async_stream.h

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//
//
// Copyright 2015 gRPC authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
//
 
#ifndef GRPCPP_SUPPORT_ASYNC_STREAM_H
#define GRPCPP_SUPPORT_ASYNC_STREAM_H
 
#include <grpc/grpc.h>
#include <grpcpp/impl/call.h>
#include <grpcpp/impl/channel_interface.h>
#include <grpcpp/impl/service_type.h>
#include <grpcpp/server_context.h>
#include <grpcpp/support/status.h>
 
#include "absl/log/absl_check.h"
 
namespace grpc {
 
namespace internal {
class ClientAsyncStreamingInterface {
 public:
  virtual ~ClientAsyncStreamingInterface() {}
 
  virtual void StartCall(void* tag) = 0;
 
  virtual void ReadInitialMetadata(void* tag) = 0;
 
  virtual void Finish(grpc::Status* status, void* tag) = 0;
};
 
template <class R>
class AsyncReaderInterface {
 public:
  virtual ~AsyncReaderInterface() {}
 
  virtual void Read(R* msg, void* tag) = 0;
};
 
template <class W>
class AsyncWriterInterface {
 public:
  virtual ~AsyncWriterInterface() {}
 
  virtual void Write(const W& msg, void* tag) = 0;
 
  virtual void Write(const W& msg, grpc::WriteOptions options, void* tag) = 0;
 
  void WriteLast(const W& msg, grpc::WriteOptions options, void* tag) {
    Write(msg, options.set_last_message(), tag);
  }
};
 
}  // namespace internal
 
template <class R>
class ClientAsyncReaderInterface
    : public internal::ClientAsyncStreamingInterface,
      public internal::AsyncReaderInterface<R> {};
 
namespace internal {
template <class R>
class ClientAsyncReaderFactory {
 public:
  template <class W>
  static ClientAsyncReader<R>* Create(grpc::ChannelInterface* channel,
                                      grpc::CompletionQueue* cq,
                                      const grpc::internal::RpcMethod& method,
                                      grpc::ClientContext* context,
                                      const W& request, bool start, void* tag) {
    grpc::internal::Call call = channel->CreateCall(method, context, cq);
    return new (
        grpc_call_arena_alloc(call.call(), sizeof(ClientAsyncReader<R>)))
        ClientAsyncReader<R>(channel, call, context, request, start, tag);
  }
};
}  // namespace internal
 
template <class R>
class ClientAsyncReader final : public ClientAsyncReaderInterface<R> {
 public:
  // always allocated against a call arena, no memory free required
  static void operator delete(void* /*ptr*/, std::size_t size) {
    ABSL_CHECK_EQ(size, sizeof(ClientAsyncReader));
  }
 
  // 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*) { ABSL_CHECK(false); }
 
  void StartCall(void* tag) override {
    ABSL_CHECK(!started_);
    started_ = true;
    StartCallInternal(tag);
  }
 
  void ReadInitialMetadata(void* tag) override {
    ABSL_CHECK(started_);
    ABSL_CHECK(!context_->initial_metadata_received_);
 
    meta_ops_.set_output_tag(tag);
    meta_ops_.RecvInitialMetadata(context_);
    call_.PerformOps(&meta_ops_);
  }
 
  void Read(R* msg, void* tag) override {
    ABSL_CHECK(started_);
    read_ops_.set_output_tag(tag);
    if (!context_->initial_metadata_received_) {
      read_ops_.RecvInitialMetadata(context_);
    }
    read_ops_.RecvMessage(msg);
    call_.PerformOps(&read_ops_);
  }
 
  void Finish(grpc::Status* status, void* tag) override {
    ABSL_CHECK(started_);
    finish_ops_.set_output_tag(tag);
    if (!context_->initial_metadata_received_) {
      finish_ops_.RecvInitialMetadata(context_);
    }
    finish_ops_.ClientRecvStatus(context_, status);
    call_.PerformOps(&finish_ops_);
  }
 
 private:
  friend class internal::ClientAsyncReaderFactory<R>;
  template <class W>
  ClientAsyncReader(grpc::ChannelInterface* channel, grpc::internal::Call call,
                    grpc::ClientContext* context, const W& request, bool start,
                    void* tag)
      : channel_(channel), context_(context), call_(call), started_(start) {
    // TODO(ctiller): don't assert
    ABSL_CHECK(
        init_ops_.SendMessage(request, channel_->memory_allocator()).ok());
    init_ops_.ClientSendClose();
    if (start) {
      StartCallInternal(tag);
    } else {
      ABSL_CHECK(tag == nullptr);
    }
  }
 
  void StartCallInternal(void* tag) {
    init_ops_.SendInitialMetadata(&context_->send_initial_metadata_,
                                  context_->initial_metadata_flags());
    init_ops_.set_output_tag(tag);
    call_.PerformOps(&init_ops_);
  }
 
  grpc::ChannelInterface* channel_;
  grpc::ClientContext* context_;
  grpc::internal::Call call_;
  bool started_;
  grpc::internal::CallOpSet<grpc::internal::CallOpSendInitialMetadata,
                            grpc::internal::CallOpSendMessage,
                            grpc::internal::CallOpClientSendClose>
      init_ops_;
  grpc::internal::CallOpSet<grpc::internal::CallOpRecvInitialMetadata>
      meta_ops_;
  grpc::internal::CallOpSet<grpc::internal::CallOpRecvInitialMetadata,
                            grpc::internal::CallOpRecvMessage<R>>
      read_ops_;
  grpc::internal::CallOpSet<grpc::internal::CallOpRecvInitialMetadata,
                            grpc::internal::CallOpClientRecvStatus>
      finish_ops_;
};
 
template <class W>
class ClientAsyncWriterInterface
    : public internal::ClientAsyncStreamingInterface,
      public internal::AsyncWriterInterface<W> {
 public:
  virtual void WritesDone(void* tag) = 0;
};
 
namespace internal {
template <class W>
class ClientAsyncWriterFactory {
 public:
  template <class R>
  static ClientAsyncWriter<W>* Create(grpc::ChannelInterface* channel,
                                      grpc::CompletionQueue* cq,
                                      const grpc::internal::RpcMethod& method,
                                      grpc::ClientContext* context, R* response,
                                      bool start, void* tag) {
    grpc::internal::Call call = channel->CreateCall(method, context, cq);
    return new (
        grpc_call_arena_alloc(call.call(), sizeof(ClientAsyncWriter<W>)))
        ClientAsyncWriter<W>(channel, call, context, response, start, tag);
  }
};
}  // namespace internal
 
template <class W>
class ClientAsyncWriter final : public ClientAsyncWriterInterface<W> {
 public:
  // always allocated against a call arena, no memory free required
  static void operator delete(void* /*ptr*/, std::size_t size) {
    ABSL_CHECK_EQ(size, sizeof(ClientAsyncWriter));
  }
 
  // 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*) { ABSL_CHECK(false); }
 
  void StartCall(void* tag) override {
    ABSL_CHECK(!started_);
    started_ = true;
    StartCallInternal(tag);
  }
 
  void ReadInitialMetadata(void* tag) override {
    ABSL_CHECK(started_);
    ABSL_CHECK(!context_->initial_metadata_received_);
 
    meta_ops_.set_output_tag(tag);
    meta_ops_.RecvInitialMetadata(context_);
    call_.PerformOps(&meta_ops_);
  }
 
  void Write(const W& msg, void* tag) override {
    ABSL_CHECK(started_);
    write_ops_.set_output_tag(tag);
    // TODO(ctiller): don't assert
    ABSL_CHECK(write_ops_.SendMessage(msg, channel_->memory_allocator()).ok());
    call_.PerformOps(&write_ops_);
  }
 
  void Write(const W& msg, grpc::WriteOptions options, void* tag) override {
    ABSL_CHECK(started_);
    write_ops_.set_output_tag(tag);
    if (options.is_last_message()) {
      options.set_buffer_hint();
      write_ops_.ClientSendClose();
    }
 
    // TODO(ctiller): don't assert
    ABSL_CHECK(
        write_ops_.SendMessage(msg, options, channel_->memory_allocator())
            .ok());
    call_.PerformOps(&write_ops_);
  }
 
  void WritesDone(void* tag) override {
    ABSL_CHECK(started_);
    write_ops_.set_output_tag(tag);
    write_ops_.ClientSendClose();
    call_.PerformOps(&write_ops_);
  }
 
  void Finish(grpc::Status* status, void* tag) override {
    ABSL_CHECK(started_);
    finish_ops_.set_output_tag(tag);
    if (!context_->initial_metadata_received_) {
      finish_ops_.RecvInitialMetadata(context_);
    }
    finish_ops_.ClientRecvStatus(context_, status);
    call_.PerformOps(&finish_ops_);
  }
 
 private:
  friend class internal::ClientAsyncWriterFactory<W>;
  template <class R>
  ClientAsyncWriter(grpc::ChannelInterface* channel, grpc::internal::Call call,
                    grpc::ClientContext* context, R* response, bool start,
                    void* tag)
      : channel_(channel), context_(context), call_(call), started_(start) {
    finish_ops_.RecvMessage(response);
    finish_ops_.AllowNoMessage();
    if (start) {
      StartCallInternal(tag);
    } else {
      ABSL_CHECK(tag == nullptr);
    }
  }
 
  void StartCallInternal(void* tag) {
    write_ops_.SendInitialMetadata(&context_->send_initial_metadata_,
                                   context_->initial_metadata_flags());
    // if corked bit is set in context, we just keep the initial metadata
    // buffered up to coalesce with later message send. No op is performed.
    if (!context_->initial_metadata_corked_) {
      write_ops_.set_output_tag(tag);
      call_.PerformOps(&write_ops_);
    }
  }
 
  grpc::ChannelInterface* channel_;
  grpc::ClientContext* context_;
  grpc::internal::Call call_;
  bool started_;
  grpc::internal::CallOpSet<grpc::internal::CallOpRecvInitialMetadata>
      meta_ops_;
  grpc::internal::CallOpSet<grpc::internal::CallOpSendInitialMetadata,
                            grpc::internal::CallOpSendMessage,
                            grpc::internal::CallOpClientSendClose>
      write_ops_;
  grpc::internal::CallOpSet<grpc::internal::CallOpRecvInitialMetadata,
                            grpc::internal::CallOpGenericRecvMessage,
                            grpc::internal::CallOpClientRecvStatus>
      finish_ops_;
};
 
template <class W, class R>
class ClientAsyncReaderWriterInterface
    : public internal::ClientAsyncStreamingInterface,
      public internal::AsyncWriterInterface<W>,
      public internal::AsyncReaderInterface<R> {
 public:
  virtual void WritesDone(void* tag) = 0;
};
 
namespace internal {
template <class W, class R>
class ClientAsyncReaderWriterFactory {
 public:
  static ClientAsyncReaderWriter<W, R>* Create(
      grpc::ChannelInterface* channel, grpc::CompletionQueue* cq,
      const grpc::internal::RpcMethod& method, grpc::ClientContext* context,
      bool start, void* tag) {
    grpc::internal::Call call = channel->CreateCall(method, context, cq);
 
    return new (grpc_call_arena_alloc(call.call(),
                                      sizeof(ClientAsyncReaderWriter<W, R>)))
        ClientAsyncReaderWriter<W, R>(channel, call, context, start, tag);
  }
};
}  // namespace internal
 
template <class W, class R>
class ClientAsyncReaderWriter final
    : public ClientAsyncReaderWriterInterface<W, R> {
 public:
  // always allocated against a call arena, no memory free required
  static void operator delete(void* /*ptr*/, std::size_t size) {
    ABSL_CHECK_EQ(size, sizeof(ClientAsyncReaderWriter));
  }
 
  // 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*) { ABSL_CHECK(false); }
 
  void StartCall(void* tag) override {
    ABSL_CHECK(!started_);
    started_ = true;
    StartCallInternal(tag);
  }
 
  void ReadInitialMetadata(void* tag) override {
    ABSL_CHECK(started_);
    ABSL_CHECK(!context_->initial_metadata_received_);
 
    meta_ops_.set_output_tag(tag);
    meta_ops_.RecvInitialMetadata(context_);
    call_.PerformOps(&meta_ops_);
  }
 
  void Read(R* msg, void* tag) override {
    ABSL_CHECK(started_);
    read_ops_.set_output_tag(tag);
    if (!context_->initial_metadata_received_) {
      read_ops_.RecvInitialMetadata(context_);
    }
    read_ops_.RecvMessage(msg);
    call_.PerformOps(&read_ops_);
  }
 
  void Write(const W& msg, void* tag) override {
    ABSL_CHECK(started_);
    write_ops_.set_output_tag(tag);
    // TODO(ctiller): don't assert
    ABSL_CHECK(write_ops_.SendMessage(msg, channel_->memory_allocator()).ok());
    call_.PerformOps(&write_ops_);
  }
 
  void Write(const W& msg, grpc::WriteOptions options, void* tag) override {
    ABSL_CHECK(started_);
    write_ops_.set_output_tag(tag);
    if (options.is_last_message()) {
      options.set_buffer_hint();
      write_ops_.ClientSendClose();
    }
    // TODO(ctiller): don't assert
    ABSL_CHECK(
        write_ops_.SendMessage(msg, options, channel_->memory_allocator())
            .ok());
    call_.PerformOps(&write_ops_);
  }
 
  void WritesDone(void* tag) override {
    ABSL_CHECK(started_);
    write_ops_.set_output_tag(tag);
    write_ops_.ClientSendClose();
    call_.PerformOps(&write_ops_);
  }
 
  void Finish(grpc::Status* status, void* tag) override {
    ABSL_CHECK(started_);
    finish_ops_.set_output_tag(tag);
    if (!context_->initial_metadata_received_) {
      finish_ops_.RecvInitialMetadata(context_);
    }
    finish_ops_.ClientRecvStatus(context_, status);
    call_.PerformOps(&finish_ops_);
  }
 
 private:
  friend class internal::ClientAsyncReaderWriterFactory<W, R>;
  ClientAsyncReaderWriter(grpc::ChannelInterface* channel,
                          grpc::internal::Call call,
                          grpc::ClientContext* context, bool start, void* tag)
      : channel_(channel), context_(context), call_(call), started_(start) {
    if (start) {
      StartCallInternal(tag);
    } else {
      ABSL_CHECK(tag == nullptr);
    }
  }
 
  void StartCallInternal(void* tag) {
    write_ops_.SendInitialMetadata(&context_->send_initial_metadata_,
                                   context_->initial_metadata_flags());
    // if corked bit is set in context, we just keep the initial metadata
    // buffered up to coalesce with later message send. No op is performed.
    if (!context_->initial_metadata_corked_) {
      write_ops_.set_output_tag(tag);
      call_.PerformOps(&write_ops_);
    }
  }
 
  grpc::ChannelInterface* channel_;
  grpc::ClientContext* context_;
  grpc::internal::Call call_;
  bool started_;
  grpc::internal::CallOpSet<grpc::internal::CallOpRecvInitialMetadata>
      meta_ops_;
  grpc::internal::CallOpSet<grpc::internal::CallOpRecvInitialMetadata,
                            grpc::internal::CallOpRecvMessage<R>>
      read_ops_;
  grpc::internal::CallOpSet<grpc::internal::CallOpSendInitialMetadata,
                            grpc::internal::CallOpSendMessage,
                            grpc::internal::CallOpClientSendClose>
      write_ops_;
  grpc::internal::CallOpSet<grpc::internal::CallOpRecvInitialMetadata,
                            grpc::internal::CallOpClientRecvStatus>
      finish_ops_;
};
 
template <class W, class R>
class ServerAsyncReaderInterface
    : public grpc::internal::ServerAsyncStreamingInterface,
      public internal::AsyncReaderInterface<R> {
 public:
  virtual void Finish(const W& msg, const grpc::Status& status, void* tag) = 0;
 
  virtual void FinishWithError(const grpc::Status& status, void* tag) = 0;
};
 
template <class W, class R>
class ServerAsyncReader final : public ServerAsyncReaderInterface<W, R> {
 public:
  explicit ServerAsyncReader(grpc::ServerContext* ctx)
      : call_(nullptr, nullptr, nullptr), ctx_(ctx) {}
 
  void SendInitialMetadata(void* tag) override {
    ABSL_CHECK(!ctx_->sent_initial_metadata_);
 
    meta_ops_.set_output_tag(tag);
    meta_ops_.SendInitialMetadata(&ctx_->initial_metadata_,
                                  ctx_->initial_metadata_flags());
    if (ctx_->compression_level_set()) {
      meta_ops_.set_compression_level(ctx_->compression_level());
    }
    ctx_->sent_initial_metadata_ = true;
    call_.PerformOps(&meta_ops_);
  }
 
  void Read(R* msg, void* tag) override {
    read_ops_.set_output_tag(tag);
    read_ops_.RecvMessage(msg);
    call_.PerformOps(&read_ops_);
  }
 
  void Finish(const W& msg, const grpc::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;
    }
    // The response is dropped if the status is not OK.
    if (status.ok()) {
      finish_ops_.ServerSendStatus(
          &ctx_->trailing_metadata_,
          finish_ops_.SendMessage(msg, ctx_->memory_allocator()));
    } else {
      finish_ops_.ServerSendStatus(&ctx_->trailing_metadata_, status);
    }
    call_.PerformOps(&finish_ops_);
  }
 
  void FinishWithError(const grpc::Status& status, void* tag) override {
    ABSL_CHECK(!status.ok());
    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;
    }
    finish_ops_.ServerSendStatus(&ctx_->trailing_metadata_, status);
    call_.PerformOps(&finish_ops_);
  }
 
 private:
  void BindCall(grpc::internal::Call* call) override { call_ = *call; }
 
  grpc::internal::Call call_;
  grpc::ServerContext* ctx_;
  grpc::internal::CallOpSet<grpc::internal::CallOpSendInitialMetadata>
      meta_ops_;
  grpc::internal::CallOpSet<grpc::internal::CallOpRecvMessage<R>> read_ops_;
  grpc::internal::CallOpSet<grpc::internal::CallOpSendInitialMetadata,
                            grpc::internal::CallOpSendMessage,
                            grpc::internal::CallOpServerSendStatus>
      finish_ops_;
};
 
template <class W>
class ServerAsyncWriterInterface
    : public grpc::internal::ServerAsyncStreamingInterface,
      public internal::AsyncWriterInterface<W> {
 public:
  virtual void Finish(const grpc::Status& status, void* tag) = 0;
 
  virtual void WriteAndFinish(const W& msg, grpc::WriteOptions options,
                              const grpc::Status& status, void* tag) = 0;
};
 
template <class W>
class ServerAsyncWriter final : public ServerAsyncWriterInterface<W> {
 public:
  explicit ServerAsyncWriter(grpc::ServerContext* ctx)
      : call_(nullptr, nullptr, nullptr), ctx_(ctx) {}
 
  void SendInitialMetadata(void* tag) override {
    ABSL_CHECK(!ctx_->sent_initial_metadata_);
 
    meta_ops_.set_output_tag(tag);
    meta_ops_.SendInitialMetadata(&ctx_->initial_metadata_,
                                  ctx_->initial_metadata_flags());
    if (ctx_->compression_level_set()) {
      meta_ops_.set_compression_level(ctx_->compression_level());
    }
    ctx_->sent_initial_metadata_ = true;
    call_.PerformOps(&meta_ops_);
  }
 
  void Write(const W& msg, void* tag) override {
    write_ops_.set_output_tag(tag);
    EnsureInitialMetadataSent(&write_ops_);
    // TODO(ctiller): don't assert
    ABSL_CHECK(write_ops_.SendMessage(msg, ctx_->memory_allocator()).ok());
    call_.PerformOps(&write_ops_);
  }
 
  void Write(const W& msg, grpc::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
    ABSL_CHECK(
        write_ops_.SendMessage(msg, options, ctx_->memory_allocator()).ok());
    call_.PerformOps(&write_ops_);
  }
 
  void WriteAndFinish(const W& msg, grpc::WriteOptions options,
                      const grpc::Status& status, void* tag) override {
    write_ops_.set_output_tag(tag);
    EnsureInitialMetadataSent(&write_ops_);
    options.set_buffer_hint();
    ABSL_CHECK(
        write_ops_.SendMessage(msg, options, ctx_->memory_allocator()).ok());
    write_ops_.ServerSendStatus(&ctx_->trailing_metadata_, status);
    call_.PerformOps(&write_ops_);
  }
 
  void Finish(const grpc::Status& status, void* tag) override {
    finish_ops_.set_output_tag(tag);
    EnsureInitialMetadataSent(&finish_ops_);
    finish_ops_.ServerSendStatus(&ctx_->trailing_metadata_, status);
    call_.PerformOps(&finish_ops_);
  }
 
 private:
  void BindCall(grpc::internal::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;
    }
  }
 
  grpc::internal::Call call_;
  grpc::ServerContext* ctx_;
  grpc::internal::CallOpSet<grpc::internal::CallOpSendInitialMetadata>
      meta_ops_;
  grpc::internal::CallOpSet<grpc::internal::CallOpSendInitialMetadata,
                            grpc::internal::CallOpSendMessage,
                            grpc::internal::CallOpServerSendStatus>
      write_ops_;
  grpc::internal::CallOpSet<grpc::internal::CallOpSendInitialMetadata,
                            grpc::internal::CallOpServerSendStatus>
      finish_ops_;
};
 
template <class W, class R>
class ServerAsyncReaderWriterInterface
    : public grpc::internal::ServerAsyncStreamingInterface,
      public internal::AsyncWriterInterface<W>,
      public internal::AsyncReaderInterface<R> {
 public:
  virtual void Finish(const grpc::Status& status, void* tag) = 0;
 
  virtual void WriteAndFinish(const W& msg, grpc::WriteOptions options,
                              const grpc::Status& status, void* tag) = 0;
};
 
template <class W, class R>
class ServerAsyncReaderWriter final
    : public ServerAsyncReaderWriterInterface<W, R> {
 public:
  explicit ServerAsyncReaderWriter(grpc::ServerContext* ctx)
      : call_(nullptr, nullptr, nullptr), ctx_(ctx) {}
 
  void SendInitialMetadata(void* tag) override {
    ABSL_CHECK(!ctx_->sent_initial_metadata_);
 
    meta_ops_.set_output_tag(tag);
    meta_ops_.SendInitialMetadata(&ctx_->initial_metadata_,
                                  ctx_->initial_metadata_flags());
    if (ctx_->compression_level_set()) {
      meta_ops_.set_compression_level(ctx_->compression_level());
    }
    ctx_->sent_initial_metadata_ = true;
    call_.PerformOps(&meta_ops_);
  }
 
  void Read(R* msg, void* tag) override {
    read_ops_.set_output_tag(tag);
    read_ops_.RecvMessage(msg);
    call_.PerformOps(&read_ops_);
  }
 
  void Write(const W& msg, void* tag) override {
    write_ops_.set_output_tag(tag);
    EnsureInitialMetadataSent(&write_ops_);
    // TODO(ctiller): don't assert
    ABSL_CHECK(write_ops_.SendMessage(msg, ctx_->memory_allocator()).ok());
    call_.PerformOps(&write_ops_);
  }
 
  void Write(const W& msg, grpc::WriteOptions options, void* tag) override {
    write_ops_.set_output_tag(tag);
    if (options.is_last_message()) {
      options.set_buffer_hint();
    }
    EnsureInitialMetadataSent(&write_ops_);
    ABSL_CHECK(
        write_ops_.SendMessage(msg, options, ctx_->memory_allocator()).ok());
    call_.PerformOps(&write_ops_);
  }
 
  //
  void WriteAndFinish(const W& msg, grpc::WriteOptions options,
                      const grpc::Status& status, void* tag) override {
    write_ops_.set_output_tag(tag);
    EnsureInitialMetadataSent(&write_ops_);
    options.set_buffer_hint();
    ABSL_CHECK(
        write_ops_.SendMessage(msg, options, ctx_->memory_allocator()).ok());
    write_ops_.ServerSendStatus(&ctx_->trailing_metadata_, status);
    call_.PerformOps(&write_ops_);
  }
 
  //
  void Finish(const grpc::Status& status, void* tag) override {
    finish_ops_.set_output_tag(tag);
    EnsureInitialMetadataSent(&finish_ops_);
 
    finish_ops_.ServerSendStatus(&ctx_->trailing_metadata_, status);
    call_.PerformOps(&finish_ops_);
  }
 
 private:
  friend class grpc::Server;
 
  void BindCall(grpc::internal::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;
    }
  }
 
  grpc::internal::Call call_;
  grpc::ServerContext* ctx_;
  grpc::internal::CallOpSet<grpc::internal::CallOpSendInitialMetadata>
      meta_ops_;
  grpc::internal::CallOpSet<grpc::internal::CallOpRecvMessage<R>> read_ops_;
  grpc::internal::CallOpSet<grpc::internal::CallOpSendInitialMetadata,
                            grpc::internal::CallOpSendMessage,
                            grpc::internal::CallOpServerSendStatus>
      write_ops_;
  grpc::internal::CallOpSet<grpc::internal::CallOpSendInitialMetadata,
                            grpc::internal::CallOpServerSendStatus>
      finish_ops_;
};
 
}  // namespace grpc
 
#endif  // GRPCPP_SUPPORT_ASYNC_STREAM_H