msquic — SETTINGS_H3_DATAGRAM with a value that is neither 0 nor 1

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

SETTINGS_H3_DATAGRAM with a value that is neither 0 nor 1 — h-datagram-setting-invalid

Clause

RFC 9297 §2.1.1 (MUST)

Class

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

Required behaviour

Close the connection with H3_SETTINGS_ERROR. Unusually for a setting, RFC 9297 pins down the invalid-value case rather than leaving it open: the value "MUST be either 0 or 1", and if one "is received with a value that is neither 0 nor 1, the receiver MUST terminate the connection with error H3_SETTINGS_ERROR". This is the setting that gates HTTP Datagrams and so WebTransport, which means a client that implements either has real parsing behind it rather than an ignored identifier.

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-datagram-setting-invalid"]'