SocksProxy

using System;
using System.Net;
using System.Net.Sockets;
using System.Text;

namespace COMail
{
    public class ConnectionException : ApplicationException
    {
        public ConnectionException(string message)
            : base(message)
        {
        }
    }

    /// <summary>
    /// Provides sock5 functionality to clients (Connect only).
    /// </summary>
    public class SocksProxy
    {

        private SocksProxy() { }

        #region ErrorMessages
        private static string[] errorMsgs = {
                                        "Operation completed successfully.",
                                        "General SOCKS server failure.",
                                        "Connection not allowed by ruleset.",
                                        "Network unreachable.",
                                        "Host unreachable.",
                                        "Connection refused.",
                                        "TTL expired.",
                                        "Command not supported.",
                                        "Address type not supported.",
                                        "Unknown error."
                                    };
        #endregion


        public static Socket ConnectToSocks(string proxyAdress, ushort proxyPort)
        {
            IPAddress proxyIP = null;
            byte[] request = new byte[257];
            byte[] response = new byte[257];
            ushort nIndex;

            try
            {
                proxyIP = IPAddress.Parse(proxyAdress);
            }
            catch (FormatException)
            {   // get the IP address
                proxyIP = Dns.GetHostByAddress(proxyAdress).AddressList[0];
            }

            IPEndPoint proxyEndPoint = new IPEndPoint(proxyIP, proxyPort);

            // open a TCP connection to SOCKS server...
            Socket s = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
            s.Connect(proxyEndPoint);

            nIndex = 0;
            request[nIndex++] = 0x05; // Version 5.
            request[nIndex++] = 0x02; // 2 Authentication methods are in packet...
            request[nIndex++] = 0x00; // NO AUTHENTICATION REQUIRED
            request[nIndex++] = 0x00; // USERNAME/PASSWORD
            // Send the authentication negotiation request...
            s.Send(request, nIndex, SocketFlags.None);

            // Receive 2 byte response...
            int nGot = s.Receive(response, 2, SocketFlags.None);
            if (nGot != 2)
                throw new ConnectionException("Bad response received from proxy server.");

            if (response[1] == 0xFF)
            {   // No authentication method was accepted close the socket.
                s.Close();
                throw new ConnectionException("None of the authentication method was accepted by proxy server.");
            }

            // Send connect request now...
            nIndex = 0;
            request[nIndex++] = 0x05;   // version 5.
            request[nIndex++] = 0x01;   // command = connect.
            request[nIndex++] = 0x00;   // Reserve = must be 0x00

            // send connect request.
            s.Send(request, nIndex, SocketFlags.None);
            s.Receive(response);    // Get variable length response...
            if (response[1] != 0x00)
                throw new ConnectionException(errorMsgs[response[1]]);
            // Success Connected...
            return s;
        }
    }
}