View Javadoc

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.example.factorial;
17  
18  import java.math.BigInteger;
19  
20  import org.jboss.netty.buffer.ChannelBuffer;
21  import org.jboss.netty.channel.Channel;
22  import org.jboss.netty.channel.ChannelHandlerContext;
23  import org.jboss.netty.handler.codec.frame.CorruptedFrameException;
24  import org.jboss.netty.handler.codec.frame.FrameDecoder;
25  
26  /**
27   * Decodes the binary representation of a {@link BigInteger} prepended
28   * with a magic number ('F' or 0x46) and a 32-bit integer length prefix into a
29   * {@link BigInteger} instance.  For example, { 'F', 0, 0, 0, 1, 42 } will be
30   * decoded into new BigInteger("42").
31   *
32   * @author <a href="http://www.jboss.org/netty/">The Netty Project</a>
33   * @author <a href="http://gleamynode.net/">Trustin Lee</a>
34   *
35   * @version $Rev: 2125 $, $Date: 2010-02-02 12:13:15 +0900 (Tue, 02 Feb 2010) $
36   */
37  public class BigIntegerDecoder extends FrameDecoder {
38  
39      @Override
40      protected Object decode(
41              ChannelHandlerContext ctx, Channel channel, ChannelBuffer buffer) throws Exception {
42          // Wait until the length prefix is available.
43          if (buffer.readableBytes() < 5) {
44              return null;
45          }
46  
47          buffer.markReaderIndex();
48  
49          // Check the magic number.
50          int magicNumber = buffer.readUnsignedByte();
51          if (magicNumber != 'F') {
52              buffer.resetReaderIndex();
53              throw new CorruptedFrameException(
54                      "Invalid magic number: " + magicNumber);
55          }
56  
57          // Wait until the whole data is available.
58          int dataLength = buffer.readInt();
59          if (buffer.readableBytes() < dataLength) {
60              buffer.resetReaderIndex();
61              return null;
62          }
63  
64          // Convert the received data into a new BigInteger.
65          byte[] decoded = new byte[dataLength];
66          buffer.readBytes(decoded);
67  
68          return new BigInteger(decoded);
69      }
70  }