Fix privoxy listening port conflict (#920)

Let TCP stack find a free port for us

Signed-off-by: Syrone Wong <wong.syrone@gmail.com>

shadowsocks-csharp/Controller/Service/PrivoxyRunner.cs

@@ -6,6 +6,7 @@ using System.IO;
 using System.Linq;
 using System.Net;
 using System.Net.NetworkInformation;
+using System.Net.Sockets;
 using System.Runtime.InteropServices;
 using System.Text;
 using System.Windows.Forms;
@@ -41,17 +42,10 @@ namespace Shadowsocks.Controller
             }
         }
 
-        public int RunningPort
-        {
-            get
-            {
-                return _runningPort;
-            }
-        }
+        public int RunningPort => _runningPort;
 
         public void Start(Configuration configuration)
         {
-            Server server = configuration.GetCurrentServer();
             if (_process == null)
             {
                 Process[] existingPrivoxy = Process.GetProcessesByName("ss_privoxy");
@@ -90,6 +84,7 @@ namespace Shadowsocks.Controller
             if (_process != null)
             {
                 KillProcess(_process);
+                _process.Dispose();
                 _process = null;
             }
             RefreshTrayArea();
@@ -160,21 +155,12 @@ namespace Shadowsocks.Controller
             int defaultPort = 8123;
             try
             {
-                IPGlobalProperties properties = IPGlobalProperties.GetIPGlobalProperties();
-                IPEndPoint[] tcpEndPoints = properties.GetActiveTcpListeners();
-
-                List<int> usedPorts = new List<int>();
-                foreach (IPEndPoint endPoint in IPGlobalProperties.GetIPGlobalProperties().GetActiveTcpListeners())
-                {
-                    usedPorts.Add(endPoint.Port);
-                }
-                for (int port = defaultPort; port <= 65535; port++)
-                {
-                    if (!usedPorts.Contains(port))
-                    {
-                        return port;
-                    }
-                }
+                // TCP stack please do me a favor
+                TcpListener l = new TcpListener(IPAddress.Loopback, 0);
+                l.Start();
+                var port = ((IPEndPoint)l.LocalEndpoint).Port;
+                l.Stop();
+                return port;
             }
             catch (Exception e)
             {
@@ -182,7 +168,6 @@ namespace Shadowsocks.Controller
                 Logging.LogUsefulException(e);
                 return defaultPort;
             }
-            throw new Exception("No free port found.");
         }
 
         [StructLayout(LayoutKind.Sequential)]