fix(h2): complete request stream on 'end' instead of waiting for 'close'

[staylor]

Problem

On a busy, long-lived multiplexed HTTP/2 session, the native 'close' event can fail to fire for a stream (the same condition #5559 addresses on the abort path). In client-h2.js, normal request completion still defers all cleanup to onRequestStreamClose, which is gated on 'close':

• request.onResponseEnd(...) + finalizeRequest(...)
• releaseRequestStream(...) (detaches the request, removes stream listeners)
• closeStreamSession(...) (decrements the session's open-stream count)
• stream[kRequestStreamState] = null

onEnd only sets state.pendingEnd = true and waits. So a stream that completes but never emits 'close' keeps its kRequestStreamState — and through it the request, response body buffers, and stream listeners — alive for the whole session lifetime. Under sustained request volume on a persistent h2 connection this grows without bound until the process OOMs.

We hit this in production on a crawler doing continuous h2 fetches over long-lived sessions: heap-retention profiles showed the request-stream state graph and off-heap response buffers accumulating, with end-of-stream / pipeline / async_hooks teardown machinery retained 15–28× over baseline. #5559 (thank you) fixed the abort path but the completion path kept leaking.

Fix

Extract the terminal cleanup into completeRequestStream(stream) and run it from both onEnd and onRequestStreamClose. A state == null guard makes it idempotent: whichever of 'end' / 'close' fires first performs the cleanup, and the other becomes a no-op (this also prevents a double closeStreamSession decrement).

Completing on 'end' releases the request graph deterministically without waiting for 'close'. Crucially it completes the response properly (onResponseEnd, which ends the consumer body) rather than force-destroying the stream — so an in-flight body is never truncated with ERR_STREAM_PREMATURE_CLOSE. Trailers already stored by onTrailers (which precedes 'end' in the normal flow) are still delivered.

Reproduction / test

Added a test (test/http2-late-data.js) that drives a normal completion through 'response' → 'trailers' → 'data' → 'end' and never emits 'close', then asserts the response completes and the stream listeners are released.

• On main: fails — onResponseEnd is never called (onCompleteCalls: 0) and listeners stay attached.
• With this change: passes.

All 24 test/http2-*.js files pass (including Dispatcher#Connect, trailers, goaway, timeout, and abort suites); eslint is clean.

Refs #5558.

[mcollina]

shorten this comment, or remove

[staylor]

Cut to two lines — just the idempotency contract; the mechanics are clear from the code.

[mcollina]

This comment is too long. It doesn't explain why this is needed but reference an issue. Update.

This should mention "blocked event loop".

[staylor]

Rewritten to lead with the why — a blocked event loop can keep 'close' from firing, stranding the stream's buffers — and dropped the bare issue reference.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.45%. Comparing base (6010668) to head (e6a99b4).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5560   +/-   ##
=======================================
  Coverage   93.44%   93.45%           
=======================================
  Files         110      110           
  Lines       37434    37441    +7     
=======================================
+ Hits        34979    34989   +10     
+ Misses       2455     2452    -3     

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[mcollina]

do we really need 2 functions?

[staylor]

Good call — the second function was just a this→arg shim. Collapsed to a single this-based completeRequestStream registered directly on 'close' and invoked via .call(stream) from onEnd, matching the onUpgradeStreamClose convention. Also cleaned up two stale comments that still referenced the old name. All 24 http2-* suites still pass.