react-cosmos/dist/shared/findNextAvailablePort.js

Sandbox for developing and testing UI components in isolation

import net from 'net';
// Inspired by https://stackoverflow.com/q/19129570
export async function findNextAvailablePort(port, retries, retriesLeft = retries) {
    return new Promise((resolve, reject) => {
        const socket = new net.Socket();
        socket.on('connect', () => {
            console.log(`[Cosmos] Port ${port} already in use, trying next...`);
            if (retriesLeft > 0) {
                socket.destroy();
                resolve(findNextAvailablePort(port + 1, retries, retriesLeft - 1));
            }
            else {
                reject(`No available port found after ${retries} retries.`);
            }
        });
        socket.on('error', (error) => {
            if (error.code === 'ECONNREFUSED')
                resolve(port);
            else
                reject(error);
        });
        socket.setTimeout(400);
        socket.on('timeout', () => {
            socket.destroy();
            resolve(port);
        });
        socket.connect(port, '0.0.0.0');
    });
}