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1   /*
2    *  Licensed to the Apache Software Foundation (ASF) under one
3    *  or more contributor license agreements.  See the NOTICE file
4    *  distributed with this work for additional information
5    *  regarding copyright ownership.  The ASF licenses this file
6    *  to you under the Apache License, Version 2.0 (the
7    *  "License"); you may not use this file except in compliance
8    *  with the License.  You may obtain a copy of the License at
9    *  
10   *    http://www.apache.org/licenses/LICENSE-2.0
11   *  
12   *  Unless required by applicable law or agreed to in writing,
13   *  software distributed under the License is distributed on an
14   *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
15   *  KIND, either express or implied.  See the License for the
16   *  specific language governing permissions and limitations
17   *  under the License. 
18   *  
19   */
20  package org.apache.mina.filter.codec.demux;
21  
22  import org.apache.mina.common.ByteBuffer;
23  import org.apache.mina.common.IoSession;
24  import org.apache.mina.filter.codec.ProtocolDecoderOutput;
25  
26  /**
27   * Decodes specific messages.
28   * 
29   * @author The Apache Directory Project (mina-dev@directory.apache.org)
30   * @version $Rev: 555855 $, $Date: 2007-07-13 05:19:00 +0200 (Fri, 13 Jul 2007) $
31   * 
32   * @see DemuxingProtocolCodecFactory
33   * @see MessageDecoderFactory
34   */
35  public interface MessageDecoder {
36      /**
37       * Represents a result from {@link #decodable(IoSession, ByteBuffer)} and
38       * {@link #decode(IoSession, ByteBuffer, ProtocolDecoderOutput)}.  Please
39       * refer to each method's documentation for detailed explanation.
40       */
41      static MessageDecoderResult OK = MessageDecoderResult.OK;
42  
43      /**
44       * Represents a result from {@link #decodable(IoSession, ByteBuffer)} and
45       * {@link #decode(IoSession, ByteBuffer, ProtocolDecoderOutput)}.  Please
46       * refer to each method's documentation for detailed explanation.
47       */
48      static MessageDecoderResult NEED_DATA = MessageDecoderResult.NEED_DATA;
49  
50      /**
51       * Represents a result from {@link #decodable(IoSession, ByteBuffer)} and
52       * {@link #decode(IoSession, ByteBuffer, ProtocolDecoderOutput)}.  Please
53       * refer to each method's documentation for detailed explanation.
54       */
55      static MessageDecoderResult NOT_OK = MessageDecoderResult.NOT_OK;
56  
57      /**
58       * Checks the specified buffer is decodable by this decoder.
59       * 
60       * @return {@link #OK} if this decoder can decode the specified buffer.
61       *         {@link #NOT_OK} if this decoder cannot decode the specified buffer.
62       *         {@link #NEED_DATA} if more data is required to determine if the
63       *         specified buffer is decodable ({@link #OK}) or not decodable
64       *         {@link #NOT_OK}.
65       */
66      MessageDecoderResult decodable(IoSession session, ByteBuffer in);
67  
68      /**
69       * Decodes binary or protocol-specific content into higher-level message objects.
70       * MINA invokes {@link #decode(IoSession, ByteBuffer, ProtocolDecoderOutput)}
71       * method with read data, and then the decoder implementation puts decoded
72       * messages into {@link ProtocolDecoderOutput}.
73       * 
74       * @return {@link #OK} if you finished decoding messages successfully.
75       *         {@link #NEED_DATA} if you need more data to finish decoding current message.
76       *         {@link #NOT_OK} if you cannot decode current message due to protocol specification violation.
77       *         
78       * @throws Exception if the read data violated protocol specification 
79       */
80      MessageDecoderResult decode(IoSession session, ByteBuffer in,
81              ProtocolDecoderOutput out) throws Exception;
82  
83      /**
84       * Invoked when the specified <tt>session</tt> is closed while this decoder was
85       * parsing the data.  This method is useful when you deal with the protocol which doesn't
86       * specify the length of a message such as HTTP response without <tt>content-length</tt>
87       * header. Implement this method to process the remaining data that
88       * {@link #decode(IoSession, ByteBuffer, ProtocolDecoderOutput)} method didn't process
89       * completely.
90       * 
91       * @throws Exception if the read data violated protocol specification
92       */
93      void finishDecode(IoSession session, ProtocolDecoderOutput out)
94              throws Exception;
95  }