1 /*
2 * Copyright 2015 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
16 package io.netty.handler.codec.http2;
17
18 import io.netty.util.internal.UnstableApi;
19
20 /**
21 * An object (used by remote flow control) that is responsible for distributing the bytes to be
22 * written across the streams in the connection.
23 */
24 @UnstableApi
25 public interface StreamByteDistributor {
26
27 /**
28 * State information for the stream, indicating the number of bytes that are currently
29 * streamable. This is provided to the {@link #updateStreamableBytes(StreamState)} method.
30 */
31 interface StreamState {
32 /**
33 * Gets the stream this state is associated with.
34 */
35 Http2Stream stream();
36
37 /**
38 * Get the amount of bytes this stream has pending to send. The actual amount written must not exceed
39 * {@link #windowSize()}!
40 * @return The amount of bytes this stream has pending to send.
41 * @see Http2CodecUtil#streamableBytes(StreamState)
42 */
43 long pendingBytes();
44
45 /**
46 * Indicates whether or not there are frames pending for this stream.
47 */
48 boolean hasFrame();
49
50 /**
51 * The size (in bytes) of the stream's flow control window. The amount written must not exceed this amount!
52 * <p>A {@link StreamByteDistributor} needs to know the stream's window size in order to avoid allocating bytes
53 * if the window size is negative. The window size being {@code 0} may also be significant to determine when if
54 * an stream has been given a chance to write an empty frame, and also enables optimizations like not writing
55 * empty frames in some situations (don't write headers until data can also be written).
56 * @return the size of the stream's flow control window.
57 * @see Http2CodecUtil#streamableBytes(StreamState)
58 */
59 int windowSize();
60 }
61
62 /**
63 * Object that performs the writing of the bytes that have been allocated for a stream.
64 */
65 interface Writer {
66 /**
67 * Writes the allocated bytes for this stream.
68 * <p>
69 * Any {@link Throwable} thrown from this method is considered a programming error.
70 * A {@code GOAWAY} frame will be sent and the will be connection closed.
71 * @param stream the stream for which to perform the write.
72 * @param numBytes the number of bytes to write.
73 */
74 void write(Http2Stream stream, int numBytes);
75 }
76
77 /**
78 * Called when the streamable bytes for a stream has changed. Until this
79 * method is called for the first time for a give stream, the stream is assumed to have no
80 * streamable bytes.
81 */
82 void updateStreamableBytes(StreamState state);
83
84 /**
85 * Explicitly update the dependency tree. This method is called independently of stream state changes.
86 * @param childStreamId The stream identifier associated with the child stream.
87 * @param parentStreamId The stream identifier associated with the parent stream. May be {@code 0},
88 * to make {@code childStreamId} and immediate child of the connection.
89 * @param weight The weight which is used relative to other child streams for {@code parentStreamId}. This value
90 * must be between 1 and 256 (inclusive).
91 * @param exclusive If {@code childStreamId} should be the exclusive dependency of {@code parentStreamId}.
92 */
93 void updateDependencyTree(int childStreamId, int parentStreamId, short weight, boolean exclusive);
94
95 /**
96 * Distributes up to {@code maxBytes} to those streams containing streamable bytes and
97 * iterates across those streams to write the appropriate bytes. Criteria for
98 * traversing streams is undefined and it is up to the implementation to determine when to stop
99 * at a given stream.
100 *
101 * <p>The streamable bytes are not automatically updated by calling this method. It is up to the
102 * caller to indicate the number of bytes streamable after the write by calling
103 * {@link #updateStreamableBytes(StreamState)}.
104 *
105 * @param maxBytes the maximum number of bytes to write.
106 * @return {@code true} if there are still streamable bytes that have not yet been written,
107 * otherwise {@code false}.
108 * @throws Http2Exception If an internal exception occurs and internal connection state would otherwise be
109 * corrupted.
110 */
111 boolean distribute(int maxBytes, Writer writer) throws Http2Exception;
112 }
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