Socks4aProxyClient.cs

/*
 *  Authors:  Benton Stark
 * 
 *  Copyright (c) 2007-2009 Starksoft, LLC (http://www.starksoft.com) 
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 * 
 */

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

namespace Starksoft.Net.Proxy
{
    /// <summary>
    /// Socks4a connection proxy class.  This class implements the Socks4a standard proxy protocol
    /// which is an extension of the Socks4 protocol 
    /// </summary>
    /// <remarks>
    /// In Socks version 4A if the client cannot resolve the destination host's domain name 
    /// to find its IP address the server will attempt to resolve it.  
    /// </remarks>
    public class Socks4aProxyClient : Socks4ProxyClient 
    {
        private const string PROXY_NAME = "SOCKS4a";

        /// <summary>
        /// Default constructor.
        /// </summary>
        public Socks4aProxyClient()
            : base()
        { }

        /// <summary>
        /// Creates a Socks4 proxy client object using the supplied TcpClient object connection.
        /// </summary>
        /// <param name="tcpClient">An open TcpClient object with an established connection.</param>
        public Socks4aProxyClient(TcpClient tcpClient) 
            : base(tcpClient)
        { }

        /// <summary>
        /// Create a Socks4a proxy client object.  The default proxy port 1080 is used.
        /// </summary>
        /// <param name="proxyHost">Host name or IP address of the proxy server.</param>
        /// <param name="proxyUserId">Proxy user identification information for an IDENTD server.</param>
        public Socks4aProxyClient(string proxyHost, string proxyUserId) 
            : base(proxyHost, proxyUserId)
        { }

        /// <summary>
        /// Create a Socks4a proxy client object.
        /// </summary>
        /// <param name="proxyHost">Host name or IP address of the proxy server.</param>
        /// <param name="proxyPort">Port used to connect to proxy server.</param>
        /// <param name="proxyUserId">Proxy user identification information.</param>
        public Socks4aProxyClient(string proxyHost, int proxyPort, string proxyUserId) 
            : base(proxyHost, proxyPort, proxyUserId)
        { }

        /// <summary>
        /// Create a Socks4 proxy client object.  The default proxy port 1080 is used.
        /// </summary>
        /// <param name="proxyHost">Host name or IP address of the proxy server.</param>
        public Socks4aProxyClient(string proxyHost) : base(proxyHost)
        { }

        /// <summary>
        /// Create a Socks4a proxy client object.
        /// </summary>
        /// <param name="proxyHost">Host name or IP address of the proxy server.</param>
        /// <param name="proxyPort">Port used to connect to proxy server.</param>
        public Socks4aProxyClient(string proxyHost, int proxyPort)
            : base(proxyHost, proxyPort)
        {  }

        /// <summary>
        /// Gets String representing the name of the proxy. 
        /// </summary>
        /// <remarks>This property will always return the value 'SOCKS4a'</remarks>
        public override string ProxyName
        {
            get { return PROXY_NAME; }
        }


        /// <summary>
        /// Sends a command to the proxy server.
        /// </summary>
        /// <param name="proxy">Proxy server data stream.</param>
        /// <param name="command">Proxy byte command to execute.</param>
        /// <param name="destinationHost">Destination host name or IP address.</param>
        /// <param name="destinationPort">Destination port number</param>
        /// <param name="userId">IDENTD user ID value.</param>
        /// <remarks>
        /// This method override the SendCommand message in the Sock4ProxyClient object.  The override adds support for the
        /// Socks4a extensions which allow the proxy client to optionally command the proxy server to resolve the 
        /// destination host IP address. 
        /// </remarks>
        internal override void SendCommand(NetworkStream proxy, byte command, string destinationHost, int destinationPort, string userId)
        {
            // PROXY SERVER REQUEST
            //Please read SOCKS4.protocol first for an description of the version 4
            //protocol. This extension is intended to allow the use of SOCKS on hosts
            //which are not capable of resolving all domain names.
            //
            //In version 4, the client sends the following packet to the SOCKS server
            //to request a CONNECT or a BIND operation:
            //
            //        +----+----+----+----+----+----+----+----+----+----+....+----+
            //        | VN | CD | DSTPORT |      DSTIP        | USERID       |NULL|
            //        +----+----+----+----+----+----+----+----+----+----+....+----+
            // # of bytes:	   1    1      2              4           variable       1
            //
            //VN is the SOCKS protocol version number and should be 4. CD is the
            //SOCKS command code and should be 1 for CONNECT or 2 for BIND. NULL
            //is a byte of all zero bits.
            //
            //For version 4A, if the client cannot resolve the destination host's
            //domain name to find its IP address, it should set the first three bytes
            //of DSTIP to NULL and the last byte to a non-zero value. (This corresponds
            //to IP address 0.0.0.x, with x nonzero. As decreed by IANA  -- The
            //Internet Assigned Numbers Authority -- such an address is inadmissible
            //as a destination IP address and thus should never occur if the client
            //can resolve the domain name.) Following the NULL byte terminating
            //USERID, the client must sends the destination domain name and termiantes
            //it with another NULL byte. This is used for both CONNECT and BIND requests.
            //
            //A server using protocol 4A must check the DSTIP in the request packet.
            //If it represent address 0.0.0.x with nonzero x, the server must read
            //in the domain name that the client sends in the packet. The server
            //should resolve the domain name and make connection to the destination
            //host if it can. 
            //
            //SOCKSified sockd may pass domain names that it cannot resolve to
            //the next-hop SOCKS server.    

            //  userId needs to be a zero length string so that the GetBytes method
            //  works properly
            if (userId == null)
                userId = "";

            byte[] destIp = {0,0,0,1};  // build the invalid ip address as specified in the 4a protocol
            byte[] destPort = GetDestinationPortBytes(destinationPort);
            byte[] userIdBytes = ASCIIEncoding.ASCII.GetBytes(userId);
            byte[] hostBytes = ASCIIEncoding.ASCII.GetBytes(destinationHost);
            byte[] request = new byte[10 + userIdBytes.Length + hostBytes.Length];

            //  set the bits on the request byte array
            request[0] = SOCKS4_VERSION_NUMBER;
            request[1] = command;
            destPort.CopyTo(request, 2);
            destIp.CopyTo(request, 4);
            userIdBytes.CopyTo(request, 8);  // copy the userid to the request byte array
            request[8 + userIdBytes.Length] = 0x00;  // null (byte with all zeros) terminator for userId
            hostBytes.CopyTo(request, 9 + userIdBytes.Length);  // copy the host name to the request byte array
            request[9 + userIdBytes.Length + hostBytes.Length] = 0x00;  // null (byte with all zeros) terminator for userId

            // send the connect request
            proxy.Write(request, 0, request.Length);

            // wait for the proxy server to send a response
            base.WaitForData(proxy);

            // PROXY SERVER RESPONSE
            // The SOCKS server checks to see whether such a request should be granted
            // based on any combination of source IP address, destination IP address,
            // destination port number, the userid, and information it may obtain by
            // consulting IDENT, cf. RFC 1413.  If the request is granted, the SOCKS
            // server makes a connection to the specified port of the destination host.
            // A reply packet is sent to the client when this connection is established,
            // or when the request is rejected or the operation fails. 
            //
            //        +----+----+----+----+----+----+----+----+
            //        | VN | CD | DSTPORT |      DSTIP        |
            //        +----+----+----+----+----+----+----+----+
            // # of bytes:	   1    1      2              4
            //
            // VN is the version of the reply code and should be 0. CD is the result
            // code with one of the following values:
            //
            //    90: request granted
            //    91: request rejected or failed
            //    92: request rejected becuase SOCKS server cannot connect to
            //        identd on the client
            //    93: request rejected because the client program and identd
            //        report different user-ids
            //
            // The remaining fields are ignored.
            //
            // The SOCKS server closes its connection immediately after notifying
            // the client of a failed or rejected request. For a successful request,
            // the SOCKS server gets ready to relay traffic on both directions. This
            // enables the client to do I/O on its connection as if it were directly
            // connected to the application server.

            // create an 8 byte response array  
            byte[] response = new byte[8];

            // read the resonse from the network stream
            proxy.Read(response, 0, 8);

            //  evaluate the reply code for an error condition
            if (response[1] != SOCKS4_CMD_REPLY_REQUEST_GRANTED)
                HandleProxyCommandError(response, destinationHost, destinationPort);
        }



    }
}