/*
    * Copyright 2014 The Netty Project
    *
    * The Netty Project licenses this file to you 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:
    *
    *   https://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 io.netty.handler.proxy;
  
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.channel.ChannelPipeline;
  import io.netty.handler.codec.socksx.v4.DefaultSocks4CommandRequest;
  import io.netty.handler.codec.socksx.v4.Socks4ClientDecoder;
  import io.netty.handler.codec.socksx.v4.Socks4ClientEncoder;
  import io.netty.handler.codec.socksx.v4.Socks4CommandResponse;
  import io.netty.handler.codec.socksx.v4.Socks4CommandStatus;
  import io.netty.handler.codec.socksx.v4.Socks4CommandType;
  
  import java.net.InetSocketAddress;
  import java.net.SocketAddress;
  
  /**
   * Handler that establishes a blind forwarding proxy tunnel using
   * <a href="https://www.openssh.com/txt/socks4.protocol">SOCKS4</a> protocol.
   */
  public final class Socks4ProxyHandler extends ProxyHandler {
  
      private static final String PROTOCOL = "socks4";
      private static final String AUTH_USERNAME = "username";
  
      private final String username;
  
      private String decoderName;
      private String encoderName;
  
      public Socks4ProxyHandler(SocketAddress proxyAddress) {
          this(proxyAddress, null);
      }
  
      public Socks4ProxyHandler(SocketAddress proxyAddress, String username) {
          super(proxyAddress);
          if (username != null && username.isEmpty()) {
              username = null;
          }
          this.username = username;
      }
  
      @Override
      public String protocol() {
          return PROTOCOL;
      }
  
      @Override
      public String authScheme() {
          return username != null? AUTH_USERNAME : AUTH_NONE;
      }
  
      public String username() {
          return username;
      }
  
      @Override
      protected void addCodec(ChannelHandlerContext ctx) throws Exception {
          ChannelPipeline p = ctx.pipeline();
          String name = ctx.name();
  
          Socks4ClientDecoder decoder = new Socks4ClientDecoder();
          p.addBefore(name, null, decoder);
  
          decoderName = p.context(decoder).name();
          encoderName = decoderName + ".encoder";
  
          p.addBefore(name, encoderName, Socks4ClientEncoder.INSTANCE);
      }
  
      @Override
      protected void removeEncoder(ChannelHandlerContext ctx) throws Exception {
          ChannelPipeline p = ctx.pipeline();
          p.remove(encoderName);
      }
  
      @Override
      protected void removeDecoder(ChannelHandlerContext ctx) throws Exception {
          ChannelPipeline p = ctx.pipeline();
          p.remove(decoderName);
      }
  
      @Override
      protected Object newInitialMessage(ChannelHandlerContext ctx) throws Exception {
          InetSocketAddress raddr = destinationAddress();
         String rhost;
         if (raddr.isUnresolved()) {
             rhost = raddr.getHostString();
         } else {
             rhost = raddr.getAddress().getHostAddress();
         }
         return new DefaultSocks4CommandRequest(
                 Socks4CommandType.CONNECT, rhost, raddr.getPort(), username != null? username : "");
     }
 
     @Override
     protected boolean handleResponse(ChannelHandlerContext ctx, Object response) throws Exception {
         final Socks4CommandResponse res = (Socks4CommandResponse) response;
         final Socks4CommandStatus status = res.status();
         if (status == Socks4CommandStatus.SUCCESS) {
             return true;
         }
 
         throw new ProxyConnectException(exceptionMessage("status: " + status));
     }
 }