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    1   /*
    2    * Copyright 2009 Red Hat, Inc.
    3    *
    4    * Red Hat licenses this file to you under the Apache License, version 2.0
    5    * (the "License"); you may not use this file except in compliance with the
    6    * 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.channel.Channel;
    20  import org.jboss.netty.channel.ChannelHandlerContext;
    21
    22  /**
    23   * A decoder that splits the received {@link ChannelBuffer}s by the fixed number
    24   * of bytes. For example, if you received the following four fragmented packets:
    25   * <pre>
    26   * +---+----+------+----+
    27   * | A | BC | DEFG | HI |
    28   * +---+----+------+----+
    29   * </pre>
    30   * A {@link FixedLengthFrameDecoder}{@code (3)} will decode them into the
    31   * following three packets with the fixed length:
    32   * <pre>
    33   * +-----+-----+-----+
    34   * | ABC | DEF | GHI |
    35   * +-----+-----+-----+
    36   * </pre>
    37   *
    38   * @author <a href="http://www.jboss.org/netty/">The Netty Project</a>
    39   * @author <a href="http://gleamynode.net/">Trustin Lee</a>
    40   *
    41   * @version $Rev:231 $, $Date:2008-06-12 16:44:50 +0900 (목, 12 6월 2008) $
    42   */
    43  public class FixedLengthFrameDecoder extends FrameDecoder {
    44
    45      private final int frameLength;
    46
    47      /**
    48       * Creates a new instance.
    49       *
    50       * @param frameLength  the length of the frame
    51       */
    52      public FixedLengthFrameDecoder(int frameLength) {
    53          if (frameLength <= 0) {
    54              throw new IllegalArgumentException(
    55                      "frameLength must be a positive integer: " + frameLength);
    56          }
    57          this.frameLength = frameLength;
    58      }
    59
    60      @Override
    61      protected Object decode(
    62              ChannelHandlerContext ctx, Channel channel, ChannelBuffer buffer) throws Exception {
    63          if (buffer.readableBytes() < frameLength) {
    64              return null;
    65          } else {
    66              return buffer.readBytes(frameLength);
    67          }
    68      }
    69  }