/*
    * Copyright 2012 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.codec.socksx.v4;
  
  import io.netty.buffer.ByteBuf;
  import io.netty.buffer.ByteBufUtil;
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.handler.codec.DecoderException;
  import io.netty.handler.codec.DecoderResult;
  import io.netty.handler.codec.ReplayingDecoder;
  import io.netty.handler.codec.socksx.SocksVersion;
  import io.netty.handler.codec.socksx.v4.Socks4ServerDecoder.State;
  import io.netty.util.CharsetUtil;
  import io.netty.util.NetUtil;
  import io.netty.util.internal.UnstableApi;
  
  import java.util.List;
  
  /**
   * Decodes a single {@link Socks4CommandRequest} from the inbound {@link ByteBuf}s.
   * On successful decode, this decoder will forward the received data to the next handler, so that
   * other handler can remove this decoder later.  On failed decode, this decoder will discard the
   * received data, so that other handler closes the connection later.
   */
  public class Socks4ServerDecoder extends ReplayingDecoder<State> {
  
      private static final int MAX_FIELD_LENGTH = 255;
  
      @UnstableApi
      public enum State {
          START,
          READ_USERID,
          READ_DOMAIN,
          SUCCESS,
          FAILURE
      }
  
      private Socks4CommandType type;
      private String dstAddr;
      private int dstPort;
      private String userId;
  
      public Socks4ServerDecoder() {
          super(State.START);
          setSingleDecode(true);
      }
  
      @Override
      protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
          try {
              switch (state()) {
              case START: {
                  final int version = in.readUnsignedByte();
                  if (version != SocksVersion.SOCKS4a.byteValue()) {
                      throw new DecoderException("unsupported protocol version: " + version);
                  }
  
                  type = Socks4CommandType.valueOf(in.readByte());
                  dstPort = ByteBufUtil.readUnsignedShortBE(in);
                  dstAddr = NetUtil.intToIpAddress(ByteBufUtil.readIntBE(in));
                  checkpoint(State.READ_USERID);
              }
              case READ_USERID: {
                  userId = readString("userid", in);
                  checkpoint(State.READ_DOMAIN);
              }
              case READ_DOMAIN: {
                  // Check for Socks4a protocol marker 0.0.0.x
                  if (!"0.0.0.0".equals(dstAddr) && dstAddr.startsWith("0.0.0.")) {
                      dstAddr = readString("dstAddr", in);
                  }
                  out.add(new DefaultSocks4CommandRequest(type, dstAddr, dstPort, userId));
                  checkpoint(State.SUCCESS);
              }
              case SUCCESS: {
                  int readableBytes = actualReadableBytes();
                  if (readableBytes > 0) {
                      out.add(in.readRetainedSlice(readableBytes));
                  }
                  break;
              }
              case FAILURE: {
                  in.skipBytes(actualReadableBytes());
                  break;
              }
              }
         } catch (Exception e) {
             fail(out, e);
         }
     }
 
     private void fail(List<Object> out, Exception cause) {
         if (!(cause instanceof DecoderException)) {
             cause = new DecoderException(cause);
         }
 
         Socks4CommandRequest m = new DefaultSocks4CommandRequest(
                 type != null? type : Socks4CommandType.CONNECT,
                 dstAddr != null? dstAddr : "",
                 dstPort != 0? dstPort : 65535,
                 userId != null? userId : "");
 
         m.setDecoderResult(DecoderResult.failure(cause));
         out.add(m);
 
         checkpoint(State.FAILURE);
     }
 
     /**
      * Reads a variable-length NUL-terminated string as defined in SOCKS4.
      */
     private static String readString(String fieldName, ByteBuf in) {
         int length = in.bytesBefore(MAX_FIELD_LENGTH + 1, (byte) 0);
         if (length < 0) {
             throw new DecoderException("field '" + fieldName + "' longer than " + MAX_FIELD_LENGTH + " chars");
         }
 
         String value = in.readSlice(length).toString(CharsetUtil.US_ASCII);
         in.skipBytes(1); // Skip the NUL.
 
         return value;
     }
 }