[nodejs]UDP example

udp-echo.js

"use strict";

const dgram = require("dgram");

const port = process.env.PORT || 44444;
const once = !!process.env.ONCE || false;

const opts = {type: "udp4", reuseAddr: true};
const socket = dgram.createSocket(opts, (msg, info) => {
    // msg: Buffer, info: {address, family, port, size}
    console.log(msg.toString(), info);
    const reply = `accept: ${msg.toString()}`;
    socket.send(Buffer.from(reply), info.port, info.address, err => {
        if (err) console.error(err);
        if (once) socket.close();
    });
}).once("listening", _ => {
    // addr: {address, family, port}
    const addr = socket.address(); 
    console.log(`wait on`, addr);
}).bind(port);

udp-send.js

"use strict";

const dgram = require("dgram");

const host = process.env.HOST || "localhost";
const port = process.env.PORT || 44444;
const msg = process.env.MSG || "Hello UDP";

const socket = dgram.createSocket("udp4", (msg, info) => {
    console.log(msg.toString(), info);
    socket.close();
});
socket.send(Buffer.from(msg), port, host, err => {
    // called after sent
    if (err) console.error(err);
    console.log(`sent ${msg} to ${host}:${port}`);
});

Compare with the TCP code: https://gist.github.com/bellbind/ec9308b909d56eaacdf5d5c050c782a3

[play on localhost]

server:

PORT=44444 node udp-echo.js

client:

PORT=44444 MSG="Hello UDP" node udp-send.js