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HTTP/2: implement RFC 9218 Extensible Prioritization Scheme for HTTP. #552

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Merged
merged 1 commit into from
Oct 3, 2025
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HTTP/2: implement RFC 9218 Extensible Prioritization Scheme for HTTP. #552

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26 changes: 17 additions & 9 deletions httpcore5-h2/src/main/java/org/apache/hc/core5/http2/config/H2Param.java
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Original file line number Diff line number Diff line change
Expand Up @@ -38,7 +38,8 @@ public enum H2Param {
MAX_CONCURRENT_STREAMS(0x3),
INITIAL_WINDOW_SIZE(0x4),
MAX_FRAME_SIZE(0x5),
MAX_HEADER_LIST_SIZE(0x6);
MAX_HEADER_LIST_SIZE(0x6),
SETTINGS_NO_RFC7540_PRIORITIES (0x9);

int code;

Expand All @@ -50,25 +51,32 @@ public int getCode() {
return code;
}

private static final H2Param[] LOOKUP_TABLE = new H2Param[6];
private static final H2Param[] LOOKUP_TABLE;
static {
for (final H2Param param: H2Param.values()) {
LOOKUP_TABLE[param.code - 1] = param;
int max = 0;
for (final H2Param p : H2Param.values()) {
if (p.code > max) {
max = p.code;
}
}
LOOKUP_TABLE = new H2Param[max + 1];
for (final H2Param p : H2Param.values()) {
LOOKUP_TABLE[p.code] = p;
}
}

public static H2Param valueOf(final int code) {
if (code < 1 || code > LOOKUP_TABLE.length) {
if (code < 0 || code >= LOOKUP_TABLE.length) {
return null;
}
return LOOKUP_TABLE[code - 1];
return LOOKUP_TABLE[code];
}

public static String toString(final int code) {
if (code < 1 || code > LOOKUP_TABLE.length) {
if (code < 0 || code >= LOOKUP_TABLE.length || LOOKUP_TABLE[code] == null) {
return Integer.toString(code);
}
return LOOKUP_TABLE[code - 1].name();
return LOOKUP_TABLE[code].name();
}

}
}
5 changes: 5 additions & 0 deletions httpcore5-h2/src/main/java/org/apache/hc/core5/http2/frame/FrameFactory.java
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Expand Up @@ -111,4 +111,9 @@ public RawFrame createWindowUpdate(final int streamId, final int increment) {
return new RawFrame(FrameType.WINDOW_UPDATE.getValue(), 0, streamId, payload);
}

public RawFrame createPriorityUpdate(final ByteBuffer payload) {
// type 0x10, flags 0, streamId 0 (connection control stream)
return new RawFrame(FrameType.PRIORITY_UPDATE.getValue(), 0, 0, payload);
}

}
29 changes: 21 additions & 8 deletions httpcore5-h2/src/main/java/org/apache/hc/core5/http2/frame/FrameType.java
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Expand Up @@ -42,9 +42,10 @@ public enum FrameType {
PING(0x06),
GOAWAY(0x07),
WINDOW_UPDATE(0x08),
CONTINUATION(0x09);
CONTINUATION(0x09),
PRIORITY_UPDATE(0x10); // 16

int value;
final int value;

FrameType(final int value) {
this.value = value;
Expand All @@ -54,25 +55,37 @@ public int getValue() {
return value;
}

private static final FrameType[] LOOKUP_TABLE = new FrameType[10];
private static final FrameType[] LOOKUP_TABLE;
static {
for (final FrameType frameType: FrameType.values()) {
LOOKUP_TABLE[frameType.value] = frameType;
int max = -1;
for (final FrameType t : FrameType.values()) {
if (t.value > max) {
max = t.value;
}
}
LOOKUP_TABLE = new FrameType[max + 1];
for (final FrameType t : FrameType.values()) {
LOOKUP_TABLE[t.value] = t;
}
}

public static FrameType valueOf(final int value) {
if (value < 0 || value >= LOOKUP_TABLE.length) {
return null;
}
return LOOKUP_TABLE[value];
return LOOKUP_TABLE[value]; // may be null for gaps (e.g., 0x0A..0x0F)
}

public static String toString(final int value) {
if (value < 0 || value >= LOOKUP_TABLE.length) {
return Integer.toString(value);
}
return LOOKUP_TABLE[value].name();
final FrameType t = LOOKUP_TABLE[value];
return t != null ? t.name() : Integer.toString(value);
}

}
/** Convenience: compare this enum to a raw frame type byte. */
public boolean same(final int rawType) {
return this.value == rawType;
}
}
96 changes: 91 additions & 5 deletions ...ore5-h2/src/main/java/org/apache/hc/core5/http2/impl/nio/AbstractH2StreamMultiplexer.java
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Expand Up @@ -31,10 +31,13 @@
import java.nio.BufferOverflowException;
import java.nio.ByteBuffer;
import java.nio.channels.SelectionKey;
import java.nio.charset.StandardCharsets;
import java.util.Deque;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Queue;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentLinkedDeque;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.atomic.AtomicInteger;
Expand Down Expand Up @@ -66,6 +69,7 @@
import org.apache.hc.core5.http.nio.command.ShutdownCommand;
import org.apache.hc.core5.http.protocol.HttpContext;
import org.apache.hc.core5.http.protocol.HttpProcessor;
import org.apache.hc.core5.http.HttpHeaders;
import org.apache.hc.core5.http2.H2ConnectionException;
import org.apache.hc.core5.http2.H2Error;
import org.apache.hc.core5.http2.H2StreamResetException;
Expand All @@ -83,6 +87,9 @@
import org.apache.hc.core5.http2.nio.AsyncPingHandler;
import org.apache.hc.core5.http2.nio.command.PingCommand;
import org.apache.hc.core5.http2.nio.command.PushResponseCommand;
import org.apache.hc.core5.http2.priority.PriorityParamsParser;
import org.apache.hc.core5.http2.priority.PriorityValue;
import org.apache.hc.core5.http2.priority.PriorityFormatter;
import org.apache.hc.core5.io.CloseMode;
import org.apache.hc.core5.reactor.Command;
import org.apache.hc.core5.reactor.ProtocolIOSession;
Expand All @@ -94,7 +101,7 @@

abstract class AbstractH2StreamMultiplexer implements Identifiable, HttpConnection {

private static final long CONNECTION_WINDOW_LOW_MARK = 10 * 1024 * 1024; // 10 MiB
private static final long CONNECTION_WINDOW_LOW_MARK = 10 * 1024 * 1024;

enum ConnectionHandshake { READY, ACTIVE, GRACEFUL_SHUTDOWN, SHUTDOWN }
enum SettingsHandshake { READY, TRANSMITTED, ACKED }
Expand Down Expand Up @@ -133,6 +140,9 @@ enum SettingsHandshake { READY, TRANSMITTED, ACKED }
private EndpointDetails endpointDetails;
private boolean goAwayReceived;

private final Map<Integer, PriorityValue> priorities = new ConcurrentHashMap<>();
private volatile boolean peerNoRfc7540Priorities;

AbstractH2StreamMultiplexer(
final ProtocolIOSession ioSession,
final FrameFactory frameFactory,
Expand Down Expand Up @@ -892,15 +902,13 @@ private void consumeFrame(final RawFrame frame) throws HttpException, IOExceptio
consumeSettingsFrame(payload);
remoteSettingState = SettingsHandshake.TRANSMITTED;
}
// Send ACK
final RawFrame response = frameFactory.createSettingsAck();
commitFrame(response);
remoteSettingState = SettingsHandshake.ACKED;
}
}
break;
case PRIORITY:
// Stream priority not supported
break;
case PUSH_PROMISE: {
acceptPushFrame();
Expand Down Expand Up @@ -985,6 +993,29 @@ private void consumeFrame(final RawFrame frame) throws HttpException, IOExceptio
}
ioSession.setEvent(SelectionKey.OP_WRITE);
break;
case PRIORITY_UPDATE: {
if (streamId != 0) {
throw new H2ConnectionException(H2Error.PROTOCOL_ERROR, "PRIORITY_UPDATE must be on stream 0");
}
final ByteBuffer payload = frame.getPayload();
if (payload == null || payload.remaining() < 4) {
throw new H2ConnectionException(H2Error.FRAME_SIZE_ERROR, "Invalid PRIORITY_UPDATE payload");
}
final int prioritizedId = payload.getInt() & 0x7fffffff;
final int len = payload.remaining();
final String field;
if (len > 0) {
final byte[] b = new byte[len];
payload.get(b);
field = new String(b, StandardCharsets.US_ASCII);
} else {
field = "";
}
final PriorityValue pv = PriorityParamsParser.parse(field).toValueWithDefaults();
priorities.put(prioritizedId, pv);
requestSessionOutput();
}
break;
}
}

Expand Down Expand Up @@ -1049,7 +1080,6 @@ private void consumeHeaderFrame(final RawFrame frame, final H2Stream stream) thr
}
final ByteBuffer payload = frame.getPayloadContent();
if (frame.isFlagSet(FrameFlag.PRIORITY)) {
// Priority not supported
payload.getInt();
payload.get();
}
Expand All @@ -1058,6 +1088,7 @@ private void consumeHeaderFrame(final RawFrame frame, final H2Stream stream) thr
if (streamListener != null) {
streamListener.onHeaderInput(this, streamId, headers);
}
recordPriorityFromHeaders(streamId, headers);
stream.consumeHeader(headers, frame.isFlagSet(FrameFlag.END_STREAM));
} else {
continuation.copyPayload(payload);
Expand All @@ -1076,6 +1107,7 @@ private void consumeContinuationFrame(final RawFrame frame, final H2Stream strea
if (streamListener != null) {
streamListener.onHeaderInput(this, streamId, headers);
}
recordPriorityFromHeaders(streamId, headers);
if (continuation.type == FrameType.PUSH_PROMISE.getValue()) {
stream.consumePromise(headers);
} else {
Expand Down Expand Up @@ -1132,6 +1164,9 @@ private void consumeSettingsFrame(final ByteBuffer payload) throws IOException {
throw new H2ConnectionException(H2Error.PROTOCOL_ERROR, ex.getMessage());
}
break;
case SETTINGS_NO_RFC7540_PRIORITIES:
peerNoRfc7540Priorities = value == 1;
break;
}
}
}
Expand Down Expand Up @@ -1324,6 +1359,38 @@ H2Stream createStream(final H2StreamChannel channel, final H2StreamHandler strea
return streams.createActive(channel, streamHandler);
}

public final void sendPriorityUpdate(final int prioritizedStreamId, final PriorityValue value) throws IOException {
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@arturobernalg By the way this method does not seem to be used anywhere. Is this intended?

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@ok2c Yes, that was intentional. The logic was inlined into the stream submit path, so the standalone helper became redundant. I'm going to removed it.

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@arturobernalg Please also remove H2RequestPriority interceptor for now. It is not being used anywhere in core and I presume your intention was to use it in client. In this case the interceptor should be in client.

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@ok2c ok2c Oct 4, 2025 •
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@arturobernalg Also PriorityFormatter is not being used anywhere in core. If they are not used in core they should not be in core. Re-submit them in client. Believe me you do not want to depend on a new release of core to be able to fix a bug in client.

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@arturobernalg Please let me know if you can live with #567. The functionality should be moved to client and we should put more work into the API design

if (value == null) {
return;
}
final String field = PriorityFormatter.format(value);
if (field == null) {
return;
}
final byte[] ascii = field.getBytes(StandardCharsets.US_ASCII);
final ByteArrayBuffer buf = new ByteArrayBuffer(4 + ascii.length);
buf.append((byte) (prioritizedStreamId >> 24));
buf.append((byte) (prioritizedStreamId >> 16));
buf.append((byte) (prioritizedStreamId >> 8));
buf.append((byte) prioritizedStreamId);
buf.append(ascii, 0, ascii.length);
final RawFrame frame = frameFactory.createPriorityUpdate(ByteBuffer.wrap(buf.array(), 0, buf.length()));
commitFrame(frame);
}

private void recordPriorityFromHeaders(final int streamId, final List<? extends Header> headers) {
if (headers == null || headers.isEmpty()) {
return;
}
for (final Header h : headers) {
if (HttpHeaders.PRIORITY.equalsIgnoreCase(h.getName())) {
final PriorityValue pv = PriorityParamsParser.parse(h.getValue()).toValueWithDefaults();
priorities.put(streamId, pv);
break;
}
}
}

class H2StreamChannelImpl implements H2StreamChannel {

private final int id;
Expand Down Expand Up @@ -1371,6 +1438,25 @@ public void submit(final List<Header> headers, final boolean endStream) throws I
return;
}
ensureNotClosed();
if (peerNoRfc7540Priorities && streams.isSameSide(id)) {
for (final Header h : headers) {
if (HttpHeaders.PRIORITY.equalsIgnoreCase(h.getName())) {
final byte[] ascii = h.getValue() != null
? h.getValue().getBytes(StandardCharsets.US_ASCII)
: new byte[0];
final ByteArrayBuffer b = new ByteArrayBuffer(4 + ascii.length);
b.append((byte) (id >> 24));
b.append((byte) (id >> 16));
b.append((byte) (id >> 8));
b.append((byte) id);
b.append(ascii, 0, ascii.length);
final ByteBuffer pl = ByteBuffer.wrap(b.array(), 0, b.length());
final RawFrame priUpd = new RawFrame(FrameType.PRIORITY_UPDATE.getValue(), 0, 0, pl);
commitFrameInternal(priUpd);
break;
}
}
}
commitHeaders(id, headers, endStream);
if (endStream) {
localClosed = true;
Expand Down Expand Up @@ -1508,4 +1594,4 @@ public String toString() {

}

}
}
3 changes: 2 additions & 1 deletion httpcore5-h2/src/main/java/org/apache/hc/core5/http2/impl/nio/ClientH2StreamMultiplexer.java
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Expand Up @@ -103,7 +103,8 @@ H2Setting[] generateSettings(final H2Config localConfig) {
new H2Setting(H2Param.MAX_CONCURRENT_STREAMS, localConfig.getMaxConcurrentStreams()),
new H2Setting(H2Param.INITIAL_WINDOW_SIZE, localConfig.getInitialWindowSize()),
new H2Setting(H2Param.MAX_FRAME_SIZE, localConfig.getMaxFrameSize()),
new H2Setting(H2Param.MAX_HEADER_LIST_SIZE, localConfig.getMaxHeaderListSize())
new H2Setting(H2Param.MAX_HEADER_LIST_SIZE, localConfig.getMaxHeaderListSize()),
new H2Setting(H2Param.SETTINGS_NO_RFC7540_PRIORITIES, 1)
};
}

Expand Down
63 changes: 63 additions & 0 deletions httpcore5-h2/src/main/java/org/apache/hc/core5/http2/priority/PriorityFormatter.java
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@@ -0,0 +1,63 @@
/*
* ====================================================================
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
* ====================================================================
*
* This software consists of voluntary contributions made by many
* individuals on behalf of the Apache Software Foundation. For more
* information on the Apache Software Foundation, please see
* <http://www.apache.org/>.
*
*/
package org.apache.hc.core5.http2.priority;


import java.util.ArrayList;
import java.util.List;

import org.apache.hc.core5.annotation.Internal;

/**
* Formats PriorityValue as RFC 9218 Structured Fields Dictionary.
* Only emits non-defaults: u when != 3, i when true.
* Returns null when both are defaults (callers should omit the header then).
*/
@Internal
public final class PriorityFormatter {

private PriorityFormatter() {
}

public static String format(final PriorityValue value) {
if (value == null) {
return null;
}
final List<String> parts = new ArrayList<>(2);
if (value.getUrgency() != PriorityValue.DEFAULT_URGENCY) {
parts.add("u=" + value.getUrgency());
}
if (value.isIncremental()) {
// In SF Dictionary, boolean true can be represented by key without value (per RFC 8941).
parts.add("i");
}
if (parts.isEmpty()) {
return null; // omit header when all defaults
}
return String.join(", ", parts);
}
}
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