncBidiStream(&cli_ctx, cq_.get(), tag(1)));
+
+  service_.RequestBidiStream(&srv_ctx, &srv_stream, cq_.get(), cq_.get(),
+                             tag(2));
+
+  cli_stream->WriteLast(send_request, WriteOptions(), tag(3));
+
+  // 65536(64KB) is the default flow control window size. Should change this
+  // number when default flow control window size changes. For the write of
+  // send_request larger than the flow control window size, tag:3 will not come
+  // up until server read is initiated. For write of send_request smaller than
+  // the flow control window size, the request can take the free ride with
+  // initial metadata due to coalescing, thus write tag:3 will come up here.
+  if (GetParam().message_content.length() < 65536) {
+    Verifier(GetParam().disable_blocking)
+        .Expect(2, true)
+        .Expect(3, true)
+        .Verify(cq_.get());
+  } else {
+    Verifier(GetParam().disable_blocking).Expect(2, true).Verify(cq_.get());
+  }
+
+  srv_stream.Read(&recv_request, tag(4));
+
+  if (GetParam().message_content.length() < 65536) {
+    Verifier(GetParam().disable_blocking).Expect(4, true).Verify(cq_.get());
+  } else {
+    Verifier(GetParam().disable_blocking)
+        .Expect(3, true)
+        .Expect(4, true)
+        .Verify(cq_.get());
+  }
+  EXPECT_EQ(send_request.message(), recv_request.message());
+
+  srv_stream.Read(&recv_request, tag(5));
+  Verifier(GetParam().disable_blocking).Expect(5, false).Verify(cq_.get());
+
+  send_response.set_message(recv_request.message());
+  srv_stream.WriteLast(send_response, WriteOptions(), tag(6));
+  srv_stream.Finish(Status::OK, tag(7));
+  cli_stream->Read(&recv_response, tag(8));
+  Verifier(GetParam().disable_blocking)
+      .Expect(6, true)
+      .Expect(7, true)
+      .Expect(8, true)
+      .Verify(cq_.get());
+  EXPECT_EQ(send_response.message(), recv_response.message());
+
+  cli_stream->Finish(&recv_status, tag(9));
+  Verifier(GetParam().disable_blocking).Expect(9, true).Verify(cq_.get());
+
+  EXPECT_TRUE(recv_status.ok());
+}
+
 // Metadata tests
 TEST_P(AsyncEnd2endTest, ClientInitialMetadataRpc) {
   ResetStub();
diff --git a/test/cpp/end2end/end2end_test.cc b/test/cpp/end2end/end2end_test.cc
index df78557c43..d3a83b188f 100644
--- a/test/cpp/end2end/end2end_test.cc
+++ b/test/cpp/end2end/end2end_test.cc
@@ -702,6 +702,21 @@ TEST_P(End2endTest, RequestStreamOneRequest) {
   EXPECT_TRUE(s.ok());
 }
 
+TEST_P(End2endTest, RequestStreamOneRequestWithCoalescingApi) {
+  ResetStub();
+  EchoRequest request;
+  EchoResponse response;
+  ClientContext context;
+
+  context.set_initial_metadata_corked(true);
+  auto stream = stub_->RequestStream(&context, &response);
+  request.set_message("hello");
+  stream->WriteLast(request, WriteOptions());
+  Status s = stream->Finish();
+  EXPECT_EQ(response.message(), request.message());
+  EXPECT_TRUE(s.ok());
+}
+
 TEST_P(End2endTest, RequestStreamTwoRequests) {
   ResetStub();
   EchoRequest request;
@@ -718,6 +733,22 @@ TEST_P(End2endTest, RequestStreamTwoRequests) {
   EXPECT_TRUE(s.ok());
 }
 
+TEST_P(End2endTest, RequestStreamTwoRequestsWithCoalescingApi) {
+  ResetStub();
+  EchoRequest request;
+  EchoResponse response;
+  ClientContext context;
+
+  context.set_initial_metadata_corked(true);
+  auto stream = stub_->RequestStream(&context, &response);
+  request.set_message("hello");
+  EXPECT_TRUE(stream->Write(request));
+  stream->WriteLast(request, WriteOptions());
+  Status s = stream->Finish();
+  EXPECT_EQ(response.message(), "hellohello");
+  EXPECT_TRUE(s.ok());
+}
+
 TEST_P(End2endTest, ResponseStream) {
   ResetStub();
   EchoRequest request;
@@ -738,6 +769,27 @@ TEST_P(End2endTest, ResponseStream) {
   EXPECT_TRUE(s.ok());
 }
 
+TEST_P(End2endTest, ResponseStreamWithCoalescingApi) {
+  ResetStub();
+  EchoRequest request;
+  EchoResponse response;
+  ClientContext context;
+  request.set_message("hello");
+  context.AddMetadata(kServerUseCoalescingApi, "1");
+
+  auto stream = stub_->ResponseStream(&context, request);
+  EXPECT_TRUE(stream->Read(&response));
+  EXPECT_EQ(response.message(), request.message() + "0");
+  EXPECT_TRUE(stream->Read(&response));
+  EXPECT_EQ(response.message(), request.message() + "1");
+  EXPECT_TRUE(stream->Read(&response));
+  EXPECT_EQ(response.message(), request.message() + "2");
+  EXPECT_FALSE(stream->Read(&response));
+
+  Status s = stream->Finish();
+  EXPECT_TRUE(s.ok());
+}
+
 TEST_P(End2endTest, BidiStream) {
   ResetStub();
   EchoRequest request;
@@ -770,6 +822,39 @@ TEST_P(End2endTest, BidiStream) {
   EXPECT_TRUE(s.ok());
 }
 
+TEST_P(End2endTest, BidiStreamWithCoalescingApi) {
+  ResetStub();
+  EchoRequest request;
+  EchoResponse response;
+  ClientContext context;
+  context.AddMetadata(kServerFinishAfterNReads, "3");
+  context.set_initial_metadata_corked(true);
+  grpc::string msg("hello");
+
+  auto stream = stub_->BidiStream(&context);
+
+  request.set_message(msg + "0");
+  EXPECT_TRUE(stream->Write(request));
+  EXPECT_TRUE(stream->Read(&response));
+  EXPECT_EQ(response.message(), request.message());
+
+  request.set_message(msg + "1");
+  EXPECT_TRUE(stream->Write(request));
+  EXPECT_TRUE(stream->Read(&response));
+  EXPECT_EQ(response.message(), request.message());
+
+  request.set_message(msg + "2");
+  stream->WriteLast(request, WriteOptions());
+  EXPECT_TRUE(stream->Read(&response));
+  EXPECT_EQ(response.message(), request.message());
+
+  EXPECT_FALSE(stream->Read(&response));
+  EXPECT_FALSE(stream->Read(&response));
+
+  Status s = stream->Finish();
+  EXPECT_TRUE(s.ok());
+}
+
 // Talk to the two services with the same name but different package names.
 // The two stubs are created on the same channel.
 TEST_P(End2endTest, DiffPackageServices) {
diff --git a/test/cpp/end2end/mock_test.cc b/test/cpp/end2end/mock_test.cc
index d6664da5a0..fdb2732e50 100644
--- a/test/cpp/end2end/mock_test.cc
+++ b/test/cpp/end2end/mock_test.cc
@@ -89,7 +89,7 @@ class MockClientReaderWriter<EchoRequest, EchoResponse> final
     return true;
   }
 
-  bool Write(const EchoRequest& msg, const WriteOptions& options) override {
+  bool Write(const EchoRequest& msg, WriteOptions options) override {
     gpr_log(GPR_INFO, "mock recv msg %s", msg.message().c_str());
     last_message_ = msg.message();
     return true;
diff --git a/test/cpp/end2end/test_service_impl.cc b/test/cpp/end2end/test_service_impl.cc
index 59d36e9cb5..11729c425c 100644
--- a/test/cpp/end2end/test_service_impl.cc
+++ b/test/cpp/end2end/test_service_impl.cc
@@ -246,6 +246,9 @@ Status TestServiceImpl::ResponseStream(ServerContext* context,
   int server_try_cancel = GetIntValueFromMetadata(
       kServerTryCancelRequest, context->client_metadata(), DO_NOT_CANCEL);
 
+  int server_coalescing_api = GetIntValueFromMetadata(
+      kServerUseCoalescingApi, context->client_metadata(), 0);
+
   if (server_try_cancel == CANCEL_BEFORE_PROCESSING) {
     ServerTryCancel(context);
     return Status::CANCELLED;
@@ -260,7 +263,11 @@ Status TestServiceImpl::ResponseStream(ServerContext* context,
 
   for (int i = 0; i < kNumResponseStreamsMsgs; i++) {
     response.set_message(request->message() + grpc::to_string(i));
-    writer->Write(response);
+    if (i == kNumResponseStreamsMsgs - 1 && server_coalescing_api != 0) {
+      writer->WriteLast(response, WriteOptions());
+    } else {
+      writer->Write(response);
+    }
   }
 
   if (server_try_cancel_thd != nullptr) {
@@ -305,10 +312,21 @@ Status TestServiceImpl::BidiStream(
         new std::thread(&TestServiceImpl::ServerTryCancel, this, context);
   }
 
+  // kServerFinishAfterNReads suggests after how many reads, the server should
+  // write the last message and send status (coalesced using WriteLast)
+  int server_write_last = GetIntValueFromMetadata(
+      kServerFinishAfterNReads, context->client_metadata(), 0);
+
+  int read_counts = 0;
   while (stream->Read(&request)) {
+    read_counts++;
     gpr_log(GPR_INFO, "recv msg %s", request.message().c_str());
     response.set_message(request.message());
-    stream->Write(response);
+    if (read_counts == server_write_last) {
+      stream->WriteLast(response, WriteOptions());
+    } else {
+      stream->Write(response);
+    }
   }
 
   if (server_try_cancel_thd != nullptr) {
diff --git a/test/cpp/end2end/test_service_impl.h b/test/cpp/end2end/test_service_impl.h
index 88e0be7bca..b1f02f93f6 100644
--- a/test/cpp/end2end/test_service_impl.h
+++ b/test/cpp/end2end/test_service_impl.h
@@ -48,6 +48,8 @@ const int kNumResponseStreamsMsgs = 3;
 const char* const kServerCancelAfterReads = "cancel_after_reads";
 const char* const kServerTryCancelRequest = "server_try_cancel";
 const char* const kDebugInfoTrailerKey = "debug-info-bin";
+const char* const kServerFinishAfterNReads = "server_finish_after_n_reads";
+const char* const kServerUseCoalescingApi = "server_use_coalescing_api";
 
 typedef enum {
   DO_NOT_CANCEL = 0,
diff --git a/test/cpp/microbenchmarks/bm_fullstack_streaming_ping_pong.cc b/test/cpp/microbenchmarks/bm_fullstack_streaming_ping_pong.cc
index cafd4843d3..c536e15a2c 100644
--- a/test/cpp/microbenchmarks/bm_fullstack_streaming_ping_pong.cc
+++ b/test/cpp/microbenchmarks/bm_fullstack_streaming_ping_pong.cc
@@ -239,6 +239,173 @@ static void BM_StreamingPingPongMsgs(benchmark::State& state) {
   state.SetBytesProcessed(msg_size * state.iterations() * 2);
 }
 
+// Repeatedly makes Streaming Bidi calls (exchanging a configurable number of
+// messages in each call) in a loop on a single channel. Different from
+// BM_StreamingPingPong we are using stream coalescing api, e.g. WriteLast,
+// WriteAndFinish, set_initial_metadata_corked. These apis aim at saving
+// sendmsg syscalls for streaming by coalescing 1. initial metadata with first
+// message; 2. final streaming message with trailing metadata.
+//
+//  First parmeter (i.e state.range(0)):  Message size (in bytes) to use
+//  Second parameter (i.e state.range(1)): Number of ping pong messages.
+//      Note: One ping-pong means two messages (one from client to server and
+//      the other from server to client):
+//  Third parameter (i.e state.range(2)): Switch between using WriteAndFinish
+//  API and WriteLast API for server.
+template <class Fixture, class ClientContextMutator, class ServerContextMutator>
+static void BM_StreamingPingPongWithCoalescingApi(benchmark::State& state) {
+  const int msg_size = state.range(0);
+  const int max_ping_pongs = state.range(1);
+  // This options is used to test out server API: WriteLast and WriteAndFinish
+  // respectively, since we can not use both of them on server side at the same
+  // time. Value 1 means we are testing out the WriteAndFinish API, and
+  // otherwise we are testing out the WriteLast API.
+  const int write_and_finish = state.range(2);
+
+  EchoTestService::AsyncService service;
+  std::unique_ptr<Fixture> fixture(new Fixture(&service));
+  {
+    EchoResponse send_response;
+    EchoResponse recv_response;
+    EchoRequest send_request;
+    EchoRequest recv_request;
+
+    if (msg_size > 0) {
+      send_request.set_message(std::string(msg_size, 'a'));
+      send_response.set_message(std::string(msg_size, 'b'));
+    }
+
+    std::unique_ptr<EchoTestService::Stub> stub(
+        EchoTestService::NewStub(fixture->channel()));
+
+    while (state.KeepRunning()) {
+      ServerContext svr_ctx;
+      ServerContextMutator svr_ctx_mut(&svr_ctx);
+      ServerAsyncReaderWriter<EchoResponse, EchoRequest> response_rw(&svr_ctx);
+      service.RequestBidiStream(&svr_ctx, &response_rw, fixture->cq(),
+                                fixture->cq(), tag(0));
+
+      ClientContext cli_ctx;
+      ClientContextMutator cli_ctx_mut(&cli_ctx);
+      cli_ctx.set_initial_metadata_corked(true);
+      // tag:1 here will never comes up, since we are not performing any op due
+      // to initial metadata coalescing.
+      auto request_rw = stub->AsyncBidiStream(&cli_ctx, fixture->cq(), tag(1));
+
+      void* t;
+      bool ok;
+      int need_tags;
+
+      // Send 'max_ping_pongs' number of ping pong messages
+      int ping_pong_cnt = 0;
+      while (ping_pong_cnt < max_ping_pongs) {
+        if (ping_pong_cnt == max_ping_pongs - 1) {
+          request_rw->WriteLast(send_request, WriteOptions(), tag(2));
+        } else {
+          request_rw->Write(send_request, tag(2));  // Start client send
+        }
+
+        need_tags = (1 << 2) | (1 << 3) | (1 << 4) | (1 << 5);
+
+        if (ping_pong_cnt == 0) {
+          // wait for the server call structure (call_hook, etc.) to be
+          // initialized (async stream between client side and server side
+          // established). It is necessary when client init metadata is
+          // coalesced
+          GPR_ASSERT(fixture->cq()->Next(&t, &ok));
+          while ((int)(intptr_t)t != 0) {
+            // In some cases tag:2 comes before tag:0 (write tag comes out
+            // first), this while loop is to make sure get tag:0.
+            int i = (int)(intptr_t)t;
+            GPR_ASSERT(need_tags & (1 << i));
+            need_tags &= ~(1 << i);
+            GPR_ASSERT(fixture->cq()->Next(&t, &ok));
+          }
+        }
+
+        response_rw.Read(&recv_request, tag(3));   // Start server recv
+        request_rw->Read(&recv_response, tag(4));  // Start client recv
+
+        while (need_tags) {
+          GPR_ASSERT(fixture->cq()->Next(&t, &ok));
+          GPR_ASSERT(ok);
+          int i = (int)(intptr_t)t;
+
+          // If server recv is complete, start the server send operation
+          if (i == 3) {
+            if (ping_pong_cnt == max_ping_pongs - 1) {
+              if (write_and_finish == 1) {
+                response_rw.WriteAndFinish(send_response, WriteOptions(),
+                                           Status::OK, tag(5));
+              } else {
+                response_rw.WriteLast(send_response, WriteOptions(), tag(5));
+                // WriteLast buffers the write, so neither server write op nor
+                // client read op will finish inside the while loop.
+                need_tags &= ~(1 << 4);
+                need_tags &= ~(1 << 5);
+              }
+            } else {
+              response_rw.Write(send_response, tag(5));
+            }
+          }
+
+          GPR_ASSERT(need_tags & (1 << i));
+          need_tags &= ~(1 << i);
+        }
+
+        ping_pong_cnt++;
+      }
+
+      if (max_ping_pongs == 0) {
+        need_tags = (1 << 6) | (1 << 7) | (1 << 8);
+      } else {
+        if (write_and_finish == 1) {
+          need_tags = (1 << 8);
+        } else {
+          // server's buffered write and the client's read of the buffered write
+          // tags should come up.
+          need_tags = (1 << 4) | (1 << 5) | (1 << 7) | (1 << 8);
+        }
+      }
+
+      // No message write or initial metadata write happened yet.
+      if (max_ping_pongs == 0) {
+        request_rw->WritesDone(tag(6));
+        // wait for server call data structure(call_hook, etc.) to be
+        // initialized, since initial metadata is corked.
+        GPR_ASSERT(fixture->cq()->Next(&t, &ok));
+        while ((int)(intptr_t)t != 0) {
+          int i = (int)(intptr_t)t;
+          GPR_ASSERT(need_tags & (1 << i));
+          need_tags &= ~(1 << i);
+          GPR_ASSERT(fixture->cq()->Next(&t, &ok));
+        }
+        response_rw.Finish(Status::OK, tag(7));
+      } else {
+        if (write_and_finish != 1) {
+          response_rw.Finish(Status::OK, tag(7));
+        }
+      }
+
+      Status recv_status;
+      request_rw->Finish(&recv_status, tag(8));
+
+      while (need_tags) {
+        GPR_ASSERT(fixture->cq()->Next(&t, &ok));
+        int i = (int)(intptr_t)t;
+        GPR_ASSERT(need_tags & (1 << i));
+        need_tags &= ~(1 << i);
+      }
+
+      GPR_ASSERT(recv_status.ok());
+    }
+  }
+
+  fixture->Finish(state);
+  fixture.reset();
+  state.SetBytesProcessed(msg_size * state.iterations() * max_ping_pongs * 2);
+}
+
 /*******************************************************************************
  * CONFIGURATIONS
  */
@@ -269,6 +436,30 @@ BENCHMARK_TEMPLATE(BM_StreamingPingPongMsgs, InProcessCHTTP2, NoOpMutator,
 BENCHMARK_TEMPLATE(BM_StreamingPingPongMsgs, TCP, NoOpMutator, NoOpMutator)
     ->Range(0, 128 * 1024 * 1024);
 
+// Generate Args for StreamingPingPongWithCoalescingApi benchmarks. Currently
+// generates args for only "small streams" (i.e streams with 0, 1 or 2 messages)
+static void StreamingPingPongWithCoalescingApiArgs(
+    benchmark::internal::Benchmark* b) {
+  int msg_size = 0;
+
+  b->Args(
+      {0, 0, 0});  // spl case: 0 ping-pong msgs (msg_size doesn't matter here)
+  b->Args(
+      {0, 0, 1});  // spl case: 0 ping-pong msgs (msg_size doesn't matter here)
+
+  for (msg_size = 0; msg_size <= 128 * 1024 * 1024;
+       msg_size == 0 ? msg_size++ : msg_size *= 8) {
+    b->Args({msg_size, 1, 0});
+    b->Args({msg_size, 2, 0});
+    b->Args({msg_size, 1, 1});
+    b->Args({msg_size, 2, 1});
+  }
+}
+
+BENCHMARK_TEMPLATE(BM_StreamingPingPongWithCoalescingApi, InProcessCHTTP2,
+                   NoOpMutator, NoOpMutator)
+    ->Apply(StreamingPingPongWithCoalescingApiArgs);
+
 }  // namespace testing
 }  // namespace grpc
 
diff --git a/tools/dockerfile/interoptest/grpc_interop_go/Dockerfile b/tools/dockerfile/interoptest/grpc_interop_go/Dockerfile
index d3bf071c72..d7a0b1786b 100644
--- a/tools/dockerfile/interoptest/grpc_interop_go/Dockerfile
+++ b/tools/dockerfile/interoptest/grpc_interop_go/Dockerfile
@@ -27,7 +27,7 @@
 # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-FROM golang:1.5
+FROM golang:latest
 
 # Using login shell removes Go from path, so we add it.
 RUN ln -s /usr/local/go/bin/go /usr/local/bin
diff --git a/tools/dockerfile/interoptest/grpc_interop_http2/Dockerfile b/tools/dockerfile/interoptest/grpc_interop_http2/Dockerfile
index acc984acb0..da00152825 100644
--- a/tools/dockerfile/interoptest/grpc_interop_http2/Dockerfile
+++ b/tools/dockerfile/interoptest/grpc_interop_http2/Dockerfile
@@ -27,7 +27,7 @@
 # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-FROM golang:1.5
+FROM golang:latest
 
 # Using login shell removes Go from path, so we add it.
 RUN ln -s /usr/local/go/bin/go /usr/local/bin
diff --git a/tools/dockerfile/stress_test/grpc_interop_stress_go/Dockerfile b/tools/dockerfile/stress_test/grpc_interop_stress_go/Dockerfile
index bbf7de7f91..c099f339ae 100644
--- a/tools/dockerfile/stress_test/grpc_interop_stress_go/Dockerfile
+++ b/tools/dockerfile/stress_test/grpc_interop_stress_go/Dockerfile
@@ -27,7 +27,7 @@
 # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-FROM golang:1.5
+FROM golang:latest
 
 # Google Cloud platform API libraries
 RUN apt-get update && apt-get install -y python-pip && apt-get clean
diff --git a/tools/run_tests/generated/tests.json b/tools/run_tests/generated/tests.json
index 6202346fc2..87142f585c 100644
--- a/tools/run_tests/generated/tests.json
+++ b/tools/run_tests/generated/tests.json
@@ -83125,6 +83125,29 @@
   }, 
   {
     "args": [
+      "test/core/end2end/fuzzers/api_fuzzer_corpus/crash-59a56fa18034a104fb9f16cd58071b6ff93b8756"
+    ], 
+    "ci_platforms": [
+      "linux"
+    ], 
+    "cpu_cost": 0.1, 
+    "exclude_configs": [
+      "tsan"
+    ], 
+    "exclude_iomgrs": [
+      "uv"
+    ], 
+    "flaky": false, 
+    "language": "c", 
+    "name": "api_fuzzer_one_entry", 
+    "platforms": [
+      "mac", 
+      "linux"
+    ], 
+    "uses_polling": false
+  }, 
+  {
+    "args": [
       "test/core/end2end/fuzzers/api_fuzzer_corpus/crash-59b587d15c0bcdb985417cd7a133cecfcc232698"
     ], 
     "ci_platforms": [
@@ -94211,6 +94234,29 @@
   }, 
   {
     "args": [
+      "test/core/end2end/fuzzers/api_fuzzer_corpus/poc-c726ee220e980ed6ad17809fd9efe2844ee61555ac08e4f88afd8901cc2dd53a"
+    ], 
+    "ci_platforms": [
+      "linux"
+    ], 
+    "cpu_cost": 0.1, 
+    "exclude_configs": [
+      "tsan"
+    ], 
+    "exclude_iomgrs": [
+      "uv"
+    ], 
+    "flaky": false, 
+    "language": "c", 
+    "name": "api_fuzzer_one_entry", 
+    "platforms": [
+      "mac", 
+      "linux"
+    ], 
+    "uses_polling": false
+  }, 
+  {
+    "args": [
       "test/core/end2end/fuzzers/api_fuzzer_corpus/timeout-0fa0559576ad2a45b06d0bfb84115963d7d48206"
     ], 
     "ci_platforms": [