Continuously streaming data with Boost::ASIO without closing socket - c++

Question

I'm trying to build an application that:
a) Runs an FDM (flight dynamics model) internally, and manages the flight data
b) Accepts connections on a TCP socket
c) Serves the flight data over said socket.
I've currently managed to get a simple string sent over TCP on my a local socket using the examples/tutorials on the Boos::ASIO website here: http://www.boost.org/doc/libs/1_56_0_b1/doc/html/boost_asio/tutorial.html
My trouble is simply that the connection closes after a single string is written, and I don't know how to keep the connection open and continuously send the data until the simulation is finished (or a stop signal is sent from the listening application).
I also have the FDM working (currently using JSBSim, and borrowing heavily from their included sample code), and can print flight data to stdout no problem. The Boost:ASIO documentation shows a few examples on how to build a server that constantly listens for messages received from the client, but none that send a stream of data out.

Answer 1

To send a stream of data out, you can use the free functions with boost::asio::streambuf.
Here's a simple demo that sends its own source to each client:
#include <boost/asio.hpp>
#include <boost/make_shared.hpp>
#include <boost/function.hpp>
#include <boost/asio/posix/stream_descriptor.hpp>
#include <fstream>
#include <iostream>
namespace io = boost::asio;
namespace ip = io::ip;
using boost::system::error_code;
using boost::make_shared;
using ip::tcp;
void start_accept(io::io_service& svc, tcp::acceptor& acc) {
// per-connection lifetimes:
auto sock = make_shared<tcp::socket>(svc);
acc.async_accept(*sock, [sock,&svc,&acc](error_code ec) {
if (!ec)
{
std::cout << "connection from " << sock->remote_endpoint() << "\n";
// copy source file to buffer data
auto data = make_shared<io::streambuf>();
std::ostream(data.get()) << std::ifstream("main.cpp").rdbuf();
// now write the whole story
io::async_write(*sock, *data, [sock,data/*keep alive*/](error_code ec, size_t transferred){});
// accept new connections too
start_accept(svc, acc);
}
});
}
int main()
{
io::io_service svc;
tcp::acceptor acc(svc, tcp::endpoint(ip::address(), 6767));
start_accept(svc, acc);
svc.run();
}
Note that for simplicity I put the full buffer in memory first, assuming you can do that (you said "and can print flight data to stdout no problem"). So, you could just write different things to the stream (the ostream line in my example).