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 * https://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.channel;
17
18 import io.netty.buffer.ByteBuf;
19 import io.netty.buffer.ByteBufAllocator;
20 import io.netty.util.Attribute;
21 import io.netty.util.AttributeKey;
22 import io.netty.util.AttributeMap;
23 import io.netty.util.concurrent.EventExecutor;
24
25 /**
26 * Enables a {@link ChannelHandler} to interact with its {@link ChannelPipeline}
27 * and other handlers. Among other things a handler can notify the next {@link ChannelHandler} in the
28 * {@link ChannelPipeline} as well as modify the {@link ChannelPipeline} it belongs to dynamically.
29 *
30 * <h3>Notify</h3>
31 *
32 * You can notify the closest handler in the same {@link ChannelPipeline} by calling one of the various methods
33 * provided here.
34 *
35 * Please refer to {@link ChannelPipeline} to understand how an event flows.
36 *
37 * <h3>Modifying a pipeline</h3>
38 *
39 * You can get the {@link ChannelPipeline} your handler belongs to by calling
40 * {@link #pipeline()}. A non-trivial application could insert, remove, or
41 * replace handlers in the pipeline dynamically at runtime.
42 *
43 * <h3>Retrieving for later use</h3>
44 *
45 * You can keep the {@link ChannelHandlerContext} for later use, such as
46 * triggering an event outside the handler methods, even from a different thread.
47 * <pre>
48 * public class MyHandler extends {@link ChannelDuplexHandler} {
49 *
50 * <b>private {@link ChannelHandlerContext} ctx;</b>
51 *
52 * public void beforeAdd({@link ChannelHandlerContext} ctx) {
53 * <b>this.ctx = ctx;</b>
54 * }
55 *
56 * public void login(String username, password) {
57 * ctx.write(new LoginMessage(username, password));
58 * }
59 * ...
60 * }
61 * </pre>
62 *
63 * <h3>Storing stateful information</h3>
64 *
65 * {@link #attr(AttributeKey)} allow you to
66 * store and access stateful information that is related with a {@link ChannelHandler} / {@link Channel} and its
67 * context. Please refer to {@link ChannelHandler} to learn various recommended
68 * ways to manage stateful information.
69 *
70 * <h3>A handler can have more than one {@link ChannelHandlerContext}</h3>
71 *
72 * Please note that a {@link ChannelHandler} instance can be added to more than
73 * one {@link ChannelPipeline}. It means a single {@link ChannelHandler}
74 * instance can have more than one {@link ChannelHandlerContext} and therefore
75 * the single instance can be invoked with different
76 * {@link ChannelHandlerContext}s if it is added to one or more {@link ChannelPipeline}s more than once.
77 * Also note that a {@link ChannelHandler} that is supposed to be added to multiple {@link ChannelPipeline}s should
78 * be marked as {@link io.netty.channel.ChannelHandler.Sharable}.
79 *
80 * <h3>Additional resources worth reading</h3>
81 * <p>
82 * Please refer to the {@link ChannelHandler}, and
83 * {@link ChannelPipeline} to find out more about inbound and outbound operations,
84 * what fundamental differences they have, how they flow in a pipeline, and how to handle
85 * the operation in your application.
86 */
87 public interface ChannelHandlerContext extends AttributeMap, ChannelInboundInvoker, ChannelOutboundInvoker {
88
89 /**
90 * Return the {@link Channel} which is bound to the {@link ChannelHandlerContext}.
91 */
92 Channel channel();
93
94 /**
95 * Returns the {@link EventExecutor} which is used to execute an arbitrary task.
96 */
97 EventExecutor executor();
98
99 /**
100 * The unique name of the {@link ChannelHandlerContext}.The name was used when then {@link ChannelHandler}
101 * was added to the {@link ChannelPipeline}. This name can also be used to access the registered
102 * {@link ChannelHandler} from the {@link ChannelPipeline}.
103 */
104 String name();
105
106 /**
107 * The {@link ChannelHandler} that is bound this {@link ChannelHandlerContext}.
108 */
109 ChannelHandler handler();
110
111 /**
112 * Return {@code true} if the {@link ChannelHandler} which belongs to this context was removed
113 * from the {@link ChannelPipeline}. Note that this method is only meant to be called from with in the
114 * {@link EventLoop}.
115 */
116 boolean isRemoved();
117
118 @Override
119 ChannelHandlerContext fireChannelRegistered();
120
121 @Override
122 ChannelHandlerContext fireChannelUnregistered();
123
124 @Override
125 ChannelHandlerContext fireChannelActive();
126
127 @Override
128 ChannelHandlerContext fireChannelInactive();
129
130 @Override
131 ChannelHandlerContext fireExceptionCaught(Throwable cause);
132
133 @Override
134 ChannelHandlerContext fireUserEventTriggered(Object evt);
135
136 @Override
137 ChannelHandlerContext fireChannelRead(Object msg);
138
139 @Override
140 ChannelHandlerContext fireChannelReadComplete();
141
142 @Override
143 ChannelHandlerContext fireChannelWritabilityChanged();
144
145 @Override
146 ChannelHandlerContext read();
147
148 @Override
149 ChannelHandlerContext flush();
150
151 /**
152 * Return the assigned {@link ChannelPipeline}
153 */
154 ChannelPipeline pipeline();
155
156 /**
157 * Return the assigned {@link ByteBufAllocator} which will be used to allocate {@link ByteBuf}s.
158 */
159 ByteBufAllocator alloc();
160
161 /**
162 * @deprecated Use {@link Channel#attr(AttributeKey)}
163 */
164 @Deprecated
165 @Override
166 <T> Attribute<T> attr(AttributeKey<T> key);
167
168 /**
169 * @deprecated Use {@link Channel#hasAttr(AttributeKey)}
170 */
171 @Deprecated
172 @Override
173 <T> boolean hasAttr(AttributeKey<T> key);
174 }