Generate random and available port
Find a free TCP port in Node.js by probing candidates with a temporary server.
1 min read
Updated
This Node.js module finds a free TCP port by attempting to listen on candidates and returning the first one that succeeds. It is useful in tests and local tooling where a fixed port would clash. The module is reproduced below.
Generate random and available port using Node.js
Network.mjs
javascript
import net from 'net';
function isUsed(port) {
return new Promise((resolve) => {
const server = net.createServer((socket) => {
socket.write('Echo server\r\n');
socket.pipe(socket);
});
server.listen(port, '127.0.0.1');
server.on('error', () => resolve(true));
server.on('listening', () => {
server.close();
resolve(false);
});
});
};
export default {
async generatePort(min, max) {
let port;
let usCurrentlyUsed;
do {
port = Math.floor(Math.random() * (max - min + 1) + min);
usCurrentlyUsed = await isUsed(port);
} while (usCurrentlyUsed);
return port;
},
};Something wrong or want to discuss this article?
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