msquic — Encoder instruction naming a static index that does not exist

Inconclusive

The client completed its request and then said nothing further before the window closed. A rejection whose CONNECTION_CLOSE was lost cannot be told apart from a client that never objected: QUIC re-sends that frame only in answer to an incoming packet, so one that goes missing is simply never seen.

The run did not establish what this client does here — either it was never put in the situation, or its answer admits more than one reading. Not a failure, and never counted as one.

What was measured

Client

msquic — .NET HttpClient + msquic, 2.7.0

Test

Encoder instruction naming a static index that does not exist — h-qpack-encoder-bad-name-index

Clause

RFC 9204 §3.1, §4.3.2 (MUST)

Class

correctness — Rejected something invalid, with the code the RFC names.

Required behaviour

Close the connection with QPACK_ENCODER_STREAM_ERROR (0x201). The same bad index means different things depending on where it arrives, and §3.1 says both: on a field line it is QPACK_DECOMPRESSION_FAILED, and "if this index is received on the encoder stream, this MUST be treated as a connection error of type QPACK_ENCODER_STREAM_ERROR". Paired deliberately with the field-line version on the neighbouring port: a client that answers both with the same code has collapsed a distinction the specification draws twice in one paragraph.

Measured

2026-09-18

Reproduce it

The suite is the judge, so the reproduction is to point the same client at the same test and let the server report what it saw.

SESSION=$(curl -sX POST https://conformance.pqcrypta.com/session | jq -r .id)
# then drive msquic at the test URL and read the verdict:
curl -s https://conformance.pqcrypta.com/report/$SESSION.json | jq '.results["h-qpack-encoder-bad-name-index"]'