PortcheckService/Program.cs

   1 using System;
   2 using System.Collections;
   3 using System.Collections.Generic;
   4 using System.Linq;
   5 using System.Net;
   6 using System.Net.Sockets;
   7 using System.Threading.Tasks;
   8
   9 namespace PortcheckService
  10 {
  11     class Program
  12     {
  13         private static UdpClient _mainSocket;
  14         private static readonly byte[] MagicSequence = new byte[4] { 0x43, 0x4f, 0x4e, 0x43 };
  15         private static readonly byte[] OurSequence = new byte[] { 0x73, 0x6d, 0x36, 0x34, 0x6f, 0x69, 0x70, 0x63, 0x30, 0x30, 0x30, 0x30 };
  16
  17         static void Main(string[] args)
  18         {
  19             Console.WriteLine("portcheck service starting up...");
  20             int port = 6460;
  21
  22             if (args.Length > 0 && int.TryParse(args[0], out port))
  23             {}
  24
  25             Console.WriteLine("using port " + port);
  26
  27             try
  28             {
  29                 IPEndPoint localEP = new IPEndPoint(IPAddress.Any, port);
  30                 _mainSocket = new UdpClient(localEP);
  31
  32                 Receive().GetAwaiter().GetResult();
  33             }
  34             catch (Exception e)
  35             {
  36                 Console.WriteLine(e);
  37             }
  38         }
  39
  40         static async Task Receive()
  41         {
  42             while (true)
  43             {
  44                 UdpReceiveResult result = await _mainSocket.ReceiveAsync();
  45                 await HandlePacket(result);
  46             }
  47         }
  48
  49         private static async Task HandlePacket(UdpReceiveResult res)
  50         {
  51             if (!ArrayCompare(OurSequence, 0, res.Buffer, 0, OurSequence.Length))
  52                 return;
  53
  54             byte[] readbackArray = new byte[MagicSequence.Length + 4];
  55
  56             Array.Copy(MagicSequence, 0, readbackArray, 0, MagicSequence.Length);
  57
  58             Array.Copy(res.RemoteEndPoint.Address.GetAddressBytes(), 0, readbackArray, MagicSequence.Length, 4);
  59
  60             short theirPort = BitConverter.ToInt16(res.Buffer, OurSequence.Length);
  61
  62             var returnEndPoint = new IPEndPoint(res.RemoteEndPoint.Address, theirPort);
  63
  64             await _mainSocket.SendAsync(readbackArray, readbackArray.Length, returnEndPoint);
  65         }
  66
  67         private static bool ArrayCompare<T>(T[] left, int leftStart, T[] right, int rightStart, int len)
  68         {
  69             for (int i = 0; i < len; i++)
  70                 if (!EqualityComparer<T>.Default.Equals(left[i], right[i]))
  71                     return false;
  72
  73             return true;
  74         }
  75     }
  76 }