--- 1/draft-ietf-httpbis-cache-digest-01.txt 2017-05-29 19:13:11.812753955 -0700 +++ 2/draft-ietf-httpbis-cache-digest-02.txt 2017-05-29 19:13:11.840754630 -0700 @@ -1,18 +1,18 @@ -Network Working Group K. Oku +HTTP Working Group K. Oku Internet-Draft DeNA Co, Ltd. -Intended status: Standards Track M. Nottingham -Expires: May 5, 2017 November 1, 2016 +Intended status: Experimental M. Nottingham +Expires: December 1, 2017 May 30, 2017 Cache Digests for HTTP/2 - draft-ietf-httpbis-cache-digest-01 + draft-ietf-httpbis-cache-digest-02 Abstract This specification defines a HTTP/2 frame type to allow clients to inform the server of their cache's contents. Servers can then use this to inform their choices of what to push to clients. Note to Readers Discussion of this draft takes place on the HTTP working group @@ -31,85 +31,89 @@ 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 May 5, 2017. + This Internet-Draft will expire on December 1, 2017. 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. 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 the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Notational Conventions . . . . . . . . . . . . . . . . . 3 2. The CACHE_DIGEST Frame . . . . . . . . . . . . . . . . . . . 3 2.1. Client Behavior . . . . . . . . . . . . . . . . . . . . . 4 2.1.1. Computing the Digest-Value . . . . . . . . . . . . . 5 2.1.2. Computing a Hash Value . . . . . . . . . . . . . . . 6 - 2.2. Server Behavior . . . . . . . . . . . . . . . . . . . . . 6 + 2.2. Server Behavior . . . . . . . . . . . . . . . . . . . . . 7 2.2.1. Querying the Digest for a Value . . . . . . . . . . . 7 - 3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 - 4. Security Considerations . . . . . . . . . . . . . . . . . . . 8 - 5. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 - 5.1. Normative References . . . . . . . . . . . . . . . . . . 9 - 5.2. Informative References . . . . . . . . . . . . . . . . . 9 - Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 10 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 + 3. The ACCEPT_CACHE_DIGEST SETTINGS Parameter . . . . . . . . . 8 + 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 + 5. Security Considerations . . . . . . . . . . . . . . . . . . . 10 + 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 + 6.1. Normative References . . . . . . . . . . . . . . . . . . 10 + 6.2. Informative References . . . . . . . . . . . . . . . . . 11 + Appendix A. Encoding the CACHE_DIGEST frame as an HTTP Header . 12 + Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 13 + Appendix C. Changes . . . . . . . . . . . . . . . . . . . . . . 13 + C.1. Since draft-ietf-httpbis-cache-digest-01 . . . . . . . . 13 + C.2. Since draft-ietf-httpbis-cache-digest-00 . . . . . . . . 13 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13 1. Introduction HTTP/2 [RFC7540] allows a server to "push" synthetic request/response pairs into a client's cache optimistically. While there is strong interest in using this facility to improve perceived Web browsing performance, it is sometimes counterproductive because the client might already have cached the "pushed" response. When this is the case, the bandwidth used to "push" the response is effectively wasted, and represents opportunity cost, because it could 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, but there is still at least one round trip of potentially wasted capacity even then. 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 what to push to clients. 1.1. Notational Conventions The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. 2. The CACHE_DIGEST Frame - The CACHE_DIGEST frame type is 0xf1. NOTE: This is an experimental - value; if standardised, a permanent value will be assigned. + The CACHE_DIGEST frame type is 0xd (decimal 13). +-------------------------------+-------------------------------+ | Origin-Len (16) | Origin? (\*) ... +-------------------------------+-------------------------------+ | Digest-Value? (\*) ... +---------------------------------------------------------------+ The CACHE_DIGEST frame payload has the following fields: Origin-Len: An unsigned, 16-bit integer indicating the length, in @@ -331,41 +336,103 @@ 2. Read the next 5 bits of "digest-value" as an integer; let "P" be two raised to the power of that value. 3. Let "hash-value" be the result of computing a hash value (Section 2.1.2). 4. Let "C" be -1. 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 integer; let "R" be its value. 7. Let "D" be "Q" * "P" + "R". 8. Increment "C" by "D" + 1. 9. If "C" is equal to "hash-value", return 'true'. 10. Otherwise, return to step 5 and continue processing; if no match is found before "digest-value" is exhausted, return 'false'. -3. IANA Considerations +3. The ACCEPT_CACHE_DIGEST SETTINGS Parameter - This draft currently has no requirements for IANA. If the - CACHE_DIGEST frame is standardised, it will need to be assigned a - frame type. + A server can notify its support for CACHE_DIGEST frame by sending the + ACCEPT_CACHE_DIGEST (0x7) SETTINGS parameter. If the server is + tempted to making optimizations based on CACHE_DIGEST frames, it + SHOULD send the SETTINGS parameter immediately after the connection + is established. -4. Security Considerations + The value of the parameter is a bit-field of which the following bits + are defined: + + FRESH (0x1): When set, it indicates that the server is willing to + make use of a digest of freshly-cached responses. + + STALE (0x2): When set, it indicates that the server is willing to + make use of a digest of stale-cached responses. + + Rest of the bits MUST be ignored and MUST be left unset when sending. + + The initial value of the parameter is zero (0x0) meaning that the + server is not interested in seeing a CACHE_DIGEST frame. + + Some underlying transports allow the server's first flight of + application data to reach the client at around the same time when the + client sends it's first flight data. When such transport (e.g., TLS + 1.3 [I-D.ietf-tls-tls13] in full-handshake mode) is used, a client + can postpone sending the CACHE_DIGEST frame until it receives a + ACCEPT_CACHE_DIGEST settings value. + + When the underlying transport does not have such property (e.g., TLS + 1.3 in 0-RTT mode), a client can reuse the settings value found in + previous connections to that origin [RFC6454] to make assumptions. + +4. IANA Considerations + + This document registers the following entry in the Permanent Message + Headers Registry, as per [RFC3864]: + + o Header field name: Cache-Digest + + o Applicable protocol: http + + o Status: experimental + + o Author/Change controller: IESG + + o Specification document(s): [this document] + + This document registers the following entry in the HTTP/2 Frame Type + Registry, as per [RFC7540]: + + o Frame Type: CACHE_DIGEST + + o Code: 0xd + + o Specification: [this document] + + This document registers the following entry in the HTTP/2 Settings + Registry, as per [RFC7540]: + + o Code: 0x7 + + o Name: ACCEPT_CACHE_DIGEST + + o Initial Value: 0x0 + + o Reference: [this document] + +5. Security Considerations The contents of a User Agent's cache can be used to re-identify or "fingerprint" the user over time, even when other identifiers (e.g., Cookies [RFC6265]) are cleared. CACHE_DIGEST allows such cache-based fingerprinting to become passive, since it allows the server to discover the state of the client's cache without any visible change in server behaviour. As a result, clients MUST mitigate for this threat when the user @@ -373,23 +440,23 @@ could be achieved in a number of ways; for example: by clearing the cache, by changing one or both of N and P, or by adding new, synthetic entries to the digest to change its contents. TODO: discuss how effective the suggested mitigations actually would be. Additionally, User Agents SHOULD NOT send CACHE_DIGEST when in "privacy mode." -5. References +6. References -5.1. Normative References +6.1. 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, . [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, DOI 10.17487/RFC3986, January 2005, . @@ -416,39 +483,128 @@ [RFC7234] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching", RFC 7234, DOI 10.17487/RFC7234, June 2014, . [RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext Transfer Protocol Version 2 (HTTP/2)", RFC 7540, DOI 10.17487/RFC7540, May 2015, . -5.2. Informative References +6.2. Informative References + + [Fetch] "Fetch Standard", n.d., . + + [I-D.ietf-tls-tls13] + Rescorla, E., "The Transport Layer Security (TLS) Protocol + Version 1.3", draft-ietf-tls-tls13-20 (work in progress), + April 2017. + + [RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration + Procedures for Message Header Fields", BCP 90, RFC 3864, + DOI 10.17487/RFC3864, September 2004, + . + + [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data + Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006, + . + + [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax + Specifications: ABNF", STD 68, RFC 5234, + DOI 10.17487/RFC5234, January 2008, + . [RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265, DOI 10.17487/RFC6265, April 2011, . [Rice] Rice, R. and J. Plaunt, "Adaptive variable-length coding for efficient compression of spacecraft television data", IEEE Transactions on Communication Technology 19.6 , 1971. -Appendix A. Acknowledgements + [Service-Workers] + Russell, A., Song, J., Archibald, J., and M. + Kruisselbrink, "Service Workers 1", October 2016, + . + +Appendix A. Encoding the CACHE_DIGEST frame as an HTTP Header + + On some web browsers that support Service Workers [Service-Workers] + but not Cache Digests (yet), it is possible to achieve the benefit of + using Cache Digests by emulating the frame using HTTP Headers. + + For the sake of interoperability with such clients, this appendix + defines how a CACHE_DIGEST frame can be encoded as an HTTP header + named "Cache-Digest". + + The definition uses the Augmented Backus-Naur Form (ABNF) notation of + [RFC5234] with the list rule extension defined in [RFC7230], + Appendix B. + + Cache-Digest = 1#digest-entity + digest-entity = digest-value *(OWS ";" OWS digest-flag) + digest-value = + digest-flag = token + + A Cache-Digest request header is defined as a list construct of + cache-digest-entities. Each cache-digest-entity corresponds to a + CACHE_DIGEST frame. + + Digest-Value is encoded using base64url [RFC4648], Section 5. Flags + that are set are encoded as digest-flags by their names that are + compared case-insensitively. + + Origin is omitted in the header form. The value is implied from the + value of the ":authority" pseudo header. Client MUST only send + Cache-Digest headers containing digests that belong to the origin + specified by the HTTP request. + + The example below contains one digest of fresh resource and has only + the "COMPLETE" flag set. + + Cache-Digest: AfdA; complete + + Clients MUST associate Cache-Digest headers to every HTTP request, + since Fetch [Fetch] - the HTTP API supported by Service Workers - + does not define the order in which the issued requests will be sent + to the server nor guarantees that all the requests will be + transmitted using a single HTTP/2 connection. + + Also, due to the fact that any header that is supplied to Fetch is + required to be end-to-end, there is an ambiguity in what a Cache- + Digest header respresents when a request is transmitted through a + proxy. The header may represent the cache state of a client or that + of a proxy, depending on how the proxy handles the header. + +Appendix B. Acknowledgements Thanks to Adam Langley and Giovanni Bajo for their explorations of - Golumb-coded sets. In particular, see + Golomb-coded sets. In particular, see http://giovanni.bajo.it/post/47119962313/golomb-coded-sets-smaller- than-bloom-filters , which refers to sample code. Thanks to Stefan Eissing for his suggestions. +Appendix C. Changes + +C.1. Since draft-ietf-httpbis-cache-digest-01 + + o Added definition of the Cache-Digest header. + + o Introduce ACCEPT_CACHE_DIGEST SETTINGS parameter. + + o Change intended status from Standard to Experimental. + +C.2. Since draft-ietf-httpbis-cache-digest-00 + + o Make the scope of a digest frame explicit and shift to stream 0. + Authors' Addresses Kazuho Oku DeNA Co, Ltd. Email: kazuhooku@gmail.com Mark Nottingham Email: mnot@mnot.net