server: keep the small-frames test inside h2's data-frame budget - #319
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`http2_early_return_keeps_connection_alive_under_small_frames` failed on loaded machines with `GOAWAY(ENHANCE_YOUR_CALM, "too_many_data_frames")`. h2 charges each small DATA frame against a connection-wide budget until it is read, including frames that are only waiting for a busy reader. A connection window's worth of the test's 105-byte frames costs about three times the budget, and the adaptive window lets the window grow further. The callers then returned silently, so the failure read as "calls were lost". The server's connection window is now pinned at 65,535 bytes and each frame carries 185 bytes, sent as a single DATA frame. A full window of unread frames then costs 25,134, under h2's minimum budget of 25,600. The callers fail with the h2 error instead of returning, and the test still fails against a reader that stops reading as soon as the handler returns. Signed-off-by: Iain McGinniss <309153+iainmcgin@users.noreply.github.com>
iainmcgin
marked this pull request as ready for review
September 22, 2026 17:08
rpb-ant
approved these changes
Sep 22, 2026
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http2_early_return_keeps_connection_alive_under_small_frames(from #313) fails most merge-queue runs on loaded 2-core runners with "calls were lost". The server is not timing out: it sendsGOAWAY(ENHANCE_YOUR_CALM, "too_many_data_frames"). Pinned to one or two CPUs locally, the test failed 62 of 64 runs, every time on that GOAWAY or the broken pipe after it. h2 (0.4.16 and later) charges each non-final DATA frame under 256 bytes256 - lenagainst a connection budget ofmax(initial window / 2, 25,600)until the application reads it, and a busy reader can leave a whole connection window unread. A window's worth of the test's 105-byte frames costs about three times that budget.The test now pins the server's connection window at 65,535 bytes and sends 185-byte frames whole, so a full window of unread frames costs 25,134, under the 25,600 minimum. With these changes it passed 190 of 190 contended runs, and it still fails against a reader that drops the body as soon as the handler returns. The
spawn_body_readerdoc comment, which said only frames of 256 bytes or more refill the budget, now says the charge is refunded when the frame is read or discarded.The same limit applies outside the test: one client-streaming call whose handler waits 2 s before reading loses its connection at about 300 small frames, and hyper does not expose h2's budget setting.