5 files changed, 674 insertions, 4 deletions

diff --git a/include/grpcpp/generic/generic_stub.h b/include/grpcpp/generic/generic_stub.h
index d509d9a520..eb014184e4 100644
--- a/include/grpcpp/generic/generic_stub.h
+++ b/include/grpcpp/generic/generic_stub.h
@@ -24,6 +24,7 @@
 #include <grpcpp/support/async_stream.h>
 #include <grpcpp/support/async_unary_call.h>
 #include <grpcpp/support/byte_buffer.h>
+#include <grpcpp/support/client_callback.h>
 #include <grpcpp/support/status.h>
 
 namespace grpc {
@@ -76,6 +77,10 @@ class GenericStub final {
                    const ByteBuffer* request, ByteBuffer* response,
                    std::function<void(Status)> on_completion);
 
+    void PrepareBidiStreamingCall(
+        ClientContext* context, const grpc::string& method,
+        experimental::ClientBidiReactor<ByteBuffer, ByteBuffer>* reactor);
+
    private:
     GenericStub* stub_;
   };
diff --git a/include/grpcpp/impl/codegen/callback_common.h b/include/grpcpp/impl/codegen/callback_common.h
index 51367cf550..f7a24204dc 100644
--- a/include/grpcpp/impl/codegen/callback_common.h
+++ b/include/grpcpp/impl/codegen/callback_common.h
@@ -145,18 +145,19 @@ class CallbackWithSuccessTag
   // or on a tag that has been Set before unless the tag has been cleared.
   void Set(grpc_call* call, std::function<void(bool)> f,
            CompletionQueueTag* ops) {
+    GPR_CODEGEN_ASSERT(call_ == nullptr);
+    g_core_codegen_interface->grpc_call_ref(call);
     call_ = call;
     func_ = std::move(f);
     ops_ = ops;
-    g_core_codegen_interface->grpc_call_ref(call);
     functor_run = &CallbackWithSuccessTag::StaticRun;
   }
 
   void Clear() {
     if (call_ != nullptr) {
-      func_ = nullptr;
       grpc_call* call = call_;
       call_ = nullptr;
+      func_ = nullptr;
       g_core_codegen_interface->grpc_call_unref(call);
     }
   }
@@ -182,10 +183,9 @@ class CallbackWithSuccessTag
   }
   void Run(bool ok) {
     void* ignored = ops_;
-    bool new_ok = ok;
     // Allow a "false" return value from FinalizeResult to silence the
     // callback, just as it silences a CQ tag in the async cases
-    bool do_callback = ops_->FinalizeResult(&ignored, &new_ok);
+    bool do_callback = ops_->FinalizeResult(&ignored, &ok);
     GPR_CODEGEN_ASSERT(ignored == ops_);
 
     if (do_callback) {
diff --git a/include/grpcpp/impl/codegen/channel_interface.h b/include/grpcpp/impl/codegen/channel_interface.h
index 6ec1ffb8c7..728a7b9049 100644
--- a/include/grpcpp/impl/codegen/channel_interface.h
+++ b/include/grpcpp/impl/codegen/channel_interface.h
@@ -53,6 +53,12 @@ template <class W, class R>
 class ClientAsyncReaderWriterFactory;
 template <class R>
 class ClientAsyncResponseReaderFactory;
+template <class W, class R>
+class ClientCallbackReaderWriterFactory;
+template <class R>
+class ClientCallbackReaderFactory;
+template <class W>
+class ClientCallbackWriterFactory;
 class InterceptedChannel;
 }  // namespace internal
 
@@ -106,6 +112,12 @@ class ChannelInterface {
   friend class ::grpc::internal::ClientAsyncReaderWriterFactory;
   template <class R>
   friend class ::grpc::internal::ClientAsyncResponseReaderFactory;
+  template <class W, class R>
+  friend class ::grpc::internal::ClientCallbackReaderWriterFactory;
+  template <class R>
+  friend class ::grpc::internal::ClientCallbackReaderFactory;
+  template <class W>
+  friend class ::grpc::internal::ClientCallbackWriterFactory;
   template <class InputMessage, class OutputMessage>
   friend class ::grpc::internal::BlockingUnaryCallImpl;
   template <class InputMessage, class OutputMessage>
diff --git a/include/grpcpp/impl/codegen/client_callback.h b/include/grpcpp/impl/codegen/client_callback.h
index 4baa819091..4d9579fd6a 100644
--- a/include/grpcpp/impl/codegen/client_callback.h
+++ b/include/grpcpp/impl/codegen/client_callback.h
@@ -22,6 +22,7 @@
 #include <functional>
 
 #include <grpcpp/impl/codegen/call.h>
+#include <grpcpp/impl/codegen/call_op_set.h>
 #include <grpcpp/impl/codegen/callback_common.h>
 #include <grpcpp/impl/codegen/channel_interface.h>
 #include <grpcpp/impl/codegen/config.h>
@@ -88,6 +89,646 @@ class CallbackUnaryCallImpl {
     call.PerformOps(ops);
   }
 };
+}  // namespace internal
+
+namespace experimental {
+
+// Forward declarations
+template <class Request, class Response>
+class ClientBidiReactor;
+template <class Response>
+class ClientReadReactor;
+template <class Request>
+class ClientWriteReactor;
+
+// NOTE: The streaming objects are not actually implemented in the public API.
+//       These interfaces are provided for mocking only. Typical applications
+//       will interact exclusively with the reactors that they define.
+template <class Request, class Response>
+class ClientCallbackReaderWriter {
+ public:
+  virtual ~ClientCallbackReaderWriter() {}
+  virtual void StartCall() = 0;
+  virtual void Write(const Request* req, WriteOptions options) = 0;
+  virtual void WritesDone() = 0;
+  virtual void Read(Response* resp) = 0;
+
+ protected:
+  void BindReactor(ClientBidiReactor<Request, Response>* reactor) {
+    reactor->BindStream(this);
+  }
+};
+
+template <class Response>
+class ClientCallbackReader {
+ public:
+  virtual ~ClientCallbackReader() {}
+  virtual void StartCall() = 0;
+  virtual void Read(Response* resp) = 0;
+
+ protected:
+  void BindReactor(ClientReadReactor<Response>* reactor) {
+    reactor->BindReader(this);
+  }
+};
+
+template <class Request>
+class ClientCallbackWriter {
+ public:
+  virtual ~ClientCallbackWriter() {}
+  virtual void StartCall() = 0;
+  void Write(const Request* req) { Write(req, WriteOptions()); }
+  virtual void Write(const Request* req, WriteOptions options) = 0;
+  void WriteLast(const Request* req, WriteOptions options) {
+    Write(req, options.set_last_message());
+  }
+  virtual void WritesDone() = 0;
+
+ protected:
+  void BindReactor(ClientWriteReactor<Request>* reactor) {
+    reactor->BindWriter(this);
+  }
+};
+
+// The user must implement this reactor interface with reactions to each event
+// type that gets called by the library. An empty reaction is provided by
+// default
+template <class Request, class Response>
+class ClientBidiReactor {
+ public:
+  virtual ~ClientBidiReactor() {}
+  virtual void OnDone(const Status& s) {}
+  virtual void OnReadInitialMetadataDone(bool ok) {}
+  virtual void OnReadDone(bool ok) {}
+  virtual void OnWriteDone(bool ok) {}
+  virtual void OnWritesDoneDone(bool ok) {}
+
+  void StartCall() { stream_->StartCall(); }
+  void StartRead(Response* resp) { stream_->Read(resp); }
+  void StartWrite(const Request* req) { StartWrite(req, WriteOptions()); }
+  void StartWrite(const Request* req, WriteOptions options) {
+    stream_->Write(req, std::move(options));
+  }
+  void StartWriteLast(const Request* req, WriteOptions options) {
+    StartWrite(req, std::move(options.set_last_message()));
+  }
+  void StartWritesDone() { stream_->WritesDone(); }
+
+ private:
+  friend class ClientCallbackReaderWriter<Request, Response>;
+  void BindStream(ClientCallbackReaderWriter<Request, Response>* stream) {
+    stream_ = stream;
+  }
+  ClientCallbackReaderWriter<Request, Response>* stream_;
+};
+
+template <class Response>
+class ClientReadReactor {
+ public:
+  virtual ~ClientReadReactor() {}
+  virtual void OnDone(const Status& s) {}
+  virtual void OnReadInitialMetadataDone(bool ok) {}
+  virtual void OnReadDone(bool ok) {}
+
+  void StartCall() { reader_->StartCall(); }
+  void StartRead(Response* resp) { reader_->Read(resp); }
+
+ private:
+  friend class ClientCallbackReader<Response>;
+  void BindReader(ClientCallbackReader<Response>* reader) { reader_ = reader; }
+  ClientCallbackReader<Response>* reader_;
+};
+
+template <class Request>
+class ClientWriteReactor {
+ public:
+  virtual ~ClientWriteReactor() {}
+  virtual void OnDone(const Status& s) {}
+  virtual void OnReadInitialMetadataDone(bool ok) {}
+  virtual void OnWriteDone(bool ok) {}
+  virtual void OnWritesDoneDone(bool ok) {}
+
+  void StartCall() { writer_->StartCall(); }
+  void StartWrite(const Request* req) { StartWrite(req, WriteOptions()); }
+  void StartWrite(const Request* req, WriteOptions options) {
+    writer_->Write(req, std::move(options));
+  }
+  void StartWriteLast(const Request* req, WriteOptions options) {
+    StartWrite(req, std::move(options.set_last_message()));
+  }
+  void StartWritesDone() { writer_->WritesDone(); }
+
+ private:
+  friend class ClientCallbackWriter<Request>;
+  void BindWriter(ClientCallbackWriter<Request>* writer) { writer_ = writer; }
+  ClientCallbackWriter<Request>* writer_;
+};
+
+}  // namespace experimental
+
+namespace internal {
+
+// Forward declare factory classes for friendship
+template <class Request, class Response>
+class ClientCallbackReaderWriterFactory;
+template <class Response>
+class ClientCallbackReaderFactory;
+template <class Request>
+class ClientCallbackWriterFactory;
+
+template <class Request, class Response>
+class ClientCallbackReaderWriterImpl
+    : public ::grpc::experimental::ClientCallbackReaderWriter<Request,
+                                                              Response> {
+ public:
+  // always allocated against a call arena, no memory free required
+  static void operator delete(void* ptr, std::size_t size) {
+    assert(size == sizeof(ClientCallbackReaderWriterImpl));
+  }
+
+  // This operator should never be called as the memory should be freed as part
+  // of the arena destruction. It only exists to provide a matching operator
+  // delete to the operator new so that some compilers will not complain (see
+  // https://github.com/grpc/grpc/issues/11301) Note at the time of adding this
+  // there are no tests catching the compiler warning.
+  static void operator delete(void*, void*) { assert(0); }
+
+  void MaybeFinish() {
+    if (--callbacks_outstanding_ == 0) {
+      reactor_->OnDone(finish_status_);
+      auto* call = call_.call();
+      this->~ClientCallbackReaderWriterImpl();
+      g_core_codegen_interface->grpc_call_unref(call);
+    }
+  }
+
+  void StartCall() override {
+    // This call initiates two batches, plus any backlog, each with a callback
+    // 1. Send initial metadata (unless corked) + recv initial metadata
+    // 2. Any read backlog
+    // 3. Recv trailing metadata, on_completion callback
+    // 4. Any write backlog
+    started_ = true;
+
+    start_tag_.Set(call_.call(),
+                   [this](bool ok) {
+                     reactor_->OnReadInitialMetadataDone(ok);
+                     MaybeFinish();
+                   },
+                   &start_ops_);
+    if (!start_corked_) {
+      start_ops_.SendInitialMetadata(&context_->send_initial_metadata_,
+                                     context_->initial_metadata_flags());
+    }
+    start_ops_.RecvInitialMetadata(context_);
+    start_ops_.set_core_cq_tag(&start_tag_);
+    call_.PerformOps(&start_ops_);
+
+    // Also set up the read and write tags so that they don't have to be set up
+    // each time
+    write_tag_.Set(call_.call(),
+                   [this](bool ok) {
+                     reactor_->OnWriteDone(ok);
+                     MaybeFinish();
+                   },
+                   &write_ops_);
+    write_ops_.set_core_cq_tag(&write_tag_);
+
+    read_tag_.Set(call_.call(),
+                  [this](bool ok) {
+                    reactor_->OnReadDone(ok);
+                    MaybeFinish();
+                  },
+                  &read_ops_);
+    read_ops_.set_core_cq_tag(&read_tag_);
+    if (read_ops_at_start_) {
+      call_.PerformOps(&read_ops_);
+    }
+
+    finish_tag_.Set(call_.call(), [this](bool ok) { MaybeFinish(); },
+                    &finish_ops_);
+    finish_ops_.ClientRecvStatus(context_, &finish_status_);
+    finish_ops_.set_core_cq_tag(&finish_tag_);
+    call_.PerformOps(&finish_ops_);
+
+    if (write_ops_at_start_) {
+      call_.PerformOps(&write_ops_);
+    }
+
+    if (writes_done_ops_at_start_) {
+      call_.PerformOps(&writes_done_ops_);
+    }
+  }
+
+  void Read(Response* msg) override {
+    read_ops_.RecvMessage(msg);
+    callbacks_outstanding_++;
+    if (started_) {
+      call_.PerformOps(&read_ops_);
+    } else {
+      read_ops_at_start_ = true;
+    }
+  }
+
+  void Write(const Request* msg, WriteOptions options) override {
+    if (start_corked_) {
+      write_ops_.SendInitialMetadata(&context_->send_initial_metadata_,
+                                     context_->initial_metadata_flags());
+      start_corked_ = false;
+    }
+    // TODO(vjpai): don't assert
+    GPR_CODEGEN_ASSERT(write_ops_.SendMessage(*msg).ok());
+
+    if (options.is_last_message()) {
+      options.set_buffer_hint();
+      write_ops_.ClientSendClose();
+    }
+    callbacks_outstanding_++;
+    if (started_) {
+      call_.PerformOps(&write_ops_);
+    } else {
+      write_ops_at_start_ = true;
+    }
+  }
+  void WritesDone() override {
+    if (start_corked_) {
+      writes_done_ops_.SendInitialMetadata(&context_->send_initial_metadata_,
+                                           context_->initial_metadata_flags());
+      start_corked_ = false;
+    }
+    writes_done_ops_.ClientSendClose();
+    writes_done_tag_.Set(call_.call(),
+                         [this](bool ok) {
+                           reactor_->OnWritesDoneDone(ok);
+                           MaybeFinish();
+                         },
+                         &writes_done_ops_);
+    writes_done_ops_.set_core_cq_tag(&writes_done_tag_);
+    callbacks_outstanding_++;
+    if (started_) {
+      call_.PerformOps(&writes_done_ops_);
+    } else {
+      writes_done_ops_at_start_ = true;
+    }
+  }
+
+ private:
+  friend class ClientCallbackReaderWriterFactory<Request, Response>;
+
+  ClientCallbackReaderWriterImpl(
+      Call call, ClientContext* context,
+      ::grpc::experimental::ClientBidiReactor<Request, Response>* reactor)
+      : context_(context),
+        call_(call),
+        reactor_(reactor),
+        start_corked_(context_->initial_metadata_corked_) {
+    this->BindReactor(reactor);
+  }
+
+  ClientContext* context_;
+  Call call_;
+  ::grpc::experimental::ClientBidiReactor<Request, Response>* reactor_;
+
+  CallOpSet<CallOpSendInitialMetadata, CallOpRecvInitialMetadata> start_ops_;
+  CallbackWithSuccessTag start_tag_;
+  bool start_corked_;
+
+  CallOpSet<CallOpClientRecvStatus> finish_ops_;
+  CallbackWithSuccessTag finish_tag_;
+  Status finish_status_;
+
+  CallOpSet<CallOpSendInitialMetadata, CallOpSendMessage, CallOpClientSendClose>
+      write_ops_;
+  CallbackWithSuccessTag write_tag_;
+  bool write_ops_at_start_{false};
+
+  CallOpSet<CallOpSendInitialMetadata, CallOpClientSendClose> writes_done_ops_;
+  CallbackWithSuccessTag writes_done_tag_;
+  bool writes_done_ops_at_start_{false};
+
+  CallOpSet<CallOpRecvMessage<Response>> read_ops_;
+  CallbackWithSuccessTag read_tag_;
+  bool read_ops_at_start_{false};
+
+  // Minimum of 2 outstanding callbacks to pre-register for start and finish
+  std::atomic_int callbacks_outstanding_{2};
+  bool started_{false};
+};
+
+template <class Request, class Response>
+class ClientCallbackReaderWriterFactory {
+ public:
+  static void Create(
+      ChannelInterface* channel, const ::grpc::internal::RpcMethod& method,
+      ClientContext* context,
+      ::grpc::experimental::ClientBidiReactor<Request, Response>* reactor) {
+    Call call = channel->CreateCall(method, context, channel->CallbackCQ());
+
+    g_core_codegen_interface->grpc_call_ref(call.call());
+    new (g_core_codegen_interface->grpc_call_arena_alloc(
+        call.call(), sizeof(ClientCallbackReaderWriterImpl<Request, Response>)))
+        ClientCallbackReaderWriterImpl<Request, Response>(call, context,
+                                                          reactor);
+  }
+};
+
+template <class Response>
+class ClientCallbackReaderImpl
+    : public ::grpc::experimental::ClientCallbackReader<Response> {
+ public:
+  // always allocated against a call arena, no memory free required
+  static void operator delete(void* ptr, std::size_t size) {
+    assert(size == sizeof(ClientCallbackReaderImpl));
+  }
+
+  // This operator should never be called as the memory should be freed as part
+  // of the arena destruction. It only exists to provide a matching operator
+  // delete to the operator new so that some compilers will not complain (see
+  // https://github.com/grpc/grpc/issues/11301) Note at the time of adding this
+  // there are no tests catching the compiler warning.
+  static void operator delete(void*, void*) { assert(0); }
+
+  void MaybeFinish() {
+    if (--callbacks_outstanding_ == 0) {
+      reactor_->OnDone(finish_status_);
+      auto* call = call_.call();
+      this->~ClientCallbackReaderImpl();
+      g_core_codegen_interface->grpc_call_unref(call);
+    }
+  }
+
+  void StartCall() override {
+    // This call initiates two batches, plus any backlog, each with a callback
+    // 1. Send initial metadata (unless corked) + recv initial metadata
+    // 2. Any backlog
+    // 3. Recv trailing metadata, on_completion callback
+    started_ = true;
+
+    start_tag_.Set(call_.call(),
+                   [this](bool ok) {
+                     reactor_->OnReadInitialMetadataDone(ok);
+                     MaybeFinish();
+                   },
+                   &start_ops_);
+    start_ops_.SendInitialMetadata(&context_->send_initial_metadata_,
+                                   context_->initial_metadata_flags());
+    start_ops_.RecvInitialMetadata(context_);
+    start_ops_.set_core_cq_tag(&start_tag_);
+    call_.PerformOps(&start_ops_);
+
+    // Also set up the read tag so it doesn't have to be set up each time
+    read_tag_.Set(call_.call(),
+                  [this](bool ok) {
+                    reactor_->OnReadDone(ok);
+                    MaybeFinish();
+                  },
+                  &read_ops_);
+    read_ops_.set_core_cq_tag(&read_tag_);
+    if (read_ops_at_start_) {
+      call_.PerformOps(&read_ops_);
+    }
+
+    finish_tag_.Set(call_.call(), [this](bool ok) { MaybeFinish(); },
+                    &finish_ops_);
+    finish_ops_.ClientRecvStatus(context_, &finish_status_);
+    finish_ops_.set_core_cq_tag(&finish_tag_);
+    call_.PerformOps(&finish_ops_);
+  }
+
+  void Read(Response* msg) override {
+    read_ops_.RecvMessage(msg);
+    callbacks_outstanding_++;
+    if (started_) {
+      call_.PerformOps(&read_ops_);
+    } else {
+      read_ops_at_start_ = true;
+    }
+  }
+
+ private:
+  friend class ClientCallbackReaderFactory<Response>;
+
+  template <class Request>
+  ClientCallbackReaderImpl(
+      Call call, ClientContext* context, Request* request,
+      ::grpc::experimental::ClientReadReactor<Response>* reactor)
+      : context_(context), call_(call), reactor_(reactor) {
+    this->BindReactor(reactor);
+    // TODO(vjpai): don't assert
+    GPR_CODEGEN_ASSERT(start_ops_.SendMessage(*request).ok());
+    start_ops_.ClientSendClose();
+  }
+
+  ClientContext* context_;
+  Call call_;
+  ::grpc::experimental::ClientReadReactor<Response>* reactor_;
+
+  CallOpSet<CallOpSendInitialMetadata, CallOpSendMessage, CallOpClientSendClose,
+            CallOpRecvInitialMetadata>
+      start_ops_;
+  CallbackWithSuccessTag start_tag_;
+
+  CallOpSet<CallOpClientRecvStatus> finish_ops_;
+  CallbackWithSuccessTag finish_tag_;
+  Status finish_status_;
+
+  CallOpSet<CallOpRecvMessage<Response>> read_ops_;
+  CallbackWithSuccessTag read_tag_;
+  bool read_ops_at_start_{false};
+
+  // Minimum of 2 outstanding callbacks to pre-register for start and finish
+  std::atomic_int callbacks_outstanding_{2};
+  bool started_{false};
+};
+
+template <class Response>
+class ClientCallbackReaderFactory {
+ public:
+  template <class Request>
+  static void Create(
+      ChannelInterface* channel, const ::grpc::internal::RpcMethod& method,
+      ClientContext* context, const Request* request,
+      ::grpc::experimental::ClientReadReactor<Response>* reactor) {
+    Call call = channel->CreateCall(method, context, channel->CallbackCQ());
+
+    g_core_codegen_interface->grpc_call_ref(call.call());
+    new (g_core_codegen_interface->grpc_call_arena_alloc(
+        call.call(), sizeof(ClientCallbackReaderImpl<Response>)))
+        ClientCallbackReaderImpl<Response>(call, context, request, reactor);
+  }
+};
+
+template <class Request>
+class ClientCallbackWriterImpl
+    : public ::grpc::experimental::ClientCallbackWriter<Request> {
+ public:
+  // always allocated against a call arena, no memory free required
+  static void operator delete(void* ptr, std::size_t size) {
+    assert(size == sizeof(ClientCallbackWriterImpl));
+  }
+
+  // This operator should never be called as the memory should be freed as part
+  // of the arena destruction. It only exists to provide a matching operator
+  // delete to the operator new so that some compilers will not complain (see
+  // https://github.com/grpc/grpc/issues/11301) Note at the time of adding this
+  // there are no tests catching the compiler warning.
+  static void operator delete(void*, void*) { assert(0); }
+
+  void MaybeFinish() {
+    if (--callbacks_outstanding_ == 0) {
+      reactor_->OnDone(finish_status_);
+      auto* call = call_.call();
+      this->~ClientCallbackWriterImpl();
+      g_core_codegen_interface->grpc_call_unref(call);
+    }
+  }
+
+  void StartCall() override {
+    // This call initiates two batches, plus any backlog, each with a callback
+    // 1. Send initial metadata (unless corked) + recv initial metadata
+    // 2. Recv trailing metadata, on_completion callback
+    // 3. Any backlog
+    started_ = true;
+
+    start_tag_.Set(call_.call(),
+                   [this](bool ok) {
+                     reactor_->OnReadInitialMetadataDone(ok);
+                     MaybeFinish();
+                   },
+                   &start_ops_);
+    if (!start_corked_) {
+      start_ops_.SendInitialMetadata(&context_->send_initial_metadata_,
+                                     context_->initial_metadata_flags());
+    }
+    start_ops_.RecvInitialMetadata(context_);
+    start_ops_.set_core_cq_tag(&start_tag_);
+    call_.PerformOps(&start_ops_);
+
+    // Also set up the read and write tags so that they don't have to be set up
+    // each time
+    write_tag_.Set(call_.call(),
+                   [this](bool ok) {
+                     reactor_->OnWriteDone(ok);
+                     MaybeFinish();
+                   },
+                   &write_ops_);
+    write_ops_.set_core_cq_tag(&write_tag_);
+
+    finish_tag_.Set(call_.call(), [this](bool ok) { MaybeFinish(); },
+                    &finish_ops_);
+    finish_ops_.ClientRecvStatus(context_, &finish_status_);
+    finish_ops_.set_core_cq_tag(&finish_tag_);
+    call_.PerformOps(&finish_ops_);
+
+    if (write_ops_at_start_) {
+      call_.PerformOps(&write_ops_);
+    }
+
+    if (writes_done_ops_at_start_) {
+      call_.PerformOps(&writes_done_ops_);
+    }
+  }
+
+  void Write(const Request* msg, WriteOptions options) override {
+    if (start_corked_) {
+      write_ops_.SendInitialMetadata(&context_->send_initial_metadata_,
+                                     context_->initial_metadata_flags());
+      start_corked_ = false;
+    }
+    // TODO(vjpai): don't assert
+    GPR_CODEGEN_ASSERT(write_ops_.SendMessage(*msg).ok());
+
+    if (options.is_last_message()) {
+      options.set_buffer_hint();
+      write_ops_.ClientSendClose();
+    }
+    callbacks_outstanding_++;
+    if (started_) {
+      call_.PerformOps(&write_ops_);
+    } else {
+      write_ops_at_start_ = true;
+    }
+  }
+  void WritesDone() override {
+    if (start_corked_) {
+      writes_done_ops_.SendInitialMetadata(&context_->send_initial_metadata_,
+                                           context_->initial_metadata_flags());
+      start_corked_ = false;
+    }
+    writes_done_ops_.ClientSendClose();
+    writes_done_tag_.Set(call_.call(),
+                         [this](bool ok) {
+                           reactor_->OnWritesDoneDone(ok);
+                           MaybeFinish();
+                         },
+                         &writes_done_ops_);
+    writes_done_ops_.set_core_cq_tag(&writes_done_tag_);
+    callbacks_outstanding_++;
+    if (started_) {
+      call_.PerformOps(&writes_done_ops_);
+    } else {
+      writes_done_ops_at_start_ = true;
+    }
+  }
+
+ private:
+  friend class ClientCallbackWriterFactory<Request>;
+
+  template <class Response>
+  ClientCallbackWriterImpl(
+      Call call, ClientContext* context, Response* response,
+      ::grpc::experimental::ClientWriteReactor<Request>* reactor)
+      : context_(context),
+        call_(call),
+        reactor_(reactor),
+        start_corked_(context_->initial_metadata_corked_) {
+    this->BindReactor(reactor);
+    finish_ops_.RecvMessage(response);
+    finish_ops_.AllowNoMessage();
+  }
+
+  ClientContext* context_;
+  Call call_;
+  ::grpc::experimental::ClientWriteReactor<Request>* reactor_;
+
+  CallOpSet<CallOpSendInitialMetadata, CallOpRecvInitialMetadata> start_ops_;
+  CallbackWithSuccessTag start_tag_;
+  bool start_corked_;
+
+  CallOpSet<CallOpGenericRecvMessage, CallOpClientRecvStatus> finish_ops_;
+  CallbackWithSuccessTag finish_tag_;
+  Status finish_status_;
+
+  CallOpSet<CallOpSendInitialMetadata, CallOpSendMessage, CallOpClientSendClose>
+      write_ops_;
+  CallbackWithSuccessTag write_tag_;
+  bool write_ops_at_start_{false};
+
+  CallOpSet<CallOpSendInitialMetadata, CallOpClientSendClose> writes_done_ops_;
+  CallbackWithSuccessTag writes_done_tag_;
+  bool writes_done_ops_at_start_{false};
+
+  // Minimum of 2 outstanding callbacks to pre-register for start and finish
+  std::atomic_int callbacks_outstanding_{2};
+  bool started_{false};
+};
+
+template <class Request>
+class ClientCallbackWriterFactory {
+ public:
+  template <class Response>
+  static void Create(
+      ChannelInterface* channel, const ::grpc::internal::RpcMethod& method,
+      ClientContext* context, Response* response,
+      ::grpc::experimental::ClientWriteReactor<Request>* reactor) {
+    Call call = channel->CreateCall(method, context, channel->CallbackCQ());
+
+    g_core_codegen_interface->grpc_call_ref(call.call());
+    new (g_core_codegen_interface->grpc_call_arena_alloc(
+        call.call(), sizeof(ClientCallbackWriterImpl<Request>)))
+        ClientCallbackWriterImpl<Request>(call, context, response, reactor);
+  }
+};
 
 }  // namespace internal
 }  // namespace grpc
diff --git a/include/grpcpp/impl/codegen/client_context.h b/include/grpcpp/impl/codegen/client_context.h
index 75b955e760..6059c3c58a 100644
--- a/include/grpcpp/impl/codegen/client_context.h
+++ b/include/grpcpp/impl/codegen/client_context.h
@@ -71,6 +71,12 @@ template <class InputMessage, class OutputMessage>
 class BlockingUnaryCallImpl;
 template <class InputMessage, class OutputMessage>
 class CallbackUnaryCallImpl;
+template <class Request, class Response>
+class ClientCallbackReaderWriterImpl;
+template <class Response>
+class ClientCallbackReaderImpl;
+template <class Request>
+class ClientCallbackWriterImpl;
 }  // namespace internal
 
 template <class R>
@@ -394,6 +400,12 @@ class ClientContext {
   friend class ::grpc::internal::BlockingUnaryCallImpl;
   template <class InputMessage, class OutputMessage>
   friend class ::grpc::internal::CallbackUnaryCallImpl;
+  template <class Request, class Response>
+  friend class ::grpc::internal::ClientCallbackReaderWriterImpl;
+  template <class Response>
+  friend class ::grpc::internal::ClientCallbackReaderImpl;
+  template <class Request>
+  friend class ::grpc::internal::ClientCallbackWriterImpl;
 
   // Used by friend class CallOpClientRecvStatus
   void set_debug_error_string(const grpc::string& debug_error_string) {