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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.SocksVersion;
25  import io.netty.handler.codec.socksx.v4.Socks4ServerDecoder.State;
26  import io.netty.util.CharsetUtil;
27  import io.netty.util.NetUtil;
28  import io.netty.util.internal.UnstableApi;
29  
30  import java.util.List;
31  
32  /**
33   * Decodes a single {@link Socks4CommandRequest} from the inbound {@link ByteBuf}s.
34   * On successful decode, this decoder will forward the received data to the next handler, so that
35   * other handler can remove this decoder later.  On failed decode, this decoder will discard the
36   * received data, so that other handler closes the connection later.
37   */
38  public class Socks4ServerDecoder extends ReplayingDecoder<State> {
39  
40      private static final int MAX_FIELD_LENGTH = 255;
41  
42      @UnstableApi
43      public enum State {
44          START,
45          READ_USERID,
46          READ_DOMAIN,
47          SUCCESS,
48          FAILURE
49      }
50  
51      private Socks4CommandType type;
52      private String dstAddr;
53      private int dstPort;
54      private String userId;
55  
56      public Socks4ServerDecoder() {
57          super(State.START);
58          setSingleDecode(true);
59      }
60  
61      @Override
62      protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
63          try {
64              switch (state()) {
65              case START: {
66                  final int version = in.readUnsignedByte();
67                  if (version != SocksVersion.SOCKS4a.byteValue()) {
68                      throw new DecoderException("unsupported protocol version: " + version);
69                  }
70  
71                  type = Socks4CommandType.valueOf(in.readByte());
72                  dstPort = ByteBufUtil.readUnsignedShortBE(in);
73                  dstAddr = NetUtil.intToIpAddress(ByteBufUtil.readIntBE(in));
74                  checkpoint(State.READ_USERID);
75              }
76              case READ_USERID: {
77                  userId = readString("userid", in);
78                  checkpoint(State.READ_DOMAIN);
79              }
80              case READ_DOMAIN: {
81                  // Check for Socks4a protocol marker 0.0.0.x
82                  if (!"0.0.0.0".equals(dstAddr) && dstAddr.startsWith("0.0.0.")) {
83                      dstAddr = readString("dstAddr", in);
84                  }
85                  out.add(new DefaultSocks4CommandRequest(type, dstAddr, dstPort, userId));
86                  checkpoint(State.SUCCESS);
87              }
88              case SUCCESS: {
89                  int readableBytes = actualReadableBytes();
90                  if (readableBytes > 0) {
91                      out.add(in.readRetainedSlice(readableBytes));
92                  }
93                  break;
94              }
95              case FAILURE: {
96                  in.skipBytes(actualReadableBytes());
97                  break;
98              }
99              }
100         } catch (Exception e) {
101             fail(out, e);
102         }
103     }
104 
105     private void fail(List<Object> out, Exception cause) {
106         if (!(cause instanceof DecoderException)) {
107             cause = new DecoderException(cause);
108         }
109 
110         Socks4CommandRequest m = new DefaultSocks4CommandRequest(
111                 type != null? type : Socks4CommandType.CONNECT,
112                 dstAddr != null? dstAddr : "",
113                 dstPort != 0? dstPort : 65535,
114                 userId != null? userId : "");
115 
116         m.setDecoderResult(DecoderResult.failure(cause));
117         out.add(m);
118 
119         checkpoint(State.FAILURE);
120     }
121 
122     /**
123      * Reads a variable-length NUL-terminated string as defined in SOCKS4.
124      */
125     private static String readString(String fieldName, ByteBuf in) {
126         int length = in.bytesBefore(MAX_FIELD_LENGTH + 1, (byte) 0);
127         if (length < 0) {
128             throw new DecoderException("field '" + fieldName + "' longer than " + MAX_FIELD_LENGTH + " chars");
129         }
130 
131         String value = in.readSlice(length).toString(CharsetUtil.US_ASCII);
132         in.skipBytes(1); // Skip the NUL.
133 
134         return value;
135     }
136 }