Question

I have this piece of code using standard sockets:

void set_fds(int sock1, int sock2, fd_set *fds) {
    FD_ZERO (fds);
    FD_SET (sock1, fds); 
    FD_SET (sock2, fds); 
}

void do_proxy(int client, int conn, char *buffer) {
    fd_set readfds; 
    int result, nfds = max(client, conn)+1;
    set_fds(client, conn, &readfds);
    while((result = select(nfds, &readfds, 0, 0, 0)) > 0) {
        if (FD_ISSET (client, &readfds)) {
            int recvd = recv(client, buffer, 256, 0);
            if(recvd <= 0)
                return;
            send_sock(conn, buffer, recvd);
        }
        if (FD_ISSET (conn, &readfds)) {
            int recvd = recv(conn, buffer, 256, 0);
            if(recvd <= 0)
                return;
            send_sock(client, buffer, recvd);
        }
        set_fds(client, conn, &readfds);
    }

I have sockets client and conn and I need to “proxy” traffic between them (this is part of a socks5 server implementation, you may see https://github.com/mfontanini/Programs-Scripts/blob/master/socks5/socks5.cpp). How can I achieve this under asio ?

I must specify that until this point both sockets were operated under blocking mode.

Tried to use this without success:

ProxySession::ProxySession(ba::io_service& ioService, socket_ptr socket, socket_ptr clientSock): ioService_(ioService), socket_(socket), clientSock_(clientSock)
{

}

void ProxySession::Start()
{
    socket_->async_read_some(boost::asio::buffer(data_, 1),
        boost::bind(&ProxySession::HandleProxyRead, this,
         boost::asio::placeholders::error,
         boost::asio::placeholders::bytes_transferred));    
}

void ProxySession::HandleProxyRead(const boost::system::error_code& error,
      size_t bytes_transferred)
{
    if (!error)
    {
      boost::asio::async_write(*clientSock_,
          boost::asio::buffer(data_, bytes_transferred),
          boost::bind(&ProxySession::HandleProxyWrite, this,
            boost::asio::placeholders::error));
    }
    else
    {
      delete this;
    }
}


void ProxySession::HandleProxyWrite(const boost::system::error_code& error)
{
   if (!error)
    {
       socket_->async_read_some(boost::asio::buffer(data_, max_length),
        boost::bind(&ProxySession::HandleProxyRead, this,
          boost::asio::placeholders::error,
         boost::asio::placeholders::bytes_transferred));
    }
    else
    {
      delete this;
    }
}

The issue is that if I do ba::read(*socket_, ba::buffer(data_,256)) I can read data that comes from my browser client through socks proxy but in the version from above ProxySession::Start does not lead to HandleProxyRead being called in any circumstances.

I don’t really need an async way of exchanging data here, it;s just that I’ve come by with this solution here. Also from where I called ProxySession->start from code I needed to introduce a sleep because otherwise the thread context from which this was executing was being shut down.

*Update 2 * See below one of my updates. The question block is getting too big.

Answer 1

The problem ca be solved by using asynchronous write/read functions in order to have something similar with presented code. Basically use async_read_some()/async_write() – or other async functions in these categories. Also in order for async processing to work one must call boost::asio::io_service.run() that will dispatch completion handler for async processing.