grpc/include/grpcpp/impl/codegen/call.h

/*
 *
 * 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_IMPL_CODEGEN_CALL_H
#define GRPCPP_IMPL_CODEGEN_CALL_H

#include <assert.h>
#include <array>
#include <cstring>
#include <functional>
#include <map>
#include <memory>
#include <vector>

#include <grpcpp/impl/codegen/byte_buffer.h>
#include <grpcpp/impl/codegen/call_hook.h>
#include <grpcpp/impl/codegen/call_wrapper.h>
#include <grpcpp/impl/codegen/client_context.h>
#include <grpcpp/impl/codegen/client_interceptor.h>
#include <grpcpp/impl/codegen/completion_queue_tag.h>
#include <grpcpp/impl/codegen/config.h>
#include <grpcpp/impl/codegen/core_codegen_interface.h>
#include <grpcpp/impl/codegen/intercepted_channel.h>
#include <grpcpp/impl/codegen/serialization_traits.h>
#include <grpcpp/impl/codegen/server_interceptor.h>
#include <grpcpp/impl/codegen/slice.h>
#include <grpcpp/impl/codegen/status.h>
#include <grpcpp/impl/codegen/string_ref.h>

#include <grpc/impl/codegen/atm.h>
#include <grpc/impl/codegen/compression_types.h>
#include <grpc/impl/codegen/grpc_types.h>

namespace grpc {

class CompletionQueue;
extern CoreCodegenInterface* g_core_codegen_interface;

namespace internal {
class Call;
class CallHook;

// TODO(yangg) if the map is changed before we send, the pointers will be a
// mess. Make sure it does not happen.
inline grpc_metadata* FillMetadataArray(
    const std::multimap<grpc::string, grpc::string>& metadata,
    size_t* metadata_count, const grpc::string& optional_error_details) {
  *metadata_count = metadata.size() + (optional_error_details.empty() ? 0 : 1);
  if (*metadata_count == 0) {
    return nullptr;
  }
  grpc_metadata* metadata_array =
      (grpc_metadata*)(g_core_codegen_interface->gpr_malloc(
          (*metadata_count) * sizeof(grpc_metadata)));
  size_t i = 0;
  for (auto iter = metadata.cbegin(); iter != metadata.cend(); ++iter, ++i) {
    metadata_array[i].key = SliceReferencingString(iter->first);
    metadata_array[i].value = SliceReferencingString(iter->second);
  }
  if (!optional_error_details.empty()) {
    metadata_array[i].key =
        g_core_codegen_interface->grpc_slice_from_static_buffer(
            kBinaryErrorDetailsKey, sizeof(kBinaryErrorDetailsKey) - 1);
    metadata_array[i].value = SliceReferencingString(optional_error_details);
  }
  return metadata_array;
}
}  // namespace internal

/// Per-message write options.
class WriteOptions {
 public:
  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; }

  /// Returns raw flags bitset.
  inline uint32_t flags() const { return flags_; }

  /// Sets flag for the disabling of compression for the next message write.
  ///
  /// \sa GRPC_WRITE_NO_COMPRESS
  inline WriteOptions& set_no_compression() {
    SetBit(GRPC_WRITE_NO_COMPRESS);
    return *this;
  }

  /// Clears flag for the disabling of compression for the next message write.
  ///
  /// \sa GRPC_WRITE_NO_COMPRESS
  inline WriteOptions& clear_no_compression() {
    ClearBit(GRPC_WRITE_NO_COMPRESS);
    return *this;
  }

  /// Get value for the flag indicating whether compression for the next
  /// message write is forcefully disabled.
  ///
  /// \sa GRPC_WRITE_NO_COMPRESS
  inline bool get_no_compression() const {
    return GetBit(GRPC_WRITE_NO_COMPRESS);
  }

  /// Sets flag indicating that the write may be buffered and need not go out on
  /// the wire immediately.
  ///
  /// \sa GRPC_WRITE_BUFFER_HINT
  inline WriteOptions& set_buffer_hint() {
    SetBit(GRPC_WRITE_BUFFER_HINT);
    return *this;
  }

  /// Clears flag indicating that the write may be buffered and need not go out
  /// on the wire immediately.
  ///
  /// \sa GRPC_WRITE_BUFFER_HINT
  inline WriteOptions& clear_buffer_hint() {
    ClearBit(GRPC_WRITE_BUFFER_HINT);
    return *this;
  }

  /// Get value for the flag indicating that the write may be buffered and need
  /// not go out on the wire immediately.
  ///
  /// \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_message() {
    last_message_ = false;
    return *this;
  }

  /// Guarantee that all bytes have been written to the socket before completing
  /// this write (usually writes are completed when they pass flow control).
  inline WriteOptions& set_write_through() {
    SetBit(GRPC_WRITE_THROUGH);
    return *this;
  }

  inline bool is_write_through() const { return GetBit(GRPC_WRITE_THROUGH); }

  /// 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;
  }

 private:
  void SetBit(const uint32_t mask) { flags_ |= mask; }

  void ClearBit(const uint32_t mask) { flags_ &= ~mask; }

  bool GetBit(const uint32_t mask) const { return (flags_ & mask) != 0; }

  uint32_t flags_;
  bool last_message_;
};

namespace internal {

/// Internal methods for setting the state
class InternalInterceptorBatchMethods
    : public experimental::InterceptorBatchMethods {
 public:
  virtual ~InternalInterceptorBatchMethods() {}

  virtual void AddInterceptionHookPoint(
      experimental::InterceptionHookPoints type) = 0;

  virtual void SetSendMessage(ByteBuffer* buf) = 0;

  virtual void SetSendInitialMetadata(
      std::multimap<grpc::string, grpc::string>* metadata) = 0;

  virtual void SetSendStatus(grpc_status_code* code,
                             grpc::string* error_details,
                             grpc::string* error_message) = 0;

  virtual void SetSendTrailingMetadata(
      std::multimap<grpc::string, grpc::string>* metadata) = 0;

  virtual void SetRecvMessage(void* message) = 0;

  virtual void SetRecvInitialMetadata(internal::MetadataMap* map) = 0;

  virtual void SetRecvStatus(Status* status) = 0;

  virtual void SetRecvTrailingMetadata(internal::MetadataMap* map) = 0;

  virtual std::unique_ptr<ChannelInterface> GetInterceptedChannel() = 0;
};

/// Default argument for CallOpSet. I is unused by the class, but can be
/// used for generating multiple names for the same thing.
template <int I>
class CallNoOp {
 protected:
  void AddOp(grpc_op* ops, size_t* nops) {}
  void FinishOp(bool* status) {}
  void SetInterceptionHookPoint(
      InternalInterceptorBatchMethods* interceptor_methods) {}
  void SetFinishInterceptionHookPoint(
      InternalInterceptorBatchMethods* interceptor_methods) {}
  void SetHijackingState(InternalInterceptorBatchMethods* interceptor_methods) {
  }
};

class CallOpSendInitialMetadata {
 public:
  CallOpSendInitialMetadata() : send_(false) {
    maybe_compression_level_.is_set = false;
  }

  void SendInitialMetadata(std::multimap<grpc::string, grpc::string>* metadata,
                           uint32_t flags) {
    maybe_compression_level_.is_set = false;
    send_ = true;
    flags_ = flags;
    metadata_map_ = metadata;
  }

  void set_compression_level(grpc_compression_level level) {
    maybe_compression_level_.is_set = true;
    maybe_compression_level_.level = level;
  }

 protected:
  void AddOp(grpc_op* ops, size_t* nops) {
    if (!send_ || hijacked_) return;
    grpc_op* op = &ops[(*nops)++];
    op->op = GRPC_OP_SEND_INITIAL_METADATA;
    op->flags = flags_;
    op->reserved = NULL;
    initial_metadata_ =
        FillMetadataArray(*metadata_map_, &initial_metadata_count_, "");
    op->data.send_initial_metadata.count = initial_metadata_count_;
    op->data.send_initial_metadata.metadata = initial_metadata_;
    op->data.send_initial_metadata.maybe_compression_level.is_set =
        maybe_compression_level_.is_set;
    if (maybe_compression_level_.is_set) {
      op->data.send_initial_metadata.maybe_compression_level.level =
          maybe_compression_level_.level;
    }
  }
  void FinishOp(bool* status) {
    if (!send_ || hijacked_) return;
    g_core_codegen_interface->gpr_free(initial_metadata_);
    send_ = false;
  }

  void SetInterceptionHookPoint(
      InternalInterceptorBatchMethods* interceptor_methods) {
    if (!send_) return;
    interceptor_methods->AddInterceptionHookPoint(
        experimental::InterceptionHookPoints::PRE_SEND_INITIAL_METADATA);
    interceptor_methods->SetSendInitialMetadata(metadata_map_);
  }

  void SetFinishInterceptionHookPoint(
      InternalInterceptorBatchMethods* interceptor_methods) {}

  void SetHijackingState(InternalInterceptorBatchMethods* interceptor_methods) {
    hijacked_ = true;
  }

  bool hijacked_ = false;
  bool send_;
  uint32_t flags_;
  size_t initial_metadata_count_;
  std::multimap<grpc::string, grpc::string>* metadata_map_;
  grpc_metadata* initial_metadata_;
  struct {
    bool is_set;
    grpc_compression_level level;
  } maybe_compression_level_;
};

class CallOpSendMessage {
 public:
  CallOpSendMessage() : send_buf_() {}

  /// Send \a message using \a options for the write. The \a options are cleared
  /// after use.
  template <class M>
  Status SendMessage(const M& message,
                     WriteOptions options) GRPC_MUST_USE_RESULT;

  template <class M>
  Status SendMessage(const M& message) GRPC_MUST_USE_RESULT;

 protected:
  void AddOp(grpc_op* ops, size_t* nops) {
    if (!send_buf_.Valid() || hijacked_) return;
    grpc_op* op = &ops[(*nops)++];
    op->op = GRPC_OP_SEND_MESSAGE;
    op->flags = write_options_.flags();
    op->reserved = NULL;
    op->data.send_message.send_message = send_buf_.c_buffer();
    // Flags are per-message: clear them after use.
    write_options_.Clear();
  }
  void FinishOp(bool* status) { send_buf_.Clear(); }

  void SetInterceptionHookPoint(
      InternalInterceptorBatchMethods* interceptor_methods) {
    if (!send_buf_.Valid()) return;
    interceptor_methods->AddInterceptionHookPoint(
        experimental::InterceptionHookPoints::PRE_SEND_MESSAGE);
    interceptor_methods->SetSendMessage(&send_buf_);
  }

  void SetFinishInterceptionHookPoint(
      InternalInterceptorBatchMethods* interceptor_methods) {}

  void SetHijackingState(InternalInterceptorBatchMethods* interceptor_methods) {
    hijacked_ = true;
  }

 private:
  bool hijacked_ = false;
  ByteBuffer send_buf_;
  WriteOptions write_options_;
};

template <class M>
Status CallOpSendMessage::SendMessage(const M& message, WriteOptions options) {
  write_options_ = options;
  bool own_buf;
  // TODO(vjpai): Remove the void below when possible
  // The void in the template parameter below should not be needed
  // (since it should be implicit) but is needed due to an observed
  // difference in behavior between clang and gcc for certain internal users
  Status result = SerializationTraits<M, void>::Serialize(
      message, send_buf_.bbuf_ptr(), &own_buf);
  if (!own_buf) {
    send_buf_.Duplicate();
  }
  return result;
}

template <class M>
Status CallOpSendMessage::SendMessage(const M& message) {
  return SendMessage(message, WriteOptions());
}

template <class R>
class CallOpRecvMessage {
 public:
  CallOpRecvMessage()
      : got_message(false),
        message_(nullptr),
        allow_not_getting_message_(false) {}

  void RecvMessage(R* message) { message_ = message; }

  // Do not change status if no message is received.
  void AllowNoMessage() { allow_not_getting_message_ = true; }

  bool got_message;

 protected:
  void AddOp(grpc_op* ops, size_t* nops) {
    if (message_ == nullptr || hijacked_) return;
    grpc_op* op = &ops[(*nops)++];
    op->op = GRPC_OP_RECV_MESSAGE;
    op->flags = 0;
    op->reserved = NULL;
    op->data.recv_message.recv_message = recv_buf_.c_buffer_ptr();
  }

  void FinishOp(bool* status) {
    if (message_ == nullptr || hijacked_) return;
    if (recv_buf_.Valid()) {
      if (*status) {
        got_message = *status =
            SerializationTraits<R>::Deserialize(recv_buf_.bbuf_ptr(), message_)
                .ok();
        recv_buf_.Release();
      } else {
        got_message = false;
        recv_buf_.Clear();
      }
    } else {
      got_message = false;
      if (!allow_not_getting_message_) {
        *status = false;
      }
    }
    message_ = nullptr;
  }

  void SetInterceptionHookPoint(
      InternalInterceptorBatchMethods* interceptor_methods) {
    interceptor_methods->SetRecvMessage(message_);
  }

  void SetFinishInterceptionHookPoint(
      InternalInterceptorBatchMethods* interceptor_methods) {
    if (!got_message) return;
    interceptor_methods->AddInterceptionHookPoint(
        experimental::InterceptionHookPoints::POST_RECV_MESSAGE);
  }
  void SetHijackingState(InternalInterceptorBatchMethods* interceptor_methods) {
    hijacked_ = true;
    if (message_ == nullptr) return;
    interceptor_methods->AddInterceptionHookPoint(
        experimental::InterceptionHookPoints::PRE_RECV_MESSAGE);
    got_message = true;
  }

 private:
  R* message_;
  ByteBuffer recv_buf_;
  bool allow_not_getting_message_;
  bool hijacked_ = false;
};

class DeserializeFunc {
 public:
  virtual Status Deserialize(ByteBuffer* buf) = 0;
  virtual ~DeserializeFunc() {}
};

template <class R>
class DeserializeFuncType final : public DeserializeFunc {
 public:
  DeserializeFuncType(R* message) : message_(message) {}
  Status Deserialize(ByteBuffer* buf) override {
    return SerializationTraits<R>::Deserialize(buf->bbuf_ptr(), message_);
  }

  ~DeserializeFuncType() override {}

 private:
  R* message_;  // Not a managed pointer because management is external to this
};

class CallOpGenericRecvMessage {
 public:
  CallOpGenericRecvMessage()
      : got_message(false), allow_not_getting_message_(false) {}

  template <class R>
  void RecvMessage(R* message) {
    // Use an explicit base class pointer to avoid resolution error in the
    // following unique_ptr::reset for some old implementations.
    DeserializeFunc* func = new DeserializeFuncType<R>(message);
    deserialize_.reset(func);
    message_ = message;
  }

  // Do not change status if no message is received.
  void AllowNoMessage() { allow_not_getting_message_ = true; }

  bool got_message;

 protected:
  void AddOp(grpc_op* ops, size_t* nops) {
    if (!deserialize_ || hijacked_) return;
    grpc_op* op = &ops[(*nops)++];
    op->op = GRPC_OP_RECV_MESSAGE;
    op->flags = 0;
    op->reserved = NULL;
    op->data.recv_message.recv_message = recv_buf_.c_buffer_ptr();
  }

  void FinishOp(bool* status) {
    if (!deserialize_ || hijacked_) return;
    if (recv_buf_.Valid()) {
      if (*status) {
        got_message = true;
        *status = deserialize_->Deserialize(&recv_buf_).ok();
        recv_buf_.Release();
      } else {
        got_message = false;
        recv_buf_.Clear();
      }
    } else {
      got_message = false;
      if (!allow_not_getting_message_) {
        *status = false;
      }
    }
    deserialize_.reset();
  }

  void SetInterceptionHookPoint(
      InternalInterceptorBatchMethods* interceptor_methods) {
    interceptor_methods->SetRecvMessage(message_);
  }

  void SetFinishInterceptionHookPoint(
      InternalInterceptorBatchMethods* interceptor_methods) {
    if (!got_message) return;
    interceptor_methods->AddInterceptionHookPoint(
        experimental::InterceptionHookPoints::POST_RECV_MESSAGE);
  }
  void SetHijackingState(InternalInterceptorBatchMethods* interceptor_methods) {
    hijacked_ = true;
    if (!deserialize_) return;
    interceptor_methods->AddInterceptionHookPoint(
        experimental::InterceptionHookPoints::PRE_RECV_MESSAGE);
  }

 private:
  void* message_;
  bool hijacked_ = false;
  std::unique_ptr<DeserializeFunc> deserialize_;
  ByteBuffer recv_buf_;
  bool allow_not_getting_message_;
};

class CallOpClientSendClose {
 public:
  CallOpClientSendClose() : send_(false) {}

  void ClientSendClose() { send_ = true; }

 protected:
  void AddOp(grpc_op* ops, size_t* nops) {
    if (!send_ || hijacked_) return;
    grpc_op* op = &ops[(*nops)++];
    op->op = GRPC_OP_SEND_CLOSE_FROM_CLIENT;
    op->flags = 0;
    op->reserved = NULL;
  }
  void FinishOp(bool* status) { send_ = false; }

  void SetInterceptionHookPoint(
      InternalInterceptorBatchMethods* interceptor_methods) {
    if (!send_) return;
    interceptor_methods->AddInterceptionHookPoint(
        experimental::InterceptionHookPoints::PRE_SEND_CLOSE);
  }

  void SetFinishInterceptionHookPoint(
      InternalInterceptorBatchMethods* interceptor_methods) {}

  void SetHijackingState(InternalInterceptorBatchMethods* interceptor_methods) {
    hijacked_ = true;
  }

 private:
  bool hijacked_ = false;
  bool send_;
};

class CallOpServerSendStatus {
 public:
  CallOpServerSendStatus() : send_status_available_(false) {}

  void ServerSendStatus(
      std::multimap<grpc::string, grpc::string>* trailing_metadata,
      const Status& status) {
    send_error_details_ = status.error_details();
    metadata_map_ = trailing_metadata;
    send_status_available_ = true;
    send_status_code_ = static_cast<grpc_status_code>(status.error_code());
    send_error_message_ = status.error_message();
  }

 protected:
  void AddOp(grpc_op* ops, size_t* nops) {
    if (!send_status_available_ || hijacked_) return;
    trailing_metadata_ = FillMetadataArray(
        *metadata_map_, &trailing_metadata_count_, send_error_details_);
    grpc_op* op = &ops[(*nops)++];
    op->op = GRPC_OP_SEND_STATUS_FROM_SERVER;
    op->data.send_status_from_server.trailing_metadata_count =
        trailing_metadata_count_;
    op->data.send_status_from_server.trailing_metadata = trailing_metadata_;
    op->data.send_status_from_server.status = send_status_code_;
    error_message_slice_ = SliceReferencingString(send_error_message_);
    op->data.send_status_from_server.status_details =
        send_error_message_.empty() ? nullptr : &error_message_slice_;
    op->flags = 0;
    op->reserved = NULL;
  }

  void FinishOp(bool* status) {
    if (!send_status_available_ || hijacked_) return;
    g_core_codegen_interface->gpr_free(trailing_metadata_);
    send_status_available_ = false;
  }

  void SetInterceptionHookPoint(
      InternalInterceptorBatchMethods* interceptor_methods) {
    if (!send_status_available_) return;
    interceptor_methods->AddInterceptionHookPoint(
        experimental::InterceptionHookPoints::PRE_SEND_STATUS);
    interceptor_methods->SetSendTrailingMetadata(metadata_map_);
    interceptor_methods->SetSendStatus(&send_status_code_, &send_error_details_,
                                       &send_error_message_);
  }

  void SetFinishInterceptionHookPoint(
      InternalInterceptorBatchMethods* interceptor_methods) {}

  void SetHijackingState(InternalInterceptorBatchMethods* interceptor_methods) {
    hijacked_ = true;
  }

 private:
  bool hijacked_ = false;
  bool send_status_available_;
  grpc_status_code send_status_code_;
  grpc::string send_error_details_;
  grpc::string send_error_message_;
  size_t trailing_metadata_count_;
  std::multimap<grpc::string, grpc::string>* metadata_map_;
  grpc_metadata* trailing_metadata_;
  grpc_slice error_message_slice_;
};

class CallOpRecvInitialMetadata {
 public:
  CallOpRecvInitialMetadata() : metadata_map_(nullptr) {}

  void RecvInitialMetadata(ClientContext* context) {
    context->initial_metadata_received_ = true;
    metadata_map_ = &context->recv_initial_metadata_;
  }

 protected:
  void AddOp(grpc_op* ops, size_t* nops) {
    if (metadata_map_ == nullptr || hijacked_) return;
    grpc_op* op = &ops[(*nops)++];
    op->op = GRPC_OP_RECV_INITIAL_METADATA;
    op->data.recv_initial_metadata.recv_initial_metadata = metadata_map_->arr();
    op->flags = 0;
    op->reserved = NULL;
  }

  void FinishOp(bool* status) {
    if (metadata_map_ == nullptr || hijacked_) return;
  }

  void SetInterceptionHookPoint(
      InternalInterceptorBatchMethods* interceptor_methods) {
    interceptor_methods->SetRecvInitialMetadata(metadata_map_);
  }

  void SetFinishInterceptionHookPoint(
      InternalInterceptorBatchMethods* interceptor_methods) {
    if (metadata_map_ == nullptr) return;
    interceptor_methods->AddInterceptionHookPoint(
        experimental::InterceptionHookPoints::POST_RECV_INITIAL_METADATA);
    metadata_map_ = nullptr;
  }

  void SetHijackingState(InternalInterceptorBatchMethods* interceptor_methods) {
    hijacked_ = true;
    if (metadata_map_ == nullptr) return;
    interceptor_methods->AddInterceptionHookPoint(
        experimental::InterceptionHookPoints::PRE_RECV_INITIAL_METADATA);
  }

 private:
  bool hijacked_ = false;
  MetadataMap* metadata_map_;
};

class CallOpClientRecvStatus {
 public:
  CallOpClientRecvStatus()
      : recv_status_(nullptr), debug_error_string_(nullptr) {}

  void ClientRecvStatus(ClientContext* context, Status* status) {
    client_context_ = context;
    metadata_map_ = &client_context_->trailing_metadata_;
    recv_status_ = status;
    error_message_ = g_core_codegen_interface->grpc_empty_slice();
  }

 protected:
  void AddOp(grpc_op* ops, size_t* nops) {
    if (recv_status_ == nullptr || hijacked_) return;
    grpc_op* op = &ops[(*nops)++];
    op->op = GRPC_OP_RECV_STATUS_ON_CLIENT;
    op->data.recv_status_on_client.trailing_metadata = metadata_map_->arr();
    op->data.recv_status_on_client.status = &status_code_;
    op->data.recv_status_on_client.status_details = &error_message_;
    op->data.recv_status_on_client.error_string = &debug_error_string_;
    op->flags = 0;
    op->reserved = NULL;
  }

  void FinishOp(bool* status) {
    if (recv_status_ == nullptr || hijacked_) return;
    grpc::string binary_error_details = metadata_map_->GetBinaryErrorDetails();
    *recv_status_ =
        Status(static_cast<StatusCode>(status_code_),
               GRPC_SLICE_IS_EMPTY(error_message_)
                   ? grpc::string()
                   : grpc::string(GRPC_SLICE_START_PTR(error_message_),
                                  GRPC_SLICE_END_PTR(error_message_)),
               binary_error_details);
    client_context_->set_debug_error_string(
        debug_error_string_ != nullptr ? debug_error_string_ : "");
    g_core_codegen_interface->grpc_slice_unref(error_message_);
    if (debug_error_string_ != nullptr) {
      g_core_codegen_interface->gpr_free((void*)debug_error_string_);
    }
  }

  void SetInterceptionHookPoint(
      InternalInterceptorBatchMethods* interceptor_methods) {
    interceptor_methods->SetRecvStatus(recv_status_);
    interceptor_methods->SetRecvTrailingMetadata(metadata_map_);
  }

  void SetFinishInterceptionHookPoint(
      InternalInterceptorBatchMethods* interceptor_methods) {
    if (recv_status_ == nullptr) return;
    interceptor_methods->AddInterceptionHookPoint(
        experimental::InterceptionHookPoints::POST_RECV_STATUS);
    recv_status_ = nullptr;
  }

  void SetHijackingState(InternalInterceptorBatchMethods* interceptor_methods) {
    hijacked_ = true;
    if (recv_status_ == nullptr) return;
    interceptor_methods->AddInterceptionHookPoint(
        experimental::InterceptionHookPoints::PRE_RECV_STATUS);
  }

 private:
  bool hijacked_ = false;
  ClientContext* client_context_;
  MetadataMap* metadata_map_;
  Status* recv_status_;
  const char* debug_error_string_;
  grpc_status_code status_code_;
  grpc_slice error_message_;
};

/// An abstract collection of call ops, used to generate the
/// grpc_call_op structure to pass down to the lower layers,
/// and as it is-a CompletionQueueTag, also massages the final
/// completion into the correct form for consumption in the C++
/// API.
class CallOpSetInterface : public CompletionQueueTag {
 public:
  /// Fills in grpc_op, starting from ops[*nops] and moving
  /// upwards.
  virtual void FillOps(internal::Call* call) = 0;

  /// Get the tag to be used at the core completion queue. Generally, the
  /// value of cq_tag will be "this". However, it can be overridden if we
  /// want core to process the tag differently (e.g., as a core callback)
  virtual void* cq_tag() = 0;

  // This will be called while interceptors are run if the RPC is a hijacked
  // RPC. This should set hijacking state for each of the ops.
  virtual void SetHijackingState() = 0;

  // Should be called after interceptors are done running
  virtual void ContinueFillOpsAfterInterception() = 0;

  // Should be called after interceptors are done running on the finalize result
  // path
  virtual void ContinueFinalizeResultAfterInterception() = 0;
};

template <class Op1 = CallNoOp<1>, class Op2 = CallNoOp<2>,
          class Op3 = CallNoOp<3>, class Op4 = CallNoOp<4>,
          class Op5 = CallNoOp<5>, class Op6 = CallNoOp<6>>
class CallOpSet;

class InterceptorBatchMethodsImpl : public InternalInterceptorBatchMethods {
 public:
  InterceptorBatchMethodsImpl() {
    for (auto i = 0;
         i < static_cast<int>(
                 experimental::InterceptionHookPoints::NUM_INTERCEPTION_HOOKS);
         i++) {
      hooks_[i] = false;
    }
  }

  virtual ~InterceptorBatchMethodsImpl() {}

  virtual bool QueryInterceptionHookPoint(
      experimental::InterceptionHookPoints type) override {
    return hooks_[static_cast<int>(type)];
  }

  virtual void Proceed() override { /* fill this */
    if (call_->client_rpc_info() != nullptr) {
      return ProceedClient();
    }
    GPR_CODEGEN_ASSERT(call_->server_rpc_info() != nullptr);
    ProceedServer();
  }

  virtual void Hijack() override {
    // Only the client can hijack when sending down initial metadata
    GPR_CODEGEN_ASSERT(!reverse_ && ops_ != nullptr &&
                       call_->client_rpc_info() != nullptr);
    // It is illegal to call Hijack twice
    GPR_CODEGEN_ASSERT(!ran_hijacking_interceptor_);
    auto* rpc_info = call_->client_rpc_info();
    rpc_info->hijacked_ = true;
    rpc_info->hijacked_interceptor_ = curr_iteration_;
    ClearHookPoints();
    ops_->SetHijackingState();
    ran_hijacking_interceptor_ = true;
    rpc_info->RunInterceptor(this, curr_iteration_);
  }

  virtual void AddInterceptionHookPoint(
      experimental::InterceptionHookPoints type) override {
    hooks_[static_cast<int>(type)] = true;
  }

  virtual ByteBuffer* GetSendMessage() override { return send_message_; }

  virtual std::multimap<grpc::string, grpc::string>* GetSendInitialMetadata()
      override {
    return send_initial_metadata_;
  }

  virtual Status GetSendStatus() override {
    return Status(static_cast<StatusCode>(*code_), *error_message_,
                  *error_details_);
  }

  virtual void ModifySendStatus(const Status& status) override {
    *code_ = static_cast<grpc_status_code>(status.error_code());
    *error_details_ = status.error_details();
    *error_message_ = status.error_message();
  }

  virtual std::multimap<grpc::string, grpc::string>* GetSendTrailingMetadata()
      override {
    return send_trailing_metadata_;
  }

  virtual void* GetRecvMessage() override { return recv_message_; }

  virtual std::multimap<grpc::string_ref, grpc::string_ref>*
  GetRecvInitialMetadata() override {
    return recv_initial_metadata_->map();
  }

  virtual Status* GetRecvStatus() override { return recv_status_; }

  virtual std::multimap<grpc::string_ref, grpc::string_ref>*
  GetRecvTrailingMetadata() override {
    return recv_trailing_metadata_->map();
  }

  virtual void SetSendMessage(ByteBuffer* buf) override { send_message_ = buf; }

  virtual void SetSendInitialMetadata(
      std::multimap<grpc::string, grpc::string>* metadata) override {
    send_initial_metadata_ = metadata;
  }

  virtual void SetSendStatus(grpc_status_code* code,
                             grpc::string* error_details,
                             grpc::string* error_message) override {
    code_ = code;
    error_details_ = error_details;
    error_message_ = error_message;
  }

  virtual void SetSendTrailingMetadata(
      std::multimap<grpc::string, grpc::string>* metadata) override {
    send_trailing_metadata_ = metadata;
  }

  virtual void SetRecvMessage(void* message) override {
    recv_message_ = message;
  }

  virtual void SetRecvInitialMetadata(internal::MetadataMap* map) override {
    recv_initial_metadata_ = map;
  }

  virtual void SetRecvStatus(Status* status) override { recv_status_ = status; }

  virtual void SetRecvTrailingMetadata(internal::MetadataMap* map) override {
    recv_trailing_metadata_ = map;
  }

  virtual std::unique_ptr<ChannelInterface> GetInterceptedChannel() override {
    auto* info = call_->client_rpc_info();
    if (info == nullptr) {
      return std::unique_ptr<ChannelInterface>(nullptr);
    }
    // The intercepted channel starts from the interceptor just after the
    // current interceptor
    return std::unique_ptr<ChannelInterface>(new internal::InterceptedChannel(
        reinterpret_cast<grpc::ChannelInterface*>(info->channel()),
        curr_iteration_ + 1));
  }

  // Clears all state
  void ClearState() {
    reverse_ = false;
    ran_hijacking_interceptor_ = false;
    ClearHookPoints();
  }

  // Prepares for Post_recv operations
  void SetReverse() {
    reverse_ = true;
    ran_hijacking_interceptor_ = false;
    ClearHookPoints();
  }

  // This needs to be set before interceptors are run
  void SetCall(Call* call) { call_ = call; }

  // This needs to be set before interceptors are run using RunInterceptors().
  // Alternatively, RunInterceptors(std::function<void(void)> f) can be used.
  void SetCallOpSetInterface(CallOpSetInterface* ops) { ops_ = ops; }

  // Returns true if no interceptors are run. This should be used only by
  // subclasses of CallOpSetInterface. SetCall and SetCallOpSetInterface should
  // have been called before this. After all the interceptors are done running,
  // either ContinueFillOpsAfterInterception or
  // ContinueFinalizeOpsAfterInterception will be called. Note that neither of
  // them is invoked if there were no interceptors registered.
  bool RunInterceptors() {
    GPR_CODEGEN_ASSERT(ops_);
    auto* client_rpc_info = call_->client_rpc_info();
    if (client_rpc_info != nullptr) {
      if (client_rpc_info->interceptors_.size() == 0) {
        return true;
      } else {
        RunClientInterceptors();
        return false;
      }
    }

    auto* server_rpc_info = call_->server_rpc_info();
    if (server_rpc_info == nullptr ||
        server_rpc_info->interceptors_.size() == 0) {
      return true;
    }
    RunServerInterceptors();
    return false;
  }

  // Returns true if no interceptors are run. Returns false otherwise if there
  // are interceptors registered. After the interceptors are done running \a f
  // will be invoked. This is to be used only by BaseAsyncRequest and
  // SyncRequest.
  bool RunInterceptors(std::function<void(void)> f) {
    // This is used only by the server for initial call request
    GPR_CODEGEN_ASSERT(reverse_ == true);
    GPR_CODEGEN_ASSERT(call_->client_rpc_info() == nullptr);
    auto* server_rpc_info = call_->server_rpc_info();
    if (server_rpc_info == nullptr ||
        server_rpc_info->interceptors_.size() == 0) {
      return true;
    }
    callback_ = std::move(f);
    RunServerInterceptors();
    return false;
  }

 private:
  void RunClientInterceptors() {
    auto* rpc_info = call_->client_rpc_info();
    if (!reverse_) {
      curr_iteration_ = 0;
    } else {
      if (rpc_info->hijacked_) {
        curr_iteration_ = rpc_info->hijacked_interceptor_;
      } else {
        curr_iteration_ = rpc_info->interceptors_.size() - 1;
      }
    }
    rpc_info->RunInterceptor(this, curr_iteration_);
  }

  void RunServerInterceptors() {
    auto* rpc_info = call_->server_rpc_info();
    if (!reverse_) {
      curr_iteration_ = 0;
    } else {
      curr_iteration_ = rpc_info->interceptors_.size() - 1;
    }
    rpc_info->RunInterceptor(this, curr_iteration_);
  }

  void ProceedClient() {
    auto* rpc_info = call_->client_rpc_info();
    if (rpc_info->hijacked_ && !reverse_ &&
        curr_iteration_ == rpc_info->hijacked_interceptor_ &&
        !ran_hijacking_interceptor_) {
      // We now need to provide hijacked recv ops to this interceptor
      ClearHookPoints();
      ops_->SetHijackingState();
      ran_hijacking_interceptor_ = true;
      rpc_info->RunInterceptor(this, curr_iteration_);
      return;
    }
    if (!reverse_) {
      curr_iteration_++;
      // We are going down the stack of interceptors
      if (curr_iteration_ < static_cast<long>(rpc_info->interceptors_.size())) {
        if (rpc_info->hijacked_ &&
            curr_iteration_ > rpc_info->hijacked_interceptor_) {
          // This is a hijacked RPC and we are done with hijacking
          ops_->ContinueFillOpsAfterInterception();
        } else {
          rpc_info->RunInterceptor(this, curr_iteration_);
        }
      } else {
        // we are done running all the interceptors without any hijacking
        ops_->ContinueFillOpsAfterInterception();
      }
    } else {
      curr_iteration_--;
      // We are going up the stack of interceptors
      if (curr_iteration_ >= 0) {
        // Continue running interceptors
        rpc_info->RunInterceptor(this, curr_iteration_);
      } else {
        // we are done running all the interceptors without any hijacking
        ops_->ContinueFinalizeResultAfterInterception();
      }
    }
  }

  void ProceedServer() {
    auto* rpc_info = call_->server_rpc_info();
    if (!reverse_) {
      curr_iteration_++;
      if (curr_iteration_ < static_cast<long>(rpc_info->interceptors_.size())) {
        return rpc_info->RunInterceptor(this, curr_iteration_);
      } else if (ops_) {
        return ops_->ContinueFillOpsAfterInterception();
      }
    } else {
      curr_iteration_--;
      // We are going up the stack of interceptors
      if (curr_iteration_ >= 0) {
        // Continue running interceptors
        return rpc_info->RunInterceptor(this, curr_iteration_);
      } else if (ops_) {
        return ops_->ContinueFinalizeResultAfterInterception();
      }
    }
    GPR_CODEGEN_ASSERT(callback_);
    callback_();
  }

  void ClearHookPoints() {
    for (auto i = 0;
         i < static_cast<int>(
                 experimental::InterceptionHookPoints::NUM_INTERCEPTION_HOOKS);
         i++) {
      hooks_[i] = false;
    }
  }

  std::array<bool,
             static_cast<int>(
                 experimental::InterceptionHookPoints::NUM_INTERCEPTION_HOOKS)>
      hooks_;

  int curr_iteration_ = 0;  // Current iterator
  bool reverse_ = false;
  bool ran_hijacking_interceptor_ = false;
  Call* call_ =
      nullptr;  // The Call object is present along with CallOpSet object
  CallOpSetInterface* ops_ = nullptr;
  std::function<void(void)> callback_;

  ByteBuffer* send_message_ = nullptr;

  std::multimap<grpc::string, grpc::string>* send_initial_metadata_;

  grpc_status_code* code_ = nullptr;
  grpc::string* error_details_ = nullptr;
  grpc::string* error_message_ = nullptr;
  Status send_status_;

  std::multimap<grpc::string, grpc::string>* send_trailing_metadata_ = nullptr;

  void* recv_message_ = nullptr;

  internal::MetadataMap* recv_initial_metadata_ = nullptr;

  Status* recv_status_ = nullptr;

  internal::MetadataMap* recv_trailing_metadata_ = nullptr;
};

/// Primary implementation of CallOpSetInterface.
/// Since we cannot use variadic templates, we declare slots up to
/// the maximum count of ops we'll need in a set. We leverage the
/// empty base class optimization to slim this class (especially
/// when there are many unused slots used). To avoid duplicate base classes,
/// the template parmeter for CallNoOp is varied by argument position.
template <class Op1, class Op2, class Op3, class Op4, class Op5, class Op6>
class CallOpSet : public CallOpSetInterface,
                  public Op1,
                  public Op2,
                  public Op3,
                  public Op4,
                  public Op5,
                  public Op6 {
 public:
  CallOpSet() : cq_tag_(this), return_tag_(this) {}
  // The copy constructor and assignment operator reset the value of
  // cq_tag_ and return_tag_ since those are only meaningful on a specific
  // object, not across objects.
  CallOpSet(const CallOpSet& other)
      : cq_tag_(this),
        return_tag_(this),
        call_(other.call_),
        done_intercepting_(false),
        interceptor_methods_(InterceptorBatchMethodsImpl()) {}

  CallOpSet& operator=(const CallOpSet& other) {
    cq_tag_ = this;
    return_tag_ = this;
    call_ = other.call_;
    done_intercepting_ = false;
    interceptor_methods_ = InterceptorBatchMethodsImpl();
    return *this;
  }

  void FillOps(Call* call) override {
    done_intercepting_ = false;
    g_core_codegen_interface->grpc_call_ref(call->call());
    call_ =
        *call;  // It's fine to create a copy of call since it's just pointers

    if (RunInterceptors()) {
      ContinueFillOpsAfterInterception();
    } else {
      // After the interceptors are run, ContinueFillOpsAfterInterception will
      // be run
    }
  }

  bool FinalizeResult(void** tag, bool* status) override {
    if (done_intercepting_) {
      // We have already finished intercepting and filling in the results. This
      // round trip from the core needed to be made because interceptors were
      // run
      *tag = return_tag_;
      *status = saved_status_;
      g_core_codegen_interface->grpc_call_unref(call_.call());
      return true;
    }

    this->Op1::FinishOp(status);
    this->Op2::FinishOp(status);
    this->Op3::FinishOp(status);
    this->Op4::FinishOp(status);
    this->Op5::FinishOp(status);
    this->Op6::FinishOp(status);
    saved_status_ = *status;
    if (RunInterceptorsPostRecv()) {
      *tag = return_tag_;
      g_core_codegen_interface->grpc_call_unref(call_.call());
      return true;
    }
    // Interceptors are going to be run, so we can't return the tag just yet.
    // After the interceptors are run, ContinueFinalizeResultAfterInterception
    return false;
  }

  void set_output_tag(void* return_tag) { return_tag_ = return_tag; }

  void* cq_tag() override { return cq_tag_; }

  /// set_cq_tag is used to provide a different core CQ tag than "this".
  /// This is used for callback-based tags, where the core tag is the core
  /// callback function. It does not change the use or behavior of any other
  /// function (such as FinalizeResult)
  void set_cq_tag(void* cq_tag) { cq_tag_ = cq_tag; }

  // This will be called while interceptors are run if the RPC is a hijacked
  // RPC. This should set hijacking state for each of the ops.
  void SetHijackingState() override {
    this->Op1::SetHijackingState(&interceptor_methods_);
    this->Op2::SetHijackingState(&interceptor_methods_);
    this->Op3::SetHijackingState(&interceptor_methods_);
    this->Op4::SetHijackingState(&interceptor_methods_);
    this->Op5::SetHijackingState(&interceptor_methods_);
    this->Op6::SetHijackingState(&interceptor_methods_);
  }

  // Should be called after interceptors are done running
  void ContinueFillOpsAfterInterception() override {
    static const size_t MAX_OPS = 6;
    grpc_op ops[MAX_OPS];
    size_t nops = 0;
    this->Op1::AddOp(ops, &nops);
    this->Op2::AddOp(ops, &nops);
    this->Op3::AddOp(ops, &nops);
    this->Op4::AddOp(ops, &nops);
    this->Op5::AddOp(ops, &nops);
    this->Op6::AddOp(ops, &nops);
    GPR_CODEGEN_ASSERT(GRPC_CALL_OK ==
                       g_core_codegen_interface->grpc_call_start_batch(
                           call_.call(), ops, nops, cq_tag(), nullptr));
  }

  // Should be called after interceptors are done running on the finalize result
  // path
  void ContinueFinalizeResultAfterInterception() override {
    done_intercepting_ = true;
    GPR_CODEGEN_ASSERT(GRPC_CALL_OK ==
                       g_core_codegen_interface->grpc_call_start_batch(
                           call_.call(), nullptr, 0, cq_tag(), nullptr));
  }

 private:
  // Returns true if no interceptors need to be run
  bool RunInterceptors() {
    interceptor_methods_.ClearState();
    interceptor_methods_.SetCallOpSetInterface(this);
    interceptor_methods_.SetCall(&call_);
    this->Op1::SetInterceptionHookPoint(&interceptor_methods_);
    this->Op2::SetInterceptionHookPoint(&interceptor_methods_);
    this->Op3::SetInterceptionHookPoint(&interceptor_methods_);
    this->Op4::SetInterceptionHookPoint(&interceptor_methods_);
    this->Op5::SetInterceptionHookPoint(&interceptor_methods_);
    this->Op6::SetInterceptionHookPoint(&interceptor_methods_);
    return interceptor_methods_.RunInterceptors();
  }
  // Returns true if no interceptors need to be run
  bool RunInterceptorsPostRecv() {
    // Call and OpSet had already been set on the set state.
    // SetReverse also clears previously set hook points
    interceptor_methods_.SetReverse();
    this->Op1::SetFinishInterceptionHookPoint(&interceptor_methods_);
    this->Op2::SetFinishInterceptionHookPoint(&interceptor_methods_);
    this->Op3::SetFinishInterceptionHookPoint(&interceptor_methods_);
    this->Op4::SetFinishInterceptionHookPoint(&interceptor_methods_);
    this->Op5::SetFinishInterceptionHookPoint(&interceptor_methods_);
    this->Op6::SetFinishInterceptionHookPoint(&interceptor_methods_);
    return interceptor_methods_.RunInterceptors();
  }

  void* cq_tag_;
  void* return_tag_;
  Call call_;
  bool done_intercepting_ = false;
  InterceptorBatchMethodsImpl interceptor_methods_;
  bool saved_status_;
};

}  // namespace internal
}  // namespace grpc

#endif  // GRPCPP_IMPL_CODEGEN_CALL_H