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.handler.codec.oneone;
17
18 import static org.jboss.netty.channel.Channels.*;
19
20 import org.jboss.netty.channel.Channel;
21 import org.jboss.netty.channel.ChannelEvent;
22 import org.jboss.netty.channel.ChannelHandlerContext;
23 import org.jboss.netty.channel.ChannelPipeline;
24 import org.jboss.netty.channel.ChannelUpstreamHandler;
25 import org.jboss.netty.channel.MessageEvent;
26 import org.jboss.netty.handler.codec.frame.DelimiterBasedFrameDecoder;
27 import org.jboss.netty.handler.codec.frame.Delimiters;
28 import org.jboss.netty.handler.codec.frame.FrameDecoder;
29
30 /**
31 * Transforms a received message into another message. Please note that this
32 * decoder must be used with a proper {@link FrameDecoder} such as
33 * {@link DelimiterBasedFrameDecoder} or you must implement proper framing
34 * mechanism by yourself if you are using a stream-based transport such as
35 * TCP/IP. A typical setup for TCP/IP would be:
36 * <pre>
37 * {@link ChannelPipeline} pipeline = ...;
38 *
39 * // Decoders
40 * pipeline.addLast("frameDecoder", new {@link DelimiterBasedFrameDecoder}(80, {@link Delimiters#nulDelimiter()}));
41 * pipeline.addLast("customDecoder", new {@link OneToOneDecoder}() { ... });
42 *
43 * // Encoder
44 * pipeline.addLast("customEncoder", new {@link OneToOneEncoder}() { ... });
45 * </pre>
46 *
47 * @apiviz.landmark
48 */
49 public abstract class OneToOneDecoder implements ChannelUpstreamHandler {
50
51 /**
52 * Creates a new instance with the current system character set.
53 */
54 protected OneToOneDecoder() {
55 }
56
57 public void handleUpstream(
58 ChannelHandlerContext ctx, ChannelEvent evt) throws Exception {
59 if (!(evt instanceof MessageEvent)) {
60 ctx.sendUpstream(evt);
61 return;
62 }
63
64 MessageEvent e = (MessageEvent) evt;
65 Object originalMessage = e.getMessage();
66 Object decodedMessage = decode(ctx, e.getChannel(), originalMessage);
67 if (originalMessage == decodedMessage) {
68 ctx.sendUpstream(evt);
69 } else if (decodedMessage != null) {
70 fireMessageReceived(ctx, decodedMessage, e.getRemoteAddress());
71 }
72 }
73
74 /**
75 * Transforms the specified received message into another message and return
76 * the transformed message. Return {@code null} if the received message
77 * is supposed to be discarded.
78 */
79 protected abstract Object decode(
80 ChannelHandlerContext ctx, Channel channel, Object msg) throws Exception;
81 }