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Open source SSH2 API
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/**
 * Copyright 2003-2014 SSHTOOLS Limited. All Rights Reserved.
 *
 * For product documentation visit https://www.sshtools.com/
 *
 * This file is part of J2SSH Maverick.
 *
 * J2SSH Maverick is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * J2SSH Maverick is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with J2SSH Maverick.  If not, see .
 */
/**
 * This file is originally from the http://sourceforge.net/projects/jsocks/
 * released under the LGPL.
 */
package socks;

import java.net.*;
import java.io.*;

/**
   SocksServerSocket allows to accept connections from one particular
   host through the SOCKS4 or SOCKS5 proxy.
*/
public class SocksServerSocket extends ServerSocket{
   //Data members
   protected Proxy proxy;
   protected String localHost;
   protected InetAddress localIP;
   protected int localPort;

   boolean doing_direct = false;
   InetAddress  remoteAddr;

   /**
    * Creates ServerSocket capable of accepting one connection
    * through the firewall, uses default Proxy.
    *@param host Host from which the connection should be recieved.
    *@param port Port number of the primary connection.
    */
   public SocksServerSocket(String host,int port)
	  throws SocksException,UnknownHostException,IOException{
      this(Proxy.defaultProxy,host,port);
   }
   /**
    *Creates ServerSocket capable of accepting one connection
    *through the firewall, uses given proxy.
    *@param p    Proxy object to use.
    *@param host Host from which the connection should be recieved.
    *@param port Port number of the primary connection.
    */
   public SocksServerSocket(Proxy p,String host,int port)
	  throws SocksException,UnknownHostException,IOException{


      super(0);
      if(p == null) throw new SocksException(Proxy.SOCKS_NO_PROXY);
      //proxy=p;
      proxy = p.copy();
      if(proxy.isDirect(host)){
         remoteAddr = InetAddress.getByName(host);
         proxy = null;
         doDirect();
      }else{
         processReply(proxy.bind(host,port));
      }
   }

   /**
    * Creates ServerSocket capable of accepting one connection
    * through the firewall, uses default Proxy.
    *@param ip Host from which the connection should be recieved.
    *@param port Port number of the primary connection.
    */
   public SocksServerSocket(InetAddress ip, int port) throws SocksException,
                                                             IOException{
      this(Proxy.defaultProxy,ip,port);
   }

   /**
    *Creates ServerSocket capable of accepting one connection
    *through the firewall, uses given proxy.
    *@param p    Proxy object to use.
    *@param ip   Host from which the connection should be recieved.
    *@param port Port number of the primary connection.
    */
   public SocksServerSocket(Proxy p,InetAddress ip, int port)
          throws SocksException,IOException{
      super(0);

      if(p == null) throw new SocksException(Proxy.SOCKS_NO_PROXY);
      this.proxy = p.copy();

      if(proxy.isDirect(ip)){
         remoteAddr = ip;
         doDirect();
      }else{
         processReply(proxy.bind(ip,port));
      }
   }


   /**
    * Accepts the incoming connection.
    */
   public Socket accept() throws IOException{
      Socket s;

      if(!doing_direct){
         if(proxy == null) return null;

         ProxyMessage msg = proxy.accept();
         s = msg.ip == null? new SocksSocket(msg.host,msg.port,proxy)
                                  : new SocksSocket(msg.ip,msg.port,proxy);
         //Set timeout back to 0
         proxy.proxySocket.setSoTimeout(0);
      }else{ //Direct Connection

          //Mimic the proxy behaviour,
          //only accept connections from the speciefed host.
          while(true){
            s = super.accept();
            if(s.getInetAddress().equals(remoteAddr)){
               //got the connection from the right host
               //Close listenning socket.
               break;
            }else
               s.close(); //Drop all connections from other hosts
          }

      }
      proxy = null;
      //Return accepted socket
      return s;
   }

   /**
    * Closes the connection to proxy if socket have not been accepted, if
    * the direct connection is used, closes direct ServerSocket. If the 
    * client socket have been allready accepted, does nothing.
    */
   public void close() throws IOException{
      super.close();
      if(proxy != null) proxy.endSession();
      proxy = null;
   }

   /**
     Get the name of the host proxy is using to listen for incoming
     connection.
     
     Usefull when address is returned by proxy as the hostname.
     @return the hostname of the address proxy is using to listen
     for incoming connection.
    */
   public String getHost(){
      return localHost;
   }

   /**
    * Get address assigned by proxy to listen for incomming
    * connections, or the local machine address if doing direct
    * connection.
    */
   public InetAddress getInetAddress(){
      if(localIP == null){
	 try{
	   localIP = InetAddress.getByName(localHost);
	 }catch(UnknownHostException e){
	   return null;
	 }
      }
      return localIP;
   }

   /**
    *  Get port assigned by proxy to listen for incoming connections, or
       the port chosen by local system, if accepting directly.
    */
   public int getLocalPort(){
      return localPort;
   }

   /**
    Set Timeout.

    @param timeout Amount of time in milliseconds, accept should wait for
                   incoming connection before failing with exception.
                   Zero timeout implies infinity.
   */
   public void setSoTimeout(int timeout) throws SocketException{
      super.setSoTimeout(timeout);
      if(!doing_direct) proxy.proxySocket.setSoTimeout(timeout);
   }


//Private Methods
//////////////////

   private void processReply(ProxyMessage reply)throws SocksException{
      localPort = reply.port;
      /*
       * If the server have assigned same host as it was contacted on
       * it might return an address of all zeros
       */
      if(reply.host.equals("0.0.0.0")){
         localIP = proxy.proxyIP;
         localHost = localIP.getHostName();
      }else{
         localHost = reply.host;
         localIP = reply.ip;
      }
   }

   private void doDirect(){
      doing_direct = true;
      localPort = super.getLocalPort();
      localIP = super.getInetAddress();
      localHost = localIP.getHostName();
   }

}