Port Finder

PortFinder.FindFreeLocalPort() returns an unused TCP port on the local machine, or 0 if none could be found. Useful for spinning up test servers, child processes, or dev-time integration harnesses without hard-coding ports.

Usage

using Servus.Network;

int port = PortFinder.FindFreeLocalPort();

if (port == 0)
    throw new InvalidOperationException("No free port available");

var server = WebApplication.CreateBuilder().Build();
server.Urls.Add($"http://localhost:{port}");
await server.StartAsync();

The method binds a socket, reads the assigned port, and releases immediately — there's an inherent race between the call and the next binder. In practice it's fine for tests and dev tooling; don't use it in a tight retry loop in production.

API

public class PortFinder
{
    public static int FindFreeLocalPort();
}