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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 io.netty.example.factorial;
17  
18  import io.netty.buffer.ByteBuf;
19  import io.netty.channel.ChannelHandlerContext;
20  import io.netty.handler.codec.MessageToByteEncoder;
21  
22  import java.math.BigInteger;
23  
24  /**
25   * Encodes a {@link Number} into the binary representation prepended with
26   * a magic number ('F' or 0x46) and a 32-bit length prefix.  For example, 42
27   * will be encoded to { 'F', 0, 0, 0, 1, 42 }.
28   */
29  public class NumberEncoder extends MessageToByteEncoder<Number> {
30  
31      @Override
32      protected void encode(ChannelHandlerContext ctx, Number msg, ByteBuf out) {
33          // Convert to a BigInteger first for easier implementation.
34          BigInteger v;
35          if (msg instanceof BigInteger) {
36              v = (BigInteger) msg;
37          } else {
38              v = new BigInteger(String.valueOf(msg));
39          }
40  
41          // Convert the number into a byte array.
42          byte[] data = v.toByteArray();
43          int dataLength = data.length;
44  
45          // Write a message.
46          out.writeByte((byte) 'F'); // magic number
47          out.writeInt(dataLength);  // data length
48          out.writeBytes(data);      // data
49      }
50  }