draft-ietf-httpbis-retrofit-05.txt   draft-ietf-httpbis-retrofit-latest.txt 
Network Working Group M. Nottingham HTTP Working Group M. Nottingham
Internet-Draft December 4, 2022 Internet-Draft February 9, 2023
Updates: 8941 (if approved)
Intended status: Standards Track Intended status: Standards Track
Expires: June 7, 2023 Expires: August 13, 2023
Retrofit Structured Fields for HTTP Retrofit Structured Fields for HTTP
draft-ietf-httpbis-retrofit-05 draft-ietf-httpbis-retrofit-latest
Abstract Abstract
This specification nominates a selection of existing HTTP fields as This specification nominates a selection of existing HTTP fields as
having syntax that is compatible with Structured Fields, so that they having syntax that is compatible with Structured Fields, so that they
can be handled as such (subject to certain caveats). can be handled as such (subject to certain caveats).
To accommodate some additional fields whose syntax is not compatible, To accommodate some additional fields whose syntax is not compatible,
it also defines mappings of their semantics into new Structured it also defines mappings of their semantics into new Structured
Fields. It does not specify how to negotiate their use. Fields. It does not specify how to negotiate their use.
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This Internet-Draft will expire on August 13, 2023.
This Internet-Draft will expire on June 7, 2023.
Copyright Notice Copyright Notice
Copyright (c) 2022 IETF Trust and the persons identified as the Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Notational Conventions . . . . . . . . . . . . . . . . . 3 1.1. Notational Conventions . . . . . . . . . . . . . . . . . 3
2. Compatible Fields . . . . . . . . . . . . . . . . . . . . . . 4 2. Compatible Fields . . . . . . . . . . . . . . . . . . . . . . 3
3. Mapped Fields . . . . . . . . . . . . . . . . . . . . . . . . 7 3. Mapped Fields . . . . . . . . . . . . . . . . . . . . . . . . 6
3.1. URLs . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.1. URLs . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.2. Dates . . . . . . . . . . . . . . . . . . . . . . . . . . 8 3.2. Dates . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.3. ETags . . . . . . . . . . . . . . . . . . . . . . . . . . 8 3.3. ETags . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.4. Links . . . . . . . . . . . . . . . . . . . . . . . . . . 9 3.4. Cookies . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.5. Cookies . . . . . . . . . . . . . . . . . . . . . . . . . 9 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 5. Security Considerations . . . . . . . . . . . . . . . . . . . 10
5. Security Considerations . . . . . . . . . . . . . . . . . . . 12 6. Normative References . . . . . . . . . . . . . . . . . . . . 11
6. Normative References . . . . . . . . . . . . . . . . . . . . 12 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 11
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction 1. Introduction
Structured Field Values for HTTP [STRUCTURED-FIELDS] introduced a Structured Field Values for HTTP [STRUCTURED-FIELDS] introduced a
data model with associated parsing and serialization algorithms for data model with associated parsing and serialization algorithms for
use by new HTTP field values. Fields that are defined as Structured use by new HTTP field values. Fields that are defined as Structured
Fields can realise a number of benefits, including: Fields can realise a number of benefits, including:
o Improved interoperability and security: precisely defined parsing o Improved interoperability and security: precisely defined parsing
and serialisation algorithms are typically not available for and serialisation algorithms are typically not available for
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| Vary | List | | Vary | List |
| X-Content-Type-Options | Item | | X-Content-Type-Options | Item |
| X-Frame-Options | Item | | X-Frame-Options | Item |
| X-XSS-Protection | List | | X-XSS-Protection | List |
+----------------------------------+-----------------+ +----------------------------------+-----------------+
Table 1: Compatible Fields Table 1: Compatible Fields
Note the following caveats regarding compatibility: Note the following caveats regarding compatibility:
Parsing differences: Some values may fail to parse as Structured
Fields, even though they are valid according to their originally
specified syntax. For example, HTTP parameter names are case-
insensitive (per Section 5.6.6 of [HTTP]), but Structured Fields
require them to be all-lowercase. Likewise, many Dictionary-based
fields (e.g., Cache-Control, Expect-CT, Pragma, Prefer,
Preference-Applied, Surrogate-Control) have case-insensitive keys.
Similarly, the parameters rule in HTTP (see Section 5.6.6 of
[HTTP]) allows whitespace before the ";" delimiter, but Structured
Fields does not. And, Section 5.6.4 of [HTTP] allows backslash-
escaping most characters in quoted strings, whereas Structured
Field Strings only escape "\" and DQUOTE. The vast majority of
fields seen in typical traffic do not exhibit these behaviors.
Error handling: Parsing algorithms specified (or just widely Error handling: Parsing algorithms specified (or just widely
implemented) for current HTTP headers may differ from those in implemented) for current HTTP headers may differ from those in
Structured Fields in details such as error handling. For example, Structured Fields in details such as error handling. For example,
HTTP specifies that repeated directives in the Cache-Control HTTP specifies that repeated directives in the Cache-Control
header field have a different precedence than that assigned by a header field have a different precedence than that assigned by a
Dictionary structured field (which Cache-Control is mapped to). Dictionary structured field (which Cache-Control is mapped to).
Parameter and Dictionary keys: HTTP parameter names are case-
insensitive (per Section 5.6.6 of [HTTP]), but Structured Fields
require them to be all-lowercase. Although the vast majority of
parameters seen in typical traffic are all-lowercase,
compatibility can be improved by force-lowercasing parameters when
parsing. Likewise, many Dictionary-based fields (e.g., Cache-
Control, Expect-CT, Pragma, Prefer, Preference-Applied, Surrogate-
Control) have case-insensitive keys, and compatibility can be
improved by force-lowercasing them when parsing.
Parameter delimitation: The parameters rule in HTTP (see
Section 5.6.6 of [HTTP]) allows whitespace before the ";"
delimiter, but Structured Fields does not. Compatibility can be
improved by allowing such whitespace when parsing.
String quoting: Section 5.6.4 of [HTTP] allows backslash-escaping
most characters in quoted strings, whereas Structured Field
Strings only escape "\" and DQUOTE. Compatibility can be improved
by unescaping other characters before parsing.
Token limitations: In Structured Fields, tokens are required to Token limitations: In Structured Fields, tokens are required to
begin with an alphabetic character or "*", whereas HTTP tokens begin with an alphabetic character or "*", whereas HTTP tokens
allow a wider range of characters. This prevents use of mapped allow a wider range of characters. This prevents use of mapped
values that begin with one of these characters. For example, values that begin with one of these characters. For example,
media types, field names, methods, range-units, character and media types, field names, methods, range-units, character and
transfer codings that begin with a number or special character transfer codings that begin with a number or special character
other than "*" might be valid HTTP protocol elements, but will not other than "*" might be valid HTTP protocol elements, but will not
be able to be represented as Structured Field Tokens. be able to be represented as Structured Field Tokens.
Integer limitations: Structured Fields Integers can have at most 15 Integer limitations: Structured Fields Integers can have at most 15
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Structured Field, which is a List of the structure described above. Structured Field, which is a List of the structure described above.
When a field value contains "*", it is represented as a Token. When a field value contains "*", it is represented as a Token.
Likewise, If-Match's field value can be mapped into the SF-If-Match Likewise, If-Match's field value can be mapped into the SF-If-Match
Structured Field in the same manner. Structured Field in the same manner.
For example: For example:
SF-If-None-Match: "abcdef"; w, "ghijkl", * SF-If-None-Match: "abcdef"; w, "ghijkl", *
3.4. Links 3.4. Cookies
The field value of the Link header field [RFC8288] can be mapped into
the SF-Link List Structured Field by considering the URI-Reference as
a String, and link-param as Parameters.
For example, this:
Link: </terms>; rel="copyright"; anchor="#foo"
can be mapped to:
SF-Link: "/terms"; rel="copyright"; anchor="#foo"
3.5. Cookies
The field values of the Cookie and Set-Cookie fields [COOKIES] can be The field values of the Cookie and Set-Cookie fields [COOKIES] can be
mapped into the SF-Cookie Structured Field (a List) and SF-Set-Cookie mapped into the SF-Cookie Structured Field (a List) and SF-Set-Cookie
Structured Field (a List), respectively. Structured Field (a List), respectively.
In each case, a cookie is represented as an Inner List containing two In each case, a cookie is represented as an Inner List containing two
Items; the cookie name and value. The cookie name is always a Items; the cookie name and value. The cookie name is always a
String; the cookie value is a String, unless it can be successfully String; the cookie value is a String, unless it can be successfully
parsed as the textual representation of another, bare Item structured parsed as the textual representation of another, bare Item structured
type (e.g., Byte Sequence, Decimal, Integer, Token, or Boolean). type (e.g., Byte Sequence, Decimal, Integer, Token, or Boolean).
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SF-Set-Cookie: ("lang" "en-US"); expires=@1623233894; SF-Set-Cookie: ("lang" "en-US"); expires=@1623233894;
samesite=Strict; secure samesite=Strict; secure
SF-Cookie: ("SID" "31d4d96e407aad42"), ("lang" "en-US") SF-Cookie: ("SID" "31d4d96e407aad42"), ("lang" "en-US")
4. IANA Considerations 4. IANA Considerations
Please add the following note to the "Hypertext Transfer Protocol Please add the following note to the "Hypertext Transfer Protocol
(HTTP) Field Name Registry": (HTTP) Field Name Registry":
The "Structured Type" column indicates the type of the field (per A prefix of "*" in the Structured Type column indicates that it is
RFC8941), if any, and may be "Dictionary", "List" or "Item". A a retrofit type (i.e., not natively Structured); see RFC nnnn.
prefix of "*" indicates that it is a retrofit type (i.e., not
natively Structured); see [this specification].
Note that field names beginning with characters other than ALPHA
or "*" will not be able to be represented as a Structured Fields
Token, and therefore may be incompatible with being mapped into
fields that refer to it; see [this specification].
Then, add a new column, "Structured Type", with the values from Then, add a new column, "Structured Type", with the values from
Section 2 assigned to the nominated registrations, prefixing each Section 2 assigned to the nominated registrations, prefixing each
with "*" to indicate that it is a retrofit type. with "*" to indicate that it is a retrofit type.
Then, add the field names in Table 5, with the corresponding Then, add the field names in Table 5, with the corresponding
Structured Type as indicated, a status of "permanent" and referring Structured Type as indicated, a status of "permanent" and referring
to this document. to this document.
+------------------------+-----------------+ +------------------------+-----------------+
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+------------------------+-----------------+ +------------------------+-----------------+
| SF-Content-Location | Item | | SF-Content-Location | Item |
| SF-Cookie | List | | SF-Cookie | List |
| SF-Date | Item | | SF-Date | Item |
| SF-ETag | Item | | SF-ETag | Item |
| SF-Expires | Item | | SF-Expires | Item |
| SF-If-Match | List | | SF-If-Match | List |
| SF-If-Modified-Since | Item | | SF-If-Modified-Since | Item |
| SF-If-None-Match | List | | SF-If-None-Match | List |
| SF-If-Unmodified-Since | Item | | SF-If-Unmodified-Since | Item |
| SF-Link | List |
| SF-Last-Modified | Item | | SF-Last-Modified | Item |
| SF-Location | Item | | SF-Location | Item |
| SF-Referer | Item | | SF-Referer | Item |
| SF-Set-Cookie | List | | SF-Set-Cookie | List |
+------------------------+-----------------+ +------------------------+-----------------+
Table 5: New Fields Table 5: New Fields
Then, add the indicated Structured Type for each existing registry
entry listed in Table 6.
+------------------------------------------+-----------------+
| Field Name | Structured Type |
+------------------------------------------+-----------------+
| Accept-CH | List |
| Cache-Status | List |
| CDN-Cache-Control | Dictionary |
| Cross-Origin-Embedder-Policy | Item |
| Cross-Origin-Embedder-Policy-Report-Only | Item |
| Cross-Origin-Opener-Policy | Item |
| Cross-Origin-Opener-Policy-Report-Only | Item |
| Origin-Agent-Cluster | Item |
| Priority | Dictionary |
| Proxy-Status | List |
+------------------------------------------+-----------------+
Table 6: Existing Fields
Finally, add a new column to the "Cookie Attribute Registry" Finally, add a new column to the "Cookie Attribute Registry"
established by [COOKIES] with the title "Structured Type", using established by [COOKIES] with the title "Structured Type", using
information from Table 4. information from Table 4.
5. Security Considerations 5. Security Considerations
Section 2 identifies existing HTTP fields that can be parsed and Section 2 identifies existing HTTP fields that can be parsed and
serialised with the algorithms defined in [STRUCTURED-FIELDS]. serialised with the algorithms defined in [STRUCTURED-FIELDS].
Variances from existing parser behavior might be exploitable, Variances from existing parser behavior might be exploitable,
particularly if they allow an attacker to target one implementation particularly if they allow an attacker to target one implementation
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8288] Nottingham, M., "Web Linking", RFC 8288,
DOI 10.17487/RFC8288, October 2017,
<https://www.rfc-editor.org/info/rfc8288>.
[STRUCTURED-FIELDS] [STRUCTURED-FIELDS]
Nottingham, M. and P. Kamp, "Structured Field Values for Nottingham, M. and P. Kamp, "Structured Field Values for
HTTP", draft-ietf-httpbis-sfbis-00 (work in progress), HTTP", draft-ietf-httpbis-sfbis-01 (work in progress),
November 2022. December 2022.
Author's Address Author's Address
Mark Nottingham Mark Nottingham
Prahran Prahran
Australia Australia
Email: mnot@mnot.net Email: mnot@mnot.net
URI: https://www.mnot.net/ URI: https://www.mnot.net/
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