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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.buffer.ChannelBuffers;
20  import org.jboss.netty.channel.Channel;
21  import org.jboss.netty.channel.ChannelHandlerContext;
22  import org.jboss.netty.handler.codec.oneone.OneToOneEncoder;
23  
24  import java.math.BigInteger;
25  
26  /**
27   * Encodes a {@link Number} into the binary representation prepended with
28   * a magic number ('F' or 0x46) and a 32-bit length prefix.  For example, 42
29   * will be encoded to { 'F', 0, 0, 0, 1, 42 }.
30   */
31  public class NumberEncoder extends OneToOneEncoder {
32  
33      @Override
34      protected Object encode(ChannelHandlerContext ctx, Channel channel, Object msg) {
35          if (!(msg instanceof Number)) {
36              // Ignore what this encoder can't encode.
37              return msg;
38          }
39  
40          // Convert to a BigInteger first for easier implementation.
41          BigInteger v;
42          if (msg instanceof BigInteger) {
43              v = (BigInteger) msg;
44          } else {
45              v = new BigInteger(String.valueOf(msg));
46          }
47  
48          // Convert the number into a byte array.
49          byte[] data = v.toByteArray();
50          int dataLength = data.length;
51  
52          // Construct a message.
53          ChannelBuffer buf = ChannelBuffers.dynamicBuffer();
54          buf.writeByte((byte) 'F'); // magic number
55          buf.writeInt(dataLength);  // data length
56          buf.writeBytes(data);      // data
57  
58          // Return the constructed message.
59          return buf;
60      }
61  }