Question

I have been stuck with this prolem for the past 5 hours or so.. Sorry if the question is too obvious/noob but I am noob myself when it comes to boost::asio or tcp/ip in general.

So here is the problem. I am trying to modify the blocking tcp server example :

void session(socket_ptr sock)
{
  try
  {
    for (;;)
    {
      char data[max_length];

      boost::system::error_code error;
      size_t length = sock->read_some(boost::asio::buffer(data), error);
      if (error == boost::asio::error::eof)
        break; // Connection closed cleanly by peer.
      else if (error)
        throw boost::system::system_error(error); // Some other error.

      boost::asio::write(*sock, boost::asio::buffer(data, length));
    }
  }
  catch (std::exception& e)
  {
    std::cerr << "Exception in thread: " << e.what() << "\n";
  }
}

What I want to do is save all the chunks or the read_some method into some buffer for this example std::string and then do something with them before sending a reply back:

const int max_length = 10;

typedef boost::shared_ptr<tcp::socket> socket_ptr;

void session(socket_ptr sock)
{
    std::string dataReceived = "";
    try
    {
        for (;;)
        {
            char data[max_length] = {'\0'};
            boost::system::error_code error;
            size_t length = sock->read_some(boost::asio::buffer(data), error);
            dataReceived += std::string(data, length);
            if (error == boost::asio::error::eof)
                break; // Connection closed cleanly by peer.
            else if (error)
                throw boost::system::system_error(error); // Some other error.
            //boost::asio::write(*sock, boost::asio::buffer(&dataReceived[0], dataReceived.size()));
        }
        boost::asio::write(*sock, boost::asio::buffer(&dataReceived[0], dataReceived.size()));
    }
    catch (std::exception& e)
    {
        std::cerr << "Exception in thread: " << e.what() << "\n";
    }
}

When I remove the write from inside the loop the client hangs. The dataReceived has all the data inside. The buffer is deliberately small so that read_some is called more than once. In the debugger the control never goes to the write method outside of the loop. I am probably doing something very wrong. But I am unable to find out what.

Side question:

What would be the simplest solution to have a socket connection between some UI and a backend process?

Answer 1

Probably it hangs because client waits for server reply and don’t send new data.

Also, server will exit form loop only when connection is closed, and there is nowhere to write data.