[Task] Upstream: expose HTTP/2 trailers in Symfony HttpClient, then move the curl gRPC wire onto it

[gplanchat]

Parent Epic: #306

Upstream: symfony/symfony#66250 — [HttpClient] Expose HTTP trailers.

The gRPC-over-curl client of #392 (CurlGrpcWorkflowServiceClient) drives curl by hand. The only reason is that the call status (grpc-status, grpc-message) arrives in the HTTP/2 trailers, and Symfony HttpClient 7.4 discards them: CurlResponse::parseHeaderLine() ignores header lines received after the body, and CURLOPT_HEADERFUNCTION cannot be overridden through extra.curl.

The Durable-as-a-Symfony-component RFC draft proposes folding the curl wire into the Temporal bridge. Inside Symfony, that wire is expected to go through HttpClient, so this upstream change comes first.

Steps

1. Follow the discussion on [HttpClient] Expose HTTP trailers symfony/symfony#66250 until the direction (getInfo('trailers') or another shape) is accepted or refused.
2. If accepted: open the pull request on symfony/symfony (curl, native HTTP/1.1 chunked, MockResponse), with tests, targeting the branch the maintainers name.
3. Once released: move CurlGrpcWorkflowServiceClient onto HttpClient when the installed version exposes trailers, and keep the raw curl path for older versions.

Done when

• [HttpClient] Expose HTTP trailers symfony/symfony#66250 has an answer from a maintainer; this ticket records it.
• Accepted: the upstream PR is merged, or this ticket names why it stalled.
• Refused: the RFC draft says the curl wire keeps raw curl, and why.
• Accepted and released: a test shows the curl wire reading grpc-status through HttpClient against temporal server start-dev; the raw curl path stays covered for older versions.

[gplanchat]

Progress, 2026-09-24.

Step 1: an answer upstream. On symfony/symfony#66250, a Symfony contributor (not a core team member) found the additive getInfo('trailers') entry reasonable, and specified it:

• null until the transfer completes successfully, and still null on failure or cancellation;
• [] when no trailers were sent, otherwise lowercase names mapped to lists of values, as in getHeaders(false);
• available no later than LastChunk, kept apart from getHeaders();
• a 4xx/5xx response that completes still exposes its trailers.

They also flagged that a gRPC caller must check both getInfo('trailers') and getHeaders(false), because of "trailers-only" responses. CurlGrpcWorkflowServiceClient (#392) already collects headers and trailers through one callback, so this case holds today. When the client moves to HttpClient, it has to check both. No core maintainer has answered yet.

Step 2: the upstream PR. symfony/symfony#66256, targeting 8.2, implements that shape on Curl, Native (the Dechunker parses the trailer section), Amp and Mock. It was tested against a small socket server sending chunked responses with trailers. Every test file was run before and after the change: the local failures are identical on both sides, and the change adds only passing tests. HTTP/2 trailers take the same curl callback, but they are not covered end to end locally.

Out of that PR, as agreed in the issue: retrying on a non-zero grpc-status, and guaranteed display in the profiler.

• [HttpClient] Expose HTTP trailers symfony/symfony#66250 has an answer (a contributor, not yet a maintainer).
• [HttpClient] Expose HTTP trailers as the trailers response info symfony/symfony#66256 merged, or the reason it stalled.
• Once released: move CurlGrpcWorkflowServiceClient onto HttpClient, keeping the raw curl path for older versions.

[gplanchat]

Progress, 2026-09-24.

• [HttpClient] Expose HTTP trailers as the trailers response info symfony/symfony#66256 merged into 8.2 by @nicolas-grekas (merge commit 4f75d5bf68). Before merging, he pushed changes onto the branch:
  • ResponseInterface::getInfo() in the contracts documents the trailers key;
  • curl returns [] rather than null for HEAD, 204 and 304 responses;
  • NativeHttpClient fails on a truncated or oversized (over 16 KiB) trailer section, as curl and Amp do, instead of returning partial trailers.
• Documentation: [HttpClient] Expose HTTP trailers as the trailers response info symfony/symfony-docs#23092, a PR against its 8.2 branch.
• Once Symfony 8.2 is released: move CurlGrpcWorkflowServiceClient onto HttpClient when the installed version exposes trailers, and keep the raw curl path for older versions. The gRPC caller must check both getInfo('trailers') and getHeaders(false), because of trailers-only responses.