WiFi drivers (e.g. ath11k on the Steam Deck) return ENOBUFS — not
EAGAIN/EWOULDBLOCK — when the tx queue is momentarily full. Rust maps
ENOBUFS to ErrorKind::Uncategorized, so `is_transient_io` (which only
matched WouldBlock/ConnRefused/ConnReset) treated it as a real error and
tore the whole stream down on a single transient burst.
This presented as a vicious Heisenbug on the Deck: the native host
streamed flawlessly on loopback and under a debugger (anything slow
enough not to fill the small ~416 KB wlan0 buffer), but died at full rate
cross-machine over WiFi — flaky hang-or-SIGKILL because tx-queue-full is
probabilistic. Diagnosed live via a forced core dump (gdb on the hung
core): the data-plane thread had bailed on a fatal send error.
Treat ENOBUFS (and asynchronous network-path blips ENETUNREACH /
EHOSTUNREACH / ENETDOWN / EHOSTDOWN) as a lossy drop like WouldBlock —
FEC + the next frame recover. Validated: 6/6 back-to-back cross-machine
streams over the Deck's WiFi, host stable, p50 ~4.4 ms (one run dropped
4/300 frames *gracefully*, 0 mismatched — the fix working as intended).
Also surface a data-plane bind/hole-punch failure directly in punktfunk1
(it was previously only reported after teardown, which a stall could
swallow entirely).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
enricobuehler
0f7f1be3c3