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don't require that extensible priorities is used #1705

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Sep 30, 2021
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don't require that extensible priorities is used #1705

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20 changes: 10 additions & 10 deletions draft-ietf-httpbis-priority.md
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Expand Up @@ -189,8 +189,9 @@ RFC 7540 stream priority (see {{Section 5.3 of RFC7540}}).

The SETTINGS_NO_RFC7540_PRIORITIES setting is defined by this document in
order to allow endpoints to explicitly opt out of using HTTP/2 priority signals
(see {{Section 5.3.2 of HTTP2}}). Endpoints are expected to use an alternative,
such as the scheme defined in this specification.
(see {{Section 5.3.2 of HTTP2}}). Endpoints are encouraged to use alternative
priority signals (for example, {{header-field}} or {{h2-update-frame}}) but
there is no requirement to use a specific signal type.

The value of SETTINGS_NO_RFC7540_PRIORITIES MUST be 0 or 1. Any value
other than 0 or 1 MUST be treated as a connection error (see {{Section 5.4.1 of
Expand All @@ -201,6 +202,13 @@ A sender MUST NOT change the SETTINGS_NO_RFC7540_PRIORITIES parameter value
after the first SETTINGS frame. Detection of a change by a receiver MUST be
treated as a connection error of type PROTOCOL_ERROR.

The SETTINGS frame precedes any HTTP/2 priority signal sent from a client, so a
server can determine if it needs to allocate any resource to signal handling
before they arrive. A server that receives SETTINGS_NO_RFC7540_PRIORITIES
with value of 1 MUST ignore HTTP/2 priority signals.

### Advice when Using Extensible Priorities as the Alternative

Until the client receives the SETTINGS frame from the server, the client SHOULD
send both the HTTP/2 priority signals and the signals of this prioritization
scheme (see {{header-field}} and {{h2-update-frame}}). When the client receives
Expand All @@ -212,14 +220,6 @@ the Priority header field ({{header-field}}), as it is an end-to-end signal that
might be useful to nodes behind the server that the client is directly connected
to.

The SETTINGS frame precedes any HTTP/2 priority signal sent from a client, so a
server can determine if it needs to allocate any resource to signal handling
before they arrive. A server that receives SETTINGS_NO_RFC7540_PRIORITIES
with value of 1 MUST ignore HTTP/2 priority signals.

Where both endpoints disable RFC 7540 stream priority, the client is expected to
send this scheme's priority signal. Handling of omitted signals is described in
{{parameters}}.

# Applicability of the Extensible Priority Scheme

Expand Down