HTTP/2: Treat clients MAX_HEADER_LIST_SIZE as advisory#16883
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Motivation: SETTINGS_MAX_HEADER_LIST_SIZE is advisory per RFC 9113 §6.5.2. When acting as a server, the remote peer is a client whose advertised value reflects what it is prepared to receive. Honoring arbitrarily small values creates a DoS vector: a client setting this to 1 byte would prevent any valid response from being sent. Modification: When running as a server, the `DefaultHttp2ConnectionEncoder` now ignore the max header list size setting from clients. Result: Clients can no longer cheaply induce errors on an HTTP/2 server by advising unreasonably smaller header size limits. The behavior of ignoring the max header list size matches other H2 implementations, like nghttp2, nginx, and envoy.
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Motivation:
SETTINGS_MAX_HEADER_LIST_SIZE is advisory per RFC 9113 §6.5.2. When acting as a server, the remote peer is a client whose advertised value reflects what it is prepared to receive. Honoring arbitrarily small values creates a DoS vector: a client setting this to 1 byte would prevent any valid response from being sent.
Modification:
When running as a server, the
DefaultHttp2ConnectionEncodernow ignore the max header list size setting from clients.Result:
Clients can no longer cheaply induce errors on an HTTP/2 server by advising unreasonably smaller header size limits.
The behavior of ignoring the max header list size matches other H2 implementations, like nghttp2, nginx, and envoy.