Header Compression for HTTP/QUIC
draft-bishop-quic-http-and-qpack-04
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QUIC Working Group M. Bishop
Internet-Draft Microsoft
Intended status: Standards Track September 25, 2017
Expires: March 29, 2018
Header Compression for HTTP/QUIC
draft-bishop-quic-http-and-qpack-04
Abstract
HTTP/2 [RFC7540] uses HPACK [RFC7541] for header compression.
However, HPACK relies on the in-order message-based semantics of the
HTTP/2 framing layer in order to function. Messages can only be
successfully decoded if processed by the decoder in the same order as
generated by the encoder. This draft refines HPACK to loosen the
ordering requirements for use over QUIC [I-D.ietf-quic-transport].
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
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on March 29, 2018.
Copyright Notice
Copyright (c) 2017 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
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
Bishop Expires March 29, 2018 [Page 1]
Internet-Draft QPACK September 2017
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. QPACK . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Basic model . . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Changes to Static and Dynamic Tables . . . . . . . . . . 4
2.2.1. Changes to Header Table Size . . . . . . . . . . . . 4
2.2.2. Dynamic Table State Synchronization . . . . . . . . . 5
2.3. Header Management Streams . . . . . . . . . . . . . . . . 6
2.3.1. Insert . . . . . . . . . . . . . . . . . . . . . . . 6
2.3.2. Delete . . . . . . . . . . . . . . . . . . . . . . . 7
2.3.3. Delete-Ack . . . . . . . . . . . . . . . . . . . . . 10
2.4. Format of Encoded Headers on Message Streams . . . . . . 10
2.4.1. Indexed Header Field Representation . . . . . . . . . 10
2.4.2. Literal Header Field Representation . . . . . . . . . 11
3. Use in HTTP/QUIC . . . . . . . . . . . . . . . . . . . . . . 12
4. Implementation trade-offs . . . . . . . . . . . . . . . . . . 12
4.1. Compression Efficiency versus Blocking Avoidance . . . . 13
4.2. Timely Delete Completion versus State Commitment . . . . 13
5. Security Considerations . . . . . . . . . . . . . . . . . . . 14
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14
8. Normative References . . . . . . . . . . . . . . . . . . . . 15
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 15
1. Introduction
HPACK has a number of features that were intended to provide
performance advantages to HTTP/2, but which don't live well in an
out-of-order environment such as that provided by QUIC.
The largest challenge is the fact that elements are referenced by a
very fluid index. Not only is the index implicit when an item is
added to the header table, the index will change without notice as
other items are added to the header table. Static entries occupy the
first 61 values, followed by dynamic entries. A newly-added dynamic
entry would cause older dynamic entries to be evicted, and the
retained items are then renumbered beginning with 62. This means
that, without processing all preceding header sets, no index into the
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