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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.example.factorial;
17  
18  import org.jboss.netty.buffer.ChannelBuffer;
19  import org.jboss.netty.channel.Channel;
20  import org.jboss.netty.channel.ChannelHandlerContext;
21  import org.jboss.netty.handler.codec.frame.CorruptedFrameException;
22  import org.jboss.netty.handler.codec.frame.FrameDecoder;
23  
24  import java.math.BigInteger;
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  public class BigIntegerDecoder extends FrameDecoder {
33  
34      @Override
35      protected Object decode(ChannelHandlerContext ctx, Channel channel, ChannelBuffer buffer) throws Exception {
36          // Wait until the length prefix is available.
37          if (buffer.readableBytes() < 5) {
38              return null;
39          }
40  
41          buffer.markReaderIndex();
42  
43          // Check the magic number.
44          int magicNumber = buffer.readUnsignedByte();
45          if (magicNumber != 'F') {
46              buffer.resetReaderIndex();
47              throw new CorruptedFrameException("Invalid magic number: " + magicNumber);
48          }
49  
50          // Wait until the whole data is available.
51          int dataLength = buffer.readInt();
52          if (buffer.readableBytes() < dataLength) {
53              buffer.resetReaderIndex();
54              return null;
55          }
56  
57          // Convert the received data into a new BigInteger.
58          byte[] decoded = new byte[dataLength];
59          buffer.readBytes(decoded);
60  
61          return new BigInteger(decoded);
62      }
63  }