How to connect two mobile clients via UDP sockets

Question

I want to make a UDP connection for voice calls between two applications. To decrease transactions over the server, I need to send the UDP packet directly from one client to another client without sending packets over the server. But I faced the below situation:

When a packet is sent to a server, the server will receive it from the router IP and a random port.
I tried to send a response from the server to the client through the router IP and port by opening a new UDP socket connection, but the client didn't receive the response.
I do the same by sending my response over the socket that already received the client message, and this time it received the client.

I failed to send UDP packets from other UDP sockets (both on the server and other clients) to my first client, even over the router IP and opened port on it.

I'm curious to know if it is possible to make client-to-client UDP connection or not?

The below code is the correct model to return respond to the client:

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

server.on('message', (msg, rinfo) => {
    console.log(`* server got: ${msg} from ${rinfo.address}:${rinfo.port}`);

    const message = Buffer.from('Some bytes to '+rinfo.address+":"+rinfo.port);
 //////↓///////////This is the receiver socket
    server.send(message, rinfo.port, rinfo.address);
 //////↑///////////
});

server.bind(8090);

By the below code, the client will not receive any response, even from the server which received the client message right now!

const dgram = require('dgram');
const server = dgram.createSocket('udp4');
const serverResponse = dgram.createSocket('udp4');

server.on('message', (msg, rinfo) => {
    console.log(`* server got: ${msg} from ${rinfo.address}:${rinfo.port}`);

    const message = Buffer.from('Some bytes to '+rinfo.address+":"+rinfo.port);
 ///////↓///////// This is the different socket instance
    serverResponse .send(message, rinfo.port, rinfo.address);
 ///////↑//////////
});

server.bind(8090);

Does this answer your question? Sending UDP packets over the Internet — Jeremy Friesner

Mahdi Saeedi Mahdi Saeedi · Accepted Answer · 2020-09-06T21:06:16

is this true? "you send a message from your client and the server receive it but when you send response to your client the client did not receive the response".

If this is true then i think that you need use a same socket object for sending and receiving because you cannot create two socket object over same port on a device.

How to connect two mobile clients via UDP sockets

1 Answers