text: 
  /* Copyright 2017 Intel Corporation
  
   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.
  ------------------------------------------------------------------------------*/
  #pragma once
  
  #include <atomic>
  #include <cstdint>
  #include <unordered_map>
  #include <memory>
  #include <queue>
  #include <sstream>
  #include <string>
  #include <thread>
  #include <vector>
  
  #include <zmqpp/context.hpp>
  #include <zmqpp/message.hpp>
  #include <zmqpp/socket.hpp>
  
  #include "proto/validator.pb.h"
  
  #include "sawtooth/future_message.h"
  
  
  namespace sawtooth {
  
  // The MessageStream provides a conduit for messages between the Transaction
  // processing instance and the validator. MessageStreams are closely tied to
  // the MessageDispatcher, the two objects coordinate the mapping of message
  // responses thru a number of shared state objects. As such MessageStreams
  // should only be created by the MessageDispatcher via the CreateStream method.
  class MessageStream {
   public:
      virtual ~MessageStream() {}
  
      // This is a helper function that takes care of serializing a protobuffer
      // defined class and then sending the serialized results to the validator.
      // Returns a FutureMessage object that will receive the response.
      template <typename T>
      FutureMessagePtr SendMessage(Message::MessageType type, const T& proto) {
          std::stringstream proto_stream;
          proto.SerializeToOstream(&proto_stream);
          std::string correlation_id = this->GenerateCorrelationId();
          FutureMessagePtr future(new FutureMessage(correlation_id));
          {
              std::unique_lock<std::mutex> lock(this->future_message_mutex);
              this->future_message_map[correlation_id] = future;
          }
          this->Send(type, proto_stream.str(), correlation_id);
          return future;
      }
  
      // This is a helper function that takes care of serializing a protobuffer
      // defined class and then sending the serialized results to the validator.
      // It uses the correlation ID that the validator initiated.
      template <typename T>
      void SendResponseMessage(Message::MessageType type,
              const T& proto,
              const std::string& correlation_id) {
          std::stringstream proto_stream;
          proto.SerializeToOstream(&proto_stream);
          this->Send(type, proto_stream.str(), correlation_id);
      }
  
   private:
      friend class MessageDispatcher;
      explicit MessageStream(zmqpp::context* context,
          std::unordered_map<std::string, std::shared_ptr<FutureMessage>>&,
          std::mutex& future_message_mutex);
  
      // Send a message to the validator
      void Send(Message::MessageType type,
          const std::string& data,
          const std::string& correlation_id);
  
      std::string GenerateCorrelationId() const;
  
      zmqpp::context* context_;
      std::unique_ptr<zmqpp::socket> socket;
  
      std::unordered_map<std::string, std::shared_ptr<FutureMessage>>& future_message_map;
      std::mutex& future_message_mutex;
  
      static std::atomic<int> correlation_counter;
  };
  
  typedef std::shared_ptr<MessageStream> MessageStreamPtr;
  
  }  // namespace sawtooth
  