text: /*
   * Copyright 2018 Google
   *
   * 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 FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_REMOTE_GRPC_UNARY_CALL_H_
  #define FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_REMOTE_GRPC_UNARY_CALL_H_
  
  #include <functional>
  #include <map>
  #include <memory>
  
  #include "Firestore/core/src/firebase/firestore/remote/grpc_call.h"
  #include "Firestore/core/src/firebase/firestore/remote/grpc_completion.h"
  #include "Firestore/core/src/firebase/firestore/util/async_queue.h"
  #include "Firestore/core/src/firebase/firestore/util/status.h"
  #include "Firestore/core/src/firebase/firestore/util/statusor.h"
  #include "grpcpp/client_context.h"
  #include "grpcpp/generic/generic_stub.h"
  #include "grpcpp/support/byte_buffer.h"
  
  namespace firebase {
  namespace firestore {
  namespace remote {
  
  class GrpcConnection;
  
  /**
   * Sends a single request to the server and invokes the given callback with the
   * server response.
   */
  class GrpcUnaryCall : public GrpcCall {
   public:
    using Callback = std::function<void(const util::StatusOr<grpc::ByteBuffer>&)>;
  
    GrpcUnaryCall(std::unique_ptr<grpc::ClientContext> context,
                  std::unique_ptr<grpc::GenericClientAsyncResponseReader> call,
                  util::AsyncQueue* worker_queue,
                  GrpcConnection* grpc_connection,
                  const grpc::ByteBuffer& request);
    ~GrpcUnaryCall();
  
    /**
     * Starts the call; the given `callback` will be invoked with the result of
     * the call. If the call fails, the `callback` will be invoked with a non-ok
     * status.
     */
    void Start(Callback&& callback);
  
    /**
     * If the call is in progress, attempts to finish the call early, effectively
     * cancelling it; otherwise, it's a no-op. Cancellation is done on best-effort
     * basis; however:
     * - the call is guaranteed to be finished when this function returns;
     * - this function is blocking but should be done very fast (order of
     *   milliseconds).
     *
     * If this function succeeds in cancelling the call, the callback will not be
     * invoked.
     */
    void FinishImmediately() override;
  
    /** Like `Finish`, but always invokes the callback with the given `status`. */
    void FinishAndNotify(const util::Status& status) override;
  
    /**
     * Returns the metadata received from the server.
     *
     * Can only be called once the `GrpcUnaryCall` has finished.
     */
    Metadata GetResponseHeaders() const override;
  
    /** For tests only */
    grpc::ClientContext* context() {
      return context_.get();
    }
  
   private:
    void Shutdown();
  
    // See comments in `GrpcStream` on lifetime issues for gRPC objects.
    std::unique_ptr<grpc::ClientContext> context_;
    std::unique_ptr<grpc::GenericClientAsyncResponseReader> call_;
    // Stored to avoid lifetime issues with gRPC.
    grpc::ByteBuffer request_;
  
    util::AsyncQueue* worker_queue_ = nullptr;
    GrpcConnection* grpc_connection_ = nullptr;
  
    GrpcCompletion* finish_completion_ = nullptr;
    Callback callback_;
  };
  
  }  // namespace remote
  }  // namespace firestore
  }  // namespace firebase
  
  #endif  // FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_REMOTE_GRPC_UNARY_CALL_H_
  