1 /*
2 * Copyright 2014 The Netty Project
3 *
4 * The Netty Project licenses this file to you under the Apache License, version 2.0 (the
5 * "License"); you may not use this file except in compliance with the License. You may obtain a
6 * 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 distributed under the License
11 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
12 * or implied. See the License for the specific language governing permissions and limitations under
13 * the License.
14 */
15 package io.netty.handler.codec.http2;
16
17 import io.netty.channel.ChannelHandlerContext;
18
19 /**
20 * A {@link Http2FlowController} for controlling the flow of outbound {@code DATA} frames to the remote
21 * endpoint.
22 */
23 public interface Http2RemoteFlowController extends Http2FlowController {
24 /**
25 * Get the {@link ChannelHandlerContext} for which to apply flow control on.
26 * <p>
27 * This is intended for us by {@link FlowControlled} implementations only. Use with caution.
28 * @return The {@link ChannelHandlerContext} for which to apply flow control on.
29 */
30 ChannelHandlerContext channelHandlerContext();
31
32 /**
33 * Queues a payload for transmission to the remote endpoint. There is no guarantee as to when the data
34 * will be written or how it will be assigned to frames.
35 * before sending.
36 * <p>
37 * Writes do not actually occur until {@link #writePendingBytes()} is called.
38 *
39 * @param stream the subject stream. Must not be the connection stream object.
40 * @param payload payload to write subject to flow-control accounting and ordering rules.
41 */
42 void addFlowControlled(Http2Stream stream, FlowControlled payload);
43
44 /**
45 * Determine if {@code stream} has any {@link FlowControlled} frames currently queued.
46 * @param stream the stream to check if it has flow controlled frames.
47 * @return {@code true} if {@code stream} has any {@link FlowControlled} frames currently queued.
48 */
49 boolean hasFlowControlled(Http2Stream stream);
50
51 /**
52 * Write all data pending in the flow controller up to the flow-control limits.
53 *
54 * @throws Http2Exception throws if a protocol-related error occurred.
55 */
56 void writePendingBytes() throws Http2Exception;
57
58 /**
59 * Set the active listener on the flow-controller.
60 *
61 * @param listener to notify when the a write occurs, can be {@code null}.
62 */
63 void listener(Listener listener);
64
65 /**
66 * Determine if the {@code stream} has bytes remaining for use in the flow control window.
67 * <p>
68 * Note that this method respects channel writability. The channel must be writable for this method to
69 * return {@code true}.
70 *
71 * @param stream The stream to test.
72 * @return {@code true} if the {@code stream} has bytes remaining for use in the flow control window and the
73 * channel is writable, {@code false} otherwise.
74 */
75 boolean isWritable(Http2Stream stream);
76
77 /**
78 * Notification that the writability of {@link #channelHandlerContext()} has changed.
79 * @throws Http2Exception If any writes occur as a result of this call and encounter errors.
80 */
81 void channelWritabilityChanged() throws Http2Exception;
82
83 /**
84 * Explicitly update the dependency tree. This method is called independently of stream state changes.
85 * @param childStreamId The stream identifier associated with the child stream.
86 * @param parentStreamId The stream identifier associated with the parent stream. May be {@code 0},
87 * to make {@code childStreamId} and immediate child of the connection.
88 * @param weight The weight which is used relative to other child streams for {@code parentStreamId}. This value
89 * must be between 1 and 256 (inclusive).
90 * @param exclusive If {@code childStreamId} should be the exclusive dependency of {@code parentStreamId}.
91 */
92 void updateDependencyTree(int childStreamId, int parentStreamId, short weight, boolean exclusive);
93
94 /**
95 * Implementations of this interface are used to progressively write chunks of the underlying
96 * payload to the stream. A payload is considered to be fully written if {@link #write} has
97 * been called at least once and it's {@link #size} is now zero.
98 */
99 interface FlowControlled {
100 /**
101 * The size of the payload in terms of bytes applied to the flow-control window.
102 * Some payloads like {@code HEADER} frames have no cost against flow control and would
103 * return 0 for this value even though they produce a non-zero number of bytes on
104 * the wire. Other frames like {@code DATA} frames have both their payload and padding count
105 * against flow-control.
106 */
107 int size();
108
109 /**
110 * Called to indicate that an error occurred before this object could be completely written.
111 * <p>
112 * The {@link Http2RemoteFlowController} will make exactly one call to either
113 * this method or {@link #writeComplete()}.
114 * </p>
115 *
116 * @param ctx The context to use if any communication needs to occur as a result of the error.
117 * This may be {@code null} if an exception occurs when the connection has not been established yet.
118 * @param cause of the error.
119 */
120 void error(ChannelHandlerContext ctx, Throwable cause);
121
122 /**
123 * Called after this object has been successfully written.
124 * <p>
125 * The {@link Http2RemoteFlowController} will make exactly one call to either
126 * this method or {@link #error(ChannelHandlerContext, Throwable)}.
127 * </p>
128 */
129 void writeComplete();
130
131 /**
132 * Writes up to {@code allowedBytes} of the encapsulated payload to the stream. Note that
133 * a value of 0 may be passed which will allow payloads with flow-control size == 0 to be
134 * written. The flow-controller may call this method multiple times with different values until
135 * the payload is fully written, i.e it's size after the write is 0.
136 * <p>
137 * When an exception is thrown the {@link Http2RemoteFlowController} will make a call to
138 * {@link #error(ChannelHandlerContext, Throwable)}.
139 * </p>
140 *
141 * @param ctx The context to use for writing.
142 * @param allowedBytes an upper bound on the number of bytes the payload can write at this time.
143 */
144 void write(ChannelHandlerContext ctx, int allowedBytes);
145
146 /**
147 * Merge the contents of the {@code next} message into this message so they can be written out as one unit.
148 * This allows many small messages to be written as a single DATA frame.
149 *
150 * @return {@code true} if {@code next} was successfully merged and does not need to be enqueued,
151 * {@code false} otherwise.
152 */
153 boolean merge(ChannelHandlerContext ctx, FlowControlled next);
154 }
155
156 /**
157 * Listener to the number of flow-controlled bytes written per stream.
158 */
159 interface Listener {
160 /**
161 * Notification that {@link Http2RemoteFlowController#isWritable(Http2Stream)} has changed for {@code stream}.
162 * <p>
163 * This method should not throw. Any thrown exceptions are considered a programming error and are ignored.
164 * @param stream The stream which writability has changed for.
165 */
166 void writabilityChanged(Http2Stream stream);
167 }
168 }