h3: replenish bidi stream credit on stream close#79
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ngtcp2 does not auto-extend MAX_STREAMS when a stream closes, so the server must call ngtcp2_conn_extend_max_streams_bidi() itself. Without it every QUIC connection was permanently capped at initial_max_streams_bidi (default 100) request streams: each served fast (TTFB ~4ms), then the connection stalled with the server idle. HttpArena baseline-h3/static-h3 collapsed to ~20 req/s per connection (1277 total at c=64) while frankenphp-trueasync hit 201k on the same client. Call ngtcp2_conn_extend_max_streams_bidi(conn, 1) for each client-initiated bidi stream (id & 3 == 0) in stream_close_cb. A/B at c=64 (-m 32, n=64000): 6400 done in 30s -> 60000 done in 10s. Add test 036 driving 150 sequential streams over one reused QUIC connection; pre-fix it stalls at 100.
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CoverageTotal lines: 81.21% → 81.41% (+0.19 pp)
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Problem
HttpArena
baseline-h3/static-h3at c=64 collapsed to ~1277 req/s (≈20 req/s per connection), server idle (CPU 12.7%), 0 packet loss, TTFB ~4ms. Same h2load client drove frankenphp-trueasync to 201k → the bottleneck is our H3 path.Root cause
stream_close_cbclosed the nghttp3 stream but never calledngtcp2_conn_extend_max_streams_bidi(). ngtcp2 does not auto-send MAX_STREAMS on close — the application must. So each QUIC connection was permanently capped atinitial_max_streams_bidi(default 100) bidi request streams; after 100 the client could not open another stream and the connection stalled.Bench arithmetic confirms it:
10496 started = 64 conn × (100 done + 64 in-flight).Fix
Call
ngtcp2_conn_extend_max_streams_bidi(conn, 1)for each client-initiated bidi stream (id & 3 == 0) instream_close_cb.Verification
H3CLIENT_REQUEST_COUNT=150: pre-fixresponse_submittedstalls at 100; post-fix all 150 complete.036-h3-stream-credit-replenish; full H3 suite 36/36 green.