Declaring Support for HTTP/2 Priorities
draft-lassey-priority-setting-00

Abstract

HTTP/2 provides a prioritization scheme but experience has shown that implementation support varies. This document defines an HTTP/2 setting that endpoints can use as an affirmative signal to indicate their support for HTTP/2 Priorities.

Status of This Memo

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This Internet-Draft will expire on January 26, 2020.

Copyright Notice

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Table of Contents

• 1. Introduction
• 2. Terminology
• 3. The SETTINGS_ENABLE_HTTP2_PRIORITIES SETTINGS Parameter
• 4. IANA Considerations
• 4.1. A New HTTP/2 Setting
• 5. Normative References
• Authors' Addresses

1. Introduction

The HTTP/2 specification defines a priority scheme in [RFC7540], Section 5.3, which some implementers have opted not to fully support. The lack of signalling about the status of the implementation has encouraged some servers to use heuristics in order to detect when the clients they are connected to do not support priorities as defined and take steps to compensate for that. The intent of this draft is to provide and affirmative signalling mechanism for each client to communicate whether or not it supports and will use the priority scheme as defined in [RFC7540], Section 5.3.

2. Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

3. The SETTINGS_ENABLE_HTTP2_PRIORITIES SETTINGS Parameter

This document adds a new SETTINGS parameter to those defined by [RFC7540], Section 6.5.2.

The new parameter name is SETTINGS_ENABLE_HTTP2_PRIORITIES. The value of the parameter MUST be 0 or 1 to indicate not supporting or supporting HTTP/2 priorities respectively. If either side sends the parameter with a value of 0, clients SHOULD NOT send priority frames and servers SHOULD NOT make any assumptions based on the presence or lack thereof of priority frames. If both sides send the parameter with a value of 1, then both parties MAY use HTTP/2 priorities as they see fit. A sender MUST NOT send the parameter with the value of 0 after previously sending a value of 1. If a client or server does not send the setting, the peer SHOULD NOT make any assumptions about its support for HTTP/2 priorities.

4. IANA Considerations

4.1. A New HTTP/2 Setting

This document registers an entry in the "HTTP/2 Settings" registry that was established by Section 11.3 of [RFC7540].

Name: SETTINGS_ENABLE_HTTP2_PRIORITIES

Code: 0xTBD

Initial Value: 1

Specification: This document

5. Normative References

Authors' Addresses