boost::asio usage in self-contained class

Question

Trying to get my head around the boost classes. What I want to do, differs from the boost asio tutorial in that, the tutorial has a main() where the io_service object is instantiated. That is then passed to the class implementing asio via its constructor.

What I want to do, is to eliminate the instantiation of io_service in the main and have the implementing class be "self-contained" in that, it will declare its own io_service and socket. I must be reading the example with tunnel-vision, because I cannot figure out how to drop the instantiation of io_service into my socket class.

At first, I was getting "error C2758: 'xxx::io_service' : must be initialized in constructor base/member initializer list". So, I thought I'd do that and added "io_service(new boost::asio::io_service()), socket(io_service)" to the class initializer list. That gave me "error C2354: 'xxx::io_service' : initialization of reference member requires a temporary variable", which, after some googling, made sense.

So, my question is, how can I adjust the tutorial code to eliminate the main()?

Answer 1

Is this what you're after:

Move the io_service into the class (not by reference). And all usages as well.

I opted to put the join into the destructor.

#include <cstdlib>
#include <deque>
#include <iostream>
#include <boost/bind.hpp>
#include <boost/asio.hpp>
#include <boost/thread/thread.hpp>
#include "chat_message.hpp"

using boost::asio::ip::tcp;

typedef std::deque<chat_message> chat_message_queue;

class chat_client
{
public:
  chat_client(std::string host, std::string portorservice)
    : io_service_(),
      thread_(boost::bind(&boost::asio::io_service::run, &io_service_)),
      socket_(io_service_)
  {
    tcp::resolver resolver(io_service_);
    tcp::resolver::query query(host, portorservice);
    tcp::resolver::iterator iterator = resolver.resolve(query);

    boost::asio::async_connect(socket_, iterator,
        boost::bind(&chat_client::handle_connect, this,
          boost::asio::placeholders::error));
  }

  void write(const chat_message& msg)
  {
    io_service_.post(boost::bind(&chat_client::do_write, this, msg));
  }

  void close()
  {
    io_service_.post(boost::bind(&chat_client::do_close, this));
  }

  ~chat_client() {
    close();
    if (thread_.joinable())
        thread_.join();
  }

private:

  void handle_connect(const boost::system::error_code& error)
  {
    if (!error)
    {
      boost::asio::async_read(socket_,
          boost::asio::buffer(read_msg_.data(), chat_message::header_length),
          boost::bind(&chat_client::handle_read_header, this,
            boost::asio::placeholders::error));
    }
  }

  void handle_read_header(const boost::system::error_code& error)
  {
    if (!error && read_msg_.decode_header())
    {
      boost::asio::async_read(socket_,
          boost::asio::buffer(read_msg_.body(), read_msg_.body_length()),
          boost::bind(&chat_client::handle_read_body, this,
            boost::asio::placeholders::error));
    }
    else
    {
      do_close();
    }
  }

  void handle_read_body(const boost::system::error_code& error)
  {
    if (!error)
    {
      std::cout.write(read_msg_.body(), read_msg_.body_length());
      std::cout << "\n";
      boost::asio::async_read(socket_,
          boost::asio::buffer(read_msg_.data(), chat_message::header_length),
          boost::bind(&chat_client::handle_read_header, this,
            boost::asio::placeholders::error));
    }
    else
    {
      do_close();
    }
  }

  void do_write(chat_message msg)
  {
    bool write_in_progress = !write_msgs_.empty();
    write_msgs_.push_back(msg);
    if (!write_in_progress)
    {
      boost::asio::async_write(socket_,
          boost::asio::buffer(write_msgs_.front().data(),
            write_msgs_.front().length()),
          boost::bind(&chat_client::handle_write, this,
            boost::asio::placeholders::error));
    }
  }

  void handle_write(const boost::system::error_code& error)
  {
    if (!error)
    {
      write_msgs_.pop_front();
      if (!write_msgs_.empty())
      {
        boost::asio::async_write(socket_,
            boost::asio::buffer(write_msgs_.front().data(),
              write_msgs_.front().length()),
            boost::bind(&chat_client::handle_write, this,
              boost::asio::placeholders::error));
      }
    }
    else
    {
      do_close();
    }
  }

  void do_close()
  {
    socket_.close();
  }

private:
  boost::asio::io_service io_service_;
  boost::thread thread_;
  tcp::socket socket_;
  chat_message read_msg_;
  chat_message_queue write_msgs_;
};

int main(int argc, char* argv[])
{
    try
    {
        if (argc != 3)
        {
            std::cerr << "Usage: chat_client <host> <port>\n";
            return 1;
        }

        chat_client c(argv[1], argv[2]);

        char line[chat_message::max_body_length + 1];
        while (std::cin.getline(line, chat_message::max_body_length + 1))
        {
            using namespace std; // For strlen and memcpy.
            chat_message msg;
            msg.body_length(strlen(line));
            memcpy(msg.body(), line, msg.body_length());
            msg.encode_header();
            c.write(msg);
        }

    }
    catch (std::exception& e)
    {
        std::cerr << "Exception: " << e.what() << "\n";
    }
}