Function isPortInUse

packages/setupWizard/src/index.ts:190–208

({ host, port }: PublishedPort)

// it ourselves — this catches any process (Docker or not, e.g. a local Postgres on
// 5432), which is the actual failure mode `docker compose up` hits.
function isPortInUse({ host, port }: PublishedPort): Promise<boolean> {
    return new Promise((resolve) => {
        const server = net.createServer();
        server.once('error', (err: NodeJS.ErrnoException) => {
            server.close(() => { /* noop */ });
            // EADDRINUSE = taken. Other errors (e.g. EACCES on privileged ports) aren't
            // a "someone else has it" conflict we can meaningfully report, so treat as free.
            resolve(err.code === 'EADDRINUSE');
        });
        server.once('listening', () => {
            server.close(() => resolve(false));
        });
        if (host === '0.0.0.0') {
            server.listen(port);
        } else {
            server.listen(port, host);
        }
    });
}

// Best-effort: maps a host port to the running Docker container(s) publishing it, so
// a conflict can name the offender. Returns an empty map if Docker isn't available.