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IETF RFC 9842
Last modified on Wednesday, October 1st, 2025
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Internet Engineering Task Force (IETF) P. Meenan, Ed.
Request for Comments: 9842 Google LLC
Category: Standards Track Y. Weiss, Ed.
ISSN: 2070-1721 Shopify Inc.
September 2025
Compression Dictionary Transport
 Abstract
This document specifies a mechanism for dictionary-based compression
in the Hypertext Transfer Protocol (HTTP). By utilizing this
technique, clients and servers can reduce the size of transmitted
data, leading to improved performance and reduced bandwidth
consumption. This document extends existing HTTP compression methods
and provides guidelines for the delivery and use of compression
dictionaries within the HTTP protocol.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/RFC 9842.
Copyright Notice
Copyright (c) 2025 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 extracted from this document must
include Revised BSD License text as described in Section 4.e of the
Trust Legal Provisions and are provided without warranty as described
in the Revised BSD License.
Table of Contents
1. Introduction
1.1. Use Cases
1.1.1. Version Upgrade
1.1.2. Common Content
1.2. Notational Conventions
2. Dictionary Negotiation
2.1. Use-As-Dictionary
2.1.1. "match"
2.1.2. "match-dest"
2.1.3. "id"
2.1.4. "type"
2.1.5. Examples
2.2. Available-Dictionary
2.2.1. Dictionary Freshness Requirement
2.2.2. Dictionary URL Matching
2.2.3. Multiple Matching Dictionaries
2.3. Dictionary-ID
3. The "compression-dictionary" Link Relation Type
4. Dictionary-Compressed Brotli
5. Dictionary-Compressed Zstandard
6. Negotiating the Content Encoding
6.1. Accept-Encoding
6.2. Content-Encoding
7. IANA Considerations
7.1. Content Encoding Registration
7.2. Header Field Registration
7.3. Link Relation Registration
8. Compatibility Considerations
9. Security Considerations
9.1. Changing Content
9.2. Reading Content
9.3. Security Mitigations
9.3.1. Cross-Origin Protection
9.3.2. Response Readability
9.3.3. Server Responsibility
10. Privacy Considerations
11. References
11.1. Normative References
11.2. Informative References
Authors' Addresses
1. Introduction
This specification defines a mechanism for using designated HTTP
[HTTP] responses as an external dictionary for future HTTP responses
for compression schemes that support using external dictionaries
(e.g., Brotli [RFC 7932] and Zstandard [ZSTD]).
This document describes the HTTP headers used for negotiating
dictionary usage and registers content-encoding values for
compressing with Brotli and Zstandard using a negotiated dictionary.
The negotiation of dictionary usage leverages HTTP's content
negotiation (see Section 12 of [HTTP]) and is usable with all
versions of HTTP.
1.1. Use Cases
Any HTTP response can be specified for use as a compression
dictionary for future HTTP requests, which provides a lot of
flexibility. Two common use cases that are seen frequently are
described below.
1.1.1. Version Upgrade
Using a previous version of a resource as a dictionary for a newer
version enables delivery of a delta-compressed version of the
changes, usually resulting in significantly smaller responses than
what can be achieved by compression alone.
For example:
Client Server
| |
| GET /app.v1.js |
|------------------------------------------------->|
| |
| 200 OK |
| Use-As-Dictionary: match="/app*js" |
| <full app.v1.js resource - 100KB compressed> |
|<-------------------------------------------------|
| |
Some time later ...
Client Server
| |
| GET /app.v2.js |
| Available-Dictionary: :pZGm1A...2a2fFG4=: |
| Accept-Encoding: gzip, br, zstd, dcb, dcz |
|------------------------------------------------->|
| |
| 200 OK |
| Content-Encoding: dcb |
| <delta-compressed app.v2.js resource - 1KB> |
|<-------------------------------------------------|
| |
Figure 1: Version Upgrade Example
1.1.2. Common Content
If several resources share common patterns in their responses, then
it can be useful to reference an external dictionary that contains
those common patterns, effectively compressing them out of the
responses. Some examples of this are common template HTML for
similar pages across a site and common keys and values in API calls.
For example:
Client Server
| |
| GET /index.html |
|--------------------------------------------------->|
| |
| 200 OK |
| Link: <.../dict>; rel="compression-dictionary" |
| <full index.html resource - 100KB compressed> |
|<---------------------------------------------------|
| |
| GET /dict |
|--------------------------------------------------->|
| |
| 200 OK |
| Use-As-Dictionary: match="/*html" |
|<---------------------------------------------------|
| |
Some time later ...
Client Server
| |
| GET /page2.html |
| Available-Dictionary: :pZGm1A...2a2fFG4=: |
| Accept-Encoding: gzip, br, zstd, dcb, dcz |
|--------------------------------------------------->|
| |
| 200 OK |
| Content-Encoding: dcb |
| <delta-compressed page2.html resource - 10KB> |
|<---------------------------------------------------|
| |
Figure 2: Common Content Example
1.2. Notational Conventions
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 [RFC 2119] [RFC 8174] when, and only when, they appear in all
capitals, as shown here.
This document uses the following terminology from Section 3 of
[STRUCTURED-FIELDS] to specify syntax and parsing: Dictionary,
String, Inner List, Token, and Byte Sequence.
This document uses the line folding strategies described in
[FOLDING].
This document also uses terminology from [HTTP] and [HTTP-CACHING].
2. Dictionary Negotiation
2.1. Use-As-Dictionary
When responding to an HTTP Request, a server can advertise that the
response can be used as a dictionary for future requests for URLs
that match the rules specified in the "Use-As-Dictionary" response
header.
The "Use-As-Dictionary" response header is a Structured Field
[STRUCTURED-FIELDS] Dictionary with values for "match", "match-dest",
"id", and "type".
2.1.1. "match"
The "match" value of the "Use-As-Dictionary" response header is a
String value that provides the URL Pattern to use for request
matching (see [URLPATTERN]).
The URL Pattern used for matching does not support using regular
expressions.
The following algorithm is used to validate that a given String value
is a valid URL Pattern that does not use regular expressions and is
for the same Origin (Section 4.3.1 of [HTTP]) as the dictionary. It
will return TRUE for a valid match pattern and FALSE for an invalid
pattern that MUST NOT be used.
1. Let MATCH be the value of "match" for the given dictionary.
2. Let URL be the URL of the dictionary request.
3. Let PATTERN be a "URL pattern struct" created by running the
steps to "create a URL pattern" by setting input=MATCH and
baseURL=URL (see Section 1.4 of [URLPATTERN]).
4. If the result of running the "has regexp groups" steps for
PATTERN returns TRUE, then return FALSE (see the last list in
Section 1.4 of [URLPATTERN]).
5. Return TRUE.
The "match" value is required and MUST be included in the "Use-As-
Dictionary" response header for the dictionary to be considered
valid.
Operating at the HTTP level, the specified match patterns will
operate on the percent-encoded version of the URL path (see Section 2
of [URL]).
For example, the URL "http://www.example.com/düsseldorf" would be
encoded as "http://www.example.com/d%C3%BCsseldorf" and a relevant
match pattern would be:
Use-As-Dictionary: match="/d%C3%BCsseldorf"
2.1.2. "match-dest"
The "match-dest" value of the "Use-As-Dictionary" response header is
an Inner List of String values that provides a list of Fetch request
destinations for the dictionary to match (see "RequestDestination" in
Section 5.4 of [FETCH]).
An empty list for "match-dest" MUST match all destinations.
For clients that do not support request destinations, the client MUST
treat it as an empty list and match all destinations.
The "match-dest" value is optional and defaults to an empty list.
2.1.3. "id"
The "id" value of the "Use-As-Dictionary" response header is a String
value that specifies a server identifier for the dictionary. If an
"id" value is present and has a string length longer than zero, then
it MUST be sent to the server in a "Dictionary-ID" request header
when the client sends an "Available-Dictionary" request header for
the same dictionary (see Section 2.2).
The server identifier MUST be treated as an opaque string by the
client.
The server identifier MUST NOT be relied upon by the server to
guarantee the contents of the dictionary. The dictionary hash MUST
be validated before use.
The "id" value string length (after any decoding) supports up to 1024
characters.
The "id" value is optional and defaults to the empty string.
2.1.4. "type"
The "type" value of the "Use-As-Dictionary" response header is a
Token value that describes the file format of the supplied
dictionary.
"raw" is defined as a dictionary format that represents an
unformatted blob of bytes suitable for any compression scheme to use.
If a client receives a dictionary with a type that it does not
understand, it MUST NOT use the dictionary.
The "type" value is optional and defaults to "raw".
2.1.5. Examples
2.1.5.1. Path Prefix
A response that contained a response header (as shown below) would
specify matching any document request for a URL with a path prefix of
/product/ on the same Origin (Section 4.3.1 of [HTTP]) as the
original request:
NOTE: '\' line wrapping per RFC 8792
Use-As-Dictionary: \
match="/product/*", match-dest=("document")
2.1.5.2. Versioned Directories
A response that contained a response header (as shown below) would
match any path that starts with "/app/" and ends with "/main.js":
Use-As-Dictionary: match="/app/*/main.js"
2.2. Available-Dictionary
When an HTTP client makes a request for a resource for which it has
an appropriate dictionary, it can add an "Available-Dictionary"
request header to the request to indicate to the server that it has a
dictionary available to use for compression.
The "Available-Dictionary" request header is a Structured Field
[STRUCTURED-FIELDS] Byte Sequence containing the SHA-256 [SHA-256]
hash of the contents of a single available dictionary.
The client MUST only send a single "Available-Dictionary" request
header with a single hash value for the best available match that it
has available.
For example:
Available-Dictionary: :pZGm1Av0IEBKARczz7exkNYsZb8LzaMrV7J32a2fFG4=:
2.2.1. Dictionary Freshness Requirement
To be considered as a match, the dictionary resource MUST be either
fresh [HTTP-CACHING] or allowed to be served stale (see [RFC 5861]).
2.2.2. Dictionary URL Matching
When a dictionary is stored as a result of a "Use-As-Dictionary"
directive, it includes a "match" string and an optional "match-dest"
string that are used to match an outgoing request from a client to
the available dictionaries.
To see if an outbound request matches a given dictionary, the
following algorithm will return TRUE for a successful match and FALSE
for no-match:
1. If the current client supports request destinations and a "match-
dest" string was provided with the dictionary:
* Let DEST be the value of "match-dest" for the given
dictionary.
* Let REQUEST_DEST be the value of the destination for the
current request.
* If DEST is not an empty list and if REQUEST_DEST is not in the
DEST list of destinations, return FALSE.
2. Let BASEURL be the URL of the dictionary request.
3. Let URL represent the URL of the outbound request being checked.
4. If the Origin of BASEURL and the Origin of URL are not the same,
return FALSE (see Section 4.3.1 of [HTTP]).
5. Let MATCH be the value of "match" for the given dictionary.
6. Let PATTERN be a "URL pattern struct" created by running the
steps to "create a URL pattern" by setting input=MATCH and
baseURL=URL (see Section 1.4 of [URLPATTERN]).
7. Return the result of running the "match" steps on PATTERN with
input=URL, which will check for a match between the request URL
and the supplied "match" string (see "Match" in Section 1.4 of
[URLPATTERN]).
2.2.3. Multiple Matching Dictionaries
When there are multiple dictionaries that match a given request URL,
the client MUST pick a single dictionary using the following rules:
1. For clients that support request destinations, a dictionary that
specifies and matches a "match-dest" takes precedence over a
match that does not use a destination.
2. Given equivalent destination precedence, the dictionary with the
longest "match" takes precedence.
3. Given equivalent destination and match length precedence, the
most recently fetched dictionary takes precedence.
2.3. Dictionary-ID
When an HTTP client makes a request for a resource for which it has
an appropriate dictionary and the dictionary was stored with a
server-provided "id" in the "Use-As-Dictionary" response header, the
client MUST echo the stored "id" in a "Dictionary-ID" request header.
The "Dictionary-ID" request header is a Structured Field
[STRUCTURED-FIELDS] String of up to 1024 characters (after any
decoding) and MUST be identical to the server-provided "id".
For example, given an HTTP response that set a dictionary ID:
Use-As-Dictionary: match="/app/*/main.js", id="dictionary-12345"
A future request that matches the given dictionary will include both
the hash and the ID:
Available-Dictionary: :pZGm1Av0IEBKARczz7exkNYsZb8LzaMrV7J32a2fFG4=:
Dictionary-ID: "dictionary-12345"
3. The "compression-dictionary" Link Relation Type
This specification defines the "compression-dictionary" link relation
type [WEB-LINKING] that provides a mechanism for an HTTP response to
provide a URL for a compression dictionary that is related to but not
directly used by the current HTTP response.
The "compression-dictionary" link relation type indicates that
fetching and caching the specified resource is likely to be
beneficial for future requests. The response to some of those future
requests likely have the ability to use the indicated resource as a
compression dictionary.
Clients can fetch the provided resource at a time that they determine
would be appropriate.
The response to the fetch for the compression dictionary needs to
include a "Use-As-Dictionary" response header and a caching response
header for it to be usable as a compression dictionary. The link
relation only provides the mechanism for triggering the fetch of the
dictionary.
The following example shows a link to a resource at
https://example.org/dict.dat that is expected to produce a
compression dictionary:
Link: <https://example.org/dict.dat>; rel="compression-dictionary"
4. Dictionary-Compressed Brotli
The "dcb" content encoding identifies a resource that is a
"Dictionary-Compressed Brotli" stream.
A "Dictionary-Compressed Brotli" stream has a fixed header that is
followed by a Shared Brotli [SHARED-BROTLI] stream. The header
consists of a fixed 4-byte sequence and a 32-byte hash of the
external dictionary that was used. The Shared Brotli stream is
created using the referenced external dictionary and a compression
window that is at most 16 MB in size.
The dictionary used for the "dcb" content encoding is a "raw"
dictionary type as defined in Section 2.1.4 and is treated as a
prefix dictionary as defined in Section 8.2 of [SHARED-BROTLI].
The 36-byte fixed header is as follows:
Magic_Number: 4 fixed bytes -- 0xff, 0x44, 0x43, 0x42.
SHA_256_Hash: 32 bytes. SHA-256 hash digest of the dictionary
[SHA-256].
Clients that announce support for dcb content encoding MUST be able
to decompress resources that were compressed with a window size of up
to 16 MB.
With Brotli compression, the full dictionary is available during
compression and decompression independent of the compression window,
allowing for delta-compression of resources larger than the
compression window.
5. Dictionary-Compressed Zstandard
The "dcz" content encoding identifies a resource that is a
"Dictionary-Compressed Zstandard" stream.
A "Dictionary-Compressed Zstandard" stream is a binary stream that
starts with a 40-byte fixed header and is followed by a Zstandard
[ZSTD] stream of the response that has been compressed with an
external dictionary.
The dictionary used for the "dcz" content encoding is a "raw"
dictionary type as defined in Section 2.1.4 and is treated as a raw
dictionary as per Section 5 of [ZSTD].
The 40-byte header consists of a fixed 8-byte sequence followed by
the 32-byte SHA-256 hash of the external dictionary that was used to
compress the resource:
Magic_Number: 8 fixed bytes -- 0x5e, 0x2a, 0x4d, 0x18, 0x20, 0x00,
0x00, 0x00.
SHA_256_Hash: 32 bytes. SHA-256 hash digest of the dictionary
[SHA-256].
The 40-byte header is a Zstandard skippable frame (little-endian
0x184D2A5E) with a 32-byte length (little-endian 0x00000020) that is
compatible with existing Zstandard decoders.
Clients that announce support for dcz content encoding MUST be able
to decompress resources that were compressed with a window size of at
least 8 MB or 1.25 times the size of the dictionary, whichever is
greater, up to a maximum of 128 MB.
The window size used will be encoded in the content (currently, this
can be expressed in powers of two only) and it MUST be lower than
this limit. An implementation MAY treat a window size that exceeds
the limit as a decoding error.
With Zstandard compression, the full dictionary is available during
compression and decompression until the size of the input exceeds the
compression window. Beyond that point, the dictionary becomes
unavailable. Using a compression window that is 1.25 times the size
of the dictionary allows for full delta compression of resources that
have grown by 25% between releases while still giving the client
control over the memory it will need to allocate for a given
response.
6. Negotiating the Content Encoding
When a compression dictionary is available to compress the response
to a given request, the encoding to be used is negotiated through the
regular mechanism for negotiating content encoding in HTTP through
the "Accept-Encoding" request header and "Content-Encoding" response
header.
The dictionary to use is negotiated separately and advertised in the
"Available-Dictionary" request header.
6.1. Accept-Encoding
When a dictionary is available for use on a given request and the
client chooses to make dictionary-based content encoding available,
the client adds the dictionary-aware content encodings that it
supports to the "Accept-Encoding" request header. For example:
Accept-Encoding: gzip, deflate, br, zstd, dcb, dcz
When a client does not have a stored dictionary that matches the
request or chooses not to use one for the request, the client MUST
NOT send its dictionary-aware content encodings in the "Accept-
Encoding" request header.
6.2. Content-Encoding
If a server supports one of the dictionary encodings advertised by
the client and chooses to compress the content of the response using
the dictionary that the client has advertised, then it sets the
"Content-Encoding" response header to the appropriate value for the
algorithm selected. For example:
Content-Encoding: dcb
If the response is cacheable, it MUST include a "Vary" header to
prevent caches from serving dictionary-compressed resources to
clients that don't support them or serving the response compressed
with the wrong dictionary. For example:
Vary: accept-encoding, available-dictionary
7. IANA Considerations
7.1. Content Encoding Registration
IANA has added the following entries to the "HTTP Content Coding
Registry" maintained at <https://www.iana.org/assignments/http-
parameters/>:
Name: dcb
Description: "Dictionary-Compressed Brotli" data format.
Reference: RFC 9842, Section 4
Name: dcz
Description: "Dictionary-Compressed Zstandard" data format.
Reference: RFC 9842, Section 5
7.2. Header Field Registration
IANA has added the following entries to the "Hypertext Transfer
Protocol (HTTP) Field Name Registry" maintained at
<https://www.iana.org/assignments/http-fields/>:
+======================+===========+=======================+
| Field Name | Status | Reference |
+======================+===========+=======================+
| Use-As-Dictionary | permanent | RFC 9842, Section 2.1 |
+----------------------+-----------+-----------------------+
| Available-Dictionary | permanent | RFC 9842, Section 2.2 |
+----------------------+-----------+-----------------------+
| Dictionary-ID | permanent | RFC 9842, Section 2.3 |
+----------------------+-----------+-----------------------+
Table 1
7.3. Link Relation Registration
IANA has added the following entry to the "Link Relation Types"
registry maintained at <https://www.iana.org/assignments/link-
relations/>:
Relation Name: compression-dictionary
Description: Refers to a compression dictionary used for content
encoding.
Reference: RFC 9842, Section 3
8. Compatibility Considerations
It is not unusual for devices to be on the network path that
intercept, inspect, and process HTTP requests (web proxies,
firewalls, intrusion detection systems, etc.). To minimize the risk
of these devices incorrectly processing dictionary-compressed
responses, compression dictionary transport MUST only be used in
secure contexts (HTTPS).
9. Security Considerations
The security considerations for Brotli [RFC 7932], Shared Brotli
[SHARED-BROTLI], and Zstandard [ZSTD] apply to the dictionary-based
versions of the respective algorithms.
9.1. Changing Content
The dictionary must be treated with the same security precautions as
the content because a change to the dictionary can result in a change
to the decompressed content.
The dictionary is validated using an SHA-256 hash of the content to
make sure that the client and server are both using the same
dictionary. The strength of the SHA-256 hash algorithm isn't
explicitly needed to counter attacks since the dictionary is being
served from the same origin as the content. That said, if a weakness
is discovered in SHA-256 and it is determined that the dictionary
negotiation should use a different hash algorithm, the "Use-As-
Dictionary" response header can be extended to specify a different
algorithm and the server would just ignore any "Available-Dictionary"
requests that do not use the updated hash.
9.2. Reading Content
The compression attacks in Section 2.6 of [RFC 7457] show that it's a
bad idea to compress data from mixed (e.g., public and private)
sources. The data sources include not only the compressed data but
also the dictionaries. For example, if secret cookies are compressed
using a public-data-only dictionary, information about the cookies is
still leaked.
The dictionary can reveal information about the compressed data and
vice versa. That is, data compressed with the dictionary can reveal
contents of the dictionary when an adversary can control parts of the
data to compress and see the compressed size. On the other hand, if
the adversary can control the dictionary, the adversary can learn
information about the compressed data.
9.3. Security Mitigations
If any of the mitigations do not pass, the client MUST drop the
response and return an error.
9.3.1. Cross-Origin Protection
To make sure that a dictionary can only impact content from the same
origin where the dictionary was served, the URL Pattern used for
matching a dictionary to requests (Section 2.1.1) is guaranteed to be
for the same origin that the dictionary is served from.
9.3.2. Response Readability
For clients, like web browsers, that provide additional protection
against the readability of the payload of a response and against user
tracking, additional protections MUST be taken to make sure that the
use of dictionary-based compression does not reveal information that
would not otherwise be available.
In these cases, dictionary compression MUST only be used when both
the dictionary and the compressed response are fully readable by the
client.
In browser terms, that means either the dictionary and compressed
response are same-origin to the context they are being fetched from
or the response is cross-origin and passes the Cross-Origin Resource
Sharing (CORS) check (see Section 4.9 of [FETCH]).
9.3.3. Server Responsibility
As with any usage of compressed content in a secure context, a
potential timing attack exists if the attacker can control any part
of the dictionary or if it can read the dictionary and control any
part of the content being compressed while performing multiple
requests that vary the dictionary or injected content. Under such an
attack, the changing size or processing time of the response reveals
information about the content, which might be sufficient to read the
supposedly secure response.
In general, a server can mitigate such attacks by preventing
variations per request, as in preventing active use of multiple
dictionaries for the same content, disabling compression when any
portion of the content comes from uncontrolled sources, and securing
access and control over the dictionary content in the same way as the
response content. In addition, the following requirements on a
server are intended to disable dictionary-aware compression when the
client provides CORS request header fields that indicate a cross-
origin request context.
The following algorithm will return FALSE for cross-origin requests
where precautions such as not using dictionary-based compression
should be considered:
1. If there is no "Sec-Fetch-Site" request header, return TRUE.
2. If the value of the "Sec-Fetch-Site" request header is "same-
origin", return TRUE.
3. If there is no "Sec-Fetch-Mode" request header, return TRUE.
4. If the value of the "Sec-Fetch-Mode" request header is "navigate"
or "same-origin", return TRUE.
5. If the value of the "Sec-Fetch-Mode" request header is "cors":
* If the response does not include an "Access-Control-Allow-
Origin" response header, return FALSE.
* If the request does not include an "Origin" request header,
return FALSE.
* If the value of the "Access-Control-Allow-Origin" response
header is "*", return TRUE.
* If the value of the "Access-Control-Allow-Origin" response
header matches the value of the "Origin" request header,
return TRUE.
6. Return FALSE.
10. Privacy Considerations
Since dictionaries are advertised in future requests using the hash
of the content of the dictionary, it is possible to abuse the
dictionary to turn it into a tracking cookie.
To mitigate any additional tracking concerns, clients MUST treat
dictionaries in the same way that they treat cookies [RFC 6265]. This
includes partitioning the storage using partitioning similar to or
stricter than the partitioning used for cookies, as well as clearing
the dictionaries whenever cookies are cleared.
11. References
11.1. Normative References
[FETCH] WHATWG, "Fetch Standard", WHATWG Living Standard,
<https://fetch.spec.whatwg.org/>. Commit snapshot:
<https://fetch.spec.whatwg.org/commit-
snapshots/5a9680638ebfc2b3b7f4efb2bef0b579a2663951/>
[FOLDING] Watsen, K., Auerswald, E., Farrel, A., and Q. Wu,
"Handling Long Lines in Content of Internet-Drafts and
RFCs", RFC 8792, DOI 10.17487/RFC 8792, June 2020,
<https://www.rfc-editor.org/info/RFC 8792>.
[HTTP] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP Semantics", STD 97, RFC 9110,
DOI 10.17487/RFC 9110, June 2022,
<https://www.rfc-editor.org/info/RFC 9110>.
[HTTP-CACHING]
Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP Caching", STD 98, RFC 9111,
DOI 10.17487/RFC 9111, June 2022,
<https://www.rfc-editor.org/info/RFC 9111>.
[RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC 2119, March 1997,
<https://www.rfc-editor.org/info/RFC 2119>.
[RFC 8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC 8174,
May 2017, <https://www.rfc-editor.org/info/RFC 8174>.
[SHA-256] Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms
(SHA and SHA-based HMAC and HKDF)", RFC 6234,
DOI 10.17487/RFC 6234, May 2011,
<https://www.rfc-editor.org/info/RFC 6234>.
[SHARED-BROTLI]
Alakuijala, J., Duong, T., Kliuchnikov, E., Szabadka, Z.,
and L. Vandevenne, Ed., "Shared Brotli Compressed Data
Format", RFC 9841, DOI 10.17487/RFC 9841, September 2025,
<https://www.rfc-editor.org/info/RFC 9841>.
[STRUCTURED-FIELDS]
Nottingham, M. and P. Kamp, "Structured Field Values for
HTTP", RFC 9651, DOI 10.17487/RFC 9651, September 2024,
<https://www.rfc-editor.org/info/RFC 9651>.
[URL] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC 3986, January 2005,
<https://www.rfc-editor.org/info/RFC 3986>.
[URLPATTERN]
WHATWG, "URL Pattern Standard", WHATWG Living Standard,
<https://urlpattern.spec.whatwg.org/>. Commit snapshot:
<https://urlpattern.spec.whatwg.org/commit-
snapshots/696b4029d52e5854044bac6b72cdb198cb962ed0/>
[WEB-LINKING]
Nottingham, M., "Web Linking", RFC 8288,
DOI 10.17487/RFC 8288, October 2017,
<https://www.rfc-editor.org/info/RFC 8288>.
[ZSTD] Collet, Y. and M. Kucherawy, Ed., "Zstandard Compression
and the 'application/zstd' Media Type", RFC 8878,
DOI 10.17487/RFC 8878, February 2021,
<https://www.rfc-editor.org/info/RFC 8878>.
11.2. Informative References
[RFC 5861] Nottingham, M., "HTTP Cache-Control Extensions for Stale
Content", RFC 5861, DOI 10.17487/RFC 5861, May 2010,
<https://www.rfc-editor.org/info/RFC 5861>.
[RFC 6265] Barth, A., "HTTP State Management Mechanism", RFC 6265,
DOI 10.17487/RFC 6265, April 2011,
<https://www.rfc-editor.org/info/RFC 6265>.
[RFC 7457] Sheffer, Y., Holz, R., and P. Saint-Andre, "Summarizing
Known Attacks on Transport Layer Security (TLS) and
Datagram TLS (DTLS)", RFC 7457, DOI 10.17487/RFC 7457,
February 2015, <https://www.rfc-editor.org/info/RFC 7457>.
[RFC 7932] Alakuijala, J. and Z. Szabadka, "Brotli Compressed Data
Format", RFC 7932, DOI 10.17487/RFC 7932, July 2016,
<https://www.rfc-editor.org/info/RFC 7932>.
Authors' Addresses
Patrick Meenan (editor)
Google LLC
Email: pmeenan@google.com
Yoav Weiss (editor)
Shopify Inc.
Email: yoav.weiss@shopify.com
RFC TOTAL SIZE: 35626 bytes
PUBLICATION DATE: Wednesday, October 1st, 2025
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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