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1   /*
2    * Copyright 2012 The Netty Project
3    *
4    * The Netty Project licenses this file to you under the Apache License,
5    * version 2.0 (the "License"); you may not use this file except in compliance
6    * with the License. You may obtain a copy of the License at:
7    *
8    *   https://www.apache.org/licenses/LICENSE-2.0
9    *
10   * Unless required by applicable law or agreed to in writing, software
11   * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
12   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
13   * License for the specific language governing permissions and limitations
14   * under the License.
15   */
16  package io.netty.handler.codec.socksx.v4;
17  
18  import io.netty.buffer.ByteBuf;
19  import io.netty.buffer.ByteBufUtil;
20  import io.netty.channel.ChannelHandlerContext;
21  import io.netty.handler.codec.DecoderException;
22  import io.netty.handler.codec.DecoderResult;
23  import io.netty.handler.codec.ReplayingDecoder;
24  import io.netty.handler.codec.socksx.v4.Socks4ClientDecoder.State;
25  import io.netty.util.NetUtil;
26  import io.netty.util.internal.UnstableApi;
27  
28  import java.util.List;
29  
30  /**
31   * Decodes a single {@link Socks4CommandResponse} from the inbound {@link ByteBuf}s.
32   * On successful decode, this decoder will forward the received data to the next handler, so that
33   * other handler can remove this decoder later.  On failed decode, this decoder will discard the
34   * received data, so that other handler closes the connection later.
35   */
36  public class Socks4ClientDecoder extends ReplayingDecoder<State> {
37  
38      @UnstableApi
39      public enum State {
40          START,
41          SUCCESS,
42          FAILURE
43      }
44  
45      public Socks4ClientDecoder() {
46          super(State.START);
47          setSingleDecode(true);
48      }
49  
50      @Override
51      protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
52          try {
53              switch (state()) {
54              case START: {
55                  final int version = in.readUnsignedByte();
56                  if (version != 0) {
57                      throw new DecoderException("unsupported reply version: " + version + " (expected: 0)");
58                  }
59  
60                  final Socks4CommandStatus status = Socks4CommandStatus.valueOf(in.readByte());
61                  final int dstPort = ByteBufUtil.readUnsignedShortBE(in);
62                  final String dstAddr = NetUtil.intToIpAddress(ByteBufUtil.readIntBE(in));
63  
64                  out.add(new DefaultSocks4CommandResponse(status, dstAddr, dstPort));
65                  checkpoint(State.SUCCESS);
66              }
67              case SUCCESS: {
68                  int readableBytes = actualReadableBytes();
69                  if (readableBytes > 0) {
70                      out.add(in.readRetainedSlice(readableBytes));
71                  }
72                  break;
73              }
74              case FAILURE: {
75                  in.skipBytes(actualReadableBytes());
76                  break;
77              }
78              }
79          } catch (Exception e) {
80              fail(out, e);
81          }
82      }
83  
84      private void fail(List<Object> out, Exception cause) {
85          if (!(cause instanceof DecoderException)) {
86              cause = new DecoderException(cause);
87          }
88  
89          Socks4CommandResponse m = new DefaultSocks4CommandResponse(Socks4CommandStatus.REJECTED_OR_FAILED);
90          m.setDecoderResult(DecoderResult.failure(cause));
91          out.add(m);
92  
93          checkpoint(State.FAILURE);
94      }
95  }