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 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 public class BigIntegerDecoder extends FrameDecoder {
33
34 @Override
35 protected Object decode(
36 ChannelHandlerContext ctx, Channel channel, ChannelBuffer buffer) throws Exception {
37 // Wait until the length prefix is available.
38 if (buffer.readableBytes() < 5) {
39 return null;
40 }
41
42 buffer.markReaderIndex();
43
44 // Check the magic number.
45 int magicNumber = buffer.readUnsignedByte();
46 if (magicNumber != 'F') {
47 buffer.resetReaderIndex();
48 throw new CorruptedFrameException(
49 "Invalid magic number: " + magicNumber);
50 }
51
52 // Wait until the whole data is available.
53 int dataLength = buffer.readInt();
54 if (buffer.readableBytes() < dataLength) {
55 buffer.resetReaderIndex();
56 return null;
57 }
58
59 // Convert the received data into a new BigInteger.
60 byte[] decoded = new byte[dataLength];
61 buffer.readBytes(decoded);
62
63 return new BigInteger(decoded);
64 }
65 }