draft-ietf-httpbis-header-structure-02.txt   draft-ietf-httpbis-header-structure-03.txt 
HTTP Working Group M. Nottingham HTTP M. Nottingham
Internet-Draft Fastly Internet-Draft Fastly
Intended status: Standards Track P-H. Kamp Intended status: Standards Track P-H. Kamp
Expires: May 31, 2018 The Varnish Cache Project Expires: August 5, 2018 The Varnish Cache Project
November 27, 2017 February 1, 2018
Structured Headers for HTTP Structured Headers for HTTP
draft-ietf-httpbis-header-structure-02 draft-ietf-httpbis-header-structure-03
Abstract Abstract
This document describes Structured Headers, a way of simplifying HTTP This document describes a set of data types and parsing algorithms
header field definition and parsing. It is intended for use by new associated with them that are intended to make it easier and safer to
specifications of HTTP header fields. This includes revisions of define and handle HTTP header fields. It is intended for use by new
existing specifications when doing so does not cause interoperability specifications of HTTP header fields as well as revisions of existing
issues. header field specifications when doing so does not cause
interoperability issues.
Note to Readers Note to Readers
_RFC EDITOR: please remove this section before publication_
Discussion of this draft takes place on the HTTP working group Discussion of this draft takes place on the HTTP working group
mailing list (ietf-http-wg@w3.org), which is archived at mailing list (ietf-http-wg@w3.org), which is archived at
https://lists.w3.org/Archives/Public/ietf-http-wg/ [1]. https://lists.w3.org/Archives/Public/ietf-http-wg/ [1].
_RFC EDITOR: please remove this section before publication_
Working Group information can be found at https://httpwg.github.io/ Working Group information can be found at https://httpwg.github.io/
[2]; source code and issues list for this draft can be found at [2]; source code and issues list for this draft can be found at
https://github.com/httpwg/http-extensions/labels/header-structure https://github.com/httpwg/http-extensions/labels/header-structure
[3]. [3].
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on May 31, 2018. This Internet-Draft will expire on August 5, 2018.
Copyright Notice Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
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the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Notational Conventions . . . . . . . . . . . . . . . . . 3
2. Specifying Structured Headers . . . . . . . . . . . . . . . . 4
3. Parsing Text into Structured Headers . . . . . . . . . . . . 5
4. Structured Header Data Types . . . . . . . . . . . . . . . . 6
4.1. Dictionaries . . . . . . . . . . . . . . . . . . . . . . 6
4.2. Lists . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.3. Parameterised Labels . . . . . . . . . . . . . . . . . . 9
4.4. Items . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.5. Integers . . . . . . . . . . . . . . . . . . . . . . . . 11
4.6. Floats . . . . . . . . . . . . . . . . . . . . . . . . . 11
4.7. Strings . . . . . . . . . . . . . . . . . . . . . . . . . 12
4.8. Labels . . . . . . . . . . . . . . . . . . . . . . . . . 14
4.9. Binary Content . . . . . . . . . . . . . . . . . . . . . 15
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
6. Security Considerations . . . . . . . . . . . . . . . . . . . 16
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
7.1. Normative References . . . . . . . . . . . . . . . . . . 16
7.2. Informative References . . . . . . . . . . . . . . . . . 17
7.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Appendix A. Changes . . . . . . . . . . . . . . . . . . . . . . 17
A.1. Since draft-ietf-httpbis-header-structure-02 . . . . . . 17
A.2. Since draft-ietf-httpbis-header-structure-01 . . . . . . 18
A.3. Since draft-ietf-httpbis-header-structure-00 . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18
1. Introduction 1. Introduction
Specifying the syntax of new HTTP header fields is an onerous task; Specifying the syntax of new HTTP header fields is an onerous task;
even with the guidance in [RFC7231], Section 8.3.1, there are many even with the guidance in [RFC7231], Section 8.3.1, there are many
decisions - and pitfalls - for a prospective HTTP header field decisions - and pitfalls - for a prospective HTTP header field
author. author.
Likewise, bespoke parsers often need to be written for specific HTTP Once a header field is defined, bespoke parsers for it often need to
headers, because each has slightly different handling of what looks be written, because each header has slightly different handling of
like common syntax. what looks like common syntax.
This document introduces structured HTTP header field values This document introduces structured HTTP header field values
(hereafter, Structured Headers) to address these problems. (hereafter, Structured Headers) to address these problems.
Structured Headers define a generic, abstract model for data, along Structured Headers define a generic, abstract model for header field
with a concrete serialisation for expressing that model in textual values, along with a concrete serialisation for expressing that model
HTTP headers, as used by HTTP/1 [RFC7230] and HTTP/2 [RFC7540]. in textual HTTP headers, as used by HTTP/1 [RFC7230] and HTTP/2
[RFC7540].
HTTP headers that are defined as Structured Headers use the types HTTP headers that are defined as Structured Headers use the types
defined in this specification to define their syntax and basic defined in this specification to define their syntax and basic
handling rules, thereby simplifying both their definition and handling rules, thereby simplifying both their definition and
parsing. parsing.
Additionally, future versions of HTTP can define alternative Additionally, future versions of HTTP can define alternative
serialisations of the abstract model of Structured Headers, allowing serialisations of the abstract model of Structured Headers, allowing
headers that use it to be transmitted more efficiently without being headers that use it to be transmitted more efficiently without being
redefined. redefined.
Note that it is not a goal of this document to redefine the syntax of Note that it is not a goal of this document to redefine the syntax of
existing HTTP headers; the mechanisms described herein are only existing HTTP headers; the mechanisms described herein are only
intended to be used with headers that explicitly opt into them. intended to be used with headers that explicitly opt into them.
To specify a header field that uses Structured Headers, see To specify a header field that uses Structured Headers, see
Section 2. Section 2.
Section 4 defines a number of abstract data types that can be used in Section 4 defines a number of abstract data types that can be used in
Structured Headers, of which only three are allowed at the "top" Structured Headers. Dictionaries and lists are only usable at the
level: lists, dictionaries, or items. "top" level, while the remaining types can be specified appear at the
top level or inside those structures.
Those abstract types can be serialised into textual headers - such as Those abstract types can be serialised into textual headers - such as
those used in HTTP/1 and HTTP/2 - using the algorithms described in those used in HTTP/1 and HTTP/2 - using the algorithms described in
Section 3. Section 3.
1.1. Notational Conventions 1.1. 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 BCP "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
This document uses the Augmented Backus-Naur Form (ABNF) notation of This document uses the Augmented Backus-Naur Form (ABNF) notation of
[RFC5234], including the DIGIT, ALPHA and DQUOTE rules from that [RFC5234], including the DIGIT, ALPHA and DQUOTE rules from that
document. It also includes the OWS rule from [RFC7230]. document. It also includes the OWS rule from [RFC7230].
2. Specifying Structured Headers 2. Specifying Structured Headers
HTTP headers that use Structured Headers need to be defined to do so A HTTP header that uses Structured Headers need to be defined to do
explicitly; recipients and generators need to know that the so explicitly; recipients and generators need to know that the
requirements of this document are in effect. The simplest way to do requirements of this document are in effect. The simplest way to do
that is by referencing this document in its definition. that is by referencing this document in its definition.
The field's definition will also need to specify the field-value's The field's definition will also need to specify the field-value's
allowed syntax, in terms of the types described in Section 4, along allowed syntax, in terms of the types described in Section 4, along
with their associated semantics. with their associated semantics.
Field definitions MUST NOT relax or otherwise modify the requirements A header field definition cannot relax or otherwise modify the
of this specification; doing so would preclude handling by generic requirements of this specification; doing so would preclude handling
software. by generic software.
However, field definitions are encouraged to clearly state additional However, header field authors are encouraged to clearly state
constraints upon the syntax, as well as the consequences when those additional constraints upon the syntax, as well as the consequences
constraints are violated. when those constraints are violated. Such additional constraints
could include additional structure (e.g., a list of URLs [RFC3986]
inside a string) that cannot be expressed using the primitives
defined here.
For example: For example:
# FooExample Header # FooExample Header
The FooExample HTTP header field conveys a list of numbers about how The FooExample HTTP header field conveys a list of integers about how
much Foo the sender has. much Foo the sender has.
FooExample is a Structured header [RFCxxxx]. Its value MUST be a FooExample is a Structured header [RFCxxxx]. Its value MUST be a
dictionary ([RFCxxxx], Section Y.Y). dictionary ([RFCxxxx], Section Y.Y).
The dictionary MUST contain: The dictionary MUST contain:
* A member whose key is "foo", and whose value is an integer * A member whose key is "foo", and whose value is an integer
([RFCxxxx], Section Y.Y), indicating the number of foos in ([RFCxxxx], Section Y.Y), indicating the number of foos in
the message. the message.
* A member whose key is "bar", and whose value is a string * A member whose key is "barUrls", and whose value is a string
([RFCxxxx], Section Y.Y), conveying the characteristic bar-ness ([RFCxxxx], Section Y.Y), conveying the Bar URLs for the message.
of the message. See below for processing requirements.
If the parsed header field does not contain both, it MUST be ignored. If the parsed header field does not contain both, it MUST be ignored.
"barUrls" contains a space-separated list of URI-references ([RFC3986],
Section 4.1):
barURLs = URI-reference *( 1*SP URI-reference )
If a member of barURLs is not a valid URI-reference, it MUST be ignored.
If a member of barURLs is a relative reference ([RFC3986], Section 4.2),
it MUST be resolved ([RFC3986], Section 5) before being used.
Note that empty header field values are not allowed by the syntax, Note that empty header field values are not allowed by the syntax,
and therefore will be considered errors. and therefore will be considered errors.
3. Parsing Requirements for Textual Headers 3. Parsing Text into Structured Headers
When a receiving implementation parses textual HTTP header fields When a receiving implementation parses textual HTTP header fields
(e.g., in HTTP/1 or HTTP/2) that are known to be Structured Headers, (e.g., in HTTP/1 or HTTP/2) that are known to be Structured Headers,
it is important that care be taken, as there are a number of edge it is important that care be taken, as there are a number of edge
cases that can cause interoperability or even security problems. cases that can cause interoperability or even security problems.
This section specifies the algorithm for doing so. This section specifies the algorithm for doing so.
Given an ASCII string input_string that represents the chosen Given an ASCII string input_string that represents the chosen
header's field-value, return the parsed header value. Note that header's field-value, return the parsed header value.
input_string may incorporate multiple header lines combined into one
comma-separated field-value, as per [RFC7230], Section 3.2.2.
1. Discard any OWS from the beginning of input_string. 1. Discard any leading OWS from input_string.
2. If the field-value is defined to be a dictionary, return the 2. If the field-value is defined to be a dictionary, let output be
result of Parsing a Dictionary from Textual headers the result of Parsing a Dictionary from Textual headers
(Section 4.7). (Section 4.1.1).
3. If the field-value is defined to be a list, return the result of 3. If the field-value is defined to be a list, let output be the
Parsing a List from Textual Headers (Section 4.8). result of Parsing a List from Text (Section 4.2.1).
4. If the field-value is defined to be a parameterised label, return 4. If the field-value is defined to be a parameterised label, let
the result of Parsing a Parameterised Label from Textual headers output be the result of Parsing a Parameterised Label from
(Section 4.4). Textual headers (Section 4.3.1).
5. Otherwise, return the result of Parsing an Item from Textual 5. Otherwise, let output be the result of Parsing an Item from Text
Headers (Section 4.6). (Section 4.4.1).
6. Discard any leading OWS from input_string.
7. If input_string is not empty, throw an error.
8. Otherwise, return output.
When generating input_string for a given header field, parsers MUST
combine all instances of it into one comma-separated field-value, as
per [RFC7230], Section 3.2.2; this assures that the header is
processed correctly.
Note that in the case of lists and dictionaries, this has the effect Note that in the case of lists and dictionaries, this has the effect
of combining multiple instances of the header field into one. of coalescing all of the values for that field. However, for
However, for singular items and parameterised labels, it has the singular items and parameterised labels, it will result in an error
effect of selecting the first value and ignoring any subsequent being thrown.
instances of the field, as well as extraneous text afterwards.
Additionally, note that the effect of the parsing algorithms as Additionally, note that the effect of the parsing algorithms as
specified is generally intolerant of syntax errors; if one is specified is generally intolerant of syntax errors; if one is
encountered, the typical response is to throw an error, thereby encountered, the typical response is to throw an error, thereby
discarding the entire header field value. This includes any non- discarding the entire header field value. This includes any non-
ASCII characters in input_string. ASCII characters in input_string.
4. Structured Header Data Types 4. Structured Header Data Types
This section defines the abstract value types that can be composed This section defines the abstract value types that can be composed
into Structured Headers, along with the textual HTTP serialisations into Structured Headers, along with the textual HTTP serialisations
of them. of them.
4.1. Numbers 4.1. Dictionaries
Abstractly, numbers are integers with an optional fractional part.
They have a maximum of fifteen digits available to be used in one or
both of the parts, as reflected in the ABNF below; this allows them
to be stored as IEEE 754 double precision numbers (binary64)
([IEEE754]).
The textual HTTP serialisation of numbers allows a maximum of fifteen
digits between the integer and fractional part, along with an
optional "-" indicating negative numbers.
number = ["-"] ( "." 1*15DIGIT /
DIGIT "." 1*14DIGIT /
2DIGIT "." 1*13DIGIT /
3DIGIT "." 1*12DIGIT /
4DIGIT "." 1*11DIGIT /
5DIGIT "." 1*10DIGIT /
6DIGIT "." 1*9DIGIT /
7DIGIT "." 1*8DIGIT /
8DIGIT "." 1*7DIGIT /
9DIGIT "." 1*6DIGIT /
10DIGIT "." 1*5DIGIT /
11DIGIT "." 1*4DIGIT /
12DIGIT "." 1*3DIGIT /
13DIGIT "." 1*2DIGIT /
14DIGIT "." 1DIGIT /
15DIGIT )
integer = ["-"] 1*15DIGIT
unsigned = 1*15DIGIT
integer and unsigned are defined as conveniences to specification
authors; if their use is specified and their ABNF is not matched, a
parser MUST consider it to be invalid.
For example, a header whose value is defined as a number could look
like:
ExampleNumberHeader: 4.5
4.1.1. Parsing Numbers from Textual Headers
TBD
4.2. Strings
Abstractly, strings are ASCII strings [RFC0020], excluding control
characters (i.e., the range 0x20 to 0x7E). Note that this excludes
tabs, newlines and carriage returns. They may be at most 1024
characters long.
The textual HTTP serialisation of strings uses a backslash ("") to Dictionaries are unordered maps of key-value pairs, where the keys
escape double quotes and backslashes in strings. are labels (Section 4.8) and the values are items (Section 4.4).
There can be between 1 and 1024 members, and keys are required to be
unique.
string = DQUOTE 1*1024(char) DQUOTE In the textual HTTP serialisation, keys and values are separated by
char = unescaped / escape ( DQUOTE / "\" ) "=" (without whitespace), and key/value pairs are separated by a
unescaped = %x20-21 / %x23-5B / %x5D-7E comma with optional whitespace. Duplicate keys MUST be considered an
escape = "\" error.
For example, a header whose value is defined as a string could look
like:
ExampleStringHeader: "hello world" dictionary = label "=" item *1023( OWS "," OWS label "=" item )
Note that strings only use DQUOTE as a delimiter; single quotes do For example, a header field whose value is defined as a dictionary
not delimit strings. Furthermore, only DQUOTE and "" can be escaped; could look like:
other sequences MUST generate an error.
Unicode is not directly supported in Structured Headers, because it ExampleDictHeader: foo=1.23, en="Applepie", da=*w4ZibGV0w6ZydGUK
causes a number of interoperability issues, and - with few exceptions
- header values do not require it.
When it is necessary for a field value to convey non-ASCII string Typically, a header field specification will define the semantics of
content, binary content (Section 4.5) SHOULD be specified, along with individual keys, as well as whether their presence is required or
a character encoding (most likely, UTF-8). optional. Recipients MUST ignore keys that are undefined or unknown,
unless the header field's specification specifically disallows them.
4.2.1. Parsing a String from Textual Headers 4.1.1. Parsing a Dictionary from Text
Given an ASCII string input_string, return an unquoted string. Given an ASCII string input_string, return a mapping of (label,
input_string is modified to remove the parsed value. item). input_string is modified to remove the parsed value.
1. Let output_string be an empty string. 1. Let dictionary be an empty, unordered mapping.
2. If the first character of input_string is not DQUOTE, throw an 2. While input_string is not empty:
error.
3. Discard the first character of input_string. 1. Let this_key be the result of running Parse Label from Text
(Section 4.8.1) with input_string. If an error is
encountered, throw it.
4. If input_string contains more than 1025 characters, throw an 2. If dictionary already contains this_key, throw an error.
error.
5. While input_string is not empty: 3. Consume a "=" from input_string; if none is present, throw
an error.
1. Let char be the result of removing the first character of 4. Let this_value be the result of running Parse Item from Text
input_string. (Section 4.4.1) with input_string. If an error is
encountered, throw it.
2. If char is a backslash ("\"): 5. Add key this_key with value this_value to dictionary.
1. If input_string is now empty, throw an error. 6. If dictionary has more than 1024 members, throw an error.
2. Else: 7. Discard any leading OWS from input_string.
1. Let next_char be the result of removing the first 8. If input_string is empty, return dictionary.
character of input_string.
2. If next_char is not DQUOTE or "\", throw an error. 9. Consume a COMMA from input_string; if no comma is present,
throw an error.
3. Append next_char to output_string. 10. Discard any leading OWS from input_string.
3. Else, if char is DQUOTE, remove the first character of 3. Return dictionary.
input_string and return output_string.
4. Else, append char to output_string. 4.2. Lists
6. Otherwise, throw an error. Lists are arrays of items (Section 4.4) or parameterised labels
(Section 4.3), with one to 1024 members.
4.3. Labels In the textual HTTP serialisation, each member is separated by a
comma and optional whitespace.
Labels are short (up to 256 characters) textual identifiers; their list = list_member 0*1023( OWS "," OWS list_member )
abstract model is identical to their expression in the textual HTTP list_member = item / parameterised
serialisation.
label = lcalpha *255( lcalpha / DIGIT / "_" / "-"/ "*" / "/" ) For example, a header field whose value is defined as a list of
lcalpha = %x61-7A ; a-z labels could look like:
Note that labels can only contain lowercase letters. ExampleLabelListHeader: foo, bar, baz_45
For example, a header whose value is defined as a label could look and a header field whose value is defined as a list of parameterised
like: labels could look like:
ExampleLabelHeader: foo/bar ExampleParamListHeader: abc/def; g="hi";j, klm/nop
4.3.1. Parsing a Label from Textual Headers 4.2.1. Parsing a List from Text
Given an ASCII string input_string, return a label. input_string is Given an ASCII string input_string, return a list of items.
modified to remove the parsed value. input_string is modified to remove the parsed value.
1. If input_string contains more than 256 characters, throw an 1. Let items be an empty array.
error.
2. If the first character of input_string is not lcalpha, throw an 2. While input_string is not empty:
error.
3. Let output_string be an empty string. 1. Let item be the result of running Parse Item from Text
(Section 4.4.1) with input_string. If an error is
encountered, throw it.
4. While input_string is not empty: 2. Append item to items.
1. Let char be the result of removing the first character of 3. If items has more than 1024 members, throw an error.
input_string.
2. If char is not one of lcalpha, DIGIT, "_", "-", "*" or "/": 4. Discard any leading OWS from input_string.
1. Prepend char to input_string. 5. If input_string is empty, return items.
2. Return output_string. 6. Consume a COMMA from input_string; if no comma is present,
throw an error.
3. Append char to output_string. 7. Discard any leading OWS from input_string.
5. Return output_string. 3. Return items.
4.4. Parameterised Labels 4.3. Parameterised Labels
Parameterised Labels are labels (Section 4.3) with up to 256 Parameterised Labels are labels (Section 4.8) with up to 256
parameters; each parameter has a label and an optional value that is parameters; each parameter has a label and an optional value that is
an item (Section 4.6). Ordering between parameters is not an item (Section 4.4). Ordering between parameters is not
significant, and duplicate parameters MUST be considered an error. significant, and duplicate parameters MUST be considered an error.
The textual HTTP serialisation uses semicolons (";") to delimit the The textual HTTP serialisation uses semicolons (";") to delimit the
parameters from each other, and equals ("=") to delimit the parameter parameters from each other, and equals ("=") to delimit the parameter
name from its value. name from its value.
parameterised = label *256( OWS ";" OWS label [ "=" item ] ) parameterised = label *256( OWS ";" OWS label [ "=" item ] )
For example, For example,
ExampleParamHeader: abc; a=1; b=2; c ExampleParamHeader: abc_123;a=1;b=2; c
4.4.1. Parsing a Parameterised Label from Textual Headers 4.3.1. Parsing a Parameterised Label from Text
Given an ASCII string input_string, return a label with an mapping of Given an ASCII string input_string, return a label with an mapping of
parameters. input_string is modified to remove the parsed value. parameters. input_string is modified to remove the parsed value.
1. Let primary_label be the result of Parsing a Label from Textual 1. Let primary_label be the result of Parsing a Label from Text
Headers (Section 4.3) from input_string. (Section 4.8.1) from input_string.
2. Let parameters be an empty mapping. 2. Let parameters be an empty, unordered mapping.
3. In a loop: 3. In a loop:
1. Consume any OWS from the beginning of input_string. 1. Discard any leading OWS from input_string.
2. If the first character of input_string is not ";", exit the 2. If the first character of input_string is not ";", exit the
loop. loop.
3. Consume a ";" character from the beginning of input_string. 3. Consume a ";" character from the beginning of input_string.
4. Consume any OWS from the beginning of input_string. 4. Discard any leading OWS from input_string.
5. let param_name be the result of Parsing a Label from Textual 5. let param_name be the result of Parsing a Label from Text
Headers (Section 4.3) from input_string. (Section 4.8.1) from input_string.
6. If param_name is already present in parameters, throw an 6. If param_name is already present in parameters, throw an
error. error.
7. Let param_value be a null value. 7. Let param_value be a null value.
8. If the first character of input_string is "=": 8. If the first character of input_string is "=":
1. Consume the "=" character at the beginning of 1. Consume the "=" character at the beginning of
input_string. input_string.
2. Let param_value be the result of Parsing an Item from 2. Let param_value be the result of Parsing an Item from
Textual Headers (Section 4.6) from input_string. Text (Section 4.4.1) from input_string.
9. If parameters has more than 255 members, throw an error. 9. If parameters has more than 255 members, throw an error.
10. Add param_name to parameters with the value param_value. 10. Add param_name to parameters with the value param_value.
4. Return the tuple (primary_label, parameters). 4. Return the tuple (primary_label, parameters).
4.5. Binary Content 4.4. Items
Arbitrary binary content up to 16K in size can be conveyed in An item is can be a integer (Section 4.5), float (Section 4.6),
Structured Headers. string (Section 4.7), label (Section 4.8) or binary content
(Section 4.9).
The textual HTTP serialisation indicates their presence by a leading item = integer / float / string / label / binary
"*", with the data encoded using Base 64 Encoding [RFC4648], without
padding (as "=" might be confused with the use of dictionaries).
binary = "*" 1*21846(base64) 4.4.1. Parsing an Item from Text
base64 = ALPHA / DIGIT / "+" / "/"
For example, a header whose value is defined as binary content could Given an ASCII string input_string, return an item. input_string is
look like: modified to remove the parsed value.
ExampleBinaryHeader: *cHJldGVuZCB0aGlzIGlzIGJpbmFyeSBjb250ZW50Lg 1. Discard any leading OWS from input_string.
4.5.1. Parsing Binary Content from Textual Headers 2. If the first character of input_string is a "-" or a DIGIT,
process input_string as a number (Section 4.5.1) and return the
result, throwing any errors encountered.
Given an ASCII string input_string, return binary content. 3. If the first character of input_string is a DQUOTE, process
input_string is modified to remove the parsed value. input_string as a string (Section 4.7.1) and return the result,
throwing any errors encountered.
1. If the first character of input_string is not "*", throw an 4. If the first character of input_string is "*", process
error. input_string as binary content (Section 4.9.1) and return the
result, throwing any errors encountered.
2. Discard the first character of input_string. 5. If the first character of input_string is an lcalpha, process
input_string as a label (Section 4.8.1) and return the result,
throwing any errors encountered.
3. Let b64_content be the result of removing content of input_string 6. Otherwise, throw an error.
up to but not including the first character that is not in ALPHA,
DIGIT, "+" or "/".
4. Let binary_content be the result of Base 64 Decoding [RFC4648] 4.5. Integers
b64_content, synthesising padding if necessary. If an error is
encountered, throw it.
5. Return binary_content. Abstractly, integers have a range of -9,223,372,036,854,775,808 to
9,223,372,036,854,775,807 inclusive (i.e., a 64-bit signed integer).
4.6. Items integer = ["-"] 1*19DIGIT
An item is can be a number (Section 4.1), string (Section 4.2), label Parsers that encounter an integer outside the range defined above
(Section 4.3) or binary content (Section 4.5). MUST throw an error. Therefore, the value "9223372036854775809"
would be invalid. Likewise, values that do not conform to the ABNF
above are invalid, and MUST throw an error.
item = number / string / label / binary For example, a header whose value is defined as a integer could look
like:
4.6.1. Parsing an Item from Textual Headers ExampleIntegerHeader: 42
Given an ASCII string input_string, return an item. input_string is 4.5.1. Parsing a Number from Text
modified to remove the parsed value.
1. Discard any OWS from the beginning of input_string. NOTE: This algorithm parses both Integers and Floats Section 4.6, and
returns the corresponding structure.
2. If the first character of input_string is a "-" or a DIGIT, 1. If the first character of input_string is not "-" or a DIGIT,
process input_string as a number (Section 4.1) and return the throw an error.
result, throwing any errors encountered.
3. If the first character of input_string is a DQUOTE, process 2. Let input_number be the result of consuming input_string up to
input_string as a string (Section 4.2) and return the result, (but not including) the first character that is not in DIGIT,
throwing any errors encountered. "-", and ".".
4. If the first character of input_string is "*", process 3. If input_number contains ".", parse it as a floating point number
input_string as binary content (Section 4.5) and return the and let output_number be the result.
result, throwing any errors encountered.
5. If the first character of input_string is an lcalpha, process 4. Otherwise, parse input_number as an integer and let output_number
input_string as a label (Section 4.3) and return the result, be the result.
throwing any errors encountered.
6. Otherwise, throw an error. 5. Return output_number.
4.7. Dictionaries 4.6. Floats
Dictionaries are unordered maps of key-value pairs, where the keys Abstractly, floats are integers with a fractional part. They have a
are labels (Section 4.3) and the values are items (Section 4.6). maximum of fifteen digits available to be used in both of the parts,
There can be between 1 and 1024 members, and keys are required to be as reflected in the ABNF below; this allows them to be stored as IEEE
unique. 754 double precision numbers (binary64) ([IEEE754]).
In the textual HTTP serialisation, keys and values are separated by The textual HTTP serialisation of floats allows a maximum of fifteen
"=" (without whitespace), and key/value pairs are separated by a digits between the integer and fractional part, with at least one
comma with optional whitespace. required on each side, along with an optional "-" indicating negative
numbers.
dictionary = label "=" item *1023( OWS "," OWS label "=" item ) float = ["-"] (
DIGIT "." 1*14DIGIT /
2DIGIT "." 1*13DIGIT /
3DIGIT "." 1*12DIGIT /
4DIGIT "." 1*11DIGIT /
5DIGIT "." 1*10DIGIT /
6DIGIT "." 1*9DIGIT /
7DIGIT "." 1*8DIGIT /
8DIGIT "." 1*7DIGIT /
9DIGIT "." 1*6DIGIT /
10DIGIT "." 1*5DIGIT /
11DIGIT "." 1*4DIGIT /
12DIGIT "." 1*3DIGIT /
13DIGIT "." 1*2DIGIT /
14DIGIT "." 1DIGIT )
For example, a header field whose value is defined as a dictionary Values that do not conform to the ABNF above are invalid, and MUST
could look like: throw an error.
ExampleDictHeader: foo=1.23, en="Applepie", da=*w4ZibGV0w6ZydGUK For example, a header whose value is defined as a float could look
like:
Typically, a header field specification will define the semantics of ExampleFloatHeader: 4.5
individual keys, as well as whether their presence is required or
optional. Recipients MUST ignore keys that are undefined or unknown,
unless the header field's specification specifically disallows them.
4.7.1. Parsing a Dictionary from Textual Headers See Section 4.5.1 for the parsing algorithm for floats.
Given an ASCII string input_string, return a mapping of (label, 4.7. Strings
item). input_string is modified to remove the parsed value.
1. Let dictionary be an empty mapping. Abstractly, strings are ASCII strings [RFC0020], excluding control
characters (i.e., the range 0x20 to 0x7E). Note that this excludes
tabs, newlines and carriage returns. They may be at most 1024
characters long.
2. While input_string is not empty: The textual HTTP serialisation of strings uses a backslash ("") to
escape double quotes and backslashes in strings.
1. Let this_key be the result of running Parse Label from string = DQUOTE 0*1024(char) DQUOTE
Textual Headers (Section 4.3) with input_string. If an error char = unescaped / escape ( DQUOTE / "\" )
is encountered, throw it. unescaped = %x20-21 / %x23-5B / %x5D-7E
escape = "\"
2. If dictionary already contains this_key, raise an error. For example, a header whose value is defined as a string could look
like:
3. Consume a "=" from input_string; if none is present, raise an ExampleStringHeader: "hello world"
Note that strings only use DQUOTE as a delimiter; single quotes do
not delimit strings. Furthermore, only DQUOTE and "" can be escaped;
other sequences MUST generate an error.
Unicode is not directly supported in Structured Headers, because it
causes a number of interoperability issues, and - with few exceptions
- header values do not require it.
When it is necessary for a field value to convey non-ASCII string
content, binary content (Section 4.9) SHOULD be specified, along with
a character encoding (most likely, UTF-8).
4.7.1. Parsing a String from Text
Given an ASCII string input_string, return an unquoted string.
input_string is modified to remove the parsed value.
1. Let output_string be an empty string.
2. If the first character of input_string is not DQUOTE, throw an
error.
3. Discard the first character of input_string.
4. While input_string is not empty:
1. Let char be the result of removing the first character of
input_string.
2. If char is a backslash ("\"):
1. If input_string is now empty, throw an error.
2. Else:
1. Let next_char be the result of removing the first
character of input_string.
2. If next_char is not DQUOTE or "\", throw an error.
3. Append next_char to output_string.
3. Else, if char is DQUOTE, return output_string.
4. Else, append char to output_string.
5. If output_string contains more than 1024 characters, throw an
error. error.
4. Let this_value be the result of running Parse Item from 5. Otherwise, throw an error.
Textual Headers (Section 4.6) with input_string. If an error
is encountered, throw it.
5. Add key this_key with value this_value to dictionary. 4.8. Labels
6. Discard any leading OWS from input_string. Labels are short (up to 256 characters) textual identifiers; their
abstract model is identical to their expression in the textual HTTP
serialisation.
7. If input_string is empty, return dictionary. label = lcalpha *255( lcalpha / DIGIT / "_" / "-"/ "*" / "/" )
lcalpha = %x61-7A ; a-z
8. Consume a COMMA from input_string; if no comma is present, Note that labels can only contain lowercase letters.
raise an error.
9. Discard any leading OWS from input_string. For example, a header whose value is defined as a label could look
like:
3. Return dictionary. ExampleLabelHeader: foo/bar
4.8. Lists 4.8.1. Parsing a Label from Text
Lists are arrays of items (Section 4.6) or parameterised labels Given an ASCII string input_string, return a label. input_string is
(Section 4.4, with one to 1024 members. modified to remove the parsed value.
In the textual HTTP serialisation, each member is separated by a 1. If the first character of input_string is not lcalpha, throw an
comma and optional whitespace. error.
list = list_member 1*1024( OWS "," OWS list_member ) 2. Let output_string be an empty string.
list_member = item / parameterised
For example, a header field whose value is defined as a list of 3. While input_string is not empty:
labels could look like:
ExampleLabelListHeader: foo, bar, baz_45 1. Let char be the result of removing the first character of
input_string.
and a header field whose value is defined as a list of parameterised 2. If char is not one of lcalpha, DIGIT, "_", "-", "*" or "/":
labels could look like:
ExampleParamListHeader: abc/def; g="hi";j, klm/nop 1. Prepend char to input_string.
4.8.1. Parsing a List from Textual Headers 2. Return output_string.
Given an ASCII string input_string, return a list of items. 3. Append char to output_string.
input_string is modified to remove the parsed value.
1. Let items be an empty array. 4. If output_string contains more than 256 characters, throw an
error.
2. While input_string is not empty: 4. Return output_string.
1. Let item be the result of running Parse Item from Textual 4.9. Binary Content
Headers (Section 4.6) with input_string. If an error is
encountered, throw it.
2. Append item to items. Arbitrary binary content up to 16K in size can be conveyed in
Structured Headers.
3. Discard any leading OWS from input_string. The textual HTTP serialisation indicates their presence by a leading
"*", with the data encoded using Base 64 Encoding [RFC4648],
Section 4.
4. If input_string is empty, return items. Parsers MUST consider encoded data that is padded an error, as "="
might be confused with the use of dictionaries). See [RFC4648],
Section 3.2.
5. Consume a COMMA from input_string; if no comma is present, Likewise, parsers MUST consider encoded data that has non-zero pad
raise an error. bits an error. See [RFC4648], Section 3.5.
6. Discard any leading OWS from input_string. This specification does not relax the requirements in [RFC4648],
Section 3.1 and 3.3; therefore, parsers MUST consider characters
outside the base64 alphabet and line feeds in encoded data as errors.
3. Return items. binary = "*" 0*21846(base64) "*"
base64 = ALPHA / DIGIT / "+" / "/"
For example, a header whose value is defined as binary content could
look like:
ExampleBinaryHeader: *cHJldGVuZCB0aGlzIGlzIGJpbmFyeSBjb250ZW50Lg*
4.9.1. Parsing Binary Content from Text
Given an ASCII string input_string, return binary content.
input_string is modified to remove the parsed value.
1. If the first character of input_string is not "*", throw an
error.
2. Discard the first character of input_string.
3. Let b64_content be the result of removing content of input_string
up to but not including the first instance of the character "_".
If there is not a "_" character before the end of input_string,
throw an error.
4. Consume the "*" character at the beginning of input_string.
5. If b64_content is has more than 21846 characters, throw an error.
6. Let binary_content be the result of Base 64 Decoding [RFC4648]
b64_content, synthesising padding if necessary. If an error is
encountered, throw it (note the requirements about recipient
behaviour in Section 4.9).
7. Return binary_content.
5. IANA Considerations 5. IANA Considerations
This draft has no actions for IANA. This draft has no actions for IANA.
6. Security Considerations 6. Security Considerations
TBD TBD
7. References 7. References
skipping to change at page 14, line 49 skipping to change at page 17, line 10
[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>.
7.2. Informative References 7.2. Informative References
[IEEE754] IEEE, "IEEE Standard for Floating-Point Arithmetic", 2008, [IEEE754] IEEE, "IEEE Standard for Floating-Point Arithmetic", 2008,
<http://grouper.ieee.org/groups/754/>. <http://grouper.ieee.org/groups/754/>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/info/rfc3986>.
[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer [RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content", RFC 7231, Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
DOI 10.17487/RFC7231, June 2014, DOI 10.17487/RFC7231, June 2014,
<https://www.rfc-editor.org/info/rfc7231>. <https://www.rfc-editor.org/info/rfc7231>.
[RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext [RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
Transfer Protocol Version 2 (HTTP/2)", RFC 7540, Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
DOI 10.17487/RFC7540, May 2015, DOI 10.17487/RFC7540, May 2015,
<https://www.rfc-editor.org/info/rfc7540>. <https://www.rfc-editor.org/info/rfc7540>.
7.3. URIs 7.3. URIs
[1] https://lists.w3.org/Archives/Public/ietf-http-wg/ [1] https://lists.w3.org/Archives/Public/ietf-http-wg/
[2] https://httpwg.github.io/ [2] https://httpwg.github.io/
[3] https://github.com/httpwg/http-extensions/labels/header-structure [3] https://github.com/httpwg/http-extensions/labels/header-structure
Appendix A. Changes Appendix A. Changes
A.1. Since draft-ietf-httpbis-header-structure-01 A.1. Since draft-ietf-httpbis-header-structure-02
Replaced with draft-nottingham-structured-headers. o Split Numbers into Integers and Floats.
A.2. Since draft-ietf-httpbis-header-structure-00 o Define number parsing.
Added signed 64bit integer type. o Tighten up binary parsing and give it an explicit end delimiter.
Drop UTF8, and settle on BCP137 ::EmbeddedUnicodeChar for h1-unicode- o Clarify that mappings are unordered.
string.
Change h1_blob delimiter to ":" since "'" is valid t_char o Allow zero-length strings.
o Improve string parsing algorithm.
o Improve limits in algorithms.
o Require parsers to combine header fields before processing.
o Throw an error on trailing garbage.
A.2. Since draft-ietf-httpbis-header-structure-01
o Replaced with draft-nottingham-structured-headers.
A.3. Since draft-ietf-httpbis-header-structure-00
o Added signed 64bit integer type.
o Drop UTF8, and settle on BCP137 ::EmbeddedUnicodeChar for h1-
unicode-string.
o Change h1_blob delimiter to ":" since "'" is valid t_char
Authors' Addresses Authors' Addresses
Mark Nottingham Mark Nottingham
Fastly Fastly
Email: mnot@mnot.net Email: mnot@mnot.net
URI: https://www.mnot.net/ URI: https://www.mnot.net/
Poul-Henning Kamp Poul-Henning Kamp
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