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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.statemachine;
    21
    22  import java.util.Queue;
    23  import java.util.concurrent.ConcurrentLinkedQueue;
    24
    25  import org.apache.mina.core.buffer.IoBuffer;
    26  import org.apache.mina.core.session.IoSession;
    27  import org.apache.mina.filter.codec.ProtocolDecoder;
    28  import org.apache.mina.filter.codec.ProtocolDecoderOutput;
    29
    30  /**
    31   * {@link ProtocolDecoder} which uses a {@link DecodingState} to decode data.
    32   * Use a {@link DecodingStateMachine} as {@link DecodingState} to create
    33   * a state machine which can decode your protocol.
    34   * <p>
    35   * NOTE: This is a stateful decoder. You should create one instance per session.
    36   * </p>
    37   *
    38   * @author <a href="http://mina.apache.org">Apache MINA Project</a>
    39   */
    40  public class DecodingStateProtocolDecoder implements ProtocolDecoder {
    41      private final DecodingState state;
    42
    43      private final Queue<IoBuffer> undecodedBuffers = new ConcurrentLinkedQueue<IoBuffer>();
    44
    45      private IoSession session;
    46
    47      /**
    48       * Creates a new instance using the specified {@link DecodingState}
    49       * instance.
    50       *
    51       * @param state the {@link DecodingState}.
    52       * @throws IllegalArgumentException if the specified state is <code>null</code>.
    53       */
    54      public DecodingStateProtocolDecoder(DecodingState state) {
    55          if (state == null) {
    56              throw new IllegalArgumentException("state");
    57          }
    58          this.state = state;
    59      }
    60
    61      /**
    62       * {@inheritDoc}
    63       */
    64      public void decode(IoSession session, IoBuffer in, ProtocolDecoderOutput out) throws Exception {
    65          if (this.session == null) {
    66              this.session = session;
    67          } else if (this.session != session) {
    68              throw new IllegalStateException(getClass().getSimpleName() + " is a stateful decoder.  "
    69                      + "You have to create one per session.");
    70          }
    71
    72          undecodedBuffers.offer(in);
    73          for (;;) {
    74              IoBuffer b = undecodedBuffers.peek();
    75              if (b == null) {
    76                  break;
    77              }
    78
    79              int oldRemaining = b.remaining();
    80              state.decode(b, out);
    81              int newRemaining = b.remaining();
    82              if (newRemaining != 0) {
    83                  if (oldRemaining == newRemaining) {
    84                      throw new IllegalStateException(DecodingState.class.getSimpleName() + " must "
    85                              + "consume at least one byte per decode().");
    86                  }
    87              } else {
    88                  undecodedBuffers.poll();
    89              }
    90          }
    91      }
    92
    93      /**
    94       * {@inheritDoc}
    95       */
    96      public void finishDecode(IoSession session, ProtocolDecoderOutput out) throws Exception {
    97          state.finishDecode(out);
    98      }
    99
    100     /**
    101      * {@inheritDoc}
    102      */
    103     public void dispose(IoSession session) throws Exception {
    104         // Do nothing
    105     }
    106 }