C# class for connecting via a SOCKS5 Proxy Server

using System;
using System.Text;
using System.Net.Sockets;
using System.Net;
 
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 ConnectToSocks5Proxy(string proxyAdress, ushort proxyPort, string destAddress, ushort destPort,
        string userName, string password)
    {
        IPAddress destIP = null;
        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];
        }
 
        // Parse destAddress (assume it in string dotted format "212.116.65.112" )
        try
        {
            destIP = IPAddress.Parse(destAddress);
        }
        catch (FormatException)
        {
            // wrong assumption its in domain name format "www.microsoft.com"
        }
 
        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 <<<<- changed to 0!!!
        // 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.");
        }
 
        byte[] rawBytes;
 
        if (/*response[1]==0x02*/false) //changed!
        {//Username/Password Authentication protocol
            nIndex = 0;
            request[nIndex++] = 0x05; // Version 5.

            // add user name
            request[nIndex++] = (byte)userName.Length;
            rawBytes = Encoding.Default.GetBytes(userName);
            rawBytes.CopyTo(request, nIndex);
            nIndex += (ushort)rawBytes.Length;
 
            // add password
            request[nIndex++] = (byte)password.Length;
            rawBytes = Encoding.Default.GetBytes(password);
            rawBytes.CopyTo(request, nIndex);
            nIndex += (ushort)rawBytes.Length;
 
            // Send the Username/Password request
            s.Send(request, nIndex, SocketFlags.None);
            // Receive 2 byte response...
            nGot = s.Receive(response, 2, SocketFlags.None);
            if (nGot != 2)
                throw new ConnectionException("Bad response received from proxy server.");
            if (response[1] != 0x00)
                throw new ConnectionException("Bad Usernaem/Password.");
        }
        // This version only supports connect command.
        // UDP and Bind are not supported.

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

        if (destIP != null)
        {// Destination adress in an IP.
            switch (destIP.AddressFamily)
            {
                case AddressFamily.InterNetwork:
                    // Address is IPV4 format
                    request[nIndex++] = 0x01;
                    rawBytes = destIP.GetAddressBytes();
                    rawBytes.CopyTo(request, nIndex);
                    nIndex += (ushort)rawBytes.Length;
                    break;
                case AddressFamily.InterNetworkV6:
                    // Address is IPV6 format
                    request[nIndex++] = 0x04;
                    rawBytes = destIP.GetAddressBytes();
                    rawBytes.CopyTo(request, nIndex);
                    nIndex += (ushort)rawBytes.Length;
                    break;
            }
        }
        else
        {// Dest. address is domain name.
            request[nIndex++] = 0x03;    // Address is full-qualified domain name.
            request[nIndex++] = Convert.ToByte(destAddress.Length); // length of address.
            rawBytes = Encoding.Default.GetBytes(destAddress);
            rawBytes.CopyTo(request, nIndex);
            nIndex += (ushort)rawBytes.Length;
        }
 
        // using big-edian byte order
        byte[] portBytes = BitConverter.GetBytes(destPort);
        for (int i = portBytes.Length - 1; i >= 0; i--)
            request[nIndex++] = portBytes[i];
 
        // 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;
    }
}