fix(http2): preserve the complete response on RST_STREAM(NO_ERROR)

[mosuem]

Note

This PR was generated by an AI coding agent (Jetski) on behalf of @mosuem.

Summary

RFC 9113 Section 8.1: "A server can send a complete response prior to the client sending an entire request if the response does not depend on any portion of the request that has not been sent and received. When this is true, a server MAY request that the client abort transmission of a request without error by sending a RST_STREAM with an error code of NO_ERROR after sending a complete response." grpc-go, for example, does exactly this after sending trailers on client-streaming calls.

Previously StreamHandler._handleRstFrame treated every RST_STREAM as abnormal: it called _closeStreamAbnormally, which dropped the messages still buffered in ConnectionMessageQueueIn / StreamMessageQueueIn (anything the application had not consumed yet, e.g. because its listener was paused) and failed the stream with StreamTransportException (errorCode: 0) — even though the complete response, including trailers, had already arrived.

Changes

• lib/src/flowcontrol/connection_queues.dart: Add ConnectionMessageQueueIn.forceDispatchStreamMessages(streamId), which hands the buffered messages of one stream to its StreamMessageQueueIn (crediting the connection window for the DATA bytes, as the regular dispatch path does).
• lib/src/streams/stream_handler.dart: In _handleRstFrame, when errorCode == NO_ERROR and the stream is HalfClosedRemote or Closed (the peer has already sent END_STREAM), flush the buffered messages, close the outgoing side and drop pending outgoing data, and complete the incoming side normally. onTerminated is still invoked with NO_ERROR. The stream keeps counting as active until the application has drained the preserved messages, exactly like a normally completed stream.

Test Verification (Fails Before $\rightarrow$ Passes After)

Added rst-stream-no-error-after-end-stream-preserves-messages in test/client_test.dart: the server sends HEADERS, DATA, trailers with END_STREAM, RST_STREAM(NO_ERROR) while the client's listener is paused (a PING/ACK round trip is used as the barrier instead of a sleep).

Before fix:

00:00 +0 -1: client-tests client-errors rst-stream-no-error-after-end-stream-preserves-messages [E]
  Expected: empty
    Actual: [
              StreamTransportException:HTTP/2 error: Stream error: Stream was terminated by peer (errorCode: 0).
            ]

After fix:

00:00 +1: All tests passed!

[github-actions]

PR Health

Coverage ✔️

File	Coverage
pkgs/http2/lib/src/flowcontrol/connection_queues.dart	💚 94 % ⬆️ 1 %
pkgs/http2/lib/src/streams/stream_handler.dart	💚 91 % ⬆️ 0 %

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// Copyright (c) 2026, the Dart project authors. Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

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Breaking changes ✔️

Package	Change	Current Version	New Version	Needed Version	Looking good?
http2	Non-Breaking	3.1.0	3.2.0-wip	3.2.0-wip	✔️

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http2	✔️ All dependencies utilized correctly.

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