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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.core.buffer.IoBuffer;
    23  import org.apache.mina.core.session.IoSession;
    24  import org.apache.mina.filter.codec.ProtocolDecoderOutput;
    25
    26  /**
    27   * Decodes a certain type of messages.
    28   * <p>
    29   * We didn't provide any <tt>dispose</tt> method for {@link MessageDecoder}
    30   * because it can give you  performance penalty in case you have a lot of
    31   * message types to handle.
    32   *
    33   * @author <a href="http://mina.apache.org">Apache MINA Project</a>
    34   *
    35   * @see DemuxingProtocolDecoder
    36   * @see MessageDecoderFactory
    37   */
    38  public interface MessageDecoder {
    39      /**
    40       * Represents a result from {@link #decodable(IoSession, IoBuffer)} and
    41       * {@link #decode(IoSession, IoBuffer, ProtocolDecoderOutput)}.  Please
    42       * refer to each method's documentation for detailed explanation.
    43       */
    44      static MessageDecoderResult OK = MessageDecoderResult.OK;
    45
    46      /**
    47       * Represents a result from {@link #decodable(IoSession, IoBuffer)} and
    48       * {@link #decode(IoSession, IoBuffer, ProtocolDecoderOutput)}.  Please
    49       * refer to each method's documentation for detailed explanation.
    50       */
    51      static MessageDecoderResult NEED_DATA = MessageDecoderResult.NEED_DATA;
    52
    53      /**
    54       * Represents a result from {@link #decodable(IoSession, IoBuffer)} and
    55       * {@link #decode(IoSession, IoBuffer, ProtocolDecoderOutput)}.  Please
    56       * refer to each method's documentation for detailed explanation.
    57       */
    58      static MessageDecoderResult NOT_OK = MessageDecoderResult.NOT_OK;
    59
    60      /**
    61       * Checks the specified buffer is decodable by this decoder.
    62       *
    63       * @return {@link #OK} if this decoder can decode the specified buffer.
    64       *         {@link #NOT_OK} if this decoder cannot decode the specified buffer.
    65       *         {@link #NEED_DATA} if more data is required to determine if the
    66       *         specified buffer is decodable ({@link #OK}) or not decodable
    67       *         {@link #NOT_OK}.
    68       */
    69      MessageDecoderResult decodable(IoSession session, IoBuffer in);
    70
    71      /**
    72       * Decodes binary or protocol-specific content into higher-level message objects.
    73       * MINA invokes {@link #decode(IoSession, IoBuffer, ProtocolDecoderOutput)}
    74       * method with read data, and then the decoder implementation puts decoded
    75       * messages into {@link ProtocolDecoderOutput}.
    76       *
    77       * @return {@link #OK} if you finished decoding messages successfully.
    78       *         {@link #NEED_DATA} if you need more data to finish decoding current message.
    79       *         {@link #NOT_OK} if you cannot decode current message due to protocol specification violation.
    80       *
    81       * @throws Exception if the read data violated protocol specification
    82       */
    83      MessageDecoderResult decode(IoSession session, IoBuffer in, ProtocolDecoderOutput out) throws Exception;
    84
    85      /**
    86       * Invoked when the specified <tt>session</tt> is closed while this decoder was
    87       * parsing the data.  This method is useful when you deal with the protocol which doesn't
    88       * specify the length of a message such as HTTP response without <tt>content-length</tt>
    89       * header. Implement this method to process the remaining data that
    90       * {@link #decode(IoSession, IoBuffer, ProtocolDecoderOutput)} method didn't process
    91       * completely.
    92       *
    93       * @throws Exception if the read data violated protocol specification
    94       */
    95      void finishDecode(IoSession session, ProtocolDecoderOutput out) throws Exception;
    96  }