ar2015 ar2015 - 3 months ago 55
C++ Question

UDP bind: Address already in use

I have no knowledge in

node.js
.

I am sending
UDP
packets in
C++
and I want to show them in
node.js
.

The problem is that both try to occupy the IP/port. Depending on which one I run, the other one fails. How should I fix this problem?

main.cpp

// g++ main.cpp -o main -std=c++11 -lboost_system -pthread

#include <iostream>
#include <stdio.h>
#include <string>
#include <boost/asio.hpp>

using boost::asio::ip::udp;


int main(int argc, char* argv[])
{

const int port=1414;
const std::string ip="127.0.0.1";

boost::asio::io_service io_service;
udp::resolver resolver(io_service);

udp::endpoint client_endpoint = *resolver.resolve({udp::v4(), ip, std::to_string(port)});
udp::socket socket(io_service, udp::endpoint(udp::v4(), port));
boost::asio::socket_base::reuse_address option(true);
socket.set_option(option);

std::string data;
for(long i=0;true;i++)
{
data=std::to_string(i+1)+"th packet";
socket.send_to(boost::asio::buffer(data.c_str(), data.length()+1), client_endpoint);
usleep(10);
}

return 0;
}


app.js

var PORT = 1414;
var HOST = '127.0.0.1';

var dgram = require('dgram');
var server = dgram.createSocket('udp4');

server.on('listening', function () {
var address = server.address();
console.log('UDP Server listening on ' + address.address + ":" + address.port);
});

server.on('message', function (message, remote) {
console.log(remote.address + ':' + remote.port +' - ' + message);

});

server.bind(PORT, HOST);


If I run the
C++
file and then the
js
one, the error is this:

events.js:160
throw er; // Unhandled 'error' event
^

Error: bind EADDRINUSE 127.0.0.1:1414
at Object.exports._errnoException (util.js:1012:11)
at exports._exceptionWithHostPort (util.js:1035:20)
at dgram.js:221:18
at _combinedTickCallback (internal/process/next_tick.js:77:11)
at process._tickCallback (internal/process/next_tick.js:98:9)
at Module.runMain (module.js:577:11)
at run (bootstrap_node.js:352:7)
at startup (bootstrap_node.js:144:9)
at bootstrap_node.js:467:3


While, if I run the
js
file first and then the
C++
one, I receive:

terminate called after throwing an instance of 'boost::exception_detail::clone_impl<boost::exception_detail::error_info_injector<boost::system::system_error> >'
what(): bind: Address already in use
Aborted (core dumped)

Answer

You need to set reuseAddr: true when creating your socket:

var server = dgram.createSocket({ type: 'udp4', reuseAddr: true });

You will also need to change how you create your socket on the C++ side. Currently the udp::socket constructor signature you're using will cause the socket to bind immediately. Unfortunately, you need to set the reuse_address option first before binding. To do that, try this intead:

udp::socket socket(io_service, udp::v4());
socket.set_option(boost::asio::socket_base::reuse_address(true));
socket.bind(udp::endpoint(udp::v4(), port));
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