fix(http2): finish() and terminate() must not hang after a failed socket write

[mosuem]

Note

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

Summary

BufferedSink (the sink behind FrameWriter) defined its completion as

_doneFuture = Future.wait([_controller.stream.pipe(dataSink), dataSink.done]);

For a dart:io Socket, done only completes after an explicit close(). When a write fails — typically SocketException: Connection reset by peer because the peer already closed the connection — addStream completes with the error, Stream.pipe does not close the sink, and Socket.done never completes. Future.wait (non-eager) then waits forever, and so does everything built on doneFuture: FrameWriter.close(), Connection.finish(), Connection.terminate(), ClientPool.terminate() / Http2Client.closed, and grpc-dart's ClientChannel.shutdown() (which awaits transport.finish()).

pipe itself already resolves through dataSink.close(), i.e. through done, in the success case, so the extra wait only ever mattered in the failure case — where it hangs.

Changes

• lib/src/async_utils/async_utils.dart: doneFuture completes once the pipe has finished. A failed write completes it normally (like a cancelled sink already did): the connection is dead and the owner learns about it through the incoming side (Connection also terminates itself when doneFuture completes).

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

• buffered-sink-done-after-failed-write in test/src/async_utils/async_utils_test.dart, using a FailingSink that behaves like a reset socket (addStream fails, done never completes without close()).
• finish-and-terminate-complete-when-the-socket-write-fails in test/client_test.dart: ClientTransportConnection.viaStreams(..., FailingSink()), then finish() / terminate() must complete.

Before fix:

00:02 +0 -1: test/src/async_utils/async_utils_test.dart: async_utils buffered-sink-done-after-failed-write [E]
  TimeoutException after 0:00:02.000000: Future not completed
00:02 +0 -2: test/client_test.dart: client-tests client-errors finish-and-terminate-complete-when-the-socket-write-fails [E]
  TimeoutException after 0:00:02.000000: Future not completed

After fix:

00:00 +2: All tests passed!

[github-actions]

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pkgs/http2/lib/src/async_utils/async_utils.dart	💚 100 %

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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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