ngtcp2 — Encoder stream setting a dynamic table capacity above the client's limit

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

ngtcp2 — ngtcp2 + nghttp3 (direct), 3c23148

Test

Encoder stream setting a dynamic table capacity above the client's limit — h-qpack-encoder-overflow

Clause

RFC 9204 §4.3.1, §6 (MUST)

Class

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

Required behaviour

Close the connection with QPACK_ENCODER_STREAM_ERROR (0x201). §4.3.1 says the new capacity "MUST be lower than or equal to the limit" the decoder advertised, and that a decoder "MUST treat a new dynamic table capacity value that exceeds this limit as a connection error of type QPACK_ENCODER_STREAM_ERROR". Unlike the other two dynamic-table tests, this one runs against every client: they all advertise a capacity of zero, and any capacity at all exceeds a limit of zero.

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=$(curl -sX POST https://conformance.pqcrypta.com/session | jq -r .id)
# then drive ngtcp2 at the test URL and read the verdict:
curl -s https://conformance.pqcrypta.com/report/$SESSION.json | jq '.results["h-qpack-encoder-overflow"]'