Laservall_solidworks_inject/Server/PortFinder.cs

using System;
using System.Net;
using System.Net.Sockets;

namespace Laservall.Solidworks.Server
{
    internal static class PortFinder
    {
        private const int PreferredPort = 18951;

        public static int FindAvailablePort()
        {
            if (IsPortAvailable(PreferredPort))
            {
                return PreferredPort;
            }

            return GetOsAssignedPort();
        }

        private static bool IsPortAvailable(int port)
        {
            TcpListener listener = null;
            try
            {
                listener = new TcpListener(IPAddress.Loopback, port);
                listener.Start();
                return true;
            }
            catch (SocketException)
            {
                return false;
            }
            finally
            {
                listener?.Stop();
            }
        }

        private static int GetOsAssignedPort()
        {
            var listener = new TcpListener(IPAddress.Loopback, 0);
            try
            {
                listener.Start();
                int port = ((IPEndPoint)listener.LocalEndpoint).Port;
                return port;
            }
            finally
            {
                listener.Stop();
            }
        }
    }
}