[UX] add port detector

NaiveSharp/MainWindow.cs

@@ -142,6 +142,56 @@ private void lblSave_Click(object sender, EventArgs e)
 
         private void btnRun_Click(object sender, EventArgs e)
         {
+            /*
+             * 0 -> Ok
+             * 1 -> 1080
+             * 2 -> 1081
+             * 3 -> 1080 & 1081
+             */
+            int status = 0;
+
+            if (Net.IsPortUsed(1080))
+            {
+                status = 1;
+            }
+            if (Net.IsPortUsed(1081))
+            {
+                if (status == 1)
+                {
+                    status = 3;
+                }
+                else
+                {
+                    status = 2;
+                }
+            }
+            DialogResult result = DialogResult.OK;
+            switch (status)
+            {
+                case 1:
+                    result = MessageBox.Show("Port 1080 is in used! NaiveProxy may not work normally!\n" +
+                        "Do you still want to continue?", "Port is in used",
+                        MessageBoxButtons.YesNo,
+                        MessageBoxIcon.Warning);
+                    break;
+                case 2:
+                    result = MessageBox.Show("Port 1081 is in used! HTTP proxy and padding may not work normally!\n" +
+                        "Do you still want to continue?", "Port is in used",
+                        MessageBoxButtons.YesNo,
+                        MessageBoxIcon.Warning);
+                    break;
+                case 3:
+                    result = MessageBox.Show("Port 1080 is in used! NaiveProxy may not work normally!\n" +
+                        "Port 1081 is in used! HTTP proxy and padding may not work normally!\n" +
+                        "Do you still want to continue?", "Port is in used",
+                        MessageBoxButtons.YesNo,
+                        MessageBoxIcon.Warning);
+                    break;
+            }
+            if (result == DialogResult.No)
+            {
+                return;
+            }
             Operation.Run();
 
             MessageBox.Show("NaiveProxy runs successfully!", "Info", MessageBoxButtons.OK, MessageBoxIcon.Information);

NaiveSharp/Module/NaiveCmdBuilder.cs

@@ -1,5 +1,4 @@
 using System;
-using System.Diagnostics;
 
 namespace NaiveSharp.Module
 {

NaiveSharp/Module/Net.cs

@@ -0,0 +1,24 @@
+using System.Net;
+using System.Net.NetworkInformation;
+
+namespace NaiveSharp.Module
+{
+    class Net
+    {
+        public static bool IsPortUsed(int port)
+        {
+            bool isPortUsed = false;
+            IPGlobalProperties ipProperties = IPGlobalProperties.GetIPGlobalProperties();
+            IPEndPoint[] ipEndPoints = ipProperties.GetActiveTcpListeners();
+            foreach (IPEndPoint endPoint in ipEndPoints)
+            {
+                if (endPoint.Port == port)
+                {
+                    isPortUsed = true;
+                    break;
+                }
+            }
+            return isPortUsed;
+        }
+    }
+}