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.buffer.ChannelBuffers;
21 import org.jboss.netty.channel.Channel;
22 import org.jboss.netty.channel.ChannelDownstreamHandler;
23 import org.jboss.netty.channel.ChannelEvent;
24 import org.jboss.netty.channel.ChannelHandlerContext;
25 import org.jboss.netty.channel.ChannelPipeline;
26 import org.jboss.netty.channel.MessageEvent;
27 import org.jboss.netty.handler.codec.frame.DelimiterBasedFrameDecoder;
28 import org.jboss.netty.handler.codec.frame.Delimiters;
29
30 /**
31 * Transforms a write request into another write request. A typical setup for
32 * TCP/IP would be:
33 * <pre>
34 * {@link ChannelPipeline} pipeline = ...;
35 *
36 * // Decoders
37 * pipeline.addLast("frameDecoder", new {@link DelimiterBasedFrameDecoder}(80, {@link Delimiters#nulDelimiter()}));
38 * pipeline.addLast("customDecoder", new {@link OneToOneDecoder}() { ... });
39 *
40 * // Encoder
41 * pipeline.addLast("customEncoder", new {@link OneToOneEncoder}() { ... });
42 * </pre>
43 *
44 * @apiviz.landmark
45 */
46 public abstract class OneToOneEncoder implements ChannelDownstreamHandler {
47
48 protected OneToOneEncoder() {
49 }
50
51 public void handleDownstream(
52 ChannelHandlerContext ctx, ChannelEvent evt) throws Exception {
53 if (!(evt instanceof MessageEvent)) {
54 ctx.sendDownstream(evt);
55 return;
56 }
57
58 MessageEvent e = (MessageEvent) evt;
59 if (!doEncode(ctx, e)) {
60 ctx.sendDownstream(e);
61 }
62 }
63
64 protected boolean doEncode(ChannelHandlerContext ctx, MessageEvent e) throws Exception {
65 Object originalMessage = e.getMessage();
66 Object encodedMessage = encode(ctx, e.getChannel(), originalMessage);
67 if (originalMessage == encodedMessage) {
68 return false;
69 } else if (encodedMessage != null) {
70 write(ctx, e.getFuture(), encodedMessage, e.getRemoteAddress());
71 }
72 return true;
73 }
74
75 /**
76 * Transforms the specified message into another message and return the
77 * transformed message. Note that you can not return {@code null}, unlike
78 * you can in {@link OneToOneDecoder#decode(ChannelHandlerContext, Channel, Object)};
79 * you must return something, at least {@link ChannelBuffers#EMPTY_BUFFER}.
80 */
81 protected abstract Object encode(
82 ChannelHandlerContext ctx, Channel channel, Object msg) throws Exception;
83 }