No-Vary-Search
draft-ietf-httpbis-no-vary-search-00
| Document | Type | Active Internet-Draft (httpbis WG) | |
|---|---|---|---|
| Authors | Domenic Denicola , Jeremy Roman | ||
| Last updated | 2024-09-27 | ||
| Replaces | draft-wicg-http-no-vary-search | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | Proposed Standard | ||
| Formats | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | WG Document | |
| Document shepherd | (None) | ||
| IESG | IESG state | I-D Exists | |
| Consensus boilerplate | Yes | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-ietf-httpbis-no-vary-search-00
HyperText Transfer Protocol D. Denicola
Internet-Draft J. Roman
Intended status: Standards Track Google LLC
Expires: 31 March 2025 27 September 2024
No-Vary-Search
draft-ietf-httpbis-no-vary-search-00
Abstract
A proposed HTTP header field for changing how URL search parameters
impact caching.
About This Document
This note is to be removed before publishing as an RFC.
The latest revision of this draft can be found at https://httpwg.org/
http-extensions/draft-ietf-httpbis-no-vary-search.html. Status
information for this document may be found at
https://datatracker.ietf.org/doc/draft-ietf-httpbis-no-vary-search/.
Discussion of this document takes place on the HTTP Working Group
mailing list (mailto:ietf-http-wg@w3.org), which is archived at
https://lists.w3.org/Archives/Public/ietf-http-wg/. Working Group
information can be found at https://httpwg.org/.
Source for this draft and an issue tracker can be found at
https://github.com/httpwg/http-extensions/labels/no-vary-search.
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
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 31 March 2025.
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Copyright Notice
Copyright (c) 2024 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 (https://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
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Conventions and Definitions . . . . . . . . . . . . . . . . . 2
2. HTTP header field definition . . . . . . . . . . . . . . . . 3
3. Data model . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Parsing . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.1. Parse a URL search variance . . . . . . . . . . . . . . . 4
4.2. Obtain a URL search variance . . . . . . . . . . . . . . 5
4.2.1. Examples . . . . . . . . . . . . . . . . . . . . . . 6
4.3. Parse a key . . . . . . . . . . . . . . . . . . . . . . . 7
4.3.1. Examples . . . . . . . . . . . . . . . . . . . . . . 7
5. Comparing . . . . . . . . . . . . . . . . . . . . . . . . . . 8
5.1. Examples . . . . . . . . . . . . . . . . . . . . . . . . 10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 11
7. Privacy Considerations . . . . . . . . . . . . . . . . . . . 11
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
9.1. Normative References . . . . . . . . . . . . . . . . . . 12
9.2. Informative References . . . . . . . . . . . . . . . . . 12
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 12
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
1. Conventions and Definitions
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.
This document also adopts some conventions and notation typical in
WHATWG and W3C usage, especially as it relates to algorithms. See
[WHATWG-INFRA].
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2. HTTP header field definition
The No-Vary-Search HTTP header field is a structured field
[STRUCTURED-FIELDS] whose value must be a dictionary (Section 3.2 of
[STRUCTURED-FIELDS]).
It has the following authoring conformance requirements:
* If present, the key-order entry's value must be a boolean
(Section 3.3.6 of [STRUCTURED-FIELDS]).
* If present, the params entry's value must be either a boolean
(Section 3.3.6 of [STRUCTURED-FIELDS]) or an inner list
(Section 3.1.1 of [STRUCTURED-FIELDS]).
* If present, the except entry's value must be an inner list
(Section 3.1.1 of [STRUCTURED-FIELDS]).
* The except entry must only be present if the params entry is also
present, and the params entry's value is the boolean value true.
The dictionary may contain entries whose keys are not one of key-
order, params, and except, but their meaning is not defined by this
specification. Implementations of this specification will ignore
such entries (but future documents may assign meaning to such
entries).
| As always, the authoring conformance requirements are not
| binding on implementations. Implementations instead need to
| implement the processing model given by the obtain a URL search
| variance algorithm (Section 4.2).
3. Data model
A _URL search variance_ consists of the following:
no-vary params
either the special value *wildcard* or a list of strings
vary params
either the special value *wildcard* or a list of strings
vary on key order
a boolean
The _default URL search variance_ is a URL search variance whose no-
vary params is an empty list, vary params is *wildcard*, and vary on
key order is true.
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The obtain a URL search variance algorithm (Section 4.2) ensures that
all URL search variances obey the following constraints:
* vary params is a list if and only if the no-vary params is
*wildcard*; and
* no-vary params is a list if and only if the vary params is
*wildcard*.
4. Parsing
4.1. Parse a URL search variance
To _parse a URL search variance_ given _value_:
1. If _value_ is null, then return the default URL search variance.
2. Let _result_ be a new URL search variance.
3. Set _result_'s vary on key order to true.
4. If _value_["key-order"] exists:
1. If _value_["key-order"] is not a boolean, then return the
default URL search variance.
2. Set _result_'s vary on key order to the boolean negation of
_value_["key-order"].
5. If _value_["params"] exists:
1. If _value_["params"] is a boolean:
1. If _value_["params"] is true, then:
1. Set _result_'s no-vary params to *wildcard*.
2. Set _result_'s vary params to the empty list.
2. Otherwise:
1. Set _result_'s no-vary params to the empty list.
2. Set _result_'s vary params to *wildcard*.
2. Otherwise, if _value_["params"] is an array:
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1. If any item in _value_["params"] is not a string, then
return the default URL search variance.
2. Set _result_'s no-vary params to the result of applying
parse a key (Section 4.3) to each item in
_value_["params"].
3. Set _result_'s vary params to *wildcard*.
3. Otherwise, return the default URL search variance.
6. If _value_["except"] exists:
1. If _value_["params"] is not true, then return the default URL
search variance.
2. If _value_["except"] is not an array, then return the default
URL search variance.
3. If any item in _value_["except"] is not a string, then return
the default URL search variance.
4. Set _result_'s vary params to the result of applying parse a
key (Section 4.3) to each item in _value_["except"].
7. Return _result_.
| In general, this algorithm is strict and tends to return the
| default URL search variance whenever it sees something it
| doesn't recognize. This is because the default URL search
| variance behavior will just cause fewer cache hits, which is an
| acceptable fallback behavior.
|
| However, unrecognized keys at the top level are ignored, to
| make it easier to extend this specification in the future. To
| avoid misbehavior with existing client software, such
| extensions will likely expand, rather than reduce, the set of
| requests that a cached response can match.
| The input to this algorithm is generally obtained by parsing a
| structured field (Section 4.2 of [STRUCTURED-FIELDS]) using
| field_type "dictionary".
4.2. Obtain a URL search variance
To _obtain a URL search variance_ given a response
(https://fetch.spec.whatwg.org/#concept-response) _response_:
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1. Let _fieldValue_ be the result of getting a structured field
value (https://fetch.spec.whatwg.org/#concept-header-list-get-
structured-header) [FETCH] given `No-Vary-Search` and
"dictionary" from _response_'s header list.
2. Return the result of parsing a URL search variance (Section 4.1)
given _fieldValue_.
4.2.1. Examples
The following illustrates how various inputs are parsed, in terms of
their impacting on the resulting no-vary params and vary params:
+========================+============================+
| Input | Result |
+========================+============================+
| No-Vary-Search: params | no-vary params: *wildcard* |
| | vary params: (empty list) |
+------------------------+----------------------------+
| No-Vary-Search: | no-vary params: « "a" » |
| params=("a") | vary params: *wildcard* |
+------------------------+----------------------------+
| No-Vary-Search: | no-vary params: *wildcard* |
| params, except=("x") | vary params: « "x" » |
+------------------------+----------------------------+
Table 1
The following inputs are all invalid and will cause the default URL
search variance to be returned:
* No-Vary-Search: unknown-key
* No-Vary-Search: key-order="not a boolean"
* No-Vary-Search: params="not a boolean or inner list"
* No-Vary-Search: params=(not-a-string)
* No-Vary-Search: params=("a"), except=("x")
* No-Vary-Search: params=(), except=()
* No-Vary-Search: params=?0, except=("x")
* No-Vary-Search: params, except=(not-a-string)
* No-Vary-Search: params, except="not an inner list"
* No-Vary-Search: params, except=?1
* No-Vary-Search: except=("x")
* No-Vary-Search: except=()
The following inputs are valid, but somewhat unconventional. They
are shown alongside their more conventional form.
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+==============================+============================+
| Input | Conventional form |
+==============================+============================+
| No-Vary-Search: params=?1 | No-Vary-Search: params |
+------------------------------+----------------------------+
| No-Vary-Search: key-order=?1 | No-Vary-Search: key-order |
+------------------------------+----------------------------+
| No-Vary-Search: params, key- | No-Vary-Search: key-order, |
| order, except=("x") | params, except=("x") |
+------------------------------+----------------------------+
| No-Vary-Search: params=?0 | (omit the header) |
+------------------------------+----------------------------+
| No-Vary-Search: params=() | (omit the header) |
+------------------------------+----------------------------+
| No-Vary-Search: key-order=?0 | (omit the header) |
+------------------------------+----------------------------+
Table 2
4.3. Parse a key
To _parse a key_ given an ASCII string _keyString_:
1. Let _keyBytes_ be the isomorphic encoding
(https://infra.spec.whatwg.org/#isomorphic-encode) [WHATWG-INFRA]
of _keyString_.
2. Replace any 0x2B (+) in _keyBytes_ with 0x20 (SP).
3. Let _keyBytesDecoded_ be the percent-decoding
(https://url.spec.whatwg.org/#percent-decode) [WHATWG-URL] of
_keyBytes_.
4. Let _keyStringDecoded_ be the UTF-8 decoding without BOM
(https://encoding.spec.whatwg.org/#utf-8-decode-without-bom)
[WHATWG-ENCODING] of _keyBytesDecoded_.
5. Return _keyStringDecoded_.
4.3.1. Examples
The parse a key algorithm allows encoding non-ASCII key strings in
the ASCII structured header format, similar to how the application/x-
www-form-urlencoded (https://url.spec.whatwg.org/#concept-urlencoded)
format [WHATWG-URL] allows encoding an entire entry list of keys and
values in ASCII URL format. For example,
No-Vary-Search: params=("%C3%A9+%E6%B0%97")
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will result in a URL search variance whose vary params are « "é 気" ».
As explained in a later example, the canonicalization process during
equivalence testing means this will treat as equivalent URL strings
such as:
* https://example.com/?é 気=1
* https://example.com/?é+気=2
* https://example.com/?%C3%A9%20気=3
* https://example.com/?%C3%A9+%E6%B0%97=4
and so on, since they all are parsed
(https://url.spec.whatwg.org/#concept-urlencoded-parser) [WHATWG-URL]
to having the same key "é 気".
5. Comparing
Two URLs (https://url.spec.whatwg.org/#concept-url) [WHATWG-URL]
_urlA_ and _urlB_ are _equivalent modulo search variance_ given a URL
search variance _searchVariance_ if the following algorithm returns
true:
1. If the scheme, username, password, host, port, or path of _urlA_
and _urlB_ differ, then return false.
2. If _searchVariance_ is equivalent to the default URL search
variance, then:
1. If _urlA_'s query equals _urlB_'s query, then return true.
2. Return false.
In this case, even URL pairs that might appear the same after
running the application/x-www-form-urlencoded parser
(https://url.spec.whatwg.org/#concept-urlencoded-parser)
[WHATWG-URL] on their queries, such as https://example.com/a and
https://example.com/a?, or https://example.com/foo?a=b&&&c and
https://example.com/foo?a=b&c=, will be treated as inequivalent.
3. Let _searchParamsA_ and _searchParamsB_ be empty lists.
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4. If _wrlA_'s query is not null, then set _searchParamsA_ to the
result of running the application/x-www-form-urlencoded parser
(https://url.spec.whatwg.org/#concept-urlencoded-parser)
[WHATWG-URL] given the isomorphic encoding
(https://infra.spec.whatwg.org/#isomorphic-encode)
[WHATWG-INFRA] of _urlA_'s query.
5. If _wrlB_'s query is not null, then set _searchParamsB_ to the
result of running the application/x-www-form-urlencoded parser
(https://url.spec.whatwg.org/#concept-urlencoded-parser)
[WHATWG-URL] given the isomorphic encoding
(https://infra.spec.whatwg.org/#isomorphic-encode)
[WHATWG-INFRA] of _urlB_'s query.
6. If _searchVariance_'s no-vary params is a list, then:
1. Set _searchParamsA_ to a list containing those items _pair_
in _searchParamsA_ where _searchVariance_'s no-vary params
does not contain _pair_[0].
2. Set _searchParamsB_ to a list containing those items _pair_
in _searchParamsB_ where _searchVariance_'s no-vary params
does not contain _pair_[0].
7. Otherwise, if _searchVariance_'s vary params is a list, then:
1. Set _searchParamsA_ to a list containing those items _pair_
in _searchParamsA_ where _searchVariance_'s vary params
contains _pair_[0].
2. Set _searchParamsB_ to a list containing those items _pair_
in _searchParamsB_ where _searchVariance_'s vary params
contains _pair_[0].
8. If _searchVariance_'s vary on key order is false, then:
1. Let _keyLessThan_ be an algorithm taking as inputs two pairs
(_keyA_, _valueA_) and (_keyB_, _valueB_), which returns
whether _keyA_ is code unit less than
(https://infra.spec.whatwg.org/#code-unit-less-than)
[WHATWG-INFRA] _keyB_.
2. Set _searchParamsA_ to the result of sorting _searchParamsA_
in ascending order with _keyLessThan_.
3. Set _searchParamsB_ to the result of sorting _searchParamsB_
in ascending order with _keyLessThan_.
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9. If _searchParamsA_'s size is not equal to _searchParamsB_'s
size, then return false.
10. Let _i_ be 0.
11. While _i_ < _searchParamsA_'s size:
1. If _searchParamsA_[_i_][0] does not equal
_searchParamsB_[_i_][0], then return false.
2. If _searchParamsA_[_i_][1] does not equal
_searchParamsB_[_i_][1], then return false.
3. Set _i_ to _i_ + 1.
12. Return true.
5.1. Examples
Due to how the application/x-www-form-urlencoded parser canonicalizes
query strings, there are some cases where query strings which do not
appear obviously equivalent, will end up being treated as equivalent
after parsing.
So, for example, given any non-default value for No-Vary-Search, such
as No-Vary-Search: key-order, we will have the following
equivalences:
https://example.com
https://example.com/?
A null query is parsed the same as an empty string
https://example.com/?a=x
https://example.com/?%61=%78
Parsing performs percent-decoding
https://example.com/?a=é
https://example.com/?a=%C3%A9
Parsing performs percent-decoding
https://example.com/?a=%f6
https://example.com/?a=%ef%bf%bd
Both values are parsed as U+FFFD (�)
https://example.com/?a=x&&&&
https://example.com/?a=x
Parsing splits on & and discards empty strings
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https://example.com/?a=
https://example.com/?a
Both parse as having an empty string value for a
https://example.com/?a=%20
https://example.com/?a=+
https://example.com/?a= &
+ and %20 are both parsed as U+0020 SPACE
6. Security Considerations
The main risk to be aware of is the impact of mismatched URLs. In
particular, this could cause the user to see a response that was
originally fetched from a URL different from the one displayed when
they hovered a link, or the URL displayed in the URL bar.
However, since the impact is limited to query parameters, this does
not cross the relevant security boundary, which is the origin
(https://html.spec.whatwg.org/multipage/browsers.html#concept-origin)
[HTML]. (Or perhaps just the host
(https://url.spec.whatwg.org/#concept-url-host), from the perspective
of web browser security UI (https://url.spec.whatwg.org/#url-
rendering-simplification). [WHATWG-URL]) Indeed, we have already
given origins complete control over how they present the (URL,
reponse body) pair, including on the client side via technology such
as history.replaceState() (https://html.spec.whatwg.org/multipage/
nav-history-apis.html#dom-history-replacestate) or service workers.
7. Privacy Considerations
This proposal is adjacent to the highly-privacy-relevant space of
navigational tracking (https://privacycg.github.io/nav-tracking-
mitigations/#terminology), which often uses query parameters to pass
along user identifiers. However, we believe this proposal itself
does not have privacy impacts. It does not interfere with existing
navigational tracking mitigations (https://privacycg.github.io/nav-
tracking-mitigations/#deployed-mitigations), or any known future ones
being contemplated. Indeed, if a page were to encode user
identifiers in its URL, the only ability this proposal gives is to
_reduce_ such user tracking by preventing server processing of such
user IDs (since the server is bypassed in favor of the cache).
[NAV-TRACKING-MITIGATIONS]
8. IANA Considerations
TODO IANA
9. References
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9.1. Normative References
[FETCH] van Kesteren, A., "Fetch Living Standard", n.d.,
<https://fetch.spec.whatwg.org/>. WHATWG
[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/rfc/rfc2119>.
[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/rfc/rfc8174>.
[STRUCTURED-FIELDS]
Nottingham, M. and P. Kamp, "Structured Field Values for
HTTP", RFC 8941, DOI 10.17487/RFC8941, February 2021,
<https://www.rfc-editor.org/rfc/rfc8941>.
[WHATWG-ENCODING]
van Kesteren, A., "Encoding Living Standard", n.d.,
<https://encoding.spec.whatwg.org/>. WHATWG
[WHATWG-INFRA]
van Kesteren, A. and D. Denicola, "Infra Living Standard",
n.d., <https://infra.spec.whatwg.org/>. WHATWG
[WHATWG-URL]
van Kesteren, A., "URL Living Standard", n.d.,
<https://url.spec.whatwg.org/>. WHATWG
9.2. Informative References
[HTML] van Kesteren, A., "HTML Living Standard", n.d.,
<https://html.spec.whatwg.org/>. WHATWG
[NAV-TRACKING-MITIGATIONS]
Snyder, P. and J. Yasskin, "Navigational-Tracking
Mitigations", n.d.,
<https://privacycg.github.io/nav-tracking-mitigations/>.
W3C Privacy CG
Acknowledgments
TODO acknowledge.
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Index
D E O P
D
default URL search variance *_Section 3, Paragraph 3_*;
Section 4.1, Paragraph 2.1.1; Section 4.1, Paragraph
2.4.2.1.1; Section 4.1, Paragraph 2.5.2.2.2.1.1;
Section 4.1, Paragraph 2.5.2.3.1; Section 4.1, Paragraph
2.6.2.1.1; Section 4.1, Paragraph 2.6.2.2.1; Section 4.1,
Paragraph 2.6.2.3.1; Section 4.1, Paragraph 3.1;
Section 4.2.1, Paragraph 3; Section 5, Paragraph 2.2.1
E
equivalent modulo search variance *_Section 5, Paragraph 1_*
O
obtain a URL search variance Section 2, Paragraph 5.1;
Section 3, Paragraph 4; *_Section 4.2, Paragraph 1_*
P
parse a key Section 4.1, Paragraph 2.5.2.2.2.2.1; Section 4.1,
Paragraph 2.6.2.4.1; *_Section 4.3, Paragraph 1_*;
Section 4.3.1, Paragraph 1
parse a URL search variance *_Section 4.1, Paragraph 1_*;
Section 4.2, Paragraph 2.2.1
Authors' Addresses
Domenic Denicola
Google LLC
Email: d@domenic.me
Jeremy Roman
Google LLC
Email: jbroman@chromium.org
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