How to detect when a boost tcp socket disconnects

Question

Suppose I have a socket:

std::shared_ptr<tcp::socket> socket( new tcp::socket(acceptor.get_io_service()) );
acceptor.async_accept( *socket, std::bind( handleAccept, this, std::placeholders::_1, socket, std::ref(acceptor)) );

And I store a weak_ptr to the said socket in a container. I need this because I want to allow clients to request for a list of other clients, so they can send messages to each other.

clients_.insert(socket);  // pseudocode

Then I run some async operations

socket->async_receive( boost::asio::buffer(&(*header), sizeof(Header))
    , 0
    , std::bind(handleReceiveHeader, this, std::placeholders::_1, std::placeholders::_2, header, socket));

How do I detect when the connection is closed so I can remove my socket from the container?

clients_.erase(socket); // pseudocode

Answer 1

A TCP socket disconnect is usually signalled in asio by an eof or a connection_reset. E.g.

  void async_receive(boost::system::error_code const& error,
                     size_t bytes_transferred)
  {
    if ((boost::asio::error::eof == error) ||
        (boost::asio::error::connection_reset == error))
    {
      // handle the disconnect.
    }
    else
    {
       // read the data 
    }
  }

I use boost::signals2 to signal the disconnect although you can always pass a pointer to a function to your socket class and then call that.

Be careful about your socket and callback lifetimes, see: boost-async-functions-and-shared-ptrs

Answer 2

There are many options, some of them are:

1. As you store weak_ptr in container - it will not prolong lifetime of socket, so when your handler will get boost::asio::error::eof (or whatever), it will not do copy/move of shared_ptr, and socket will be deleted (if you don't have any others shared_ptrs to it). So, you can do something like: if(socket.expired()) clients_.erase(socket);

2. Check error code in your handler - it will indicate when connection is closed. Using this info - you can call clients_.erase from handler itself.

Could you give an example of #2?

It will be something like:

socket->async_receive
(
    boost::asio::buffer(&(*header), sizeof(Header)), 0,
    [=, &clients_](const system::error_code& error, size_t bytes_transferred)
    {
        if(error) // or some specific code
        {
            clients_.erase(socket); // pseudocode
        }
        else
        {
            // continue, launch new operation, etc
        }
    }
);