Client cannot receive data - Exception with socket.async_receive in client - c++

Question

I have a simple version of a client using boost asio. The client is suppose to receive a response from the server once it sends data. Here is the code of the client
void RunClient()
{
try
{
boost::asio::io_service io_service;
boost::asio::ip::tcp::resolver resolver(io_service);
boost::asio::ip::tcp::resolver::query query( "127.0.0.1", boost::lexical_cast< std::string >( 7777 )); //9100
boost::asio::ip::tcp::resolver::iterator endpoint_iterator = resolver.resolve(query);
boost::asio::ip::tcp::socket socket(io_service);
socket.async_receive(boost::asio::buffer(buf_client, 3000), 0, ClientReceiveEvent);
boost::asio::connect(socket, endpoint_iterator);
boost::system::error_code ignored_error;
std::cout << "Sending message \n";
boost::asio::write(socket, boost::asio::buffer("Data to send"), ignored_error);
io_service.run();
}
catch (std::exception & ex)
{
std::cout << "[" << boost::this_thread::get_id()<< "] Exception: " << ex.what() << std::endl;
}
}
Here is my ClientReceiveEvent
void ClientReceiveEvent(const boost::system::error_code& error, std::size_t bytes_transferred)
{
if(!error)
{
std::cout << "Message: " << buf_client.data() << std::endl;
}
else
{
std::cout << "Error occurred." << error.message() << std::endl;
}
}
I am getting an error from the above method for incoming data
Error occurred.The file handle supplied is not valid
Any suggestion what i am doing wrong in the client ?
Update:
I got the code working however I am confused as to why the statement
socket->async_receive(boost::asio::buffer(buf_client, 3000), 0, ClientReceiveEvent);
needs to be placed after connect. and why the statement
io_service->run();
needs to be placed at the end. I thought this starts the asynch process.
I also wanted to know how would i resend data to the server. I could send it once successfully. How do i resend the command again?
The working code is:
boost::shared_ptr< boost::asio::io_service > io_service(new boost::asio::io_service);
boost::shared_ptr< boost::asio::ip::tcp::socket > socket( new boost::asio::ip::tcp::socket( *io_service ) );
boost::asio::ip::tcp::resolver resolver(*io_service);
boost::asio::ip::tcp::resolver::query query( "127.0.0.1", boost::lexical_cast< std::string >( 7777 )); //9100
boost::asio::ip::tcp::resolver::iterator endpoint_iterator = resolver.resolve(query);
socket->connect(endpoint_iterator->endpoint());
socket->async_receive(boost::asio::buffer(buf_client, 3000), 0, ClientReceiveEvent);
boost::system::error_code ignored_error;
std::cout << "Sending message \n";
boost::asio::write(*socket, boost::asio::buffer("some data"), ignored_error);
io_service->run();

Answer 1

Although async_receive schedules a read action that will execute after the code calls run(), it still needs a connected socket at the moment you are calling the async_receive function itself. This is because internally, async_receive is implemented as follows:
this->get_service().async_receive(this->get_implementation(),buffers, 0, BOOST_ASIO_MOVE_CAST(ReadHandler)(handler));
The this->get_implementation() expression returns a copy of the internal socket handle as it is at that time, unconnected in your case.
In other words, after the async read has been scheduled, it won't help connecting the socket, because the read will have been scheduled on an unconnected socket.