C# 如何判断本机网络端口是否可用

无论是TCP端口还是UDP端口，在同一台机器上只能开启一个。为了能够让我们正常启用端口，我们不得不查询本机端口是否已经占用，如果已经占用，我们就需要查询其它可用端口，并启动连接。

那如何查找空闲的网络端口呢？

请看具体演示代码：

    public class FreePort
    {
        private const string PortReleaseGuid = "8875BD8E-4D5B-11DE-B2F4-691756D89593";

        //查找TCP可用端口
        public static int FindNextAvailableTCPPort(int startPort)
        {
            int port = startPort;
            bool isAvailable = true;

            var mutex = new Mutex(false, string.Concat("Global/", PortReleaseGuid));
            mutex.WaitOne();
            try
            {
                IPGlobalProperties ipGlobalProperties = IPGlobalProperties.GetIPGlobalProperties();
                IPEndPoint[] endPoints = ipGlobalProperties.GetActiveTcpListeners();

                do
                {
                    if (!isAvailable)
                    {
                        port++;
                        isAvailable = true;
                    }

                    foreach (IPEndPoint endPoint in endPoints)
                    {
                        if (endPoint.Port != port) continue;
                        isAvailable = false;
                        break;
                    }

                } while (!isAvailable && port < IPEndPoint.MaxPort);

                if (!isAvailable)
                    throw new ApplicationException("Not able to find a free TCP port.");

                return port;
            }
            finally
            {
                mutex.ReleaseMutex();
            }
        }

        //查找UDP可用端口
        public static int FindNextAvailableUDPPort(int startPort)
        {
            int port = startPort;
            bool isAvailable = true;

            var mutex = new Mutex(false, string.Concat("Global/", PortReleaseGuid));
            mutex.WaitOne();
            try
            {
                IPGlobalProperties ipGlobalProperties = IPGlobalProperties.GetIPGlobalProperties();
                IPEndPoint[] endPoints = ipGlobalProperties.GetActiveUdpListeners();

                do
                {
                    if (!isAvailable)
                    {
                        port++;
                        isAvailable = true;
                    }

                    foreach (IPEndPoint endPoint in endPoints)
                    {
                        if (endPoint.Port != port)
                            continue;
                        isAvailable = false;
                        break;
                    }

                } while (!isAvailable && port < IPEndPoint.MaxPort);

                if (!isAvailable)
                    throw new ApplicationException("Not able to find a free UDP port.");

                return port;
            }
            finally
            {
                mutex.ReleaseMutex();
            }
        }
    }