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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    *   http://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 org.jboss.netty.handler.codec.frame;
    17
    18  import org.jboss.netty.buffer.ChannelBuffer;
    19  import org.jboss.netty.buffer.ChannelBufferFactory;
    20  import org.jboss.netty.channel.Channel;
    21  import org.jboss.netty.channel.ChannelHandlerContext;
    22
    23  /**
    24   * A decoder that splits the received {@link ChannelBuffer}s by the fixed number
    25   * of bytes. For example, if you received the following four fragmented packets:
    26   * <pre>
    27   * +---+----+------+----+
    28   * | A | BC | DEFG | HI |
    29   * +---+----+------+----+
    30   * </pre>
    31   * A {@link FixedLengthFrameDecoder}{@code (3)} will decode them into the
    32   * following three packets with the fixed length:
    33   * <pre>
    34   * +-----+-----+-----+
    35   * | ABC | DEF | GHI |
    36   * +-----+-----+-----+
    37   * </pre>
    38   */
    39  public class FixedLengthFrameDecoder extends FrameDecoder {
    40
    41      private final int frameLength;
    42      private final boolean allocateFullBuffer;
    43
    44      /**
    45       * Calls {@link #FixedLengthFrameDecoder(int, boolean)} with <code>false</code>
    46       */
    47      public FixedLengthFrameDecoder(int frameLength) {
    48          this(frameLength, false);
    49      }
    50
    51      /**
    52       * Creates a new instance.
    53       *
    54       * @param frameLength
    55       *        the length of the frame
    56       * @param allocateFullBuffer
    57       *        <code>true</code> if the cumulative {@link ChannelBuffer} should use the
    58       *        {@link #frameLength} as its initial size
    59       */
    60      public FixedLengthFrameDecoder(int frameLength, boolean allocateFullBuffer) {
    61          if (frameLength <= 0) {
    62              throw new IllegalArgumentException(
    63                      "frameLength must be a positive integer: " + frameLength);
    64          }
    65          this.frameLength = frameLength;
    66          this.allocateFullBuffer = allocateFullBuffer;
    67      }
    68
    69      @Override
    70      protected Object decode(
    71              ChannelHandlerContext ctx, Channel channel, ChannelBuffer buffer) throws Exception {
    72          if (buffer.readableBytes() < frameLength) {
    73              return null;
    74          } else {
    75              return buffer.readBytes(frameLength);
    76          }
    77      }
    78
    79      @Override
    80      protected ChannelBuffer newCumulationBuffer(ChannelHandlerContext ctx, int minimumCapacity) {
    81          ChannelBufferFactory factory = ctx.getChannel().getConfig().getBufferFactory();
    82          if (allocateFullBuffer) {
    83              return factory.getBuffer(frameLength);
    84
    85          }
    86          return super.newCumulationBuffer(ctx, minimumCapacity);
    87      }
    88  }