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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  }