Internet DRAFT - draft-kerwin-http2-nak-frame
draft-kerwin-http2-nak-frame
Network Working Group M. Kerwin
Internet-Draft August 9, 2019
Intended status: Standards Track
Expires: February 10, 2020
HTTP/2 "Dropped Frame" Frame
draft-kerwin-http2-nak-frame-02
Abstract
This document defines an extension to the Hypertext Transfer Protocol
Version 2 (HTTP/2) that allows an endpoint to signal to its peer that
an unsupported extension frame was discarded.
Note to Readers
The issues list for this draft can be found at
<https://github.com/phluid61/internet-drafts/labels/
HTTP%2F2%20NAK%20Frame>
The most recent (often unpublished) draft is at
<https://phluid61.github.io/internet-drafts/http2-nak-frame/>
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
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This Internet-Draft will expire on February 10, 2020.
Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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(https://trustee.ietf.org/license-info) in effect on the date of
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Notational Conventions . . . . . . . . . . . . . . . . . 2
2. Additions to HTTP/2 . . . . . . . . . . . . . . . . . . . . . 3
2.1. DROPPED_FRAME . . . . . . . . . . . . . . . . . . . . . . 3
3. Security Considerations . . . . . . . . . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
4.1. HTTP/2 Frame Type Registry Update . . . . . . . . . . . . 4
5. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
5.1. Normative References . . . . . . . . . . . . . . . . . . 5
5.2. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Appendix A. Changelog . . . . . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
Out of the box, the Hypertext Transfer Protocol Version 2 (HTTP/2)
[RFC7540] makes provision for extension frames to be sent on a
connection, with or without prior agreement from either peer, with
the assertion that "implementations MUST discard frames that have
unknown or unsupported types" ([RFC7540], Section 5.5). However it
can be useful to explicitly notify the peer if such a frame is
discarded.
This document defines an extension to HTTP/2 that allows a peer to
signal that a received frame was discarded, without altering the
stream or connection state ([RFC7540], Section 5.1), and in
particular without triggering an error condition.
1.1. Notational Conventions
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.
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2. Additions to HTTP/2
This document introduces a new HTTP/2 frame type ([RFC7540],
Section 11.2).
2.1. DROPPED_FRAME
[[NOTE-1: This is an experimental value; if standardised, a permanent
value will be assigned. --MK]]
DROPPED_FRAME frames (type code=0xf1) can be sent on a connection at
any time after the connection preface except in the middle of a
header block ([RFC7540], Section 4.3) to indicate that a received
extension frame was discarded without any other action being taken.
+---------------+
| Type (8) |
+---------------+
DROPPED_FRAME Frame Payload
The DROPPED_FRAME frame contains a single 8-bit integer containing
the value of the Type field from the discarded frame.
The DROPPED_FRAME frame does not define any flags.
An endpoint SHOULD send a DROPPED_FRAME frame for an unknown or
unsupported extension frame type the first time it discards a frame
of that type.
An endpoint MAY send a DROPPED_FRAME frame for a particular frame
type only once, even if it discards multiple frames of that type.
An endpoint that receives a DROPPED_FRAME frame ought to take it as
an indication that the extension is not supported by the peer, and
MAY subsequently choose not to send further frames of that type or to
attempt extension negotiation with the peer.
Receipt of a DROPPED_FRAME frame does not necessarily mean that all
frames on that connection with the discarded type will be discarded
in future. A transparent intermediary that forwards an extension
frame in one direction and a corresponding DROPPED_FRAME frame in the
other direction MUST NOT intercept future frames of that type and
preemptively reply with a DROPPED_FRAME frame.
DROPPED_FRAME frames are not associated with any individual stream.
If a DROPPED_FRAME frame is received with a stream identifier field
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value other than 0x0, the recipient MUST respond with a connection
error ([RFC7540], Section 5.4.1) of type PROTOCOL_ERROR.
Receipt of a DROPPED_FRAME frame with a length field value other than
1 MUST be treated as a connection error ([RFC7540], Section 5.4.1) of
type FRAME_SIZE_ERROR.
An endpoint MUST NOT send a DROPPED_FRAME frame with a Type of
DROPPED_FRAME (0xf1). If a DROPPED_FRAME frame is received with a
Type field value of 0xf1, the recipient MUST respond with a
connection error ([RFC7540], Section 5.4.1) of type PROTOCOL_ERROR.
Likewise, an endpoint MUST NOT send a DROPPED_FRAME frame for a type
it does not discard - including the frame types defined in [RFC7540],
Section 6, unless otherwise negotiated. If a DROPPED_FRAME frame is
received for a type that can not be discarded by the sending peer,
the recipient MUST respond with a connection error ([RFC7540],
Section 5.4.1) of type PROTOCOL_ERROR.
Extensions that define new HTTP/2 frame types MAY specify behaviours
in response to DROPPED_FRAME frames with those types, however
extensions that change the semantics of existing protocol components,
including those defined in this document, MUST be negotiated before
being used ([RFC7540], Section 5.5).
3. Security Considerations
Receipt of a DROPPED_FRAME frame does not guarantee that the sending
peer will send one for every frame type it drops, and the absence of
a DROPPED_FRAME frame does not imply that the peer has not discarded
a frame. Implementations MUST NOT depend on the use of DROPPED_FRAME
frames to indicate acceptance or rejection of extension frames.
4. IANA Considerations
This document updates the registry for frame types in the "Hypertext
Transfer Protocol (HTTP) 2 Parameters" section.
4.1. HTTP/2 Frame Type Registry Update
This document updates the "HTTP/2 Frame Type" registry ([RFC7540],
Section 11.2). The entries in the following table are registered by
this document.
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+---------------+------+-------------+
| Frame Type | Code | Section |
+---------------+------+-------------+
| DROPPED_FRAME | TBD | Section 2.1 |
+---------------+------+-------------+
5. References
5.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
DOI 10.17487/RFC7540, May 2015,
<https://www.rfc-editor.org/info/rfc7540>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
Appendix A. Changelog
Since -01:
o use experimental value for frame ID
o forbid sending a DROPPED_FRAME for any frame that isn't dropped
Since -00:
o Largely editorial; clarifications about when a frame can be
received and what it can reasonably contain.
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Author's Address
Matthew Kerwin
Email: matthew@kerwin.net.au
URI: https://matthew.kerwin.net.au/
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