The quic-interop-runner against aioquic surfaced two real bugs in the
writer's CLOSING-status branch, both visible on the wire as a single
~45-byte UDP datagram instead of a properly framed close.
§10.2.3 — at Initial / Handshake levels only CONNECTION_CLOSE (Transport,
0x1c) is allowed. The application-level form (0x1d) leaks app state
pre-handshake. The writer was unconditionally building a 0x1d frame and
shipping it inside an Initial packet; aioquic dropped it silently.
§14.1 — any client datagram containing an Initial MUST be ≥ 1200 bytes
in UDP-payload terms. The CLOSING branch bypassed the existing padding
logic, so close-only Initial datagrams went out at ~45 bytes and
servers correctly rejected them (also as malformed).
Fix replaces the CLOSING branch with a dedicated `buildClosingDatagram`
helper:
- Application keys present → 0x1d, original error code + reason.
- Pre-1-RTT (Handshake or Initial) → 0x1c with errorCode =
APPLICATION_ERROR (0x0c), frameType=0, empty reason.
- Initial level: build at natural size, rewind PN if < 1200, rebuild
with PADDING-frame deficit inside the AEAD envelope.
Plus a regression test covering both: pre-handshake close datagram size
≥ 1200, and ConnectionCloseFrame round-trips 0x1c vs 0x1d for the right
constructor inputs.
NOT addressed yet: why our ClientHello at PN=0 doesn't appear in the
runner pcap (only PN=1 close does). With this fix the close packet is
now well-formed; the next runner run will tell us whether the missing
ClientHello is a sim/capture artifact or a separate writer bug.
https://claude.ai/code/session_01HcvfQq1ttPV9PkRoJb4nyT
Claude
59438d5283