draft-ietf-httpbis-retrofit-06.txt   draft-ietf-httpbis-retrofit-latest.txt 
HTTP Working Group M. Nottingham HTTP Working Group M. Nottingham
Internet-Draft March 31, 2023 Internet-Draft August 22, 2024
Intended status: Standards Track Intended status: Standards Track
Expires: October 2, 2023 Expires: February 23, 2025
Retrofit Structured Fields for HTTP Retrofit Structured Fields for HTTP
draft-ietf-httpbis-retrofit-06 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
having syntax that is compatible with Structured Fields, so that they whose values are compatible with Structured Fields syntax, so that
can be handled as such (subject to certain caveats). they 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 Structured Fields.
Fields. It does not specify how to negotiate their use. It does not specify how to convey them in HTTP messages.
About This Document About This Document
This note is to be removed before publishing as an RFC. This note is to be removed before publishing as an RFC.
Status information for this document may be found at Status information for this document may be found at
<https://datatracker.ietf.org/doc/draft-ietf-httpbis-retrofit/>. <https://datatracker.ietf.org/doc/draft-ietf-httpbis-retrofit/>.
Discussion of this document takes place on the HTTP Working Group Discussion of this document takes place on the HTTP Working Group
mailing list (<mailto:ietf-http-wg@w3.org>), which is archived at mailing list (<mailto:ietf-http-wg@w3.org>), which is archived at
skipping to change at page 2, line 4 skipping to change at page 2, line 4
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on October 2, 2023. This Internet-Draft will expire on February 23, 2025.
Copyright Notice Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the Copyright (c) 2024 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. Using Retrofit Structured Fields . . . . . . . . . . . . 3
2. Compatible Fields . . . . . . . . . . . . . . . . . . . . . . 3 1.2. Notational Conventions . . . . . . . . . . . . . . . . . 4
3. Mapped Fields . . . . . . . . . . . . . . . . . . . . . . . . 6 2. Compatible Fields . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Caveats . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Mapped Fields . . . . . . . . . . . . . . . . . . . . . . . . 7
3.1. URLs . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.1. URLs . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.2. Dates . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.2. Dates . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.3. ETags . . . . . . . . . . . . . . . . . . . . . . . . . . 8 3.3. ETags . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.4. Cookies . . . . . . . . . . . . . . . . . . . . . . . . . 8 3.4. Cookies . . . . . . . . . . . . . . . . . . . . . . . . . 9
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
5. Security Considerations . . . . . . . . . . . . . . . . . . . 10 5. Security Considerations . . . . . . . . . . . . . . . . . . . 11
6. Normative References . . . . . . . . . . . . . . . . . . . . 11 6. Normative References . . . . . . . . . . . . . . . . . . . . 11
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 11 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 12
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 bring advantages that include:
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
fields defined with just ABNF and/or prose. fields defined with just ABNF and/or prose.
o Reuse of common implementations: many parsers for other fields are o Reuse of common implementations: many parsers for other fields are
specific to a single field or a small family of fields. specific to a single field or a small family of fields.
o Canonical form: because a deterministic serialisation algorithm is o Canonical form: because a deterministic serialisation algorithm is
defined for each type, Structure Fields have a canonical defined for each type, Structure Fields have a canonical
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can be handled as Structured Fields, so that these benefits can be can be handled as Structured Fields, so that these benefits can be
realised -- thereby making them Retrofit Structured Fields. realised -- thereby making them Retrofit Structured Fields.
It does so using two techniques. Section 2 lists compatible fields It does so using two techniques. Section 2 lists compatible fields
-- those that can be handled as if they were Structured Fields due to -- those that can be handled as if they were Structured Fields due to
the similarity of their defined syntax to that in Structured Fields. the similarity of their defined syntax to that in Structured Fields.
Section 3 lists mapped fields -- those whose syntax needs to be Section 3 lists mapped fields -- those whose syntax needs to be
transformed into an underlying data model which is then mapped into transformed into an underlying data model which is then mapped into
that defined by Structured Fields. that defined by Structured Fields.
Note that while implementations can parse and serialise compatible 1.1. Using Retrofit Structured Fields
fields as Structured Fields subject to the caveats in Section 2, a
sender cannot generate mapped fields from Section 3 and expect them
to be understood and acted upon by the recipient without prior
negotiation. This specification does not define such a mechanism.
1.1. Notational Conventions Retrofitting data structures onto existing and widely-deployed HTTP
fields requires careful handling to assure interoperability and
security. This section highlights considerations for applications
that use Retrofit Structured Fields.
While the majority of field values seen in HTTP traffic should be
able to be parsed or mapped successfully, some will not. An
application using Retrofit Structured Fields will need to define how
unsuccessful values will be handled.
For example, an API that exposes field values using Structured Fields
data types might make the field value available as a string in cases
where the field did not successfully parse or map.
The mapped field values described in Section 3 are not compatible
with the original syntax of their fields, and so cannot be used
unless parties processing them have explicitly indicated their
support for that form of the field value. An application using
Retrofit Structured Fields will need to define how to negotiate
support for them.
For example, an alternative serialization of fields that takes
advantage of Structured Fields would need to establish an explicit
negotiation mechanism to assure that both peers would handle that
serialization appropriately before using it.
See also the security considerations in Section 5.
1.2. 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", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in "OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
2. Compatible Fields 2. Compatible Fields
The HTTP fields listed in Table 1 can usually have their values The HTTP fields listed in Table 1 have values that can be handled as
handled as Structured Fields according to the listed parsing and Structured Field Values according to the parsing and serialisation
serialisation algorithms in [STRUCTURED-FIELDS], subject to the algorithms in [STRUCTURED-FIELDS] corresponding to the listed top-
listed caveats. level type, subject to the caveats in Section 2.1.
The listed types are chosen for compatibility with the defined syntax The top-level types are chosen for compatibility with the defined
of the field as well as with actual internet traffic. However, not syntax of the field as well as with actual internet traffic.
all instances of these fields will successfully parse. This might be However, not all instances of these fields will successfully parse as
because the field value is clearly invalid, or it might be because it a Structured Field Value. This might be because the field value is
is valid but not parseable as a Structured Field. clearly invalid, or it might be because it is valid but not parseable
as a Structured Field.
An application using this specification will need to consider how to An application using this specification will need to consider how to
handle such field values. Depending on its requirements, it might be handle such field values. Depending on its requirements, it might be
advisable to reject such values, treat them as opaque strings, or advisable to reject such values, treat them as opaque strings, or
attempt to recover a structured value from them in an ad hoc fashion. attempt to recover a Structured Field Value from them in an ad hoc
fashion.
+----------------------------------+-----------------+ +----------------------------------+-----------------+
| Field Name | Structured Type | | Field Name | Structured Type |
+----------------------------------+-----------------+ +----------------------------------+-----------------+
| Accept | List | | Accept | List |
| Accept-Encoding | List | | Accept-Encoding | List |
| Accept-Language | List | | Accept-Language | List |
| Accept-Patch | List | | Accept-Patch | List |
| Accept-Post | List | | Accept-Post | List |
| Accept-Ranges | List | | Accept-Ranges | List |
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| TE | List | | TE | List |
| Timing-Allow-Origin | List | | Timing-Allow-Origin | List |
| Trailer | List | | Trailer | List |
| Transfer-Encoding | List | | Transfer-Encoding | List |
| Upgrade-Insecure-Requests | Item | | Upgrade-Insecure-Requests | Item |
| 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
2.1. Caveats
Note the following caveats regarding compatibility: Note the following caveats regarding compatibility:
Parsing differences: Some values may fail to parse as Structured Parsing differences: Some values may fail to parse as Structured
Fields, even though they are valid according to their originally Fields, even though they are valid according to their originally
specified syntax. For example, HTTP parameter names are case- specified syntax. For example, HTTP parameter names are case-
insensitive (per Section 5.6.6 of [HTTP]), but Structured Fields insensitive (per Section 5.6.6 of [HTTP]), but Structured Fields
require them to be all-lowercase. Likewise, many Dictionary-based require them to be all-lowercase. Likewise, many Dictionary-based
fields (e.g., Cache-Control, Expect-CT, Pragma, Prefer, fields (e.g., Cache-Control, Expect-CT, Pragma, Prefer,
Preference-Applied, Surrogate-Control) have case-insensitive keys. Preference-Applied, Surrogate-Control) have case-insensitive keys.
Similarly, the parameters rule in HTTP (see Section 5.6.6 of Similarly, the parameters rule in HTTP (see Section 5.6.6 of
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requirements. requirements.
Retry-After: Only the delta-seconds form of Retry-After can be Retry-After: Only the delta-seconds form of Retry-After can be
represented; a Retry-After value containing a http-date will need represented; a Retry-After value containing a http-date will need
to be converted into delta-seconds to be conveyed as a Structured to be converted into delta-seconds to be conveyed as a Structured
Field Value. Field Value.
3. Mapped Fields 3. Mapped Fields
Some HTTP field values have syntax that cannot be successfully parsed Some HTTP field values have syntax that cannot be successfully parsed
as Structured Fields. Instead, it is necessary to map them into a as Structured Field values. Instead, it is necessary to map them
separate Structured Field with an alternative name. into a Structured Field value.
For example, the Date HTTP header field carries a date: For example, the Date HTTP header field carries a date:
Date: Sun, 06 Nov 1994 08:49:37 GMT Date: Sun, 06 Nov 1994 08:49:37 GMT
Its value would be mapped to: Its value would be mapped to:
SF-Date: @784111777 @784111777
As in Section 2, these fields are unable to carry values that are not
valid Structured Fields, and so an application using this
specification will need to how to support such values. Typically,
handling them using the original field name is sufficient.
Each field name listed below indicates a replacement field name and a Unlike those listed in Section 2, these representations are not
means of mapping its original value into a Structured Field. compatible with the original fields' syntax, and MUST NOT be used
unless they are explicitly and unambiguously supported. For example,
this means that sending them to a next-hop recipient in HTTP requires
prior negotiation. This specification does not define how to do so.
3.1. URLs 3.1. URLs
The field names in Table 2 (paired with their mapped field names) The field names in Table 2 have values that can be mapped into
have values that can be mapped into Structured Fields by treating the Structured Field values by treating the original field's value as a
original field's value as a String. String.
+------------------+---------------------+ +------------------+
| Field Name | Mapped Field Name | | Field Name |
+------------------+---------------------+ +------------------+
| Content-Location | SF-Content-Location | | Content-Location |
| Location | SF-Location | | Location |
| Referer | SF-Referer | | Referer |
+------------------+---------------------+ +------------------+
Table 2: URL Fields Table 2: URL Fields
For example, this Location field For example, this Location field:
Location: https://example.com/foo Location: https://example.com/foo
could be mapped as: would have a mapped value of:
SF-Location: "https://example.com/foo" "https://example.com/foo"
3.2. Dates 3.2. Dates
The field names in Table 3 (paired with their mapped field names) The field names in Table 3 have values that can be mapped into
have values that can be mapped into Structured Fields by parsing Structured Field values by parsing their payload according to
their payload according to Section 5.6.7 of [HTTP] and representing Section 5.6.7 of [HTTP] and representing the result as a Date.
the result as a Date.
+---------------------+------------------------+ +---------------------+
| Field Name | Mapped Field Name | | Field Name |
+---------------------+------------------------+ +---------------------+
| Date | SF-Date | | Date |
| Expires | SF-Expires | | Expires |
| If-Modified-Since | SF-If-Modified-Since | | If-Modified-Since |
| If-Unmodified-Since | SF-If-Unmodified-Since | | If-Unmodified-Since |
| Last-Modified | SF-Last-Modified | | Last-Modified |
+---------------------+------------------------+ +---------------------+
Table 3: Date Fields Table 3: Date Fields
For example, an Expires field could be mapped as: For example, an Expires field's value could be mapped as:
SF-Expires: @1659578233 @1659578233
3.3. ETags 3.3. ETags
The field value of the ETag header field can be mapped into the SF- The field value of the ETag header field can be mapped into a
ETag Structured Field by representing the entity-tag as a String, and Structured Field value by representing the entity-tag as a String,
the weakness flag as a Boolean "w" parameter on it, where true and the weakness flag as a Boolean "w" parameter on it, where true
indicates that the entity-tag is weak; if 0 or unset, the entity-tag indicates that the entity-tag is weak; if 0 or unset, the entity-tag
is strong. is strong.
For example, this: For example, this ETag header field:
ETag: W/"abcdef" ETag: W/"abcdef"
SF-ETag: "abcdef"; w would have a mapped value of:
If-None-Match's field value can be mapped into the SF-If-None-Match "abcdef"; w
Structured Field, which is a List of the structure described above.
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 If-None-Match's field value can be mapped into a Structured Field
Structured Field in the same manner. value which is a List of the structure described above. When a field
value contains "*", it is represented as a Token.
For example: Likewise, If-Match's field value can be mapped into a Structured
Field value in the same manner.
SF-If-None-Match: "abcdef"; w, "ghijkl", * For example, this If-None-Match field:
If-None-Match: W/"abcdef", "ghijkl", *
would have a mapped value of:
"abcdef"; w, "ghijkl", *
3.4. Cookies 3.4. 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 Structured Fields Lists.
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).
Cookie attributes map to Parameters on the Inner List, with the Cookie attributes map to Parameters on the Inner List, with the
parameter name being forced to lowercase. Cookie attribute values parameter name being forced to lowercase. Cookie attribute values
are Strings unless a specific type is defined for them. This are Strings unless a specific type is defined for them. This
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| Path | String | | Path | String |
| Secure | Boolean | | Secure | Boolean |
| SameSite | Token | | SameSite | Token |
+----------------+-----------------+ +----------------+-----------------+
Table 4: Set-Cookie Parameter Types Table 4: Set-Cookie Parameter Types
The Expires attribute is mapped to a Date representation of parsed- The Expires attribute is mapped to a Date representation of parsed-
cookie-date (see Section 5.1.1 of [COOKIES]). cookie-date (see Section 5.1.1 of [COOKIES]).
For example, these unstructured fields: For example, this Set-Cookie field:
Set-Cookie: lang=en-US; Expires=Wed, 09 Jun 2021 10:18:14 GMT; Set-Cookie: Lang=en-US; Expires=Wed, 09 Jun 2021 10:18:14 GMT;
samesite=Strict; secure samesite=Strict; secure
Cookie: SID=31d4d96e407aad42; lang=en-US
can be mapped into: would have a mapped value of:
SF-Set-Cookie: ("lang" "en-US"); expires=@1623233894; ("Lang" "en-US"); expires=@1623233894;
samesite=Strict; secure samesite=Strict; secure
SF-Cookie: ("SID" "31d4d96e407aad42"), ("lang" "en-US")
And this Cookie field:
Cookie: SID=31d4d96e407aad42; lang=en-US
would have a mapped value of:
("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":
A prefix of "*" in the Structured Type column indicates that it is A prefix of "*" in the Structured Type column indicates that it is
a retrofit type (i.e., not natively Structured); see RFC nnnn. a retrofit type (i.e., not natively Structured); see RFC nnnn.
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
Structured Type as indicated, a status of "permanent" and referring
to this document.
+------------------------+-----------------+
| Field Name | Structured Type |
+------------------------+-----------------+
| SF-Content-Location | Item |
| SF-Cookie | List |
| SF-Date | Item |
| SF-ETag | Item |
| SF-Expires | Item |
| SF-If-Match | List |
| SF-If-Modified-Since | Item |
| SF-If-None-Match | List |
| SF-If-Unmodified-Since | Item |
| SF-Last-Modified | Item |
| SF-Location | Item |
| SF-Referer | Item |
| SF-Set-Cookie | List |
+------------------------+-----------------+
Table 5: New 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
in a chain (e.g., an intermediary). However, given the considerable in a chain (e.g., an intermediary). However, given the considerable
variance in parsers already deployed, convergence towards a single variance in parsers already deployed, convergence towards a single
parsing algorithm is likely to have a net security benefit in the parsing algorithm is likely to have a net security benefit in the
longer term. longer term.
Section 3 defines alternative representations of existing fields. Section 3 defines alternative representations of existing fields.
Because downstream consumers might interpret the message differently Because downstream consumers might interpret the message differently
based upon whether they recognise the alternative representation, based upon whether they recognise the alternative representation,
implementations are prohibited from generating such fields unless implementations are prohibited from generating such values unless
they have negotiated support for them with their peer. This they have negotiated support for them with their peer. This
specification does not define such a mechanism, but any such specification does not define such a mechanism, but any such
definition needs to consider the implications of doing so carefully. definition needs to consider the implications of doing so carefully.
6. Normative References 6. Normative References
[COOKIES] Bingler, S., West, M., and J. Wilander, "Cookies: HTTP [COOKIES] Bingler, S., West, M., and J. Wilander, "Cookies: HTTP
State Management Mechanism", draft-ietf-httpbis- State Management Mechanism", draft-ietf-httpbis-
rfc6265bis-11 (work in progress), November 2022. rfc6265bis-15 (work in progress), July 2024.
[HTTP] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, [HTTP] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP Semantics", STD 97, RFC 9110, Ed., "HTTP Semantics", STD 97, RFC 9110,
DOI 10.17487/RFC9110, June 2022, DOI 10.17487/RFC9110, June 2022,
<https://www.rfc-editor.org/info/rfc9110>. <https://www.rfc-editor.org/info/rfc9110>.
[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>.
[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-01 (work in progress), HTTP", draft-ietf-httpbis-sfbis-06 (work in progress),
December 2022. April 2024.
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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