draft-ietf-httpbis-cache-digest-01.txt   draft-ietf-httpbis-cache-digest-latest.txt 
Network Working Group K. Oku HTTP Working Group K. Oku
Internet-Draft DeNA Co, Ltd. Internet-Draft DeNA Co, Ltd.
Intended status: Standards Track M. Nottingham Intended status: Standards Track M. Nottingham
Expires: May 4, 2017 October 31, 2016 Expires: August 24, 2017 February 20, 2017
Cache Digests for HTTP/2 Cache Digests for HTTP/2
draft-ietf-httpbis-cache-digest-01 draft-ietf-httpbis-cache-digest-latest
Abstract Abstract
This specification defines a HTTP/2 frame type to allow clients to This specification defines a HTTP/2 frame type to allow clients to
inform the server of their cache's contents. Servers can then use inform the server of their cache's contents. Servers can then use
this to inform their choices of what to push to clients. this to inform their choices of what to push to clients.
Note to Readers Note to Readers
Discussion of this draft takes place on the HTTP working group Discussion of this draft takes place on the HTTP working group
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on May 4, 2017. This Internet-Draft will expire on August 24, 2017.
Copyright Notice Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
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might already have cached the "pushed" response. might already have cached the "pushed" response.
When this is the case, the bandwidth used to "push" the response is When this is the case, the bandwidth used to "push" the response is
effectively wasted, and represents opportunity cost, because it could effectively wasted, and represents opportunity cost, because it could
be used by other, more relevant responses. HTTP/2 allows a stream to be used by other, more relevant responses. HTTP/2 allows a stream to
be cancelled by a client using a RST_STREAM frame in this situation, be cancelled by a client using a RST_STREAM frame in this situation,
but there is still at least one round trip of potentially wasted but there is still at least one round trip of potentially wasted
capacity even then. capacity even then.
This specification defines a HTTP/2 frame type to allow clients to This specification defines a HTTP/2 frame type to allow clients to
inform the server of their cache's contents using a Golumb-Rice Coded inform the server of their cache's contents using a Golomb-Rice Coded
Set [Rice]. Servers can then use this to inform their choices of Set [Rice]. Servers can then use this to inform their choices of
what to push to clients. what to push to clients.
1.1. Notational Conventions 1.1. Notational Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
2. The CACHE_DIGEST Frame 2. The CACHE_DIGEST Frame
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following algorithm: following algorithm:
1. Read the first 5 bits of "digest-value" as an integer; let "N" 1. Read the first 5 bits of "digest-value" as an integer; let "N"
be two raised to the power of that value. be two raised to the power of that value.
2. Read the next 5 bits of "digest-value" as an integer; let "P" be 2. Read the next 5 bits of "digest-value" as an integer; let "P" be
two raised to the power of that value. two raised to the power of that value.
3. Let "hash-value" be the result of computing a hash value 3. Let "hash-value" be the result of computing a hash value
(Section 2.1.2). (Section 2.1.2).
4. Let "C" be -1. 4. Let "C" be -1.
5. Read '0' bits from "digest-value" until a '1' bit is found; let 5. Read '0' bits from "digest-value" until a '1' bit is found; let
"Q" bit the number of '0' bits. Discard the '1'. "Q" be the number of '0' bits. Discard the '1'.
6. Read log2("P") bits from "digest-value" after the '1' as an 6. Read log2("P") bits from "digest-value" after the '1' as an
integer; let "R" be its value. integer; let "R" be its value.
7. Let "D" be "Q" * "P" + "R". 7. Let "D" be "Q" * "P" + "R".
8. Increment "C" by "D" + 1. 8. Increment "C" by "D" + 1.
9. If "C" is equal to "hash-value", return 'true'. 9. If "C" is equal to "hash-value", return 'true'.
10. Otherwise, return to step 5 and continue processing; if no match 10. Otherwise, return to step 5 and continue processing; if no match
is found before "digest-value" is exhausted, return 'false'. is found before "digest-value" is exhausted, return 'false'.
3. IANA Considerations 3. IANA Considerations
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DOI 10.17487/RFC6265, April 2011, DOI 10.17487/RFC6265, April 2011,
<http://www.rfc-editor.org/info/rfc6265>. <http://www.rfc-editor.org/info/rfc6265>.
[Rice] Rice, R. and J. Plaunt, "Adaptive variable-length coding [Rice] Rice, R. and J. Plaunt, "Adaptive variable-length coding
for efficient compression of spacecraft television data", for efficient compression of spacecraft television data",
IEEE Transactions on Communication Technology 19.6 , 1971. IEEE Transactions on Communication Technology 19.6 , 1971.
Appendix A. Acknowledgements Appendix A. Acknowledgements
Thanks to Adam Langley and Giovanni Bajo for their explorations of Thanks to Adam Langley and Giovanni Bajo for their explorations of
Golumb-coded sets. In particular, see http://giovanni.bajo.it/post/ Golomb-coded sets. In particular, see http://giovanni.bajo.it/post/
47119962313/golomb-coded-sets-smaller-than-bloom-filters, which 47119962313/golomb-coded-sets-smaller-than-bloom-filters, which
refers to sample code. refers to sample code.
Thanks to Stefan Eissing for his suggestions. Thanks to Stefan Eissing for his suggestions.
Authors' Addresses Authors' Addresses
Kazuho Oku Kazuho Oku
DeNA Co, Ltd. DeNA Co, Ltd.
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