SocksServerSocket.java

/*
 * Copyright 2015-2025 the original author or authors.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package sockslib.client;

import sockslib.common.SocksException;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.IOException;
import java.net.InetAddress;
import java.net.InetSocketAddress;
import java.net.ServerSocket;
import java.net.Socket;
import java.net.SocketAddress;

/**
 * The class <code>SocksServerSocket</code> is server socket that can bind a port at SOCKS server
 * and accept a connection. This server socket can only accept one connection from specified IP
 * address and port.<br>
 * <p>
 * You can build a TCP server in SOCKS server easily by using following codes:
 * </p>
 * <pre>
 * SocksProxy proxy = new Socks5(new InetSocketAddress("foo.com", 1080));
 * //Create SOCKS5 proxy.
 *
 * ServerSocket serverSocket = new SocksServerSocket(proxy, inetAddress, 8080);
 * // Get bind address in SOCKS server.
 * InetAddress bindAddress = ((SocksServerSocket) serverSocket).getBindAddress();
 * // Get bind port in SOKCS server.
 * int bindPort = ((SocksServerSocket) serverSocket).getBindPort();
 * Socket socket = serverSocket.accept();
 * </pre>
 *
 * @author Youchao Feng
 * @version 1.0
 * @date Mar 25, 2015 11:40:36 AM
 */
public class SocksServerSocket extends ServerSocket {

  /**
   * Logger.
   */
  protected static final Logger logger = LoggerFactory.getLogger(SocksServerSocket.class);

  /**
   * SOCKS proxy.
   */
  private SocksProxy proxy;

  /**
   * The remote host's IP address that will connect the server.
   */
  private InetAddress incomeAddress;


  /**
   * The remote host's port that will connect the server.
   */
  private int incomePort;


  /**
   * Server's IP address.
   */
  private InetAddress bindAddress;

  /**
   * Server's port.
   */
  private int bindPort;

  /**
   * If {@link #accept()} is called, it will be <code>true</code>.
   */
  private boolean alreadyAccepted = false;


  /**
   * Constructs a server socket. This server socket will established in SOCKS server.
   *
   * @param proxy       SOCKS proxy.
   * @param inetAddress The IP address that server socket will accept.
   * @param port        The port that server socket will accept.
   * @throws SocksException If any error about SOCKS protocol occurs.
   * @throws IOException    If any I/O error occurs.
   */
  public SocksServerSocket(SocksProxy proxy, InetAddress inetAddress, int port) throws
      SocksException, IOException {
    this.proxy = proxy.copy();
    this.incomePort = port;
    this.incomeAddress = inetAddress;
    this.proxy.buildConnection();
    // Send BIND command to SOCKS server.
    CommandReplyMessage replyMesasge = this.proxy.requestBind(incomeAddress, incomePort);
    // Get a bind IP and port in proxy server.
    bindAddress = replyMesasge.getIp();
    bindPort = replyMesasge.getPort();
    logger.debug("Bind at {}:{}", bindAddress, bindPort);
  }

  /**
   * Accepts a connection.<br>
   * <b>Notice:</b> This method can be called only once. It will throw SocksException if this method
   * is called more than once.
   */
  @Override
  public synchronized Socket accept() throws SocksException, IOException {

    if (alreadyAccepted) {
      throw new SocksException("SOCKS4/SOCKS5 protocol only allows one income connection");
    }

    alreadyAccepted = true;
    return proxy.accept();
  }

  public InetAddress getBindAddress() {
    return bindAddress;
  }

  public void setBindAddress(InetAddress bindAddress) {
    this.bindAddress = bindAddress;
  }

  public int getBindPort() {
    return bindPort;
  }

  public void setBindPort(int bindPort) {
    this.bindPort = bindPort;
  }

  public SocketAddress getBindSocketAddress() {
    return new InetSocketAddress(bindAddress, bindPort);
  }
}