System.Net.Tests.UrlPrefix.UrlPrefix C# (CSharp) Method

        static UrlPrefix()
        {
            // Find a URL prefix that is not in use on this machine *and* uses a port that's not in use.
            // Once we find this prefix, keep a listener on it for the duration of the process, so other processes
            // can't steal it.

            Guid processGuid = Guid.NewGuid();

            for (int port = 1024; port <= IPEndPoint.MaxPort; port++)
            {
                string prefix = $"http://localhost:{port}/{processGuid:N}/";

                var listener = new HttpListener();
                try
                {
                    listener.Prefixes.Add(prefix);
                    listener.Start();

                    s_processPrefixListener = listener;
                    s_processPrefix = prefix;
                    break;
                }
                catch (Exception e)
                {
                    // can't use this prefix
                    listener.Close();

                    // Remember the exception for later
                    s_processPrefixException = e;

                    // If this is not an HttpListenerException, something very wrong has happened, and there's no point
                    // in trying again.
                    if (!(e is HttpListenerException))
                        break;
                }
            }

            // At this point, either we've reserved a prefix, or we've tried everything and failed.  If we failed,
            // we've saved the exception for later.  We'll defer actually *throwing* the exception until a test
            // asks for the prefix, because dealing with a type initialization exception is not nice in xunit.
        }