draft-ietf-httpbis-header-structure-14.txt   draft-ietf-httpbis-header-structure-latest.txt 
HTTP Working Group M. Nottingham HTTP Working Group M. Nottingham
Internet-Draft Fastly Internet-Draft Fastly
Intended status: Standards Track P-H. Kamp Intended status: Standards Track P-H. Kamp
Expires: May 2, 2020 The Varnish Cache Project Expires: July 27, 2020 The Varnish Cache Project
October 30, 2019 January 24, 2020
Structured Headers for HTTP Structured Headers for HTTP
draft-ietf-httpbis-header-structure-14 draft-ietf-httpbis-header-structure-latest
Abstract Abstract
This document describes a set of data types and associated algorithms This document describes a set of data types and associated algorithms
that are intended to make it easier and safer to define and handle that are intended to make it easier and safer to define and handle
HTTP header fields. It is intended for use by specifications of new HTTP header fields. It is intended for use by specifications of new
HTTP header fields that wish to use a common syntax that is more HTTP header fields that wish to use a common syntax that is more
restrictive than traditional HTTP field values. restrictive than traditional HTTP field values.
Note to Readers Note to Readers
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
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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 2, 2020. This Internet-Draft will expire on July 27, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Provisions Relating to IETF Documents Provisions Relating to IETF Documents
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publication of this document. Please review these documents publication of this document. Please review these documents
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to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
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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 Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Intentionally Strict Processing . . . . . . . . . . . . . 4 1.1. Intentionally Strict Processing . . . . . . . . . . . . . 4
1.2. Notational Conventions . . . . . . . . . . . . . . . . . 4 1.2. Notational Conventions . . . . . . . . . . . . . . . . . 5
2. Defining New Structured Headers . . . . . . . . . . . . . . . 5 2. Defining New Structured Headers . . . . . . . . . . . . . . . 5
3. Structured Data Types . . . . . . . . . . . . . . . . . . . . 7 3. Structured Data Types . . . . . . . . . . . . . . . . . . . . 7
3.1. Lists . . . . . . . . . . . . . . . . . . . . . . . . . . 8 3.1. Lists . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.2. Dictionaries . . . . . . . . . . . . . . . . . . . . . . 9 3.1.1. Inner Lists . . . . . . . . . . . . . . . . . . . . . 8
3.3. Items . . . . . . . . . . . . . . . . . . . . . . . . . . 10 3.1.2. Parameters . . . . . . . . . . . . . . . . . . . . . 9
4. Working With Structured Headers in HTTP Headers . . . . . . . 13 3.2. Dictionaries . . . . . . . . . . . . . . . . . . . . . . 10
4.1. Serializing Structured Headers . . . . . . . . . . . . . 13 3.3. Items . . . . . . . . . . . . . . . . . . . . . . . . . . 11
4.2. Parsing Header Fields into Structured Headers . . . . . . 20 3.3.1. Integers . . . . . . . . . . . . . . . . . . . . . . 12
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30 3.3.2. Decimals . . . . . . . . . . . . . . . . . . . . . . 12
6. Security Considerations . . . . . . . . . . . . . . . . . . . 30 3.3.3. Strings . . . . . . . . . . . . . . . . . . . . . . . 12
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 30 3.3.4. Tokens . . . . . . . . . . . . . . . . . . . . . . . 13
7.1. Normative References . . . . . . . . . . . . . . . . . . 30 3.3.5. Byte Sequences . . . . . . . . . . . . . . . . . . . 13
7.2. Informative References . . . . . . . . . . . . . . . . . 31 3.3.6. Booleans . . . . . . . . . . . . . . . . . . . . . . 14
7.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 31 4. Working With Structured Headers in HTTP Headers . . . . . . . 14
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 32 4.1. Serializing Structured Headers . . . . . . . . . . . . . 14
Appendix B. Frequently Asked Questions . . . . . . . . . . . . . 32 4.1.1. Serializing a List . . . . . . . . . . . . . . . . . 15
B.1. Why not JSON? . . . . . . . . . . . . . . . . . . . . . . 32 4.1.2. Serializing a Dictionary . . . . . . . . . . . . . . 17
B.2. Structured Headers don't "fit" my data. . . . . . . . . . 33 4.1.3. Serializing an Item . . . . . . . . . . . . . . . . . 17
Appendix C. Implementation Notes . . . . . . . . . . . . . . . . 33 4.1.4. Serializing an Integer . . . . . . . . . . . . . . . 18
Appendix D. Changes . . . . . . . . . . . . . . . . . . . . . . 34 4.1.5. Serializing a Decimal . . . . . . . . . . . . . . . . 19
D.1. Since draft-ietf-httpbis-header-structure-13 . . . . . . 34 4.1.6. Serializing a String . . . . . . . . . . . . . . . . 19
D.2. Since draft-ietf-httpbis-header-structure-12 . . . . . . 34 4.1.7. Serializing a Token . . . . . . . . . . . . . . . . . 20
D.3. Since draft-ietf-httpbis-header-structure-11 . . . . . . 34 4.1.8. Serializing a Byte Sequence . . . . . . . . . . . . . 20
D.4. Since draft-ietf-httpbis-header-structure-10 . . . . . . 34 4.1.9. Serializing a Boolean . . . . . . . . . . . . . . . . 21
D.5. Since draft-ietf-httpbis-header-structure-09 . . . . . . 35 4.2. Parsing Header Fields into Structured Headers . . . . . . 21
D.6. Since draft-ietf-httpbis-header-structure-08 . . . . . . 35 4.2.1. Parsing a List . . . . . . . . . . . . . . . . . . . 22
D.7. Since draft-ietf-httpbis-header-structure-07 . . . . . . 35 4.2.2. Parsing a Dictionary . . . . . . . . . . . . . . . . 24
D.8. Since draft-ietf-httpbis-header-structure-06 . . . . . . 36 4.2.3. Parsing an Item . . . . . . . . . . . . . . . . . . . 25
D.9. Since draft-ietf-httpbis-header-structure-05 . . . . . . 36 4.2.4. Parsing a Number . . . . . . . . . . . . . . . . . . 27
D.10. Since draft-ietf-httpbis-header-structure-04 . . . . . . 36 4.2.5. Parsing a String . . . . . . . . . . . . . . . . . . 28
D.11. Since draft-ietf-httpbis-header-structure-03 . . . . . . 36 4.2.6. Parsing a Token . . . . . . . . . . . . . . . . . . . 29
D.12. Since draft-ietf-httpbis-header-structure-02 . . . . . . 36 4.2.7. Parsing a Byte Sequence . . . . . . . . . . . . . . . 29
D.13. Since draft-ietf-httpbis-header-structure-01 . . . . . . 37 4.2.8. Parsing a Boolean . . . . . . . . . . . . . . . . . . 30
D.14. Since draft-ietf-httpbis-header-structure-00 . . . . . . 37 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 31
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 37 6. Security Considerations . . . . . . . . . . . . . . . . . . . 31
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 31
7.1. Normative References . . . . . . . . . . . . . . . . . . 31
7.2. Informative References . . . . . . . . . . . . . . . . . 32
7.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 33
Appendix B. Frequently Asked Questions . . . . . . . . . . . . . 33
B.1. Why not JSON? . . . . . . . . . . . . . . . . . . . . . . 33
B.2. Structured Headers don't "fit" my data. . . . . . . . . . 34
Appendix C. Implementation Notes . . . . . . . . . . . . . . . . 34
Appendix D. Changes . . . . . . . . . . . . . . . . . . . . . . 35
D.1. Since draft-ietf-httpbis-header-structure-14 . . . . . . 35
D.2. Since draft-ietf-httpbis-header-structure-13 . . . . . . 35
D.3. Since draft-ietf-httpbis-header-structure-12 . . . . . . 36
D.4. Since draft-ietf-httpbis-header-structure-11 . . . . . . 36
D.5. Since draft-ietf-httpbis-header-structure-10 . . . . . . 36
D.6. Since draft-ietf-httpbis-header-structure-09 . . . . . . 36
D.7. Since draft-ietf-httpbis-header-structure-08 . . . . . . 37
D.8. Since draft-ietf-httpbis-header-structure-07 . . . . . . 37
D.9. Since draft-ietf-httpbis-header-structure-06 . . . . . . 38
D.10. Since draft-ietf-httpbis-header-structure-05 . . . . . . 38
D.11. Since draft-ietf-httpbis-header-structure-04 . . . . . . 38
D.12. Since draft-ietf-httpbis-header-structure-03 . . . . . . 38
D.13. Since draft-ietf-httpbis-header-structure-02 . . . . . . 38
D.14. Since draft-ietf-httpbis-header-structure-01 . . . . . . 39
D.15. Since draft-ietf-httpbis-header-structure-00 . . . . . . 39
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 39
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 Section 8.3.1 of [RFC7231], there are many even with the guidance in Section 8.3.1 of [RFC7231], there are many
decisions - and pitfalls - for a prospective HTTP header field decisions - and pitfalls - for a prospective HTTP header field
author. author.
Once a header field is defined, bespoke parsers and serializers often Once a header field is defined, bespoke parsers and serializers often
need to be written, because each header has slightly different need to be written, because each header has slightly different
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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 algorithms to specify parsing and serialisation This document uses algorithms to specify parsing and serialisation
behaviours, and the Augmented Backus-Naur Form (ABNF) notation of behaviours, and the Augmented Backus-Naur Form (ABNF) notation of
[RFC5234] to illustrate expected syntax in HTTP header fields. In [RFC5234] to illustrate expected syntax in HTTP header fields. In
doing so, uses the VCHAR, SP, DIGIT, ALPHA and DQUOTE rules from doing so, uses the VCHAR, SP, DIGIT, ALPHA and DQUOTE rules from
[RFC5234]. It also includes the OWS and tchar rules from [RFC7230]. [RFC5234]. It also includes the tchar rule from [RFC7230].
When parsing from HTTP header fields, implementations MUST follow the When parsing from HTTP header fields, implementations MUST follow the
algorithms, but MAY vary in implementation so as the behaviours are algorithms, but MAY vary in implementation so as the behaviours are
indistinguishable from specified behaviour. If there is disagreement indistinguishable from specified behaviour. If there is disagreement
between the parsing algorithms and ABNF, the specified algorithms between the parsing algorithms and ABNF, the specified algorithms
take precedence. In some places, the algorithms are "greedy" with take precedence. In some places, the algorithms are "greedy" with
whitespace, but this should not affect conformance. whitespace, but this should not affect conformance.
For serialisation to header fields, the ABNF illustrates the range of For serialisation to header fields, the ABNF illustrates the range of
acceptable wire representations with as much fidelity as possible, acceptable wire representations with as much fidelity as possible,
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to accommodate more information, if need be. As a result, header to accommodate more information, if need be. As a result, header
specifications are discouraged from defining the presence of an specifications are discouraged from defining the presence of an
unrecognised parameter as an error condition. unrecognised parameter as an error condition.
Conversely, inner lists are only valid when a header definition Conversely, inner lists are only valid when a header definition
explicitly allows them. explicitly allows them.
Note that a header field definition cannot relax the requirements of Note that a header field definition cannot relax the requirements of
this specification because doing so would preclude handling by this specification because doing so would preclude handling by
generic software; they can only add additional constraints (for generic software; they can only add additional constraints (for
example, on the numeric range of integers and floats, the format of example, on the numeric range of integers and decimals, the format of
strings and tokens, the types allowed in a dictionary's values, or strings and tokens, the types allowed in a dictionary's values, or
the number of items in a list). Likewise, header field definitions the number of items in a list). Likewise, header field definitions
can only use Structured Headers for the entire header field value, can only use Structured Headers for the entire header field value,
not a portion thereof. not a portion thereof.
This specification defines minimums for the length or number of This specification defines minimums for the length or number of
various structures supported by Structured Headers implementations. various structures supported by Structured Headers implementations.
It does not specify maximum sizes in most cases, but header authors It does not specify maximum sizes in most cases, but header authors
should be aware that HTTP implementations do impose various limits on should be aware that HTTP implementations do impose various limits on
the size of individual header fields, the total number of fields, the size of individual header fields, the total number of fields,
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for the message. See below for processing requirements. for the message. See below for processing requirements.
"fooUrl" contains a URI-reference (Section 4.1 of "fooUrl" contains a URI-reference (Section 4.1 of
[RFC3986], Section 4.1). If its value is not a valid URI-reference, [RFC3986], Section 4.1). If its value is not a valid URI-reference,
that URL MUST be ignored. If its value is a relative reference that URL MUST be ignored. If its value is a relative reference
(Section 4.2 of [RFC3986]), it MUST be resolved (Section 5 of (Section 4.2 of [RFC3986]), it MUST be resolved (Section 5 of
[RFC3986]) before being used. [RFC3986]) before being used.
For example: For example:
Foo-Example: 2; fooUrl="https://foo.example.com/" Foo-Example: 2; foourl="https://foo.example.com/"
3. Structured Data Types 3. Structured 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. The ABNF provided represents the on-wire into Structured Headers. The ABNF provided represents the on-wire
format in HTTP headers. format in HTTP headers.
In summary: In summary:
o There are three top-level types that a HTTP header can be defined o There are three top-level types that a HTTP header can be defined
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pairs. pairs.
3.1. Lists 3.1. Lists
Lists are arrays of zero or more members, each of which can be an Lists are arrays of zero or more members, each of which can be an
item (Section 3.3) or an inner list (Section 3.1.1), both of which item (Section 3.3) or an inner list (Section 3.1.1), both of which
can be parameterised (Section 3.1.2). can be parameterised (Section 3.1.2).
The ABNF for lists in HTTP headers is: The ABNF for lists in HTTP headers is:
sh-list = list-member *( OWS "," OWS list-member ) sh-list = list-member *( *SP "," *SP list-member )
list-member = sh-item / inner-list list-member = sh-item / inner-list
In HTTP headers, each member is separated by a comma and optional In HTTP headers, each member is separated by a comma and optional
whitespace. For example, a header field whose value is defined as a whitespace. For example, a header field whose value is defined as a
list of strings could look like: list of strings could look like:
Example-StrListHeader: "foo", "bar", "It was the best of times." Example-StrListHeader: "foo", "bar", "It was the best of times."
In HTTP headers, an empty list is denoted by not serialising the In HTTP headers, an empty list is denoted by not serialising the
header at all. header at all.
Note that lists can have their members split across multiple
instances inside a block of fields; for example, the following are
equivalent:
Example-Hdr: foo, bar
and
Example-Hdr: foo
Example-Hdr: bar
However, members of a list cannot be safely split between instances;
see Section 4.2 for details.
Parsers MUST support lists containing at least 1024 members. Header Parsers MUST support lists containing at least 1024 members. Header
specifications can constrain the types and cardinality of individual specifications can constrain the types and cardinality of individual
list values as they require. list values as they require.
3.1.1. Inner Lists 3.1.1. Inner Lists
An inner list is an array of zero or more items (Section 3.3). Both An inner list is an array of zero or more items (Section 3.3). Both
the individual items and the inner-list itself can be parameterised the individual items and the inner-list itself can be parameterised
(Section 3.1.2). (Section 3.1.2).
The ABNF for inner-lists in HTTP headers is: The ABNF for inner-lists in HTTP headers is:
inner-list = "(" OWS [ sh-item *( SP OWS sh-item ) OWS ] ")" inner-list = "(" *SP [ sh-item *( 1*SP sh-item ) *SP ] ")"
*parameter *parameter
In HTTP headers, inner lists are denoted by surrounding parenthesis, In HTTP headers, inner lists are denoted by surrounding parenthesis,
and have their values delimited by a single space. A header field and have their values delimited by a single space. A header field
whose value is defined as a list of inner-lists of strings could look whose value is defined as a list of inner-lists of strings could look
like: like:
Example-StrListListHeader: ("foo" "bar"), ("baz"), ("bat" "one"), () Example-StrListListHeader: ("foo" "bar"), ("baz"), ("bat" "one"), ()
Note that the last member in this example is an empty inner list. Note that the last member in this example is an empty inner list.
A header field whose value is defined as a list of inner-lists with A header field whose value is defined as a list of inner-lists with
parameters at both levels could look like: parameters at both levels could look like:
Example-ListListParam: ("foo"; a=1;b=2);lvl=5, ("bar", "baz");lvl=1 Example-ListListParam: ("foo"; a=1;b=2);lvl=5, ("bar" "baz");lvl=1
Parsers MUST support inner-lists containing at least 256 members. Parsers MUST support inner-lists containing at least 256 members.
Header specifications can constrain the types and cardinality of Header specifications can constrain the types and cardinality of
individual inner-list members as they require. individual inner-list members as they require.
3.1.2. Parameters 3.1.2. Parameters
Parameters are an ordered map of key-values pairs that are associated Parameters are an ordered map of key-values pairs that are associated
with an item (Section 3.3) or inner-list (Section 3.1.1). The keys with an item (Section 3.3) or inner-list (Section 3.1.1). The keys
are required to be unique within the scope of a map of parameters, are unique within the scope of a map of parameters, and the values
and the values are bare items (i.e., they themselves cannot be are bare items (i.e., they themselves cannot be parameterised; see
parameterised; see Section 3.3). Section 3.3).
The ABNF for parameters in HTTP headers is: The ABNF for parameters in HTTP headers is:
parameter = ";" OWS param-name [ "=" param-value ] parameter = ";" *SP param-name [ "=" param-value ]
param-name = key param-name = key
key = lcalpha *( lcalpha / DIGIT / "_" / "-" / "*" ) key = lcalpha *( lcalpha / DIGIT / "_" / "-" / "." / "*" )
lcalpha = %x61-7A ; a-z lcalpha = %x61-7A ; a-z
param-value = bare-item param-value = bare-item
In HTTP headers, parameters are separated from their item or inner- In HTTP headers, parameters are separated from their item or inner-
list and each other by semicolons. For example: list and each other by semicolons. For example:
Example-ParamListHeader: abc;a=1;b=2; cde_456, (ghi;jk=4 l);q="9";r=w Example-ParamListHeader: abc;a=1;b=2; cde_456, (ghi;jk=4 l);q="9";r=w
Parameters whose value is Boolean true MUST omit that value when
serialised. For example:
Example-IntHeader: 1; a; b=?0
Note that this requirement is only on serialisation; parsers are
still required to correctly handle the true value when it appears in
parameters.
Parsers MUST support at least 256 parameters on an item or inner- Parsers MUST support at least 256 parameters on an item or inner-
list, and support parameter keys with at least 64 characters. Header list, and support parameter keys with at least 64 characters. Header
specifications can constrain the types and cardinality of individual specifications can constrain the types and cardinality of individual
parameter names and values as they require. parameter names and values as they require.
3.2. Dictionaries 3.2. Dictionaries
Dictionaries are ordered maps of name-value pairs, where the names Dictionaries are ordered maps of name-value pairs, where the names
are short, textual strings and the values are items (Section 3.3) or are short, textual strings and the values are items (Section 3.3) or
arrays of items, both of which can be parameterised (Section 3.1.2). arrays of items, both of which can be parameterised (Section 3.1.2).
There can be zero or more members, and their names are required to be There can be zero or more members, and their names are unique in the
unique within the scope of the dictionary they occur within. scope of the dictionary they occur within.
Implementations MUST provide access to dictionaries both by index and Implementations MUST provide access to dictionaries both by index and
by name. Specifications MAY use either means of accessing the by name. Specifications MAY use either means of accessing the
members. members.
The ABNF for dictionaries in HTTP headers is: The ABNF for dictionaries in HTTP headers is:
sh-dictionary = dict-member *( OWS "," OWS dict-member ) sh-dictionary = dict-member *( *SP "," *SP dict-member )
dict-member = member-name "=" member-value dict-member = member-name [ "=" member-value ]
member-name = key member-name = key
member-value = sh-item / inner-list member-value = sh-item / inner-list
In HTTP headers, members are separated by a comma with optional In HTTP headers, members are separated by a comma with optional
whitespace, while names and values are separated by "=" (without whitespace, while names and values are separated by "=" (without
whitespace). For example: whitespace). For example:
Example-DictHeader: en="Applepie", da=*w4ZibGV0w6ZydGU=* Example-DictHeader: en="Applepie", da=:w4ZibGV0w6ZydGU=:
Members whose value is Boolean true MUST omit that value when
serialised, unless it has parameters. For example, here both "b" and
"c" are true, but "c"'s value is serialised because it has
parameters:
Example-DictHeader: a=?0, b, c=?1; foo=bar
Note that this requirement is only on serialisation; parsers are
still required to correctly handle the true value when it appears in
dictionary values.
A dictionary with a member whose value is an inner-list of tokens: A dictionary with a member whose value is an inner-list of tokens:
Example-DictListHeader: rating=1.5, feelings=(joy sadness) Example-DictListHeader: rating=1.5, feelings=(joy sadness)
A dictionary with a mix of singular and list values, some with A dictionary with a mix of singular and list values, some with
parameters: parameters:
Example-MixDict: a=(1 2), b=3, c=4;aa=bb, d=(5 6);valid=?1 Example-MixDict: a=(1 2), b=3, c=4;aa=bb, d=(5 6);valid=?1
As with lists, an empty dictionary is represented in HTTP headers by As with lists, an empty dictionary is represented in HTTP headers by
omitting the entire header field. omitting the entire header field.
Typically, a header field specification will define the semantics of Typically, a header field specification will define the semantics of
dictionaries by specifying the allowed type(s) for individual member dictionaries by specifying the allowed type(s) for individual member
names, as well as whether their presence is required or optional. names, as well as whether their presence is required or optional.
Recipients MUST ignore names that are undefined or unknown, unless Recipients MUST ignore names that are undefined or unknown, unless
the header field's specification specifically disallows them. the header field's specification specifically disallows them.
Note that dictionaries can have their members split across multiple
instances inside a block of fields; for example, the following are
equivalent:
Example-Hdr: foo=1, bar=2
and
Example-Hdr: foo=1
Example-Hdr: bar=2
However, members of a dictionary cannot be safely split between
instances; see Section 4.2 for details.
Parsers MUST support dictionaries containing at least 1024 name/value Parsers MUST support dictionaries containing at least 1024 name/value
pairs, and names with at least 64 characters. pairs, and names with at least 64 characters.
3.3. Items 3.3. Items
An item is can be a integer (Section 3.3.1), float (Section 3.3.2), An item is can be a integer (Section 3.3.1), decimal (Section 3.3.2),
string (Section 3.3.3), token (Section 3.3.4), byte sequence string (Section 3.3.3), token (Section 3.3.4), byte sequence
(Section 3.3.5), or Boolean (Section 3.3.6). It can have associated (Section 3.3.5), or Boolean (Section 3.3.6). It can have associated
parameters (Section 3.1.2). parameters (Section 3.1.2).
The ABNF for items in HTTP headers is: The ABNF for items in HTTP headers is:
sh-item = bare-item *parameter sh-item = bare-item *parameter
bare-item = sh-integer / sh-float / sh-string / sh-token / sh-binary bare-item = sh-integer / sh-decimal / sh-string / sh-token / sh-binary
/ sh-boolean / sh-boolean
For example, a header field that is defined to be an Item that is an For example, a header field that is defined to be an Item that is an
integer might look like: integer might look like:
Example-IntItemHeader: 5 Example-IntItemHeader: 5
or with parameters: or with parameters:
Example-IntItemHeader: 5; foo=bar Example-IntItemHeader: 5; foo=bar
skipping to change at page 11, line 22 skipping to change at page 12, line 24
sh-integer = ["-"] 1*15DIGIT sh-integer = ["-"] 1*15DIGIT
For example: For example:
Example-IntegerHeader: 42 Example-IntegerHeader: 42
Note that commas in integers are used in this section's prose only Note that commas in integers are used in this section's prose only
for readability; they are not valid in the wire format. for readability; they are not valid in the wire format.
3.3.2. Floats 3.3.2. Decimals
Floats are decimal numbers with an integer and a fractional Decimals are numbers with an integer and a fractional component. The
component. The fractional component has at most six digits of Integer component has at most 12 digits; the fractional component has
precision. Additionally, like integers, it can have no more than at most three digits.
fifteen digits in total, which in some cases further constrains its
precision.
The ABNF for floats in HTTP headers is: The ABNF for decimals in HTTP headers is:
sh-float = ["-"] (1*9DIGIT "." 1*6DIGIT / sh-decimal = ["-"] 1*12DIGIT "." 1*3DIGIT
10DIGIT "." 1*5DIGIT /
11DIGIT "." 1*4DIGIT /
12DIGIT "." 1*3DIGIT /
13DIGIT "." 1*2DIGIT /
14DIGIT "." 1DIGIT )
For example, a header whose value is defined as a float could look For example, a header whose value is defined as a decimal could look
like: like:
Example-FloatHeader: 4.5 Example-DecimalHeader: 4.5
3.3.3. Strings 3.3.3. Strings
Strings are zero or more printable ASCII [RFC0020] characters (i.e., Strings are zero or more printable ASCII [RFC0020] characters (i.e.,
the range %x20 to %x7E). Note that this excludes tabs, newlines, the range %x20 to %x7E). Note that this excludes tabs, newlines,
carriage returns, etc. carriage returns, etc.
The ABNF for strings in HTTP headers is: The ABNF for strings in HTTP headers is:
sh-string = DQUOTE *(chr) DQUOTE sh-string = DQUOTE *(chr) DQUOTE
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Parsers MUST support strings with at least 1024 characters. Parsers MUST support strings with at least 1024 characters.
3.3.4. Tokens 3.3.4. Tokens
Tokens are short textual words; their abstract model is identical to Tokens are short textual words; their abstract model is identical to
their expression in the HTTP header serialisation. their expression in the HTTP header serialisation.
The ABNF for tokens in HTTP headers is: The ABNF for tokens in HTTP headers is:
sh-token = ALPHA *( tchar / ":" / "/" ) sh-token = ( ALPHA / "\*" ) *( tchar / ":" / "/" )
Parsers MUST support tokens with at least 512 characters. Parsers MUST support tokens with at least 512 characters.
Note that a Structured Header token allows the characters as the Note that a Structured Header token allows the characters as the
"token" ABNF rule defined in [RFC7230], with the exceptions that the "token" ABNF rule defined in [RFC7230], with the exceptions that the
first character is required to be ALPHA, and ":" and "/" are also first character is required to be either ALPHA or "*", and ":" and
allowed. "/" are also allowed in subsequent characters.
3.3.5. Byte Sequences 3.3.5. Byte Sequences
Byte sequences can be conveyed in Structured Headers. Byte sequences can be conveyed in Structured Headers.
The ABNF for a byte sequence in HTTP headers is: The ABNF for a byte sequence in HTTP headers is:
sh-binary = "*" *(base64) "*" sh-binary = ":" *(base64) ":"
base64 = ALPHA / DIGIT / "+" / "/" / "=" base64 = ALPHA / DIGIT / "+" / "/" / "="
In HTTP headers, a byte sequence is delimited with asterisks and In HTTP headers, a byte sequence is delimited with colons and encoded
encoded using base64 ([RFC4648], Section 4). For example: using base64 ([RFC4648], Section 4). For example:
Example-BinaryHdr: *cHJldGVuZCB0aGlzIGlzIGJpbmFyeSBjb250ZW50Lg==* Example-BinaryHdr: :cHJldGVuZCB0aGlzIGlzIGJpbmFyeSBjb250ZW50Lg==:
Parsers MUST support byte sequences with at least 16384 octets after Parsers MUST support byte sequences with at least 16384 octets after
decoding. decoding.
3.3.6. Booleans 3.3.6. Booleans
Boolean values can be conveyed in Structured Headers. Boolean values can be conveyed in Structured Headers.
The ABNF for a Boolean in HTTP headers is: The ABNF for a Boolean in HTTP headers is:
skipping to change at page 13, line 41 skipping to change at page 14, line 35
This section defines how to serialize and parse Structured Headers in This section defines how to serialize and parse Structured Headers in
header fields, and protocols compatible with them (e.g., in HTTP/2 header fields, and protocols compatible with them (e.g., in HTTP/2
[RFC7540] before HPACK [RFC7541] is applied). [RFC7540] before HPACK [RFC7541] is applied).
4.1. Serializing Structured Headers 4.1. Serializing Structured Headers
Given a structure defined in this specification, return an ASCII Given a structure defined in this specification, return an ASCII
string suitable for use in a HTTP header value. string suitable for use in a HTTP header value.
1. If the structure is a dictionary or list and its value is empty 1. If the structure is a Dictionary or List and its value is empty
(i.e., it has no members), do not serialize the field at all (i.e., it has no members), do not serialize the field at all
(i.e., omit both the field-name and field-value). (i.e., omit both the field-name and field-value).
2. If the structure is a dictionary, let output_string be the result 2. If the structure is a Dictionary, let output_string be the result
of running Serializing a Dictionary (Section 4.1.2) with the of running Serializing a Dictionary (Section 4.1.2) with the
structure. structure.
3. Else if the structure is a list, let output_string be the result 3. Else if the structure is a List, let output_string be the result
of running Serializing a List (Section 4.1.1) with the structure. of running Serializing a List (Section 4.1.1) with the structure.
4. Else if the structure is an item, let output_string be the result 4. Else if the structure is an Item, let output_string be the result
of running Serializing an Item (Section 4.1.3) with the of running Serializing an Item (Section 4.1.3) with the
structure. structure.
5. Else, fail serialisation. 5. Else, fail serialisation.
6. Return output_string converted into an array of bytes, using 6. Return output_string converted into an array of bytes, using
ASCII encoding [RFC0020]. ASCII encoding [RFC0020].
4.1.1. Serializing a List 4.1.1. Serializing a List
Given an array of (member-value, parameters) tuples as input_list, Given an array of (member_value, parameters) tuples as input_list,
return an ASCII string suitable for use in a HTTP header value. return an ASCII string suitable for use in a HTTP header value.
1. Let output be an empty string. 1. Let output be an empty string.
2. For each (member-value, parameters) of input_list: 2. For each (member_value, parameters) of input_list:
1. If member-value is an array, append the result of running 1. If member_value is an array, append the result of running
Serialising an Inner List (Section 4.1.1.1) with (member- Serialising an Inner List (Section 4.1.1.1) with
value, parameters) to output. (member_value, parameters) to output.
2. Otherwise, append the result of running Serializing an Item 2. Otherwise, append the result of running Serializing an Item
(Section 4.1.3) with (member-value, parameters) to output. (Section 4.1.3) with (member_value, parameters) to output.
3. If more member-values remain in input_list: 3. If more member_values remain in input_list:
1. Append a COMMA to output. 1. Append a COMMA to output.
2. Append a single WS to output. 2. Append a single SP to output.
3. Return output. 3. Return output.
4.1.1.1. Serialising an Inner List 4.1.1.1. Serialising an Inner List
Given an array of (member-value, parameters) tuples as inner_list, Given an array of (member_value, parameters) tuples as inner_list,
and parameters as list_parameters, return an ASCII string suitable and parameters as list_parameters, return an ASCII string suitable
for use in a HTTP header value. for use in a HTTP header value.
1. Let output be the string "(". 1. Let output be the string "(".
2. For each (member-value, parameters) of inner_list: 2. For each (member_value, parameters) of inner_list:
1. Append the result of running Serializing an Item 1. Append the result of running Serializing an Item
(Section 4.1.3) with (member-value, parameters) to output. (Section 4.1.3) with (member_value, parameters) to output.
2. If more values remain in inner_list, append a single WS to 2. If more values remain in inner_list, append a single SP to
output. output.
3. Append ")" to output. 3. Append ")" to output.
4. Append the result of running Serializing Parameters 4. Append the result of running Serializing Parameters
Section 4.1.1.2 with list_parameters to output. Section 4.1.1.2 with list_parameters to output.
5. Return output. 5. Return output.
4.1.1.2. Serializing Parameters 4.1.1.2. Serializing Parameters
Given an ordered dictionary as input_parameters (each member having a Given an ordered dictionary as input_parameters (each member having a
param-name and a param-value), return an ASCII string suitable for param_name and a param_value), return an ASCII string suitable for
use in a HTTP header value. use in a HTTP header value.
1. Let output be an empty string. 1. Let output be an empty string.
2. For each parameter-name with a value of param-value in 2. For each parameter-name with a value of param_value in
input_parameters: input_parameters:
1. Append ";" to output. 1. Append ";" to output.
2. Append the result of running Serializing a Key 2. Append the result of running Serializing a Key
(Section 4.1.1.3) with param-name to output. (Section 4.1.1.3) with param_name to output.
3. If param-value is not null: 3. If param_value is not Boolean true:
1. Append "=" to output. 1. Append "=" to output.
2. Append the result of running Serializing a bare Item 2. Append the result of running Serializing a bare Item
(Section 4.1.3.1) with param-value to output. (Section 4.1.3.1) with param_value to output.
3. Return output. 3. Return output.
4.1.1.3. Serializing a Key 4.1.1.3. Serializing a Key
Given a key as input_key, return an ASCII string suitable for use in Given a key as input_key, return an ASCII string suitable for use in
a HTTP header value. a HTTP header value.
1. If input_key is not a sequence of characters, or contains 1. If input_key is not a sequence of characters, or contains
characters not in lcalpha, DIGIT, "*", "_", or "-", fail characters not in lcalpha, DIGIT, "_", "-", ".", or "*" fail
serialisation. serialisation.
2. Let output be an empty string. 2. If the first character of input_key is not lcalpha, fail parsing.
3. Append input_key to output. 3. Let output be an empty string.
4. Return output. 4. Append input_key to output.
5. Return output.
4.1.2. Serializing a Dictionary 4.1.2. Serializing a Dictionary
Given an ordered dictionary as input_dictionary (each member having a Given an ordered dictionary as input_dictionary (each member having a
member-name and a tuple value of (member-value, parameters)), return member_name and a tuple value of (member_value, parameters)), return
an ASCII string suitable for use in a HTTP header value. an ASCII string suitable for use in a HTTP header value.
1. Let output be an empty string. 1. Let output be an empty string.
2. For each member-name with a value of (member-value, parameters) 2. For each member_name with a value of (member_value, parameters)
in input_dictionary: in input_dictionary:
1. Append the result of running Serializing a Key 1. Append the result of running Serializing a Key
(Section 4.1.1.3) with member's member-name to output. (Section 4.1.1.3) with member's member_name to output.
2. Append "=" to output. 3. If member_value is not Boolean true or parameters is not empty:
3. If member-value is an array, append the result of running 1. Append "=" to output.
Serialising an Inner List (Section 4.1.1.1) with (member-
value, parameters) to output.
4. Otherwise, append the result of running Serializing an Item 1. If member_value is an array, append the result of running
(Section 4.1.3) with (member-value, parameters) to output. Serialising an Inner List (Section 4.1.1.1) with
(member_value, parameters) to output.
5. If more members remain in input_dictionary: 2. Otherwise, append the result of running Serializing an
Item (Section 4.1.3) with (member_value, parameters) to
output.
1. Append a COMMA to output. 4. If more members remain in input_dictionary:
2. Append a single WS to output. 1. Append a COMMA to output.
3. Return output. 2. Append a single SP to output.
5. Return output.
4.1.3. Serializing an Item 4.1.3. Serializing an Item
Given an item bare_item and parameters item_parameters as input, Given an item bare_item and parameters item_parameters as input,
return an ASCII string suitable for use in a HTTP header value. return an ASCII string suitable for use in a HTTP header value.
1. Let output be an empty string. 1. Let output be an empty string.
2. Append the result of running Serializing a Bare Item 2. Append the result of running Serializing a Bare Item
Section 4.1.3.1 with bare_item to output. Section 4.1.3.1 with bare_item to output.
skipping to change at page 17, line 13 skipping to change at page 18, line 13
4. Return output. 4. Return output.
4.1.3.1. Serialising a Bare Item 4.1.3.1. Serialising a Bare Item
Given an item as input_item, return an ASCII string suitable for use Given an item as input_item, return an ASCII string suitable for use
in a HTTP header value. in a HTTP header value.
1. If input_item is an integer, return the result of running 1. If input_item is an integer, return the result of running
Serializing an Integer (Section 4.1.4) with input_item. Serializing an Integer (Section 4.1.4) with input_item.
2. If input_item is a float, return the result of running 2. If input_item is a decimal, return the result of running
Serializing a Float (Section 4.1.5) with input_item. Serializing a Decimal (Section 4.1.5) with input_item.
3. If input_item is a string, return the result of running 3. If input_item is a string, return the result of running
Serializing a String (Section 4.1.6) with input_item. Serializing a String (Section 4.1.6) with input_item.
4. If input_item is a token, return the result of running 4. If input_item is a token, return the result of running
Serializing a Token (Section 4.1.7) with input_item. Serializing a Token (Section 4.1.7) with input_item.
5. If input_item is a Boolean, return the result of running 5. If input_item is a Boolean, return the result of running
Serializing a Boolean (Section 4.1.9) with input_item. Serializing a Boolean (Section 4.1.9) with input_item.
skipping to change at page 18, line 5 skipping to change at page 19, line 5
2. Let output be an empty string. 2. Let output be an empty string.
3. If input_integer is less than (but not equal to) 0, append "-" to 3. If input_integer is less than (but not equal to) 0, append "-" to
output. output.
4. Append input_integer's numeric value represented in base 10 using 4. Append input_integer's numeric value represented in base 10 using
only decimal digits to output. only decimal digits to output.
5. Return output. 5. Return output.
4.1.5. Serializing a Float 4.1.5. Serializing a Decimal
Given a float as input_float, return an ASCII string suitable for use
in a HTTP header value.
1. Let output be an empty string. Given a decimal_number as input_decimal, return an ASCII string
suitable for use in a HTTP header value.
2. If input_float is less than (but not equal to) 0, append "-" to 1. Let output be an empty string.
output.
3. Append input_float's integer component represented in base 10 2. If input_decimal is less than (but not equal to) 0, append "-" to
(using only decimal digits) to output; if it is zero, append output.
"0".
4. Let integer_digits be the number of characters appended in the 3. Append input_decimal's integer component represented in base 10
previous step. (using only decimal digits) to output; if it is zero, append "0".
5. If integer_digits is greater than 14, fail serialisation. 4. If the number of characters appended in the previous step is
greater than 12, fail serialisation.
6. Let digits_avail be 15 minus integer_digits. 5. Append "." to output.
7. Let fractional_digits_avail be the minimum of digits_avail and 6. If input_decimal's fractional component is zero, append "0" to
6. output.
8. Append "." to output. 7. Else if input_decimal's fractional component has up to three
digits, append them represented in base 10 (using only decimal
digits) to output.
9. Append at most fractional_digits_avail digits of input_float's 8. Otherwise, append the first three digits of input_decimal's
fractional component represented in base 10 to output (using fractional component (represented in base 10, using only decimal
only decimal digits, and truncating any remaining digits); if it digits) to output, rounding the final digit to the nearest value,
is zero, append "0". or to the even value if it is equidistant.
10. Return output. 9. Return output.
4.1.6. Serializing a String 4.1.6. Serializing a String
Given a string as input_string, return an ASCII string suitable for Given a string as input_string, return an ASCII string suitable for
use in a HTTP header value. use in a HTTP header value.
1. If input_string is not a sequence of characters, or contains 1. If input_string is not a sequence of characters, or contains
characters in the range %x00-1f or %x7f (i.e., is not in VCHAR or characters in the range %x00-1f or %x7f (i.e., is not in VCHAR or
SP), fail serialisation. SP), fail serialisation.
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5. Append DQUOTE to output. 5. Append DQUOTE to output.
6. Return output. 6. Return output.
4.1.7. Serializing a Token 4.1.7. Serializing a Token
Given a token as input_token, return an ASCII string suitable for use Given a token as input_token, return an ASCII string suitable for use
in a HTTP header value. in a HTTP header value.
1. If input_token is not a sequence of characters, or contains 1. If input_token is not a sequence of characters, the first
characters not allowed by the tchar ABNF rule, fail character is not ALPHA or "*", or the remaining contain a
serialisation. character not in tchar, ":" or "/", fail serialisation.
2. Let output be an empty string. 2. Let output be an empty string.
3. Append input_token to output. 3. Append input_token to output.
4. Return output. 4. Return output.
4.1.8. Serializing a Byte Sequence 4.1.8. Serializing a Byte Sequence
Given a byte sequence as input_bytes, return an ASCII string suitable Given a byte sequence as input_bytes, return an ASCII string suitable
for use in a HTTP header value. for use in a HTTP header value.
1. If input_bytes is not a sequence of bytes, fail serialisation. 1. If input_bytes is not a sequence of bytes, fail serialisation.
2. Let output be an empty string. 2. Let output be an empty string.
3. Append "*" to output. 3. Append ":" to output.
4. Append the result of base64-encoding input_bytes as per 4. Append the result of base64-encoding input_bytes as per
[RFC4648], Section 4, taking account of the requirements below. [RFC4648], Section 4, taking account of the requirements below.
5. Append "*" to output. 5. Append ":" to output.
6. Return output. 6. Return output.
The encoded data is required to be padded with "=", as per [RFC4648], The encoded data is required to be padded with "=", as per [RFC4648],
Section 3.2. Section 3.2.
Likewise, encoded data SHOULD have pad bits set to zero, as per Likewise, encoded data SHOULD have pad bits set to zero, as per
[RFC4648], Section 3.5, unless it is not possible to do so due to [RFC4648], Section 3.5, unless it is not possible to do so due to
implementation constraints. implementation constraints.
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doing so. doing so.
Given an array of bytes input_bytes that represents the chosen Given an array of bytes input_bytes that represents the chosen
header's field-value (which is empty if that header is not present), header's field-value (which is empty if that header is not present),
and header_type (one of "dictionary", "list", or "item"), return the and header_type (one of "dictionary", "list", or "item"), return the
parsed header value. parsed header value.
1. Convert input_bytes into an ASCII string input_string; if 1. Convert input_bytes into an ASCII string input_string; if
conversion fails, fail parsing. conversion fails, fail parsing.
2. Discard any leading OWS from input_string. 2. Discard any leading SP characters from input_string.
3. If header_type is "list", let output be the result of running 3. If header_type is "list", let output be the result of running
Parsing a List (Section 4.2.1) with input_string. Parsing a List (Section 4.2.1) with input_string.
4. If header_type is "dictionary", let output be the result of 4. If header_type is "dictionary", let output be the result of
running Parsing a Dictionary (Section 4.2.2) with input_string. running Parsing a Dictionary (Section 4.2.2) with input_string.
5. If header_type is "item", let output be the result of running 5. If header_type is "item", let output be the result of running
Parsing an Item (Section 4.2.3) with input_string. Parsing an Item (Section 4.2.3) with input_string.
6. Discard any leading OWS from input_string. 6. Discard any leading SP characters from input_string.
7. If input_string is not empty, fail parsing. 7. If input_string is not empty, fail parsing.
8. Otherwise, return output. 8. Otherwise, return output.
When generating input_bytes, parsers MUST combine all instances of When generating input_bytes, parsers MUST combine all instances of
the target header field into one comma-separated field-value, as per the target header field into one comma-separated field-value, as per
[RFC7230], Section 3.2.2; this assures that the header is processed [RFC7230], Section 3.2.2; this assures that the header is processed
correctly. correctly.
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concatenating all instances of the header field, as long as concatenating all instances of the header field, as long as
individual individual members of the top-level data structure are not individual individual members of the top-level data structure are not
split across multiple header instances. split across multiple header instances.
Strings split across multiple header instances will have Strings split across multiple header instances will have
unpredictable results, because comma(s) and whitespace inserted upon unpredictable results, because comma(s) and whitespace inserted upon
combination will become part of the string output by the parser. combination will become part of the string output by the parser.
Since concatenation might be done by an upstream intermediary, the Since concatenation might be done by an upstream intermediary, the
results are not under the control of the serializer or the parser. results are not under the control of the serializer or the parser.
Tokens, Integers, Floats and Byte Sequences cannot be split across Tokens, Integers, Decimals and Byte Sequences cannot be split across
multiple headers because the inserted commas will cause parsing to multiple headers because the inserted commas will cause parsing to
fail. fail.
If parsing fails - including when calling another algorithm - the If parsing fails - including when calling another algorithm - the
entire header field's value MUST be ignored (i.e., treated as if the entire header field's value MUST be ignored (i.e., treated as if the
header field were not present in the message). This is intentionally header field were not present in the message). This is intentionally
strict, to improve interoperability and safety, and specifications strict, to improve interoperability and safety, and specifications
referencing this document are not allowed to loosen this requirement. referencing this document are not allowed to loosen this requirement.
Note that this requirement does not apply to an implementation that Note that this requirement does not apply to an implementation that
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(item_or_inner_list, parameters) tuples. input_string is modified to (item_or_inner_list, parameters) tuples. input_string is modified to
remove the parsed value. remove the parsed value.
1. Let members be an empty array. 1. Let members be an empty array.
2. While input_string is not empty: 2. While input_string is not empty:
1. Append the result of running Parsing an Item or Inner List 1. Append the result of running Parsing an Item or Inner List
(Section 4.2.1.1) with input_string to members. (Section 4.2.1.1) with input_string to members.
2. Discard any leading OWS from input_string. 2. Discard any leading SP characters from input_string.
3. If input_string is empty, return members. 3. If input_string is empty, return members.
4. Consume the first character of input_string; if it is not 4. Consume the first character of input_string; if it is not
COMMA, fail parsing. COMMA, fail parsing.
5. Discard any leading OWS from input_string. 5. Discard any leading SP characters from input_string.
6. If input_string is empty, there is a trailing comma; fail 6. If input_string is empty, there is a trailing comma; fail
parsing. parsing.
3. No structured data has been found; return members (which is 3. No structured data has been found; return members (which is
empty). empty).
4.2.1.1. Parsing an Item or Inner List 4.2.1.1. Parsing an Item or Inner List
Given an ASCII string as input_string, return the tuple Given an ASCII string as input_string, return the tuple
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parameters), where inner_list is an array of (bare_item, parameters) parameters), where inner_list is an array of (bare_item, parameters)
tuples. input_string is modified to remove the parsed value. tuples. input_string is modified to remove the parsed value.
1. Consume the first character of input_string; if it is not "(", 1. Consume the first character of input_string; if it is not "(",
fail parsing. fail parsing.
2. Let inner_list be an empty array. 2. Let inner_list be an empty array.
3. While input_string is not empty: 3. While input_string is not empty:
1. Discard any leading OWS from input_string. 1. Discard any leading SP characters from input_string.
2. If the first character of input_string is ")": 2. If the first character of input_string is ")":
1. Consume the first character of input_string. 1. Consume the first character of input_string.
2. Let parameters be the result of running Parsing 2. Let parameters be the result of running Parsing
Parameters (Section 4.2.3.2) with input_string. Parameters (Section 4.2.3.2) with input_string.
3. Return the tuple (inner_list, parameters). 3. Return the tuple (inner_list, parameters).
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4.2.2. Parsing a Dictionary 4.2.2. Parsing a Dictionary
Given an ASCII string as input_string, return an ordered map whose Given an ASCII string as input_string, return an ordered map whose
values are (item_or_inner_list, parameters) tuples. input_string is values are (item_or_inner_list, parameters) tuples. input_string is
modified to remove the parsed value. modified to remove the parsed value.
1. Let dictionary be an empty, ordered map. 1. Let dictionary be an empty, ordered map.
2. While input_string is not empty: 2. While input_string is not empty:
1. Let this_key be the result of running Parsing a Key 1. Let this_key be the result of running Parsing a Key
(Section 4.2.3.3) with input_string. (Section 4.2.3.3) with input_string.
2. If dictionary already contains the name this_key, there is a 2. If the first character of input_string is "=":
duplicate; fail parsing.
3. Consume the first character of input_string; if it is not 1. Consume the first character of input_string.
"=", fail parsing.
4. Let member be the result of running Parsing an Item or Inner 2. Let member be the result of running Parsing an Item or
List (Section 4.2.1.1) with input_string. Inner List (Section 4.2.1.1) with input_string.
5. Add name this_key with value member to dictionary. 3. Otherwise:
6. Discard any leading OWS from input_string. 1. Let value be Boolean true.
7. If input_string is empty, return dictionary. 2. Let parameters be an empty, ordered map.
8. Consume the first character of input_string; if it is not 3. Let member be the tuple (value, parameters).
COMMA, fail parsing.
9. Discard any leading OWS from input_string. 4. Add name this_key with value member to dictionary. If
dictionary already contains a name this_key (comparing
character-for-character), overwrite its value.
10. If input_string is empty, there is a trailing comma; fail 5. Discard any leading SP characters from input_string.
parsing.
6. If input_string is empty, return dictionary.
7. Consume the first character of input_string; if it is not
COMMA, fail parsing.
8. Discard any leading SP characters from input_string.
9. If input_string is empty, there is a trailing comma; fail
parsing.
3. No structured data has been found; return dictionary (which is 3. No structured data has been found; return dictionary (which is
empty). empty).
4.2.3. Parsing an Item 4.2.3. Parsing an Item
Given an ASCII string as input_string, return a (bare_item, Given an ASCII string as input_string, return a (bare_item,
parameters) tuple. input_string is modified to remove the parsed parameters) tuple. input_string is modified to remove the parsed
value. value.
skipping to change at page 24, line 40 skipping to change at page 25, line 43
input_string is modified to remove the parsed value. input_string is modified to remove the parsed value.
1. If the first character of input_string is a "-" or a DIGIT, 1. If the first character of input_string is a "-" or a DIGIT,
return the result of running Parsing a Number (Section 4.2.4) return the result of running Parsing a Number (Section 4.2.4)
with input_string. with input_string.
2. If the first character of input_string is a DQUOTE, return the 2. If the first character of input_string is a DQUOTE, return the
result of running Parsing a String (Section 4.2.5) with result of running Parsing a String (Section 4.2.5) with
input_string. input_string.
3. If the first character of input_string is "*", return the result 3. If the first character of input_string is ":", return the result
of running Parsing a Byte Sequence (Section 4.2.7) with of running Parsing a Byte Sequence (Section 4.2.7) with
input_string. input_string.
4. If the first character of input_string is "?", return the result 4. If the first character of input_string is "?", return the result
of running Parsing a Boolean (Section 4.2.8) with input_string. of running Parsing a Boolean (Section 4.2.8) with input_string.
5. If the first character of input_string is an ALPHA, return the 5. If the first character of input_string is an ALPHA or "*", return
result of running Parsing a Token (Section 4.2.6) with the result of running Parsing a Token (Section 4.2.6) with
input_string. input_string.
6. Otherwise, the item type is unrecognized; fail parsing. 6. Otherwise, the item type is unrecognized; fail parsing.
4.2.3.2. Parsing Parameters 4.2.3.2. Parsing Parameters
Given an ASCII string as input_string, return an ordered map whose Given an ASCII string as input_string, return an ordered map whose
values are bare items. input_string is modified to remove the parsed values are bare items. input_string is modified to remove the parsed
value. value.
1. Let parameters be an empty, ordered map. 1. Let parameters be an empty, ordered map.
2. While input_string is not empty: 2. While input_string is not empty:
1. If the first character of input_string is not ";", exit the 1. If the first character of input_string is not ";", exit the
loop. loop.
2. Consume a ";" character from the beginning of input_string. 2. Consume a ";" character from the beginning of input_string.
3. Discard any leading OWS from input_string. 3. Discard any leading SP characters from input_string.
4. let param_name be the result of running Parsing a Key 4. let param_name be the result of running Parsing a Key
(Section 4.2.3.3) with input_string. (Section 4.2.3.3) with input_string.
5. If param_name is already present in parameters, there is a 5. Let param_value be Boolean true.
duplicate; fail parsing.
6. Let param_value be a null value.
7. If the first character of input_string is "=": 6. 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 running Parsing a Bare 2. Let param_value be the result of running Parsing a Bare
Item (Section 4.2.3.1) with input_string. Item (Section 4.2.3.1) with input_string.
8. Append key param_name with value param_value to parameters. 7. Append key param_name with value param_value to parameters.
If parameters already contains a name param_name (comparing
character-for-character), overwrite its value.
3. Return parameters. 3. Return parameters.
4.2.3.3. Parsing a Key from Text 4.2.3.3. Parsing a Key
Given an ASCII string as input_string, return a key. input_string is Given an ASCII string as input_string, return a key. input_string is
modified to remove the parsed value. modified to remove the parsed value.
1. If the first character of input_string is not lcalpha, fail 1. If the first character of input_string is not lcalpha, fail
parsing. parsing.
2. Let output_string be an empty string. 2. Let output_string be an empty string.
3. While input_string is not empty: 3. While input_string is not empty:
1. If the first character of input_string is not one of lcalpha, 1. If the first character of input_string is not one of lcalpha,
DIGIT, "*", "_", or "-", return output_string. DIGIT, "_", "-", ".", or "*", return output_string.
2. Let char be the result of removing the first character of 2. Let char be the result of removing the first character of
input_string. input_string.
3. Append char to output_string. 3. Append char to output_string.
4. Return output_string. 4. Return output_string.
4.2.4. Parsing a Number from Text 4.2.4. Parsing a Number
Given an ASCII string as input_string, return a number. input_string Given an ASCII string as input_string, return a number. input_string
is modified to remove the parsed value. is modified to remove the parsed value.
NOTE: This algorithm parses both Integers (Section 3.3.1) and Floats NOTE: This algorithm parses both Integers (Section 3.3.1) and
(Section 3.3.2), and returns the corresponding structure. Decimals (Section 3.3.2), and returns the corresponding structure.
1. Let type be "integer". 1. Let type be "integer".
2. Let sign be 1. 2. Let sign be 1.
3. Let input_number be an empty string. 3. Let input_number be an empty string.
4. If the first character of input_string is "-", consume it and 4. If the first character of input_string is "-", consume it and
set sign to -1. set sign to -1.
skipping to change at page 26, line 45 skipping to change at page 27, line 47
6. If the first character of input_string is not a DIGIT, fail 6. If the first character of input_string is not a DIGIT, fail
parsing. parsing.
7. While input_string is not empty: 7. While input_string is not empty:
1. Let char be the result of consuming the first character of 1. Let char be the result of consuming the first character of
input_string. input_string.
2. If char is a DIGIT, append it to input_number. 2. If char is a DIGIT, append it to input_number.
3. Else, if type is "integer" and char is ".", append char to 3. Else, if type is "integer" and char is ".":
input_number and set type to "float".
1. If input_number contains more than 12 characters, fail
parsing.
2. Otherwise, append char to input_number and set type to
"decimal".
4. Otherwise, prepend char to input_string, and exit the loop. 4. Otherwise, prepend char to input_string, and exit the loop.
5. If type is "integer" and input_number contains more than 15 5. If type is "integer" and input_number contains more than 15
characters, fail parsing. characters, fail parsing.
6. If type is "float" and input_number contains more than 16 6. If type is "decimal" and input_number contains more than 16
characters, fail parsing. characters, fail parsing.
8. If type is "integer": 8. If type is "integer":
1. Parse input_number as an integer and let output_number be 1. Parse input_number as an integer and let output_number be
the product of the result and sign. the product of the result and sign.
2. If output_number is outside the range defined in 2. If output_number is outside the range -999,999,999,999,999
Section 3.3.1, fail parsing. to 999,999,999,999,999 inclusive, fail parsing.
9. Otherwise: 9. Otherwise:
1. If the final character of input_number is ".", fail parsing. 1. If the final character of input_number is ".", fail parsing.
2. If the number of characters after "." in input_number is 2. If the number of characters after "." in input_number is
greater than six, fail parsing. greater than three, fail parsing.
3. Parse input_number as a float and let output_number be the 3. Parse input_number as a decimal number and let output_number
product of the result and sign. be the product of the result and sign.
10. Return output_number. 10. Return output_number.
4.2.5. Parsing a String from Text 4.2.5. Parsing a String
Given an ASCII string as input_string, return an unquoted string. Given an ASCII string as input_string, return an unquoted string.
input_string is modified to remove the parsed value. input_string is modified to remove the parsed value.
1. Let output_string be an empty string. 1. Let output_string be an empty string.
2. If the first character of input_string is not DQUOTE, fail 2. If the first character of input_string is not DQUOTE, fail
parsing. parsing.
3. Discard the first character of input_string. 3. Discard the first character of input_string.
skipping to change at page 28, line 17 skipping to change at page 29, line 26
3. Else, if char is DQUOTE, return output_string. 3. Else, if char is DQUOTE, return output_string.
4. Else, if char is in the range %x00-1f or %x7f (i.e., is not 4. Else, if char is in the range %x00-1f or %x7f (i.e., is not
in VCHAR or SP), fail parsing. in VCHAR or SP), fail parsing.
5. Else, append char to output_string. 5. Else, append char to output_string.
5. Reached the end of input_string without finding a closing DQUOTE; 5. Reached the end of input_string without finding a closing DQUOTE;
fail parsing. fail parsing.
4.2.6. Parsing a Token from Text 4.2.6. Parsing a Token
Given an ASCII string as input_string, return a token. input_string Given an ASCII string as input_string, return a token. input_string
is modified to remove the parsed value. is modified to remove the parsed value.
1. If the first character of input_string is not ALPHA, fail 1. If the first character of input_string is not ALPHA or "*", fail
parsing. parsing.
2. Let output_string be an empty string. 2. Let output_string be an empty string.
3. While input_string is not empty: 3. While input_string is not empty:
1. If the first character of input_string is not allowed by the 1. If the first character of input_string is not in tchar, ":"
tchar ABNF rule, return output_string. or "/", return output_string.
2. Let char be the result of consuming the first character of 2. Let char be the result of consuming the first character of
input_string. input_string.
3. Append char to output_string. 3. Append char to output_string.
4. Return output_string. 4. Return output_string.
4.2.7. Parsing a Byte Sequence from Text 4.2.7. Parsing a Byte Sequence
Given an ASCII string as input_string, return a byte sequence. Given an ASCII string as input_string, return a byte sequence.
input_string is modified to remove the parsed value. input_string is modified to remove the parsed value.
1. If the first character of input_string is not "*", fail parsing. 1. If the first character of input_string is not ":", fail parsing.
2. Discard the first character of input_string. 2. Discard the first character of input_string.
3. If there is not a "*" character before the end of input_string, 3. If there is not a ":" character before the end of input_string,
fail parsing. fail parsing.
4. Let b64_content be the result of consuming content of 4. Let b64_content be the result of consuming content of
input_string up to but not including the first instance of the input_string up to but not including the first instance of the
character "*". character ":".
5. Consume the "*" character at the beginning of input_string. 5. Consume the ":" character at the beginning of input_string.
6. If b64_content contains a character not included in ALPHA, DIGIT, 6. If b64_content contains a character not included in ALPHA, DIGIT,
"+", "/" and "=", fail parsing. "+", "/" and "=", fail parsing.
7. Let binary_content be the result of Base 64 Decoding [RFC4648] 7. Let binary_content be the result of Base 64 Decoding [RFC4648]
b64_content, synthesizing padding if necessary (note the b64_content, synthesizing padding if necessary (note the
requirements about recipient behaviour below). requirements about recipient behaviour below).
8. Return binary_content. 8. Return binary_content.
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Because some implementations of base64 do not allow rejection of Because some implementations of base64 do not allow rejection of
encoded data that has non-zero pad bits (see [RFC4648], Section 3.5), encoded data that has non-zero pad bits (see [RFC4648], Section 3.5),
parsers SHOULD NOT fail when it is present, unless they cannot be parsers SHOULD NOT fail when it is present, unless they cannot be
configured to do so. configured to do so.
This specification does not relax the requirements in [RFC4648], This specification does not relax the requirements in [RFC4648],
Section 3.1 and 3.3; therefore, parsers MUST fail on characters Section 3.1 and 3.3; therefore, parsers MUST fail on characters
outside the base64 alphabet, and on line feeds in encoded data. outside the base64 alphabet, and on line feeds in encoded data.
4.2.8. Parsing a Boolean from Text 4.2.8. Parsing a Boolean
Given an ASCII string as input_string, return a Boolean. input_string Given an ASCII string as input_string, return a Boolean. input_string
is modified to remove the parsed value. is modified to remove the parsed value.
1. If the first character of input_string is not "?", fail parsing. 1. If the first character of input_string is not "?", fail parsing.
2. Discard the first character of input_string. 2. Discard the first character of input_string.
3. If the first character of input_string matches "1", discard the 3. If the first character of input_string matches "1", discard the
first character, and return true. first character, and return true.
skipping to change at page 33, line 22 skipping to change at page 34, line 22
Sometimes, this can be achieved by creating limited substructures in Sometimes, this can be achieved by creating limited substructures in
values, and/or using more than one header. For example, consider: values, and/or using more than one header. For example, consider:
Example-Thing: name="Widget", cost=89.2, descriptions=(foo bar) Example-Thing: name="Widget", cost=89.2, descriptions=(foo bar)
Example-Description: foo; url="https://example.net"; context=123, Example-Description: foo; url="https://example.net"; context=123,
bar; url="https://example.org"; context=456 bar; url="https://example.org"; context=456
Since the description contains an array of key/value pairs, we use a Since the description contains an array of key/value pairs, we use a
List to represent them, with the token for each item in the array List to represent them, with the token for each item in the array
used to identify it in the "descriptions" member of the Example-Thing used to identify it in the "descriptions" member of the Example-Thing
header. dictionary header.
When specifying more than one header, it's important to remember to When specifying more than one header, it's important to remember to
describe what a processor's behaviour should be when one of the describe what a processor's behaviour should be when one of the
headers is missing. headers is missing.
If you need to fit arbitrarily complex data into a header, Structured If you need to fit arbitrarily complex data into a header, Structured
Headers is probably a poor fit for your use case. Headers is probably a poor fit for your use case.
Appendix C. Implementation Notes Appendix C. Implementation Notes
skipping to change at page 34, line 9 skipping to change at page 35, line 9
Likewise, implementations should note that it's important to preserve Likewise, implementations should note that it's important to preserve
the distinction between tokens and strings. While most programming the distinction between tokens and strings. While most programming
languages have native types that map to the other types well, it may languages have native types that map to the other types well, it may
be necessary to create a wrapper "token" object or use a parameter on be necessary to create a wrapper "token" object or use a parameter on
functions to assure that these types remain separate. functions to assure that these types remain separate.
Appendix D. Changes Appendix D. Changes
_RFC Editor: Please remove this section before publication._ _RFC Editor: Please remove this section before publication._
D.1. Since draft-ietf-httpbis-header-structure-13 D.1. Since draft-ietf-httpbis-header-structure-14
o Editorial improvements.
o Allow empty dictionary values (#992).
o Change value of omitted parameter value to True (#995).
o Explain more about splitting dictionaries and lists across header
instances (#997).
o Disallow HTAB, replace OWS with spaces (#998).
o Change byte sequence delimiters from "*" to ":" (#991).
o Allow tokens to start with "*" (#991).
o Change Floats to fixed-precision Decimals (#982).
o Round the fractional component of decimal, rather than truncating
it (#982).
o Handle duplicate dictionary and parameter keys by overwriting
their values, rather than failing (#997).
o Allow "." in key (#1027).
o Check first character of key in serialisation (#1037).
D.2. Since draft-ietf-httpbis-header-structure-13
o Editorial improvements. o Editorial improvements.
o Define "structured header name" and "structured header value" o Define "structured header name" and "structured header value"
terms (#908). terms (#908).
o Corrected text about valid characters in strings (#931). o Corrected text about valid characters in strings (#931).
o Removed most instances of the word "textual", as it was redundant o Removed most instances of the word "textual", as it was redundant
(#915). (#915).
o Allowed parameters on Items and Inner Lists (#907). o Allowed parameters on Items and Inner Lists (#907).
o Expand the range of characters in token (#961). o Expand the range of characters in token (#961).
o Disallow OWS before ";" delimiter in parameters (#961). o Disallow OWS before ";" delimiter in parameters (#961).
D.2. Since draft-ietf-httpbis-header-structure-12 D.3. Since draft-ietf-httpbis-header-structure-12
o Editorial improvements. o Editorial improvements.
o Reworked float serialisation (#896). o Reworked float serialisation (#896).
o Don't add a trailing space in inner-list (#904). o Don't add a trailing space in inner-list (#904).
D.3. Since draft-ietf-httpbis-header-structure-11 D.4. Since draft-ietf-httpbis-header-structure-11
o Allow * in key (#844). o Allow * in key (#844).
o Constrain floats to six digits of precision (#848). o Constrain floats to six digits of precision (#848).
o Allow dictionary members to have parameters (#842). o Allow dictionary members to have parameters (#842).
D.4. Since draft-ietf-httpbis-header-structure-10 D.5. Since draft-ietf-httpbis-header-structure-10
o Update abstract (#799). o Update abstract (#799).
o Input and output are now arrays of bytes (#662). o Input and output are now arrays of bytes (#662).
o Implementations need to preserve difference between token and o Implementations need to preserve difference between token and
string (#790). string (#790).
o Allow empty dictionaries and lists (#781). o Allow empty dictionaries and lists (#781).
o Change parameterized lists to have primary items (#797). o Change parameterized lists to have primary items (#797).
o Allow inner lists in both dictionaries and lists; removes lists of o Allow inner lists in both dictionaries and lists; removes lists of
lists (#816). lists (#816).
o Subsume Parameterised Lists into Lists (#839). o Subsume Parameterised Lists into Lists (#839).
D.5. Since draft-ietf-httpbis-header-structure-09 D.6. Since draft-ietf-httpbis-header-structure-09
o Changed Boolean from T/F to 1/0 (#784). o Changed Boolean from T/F to 1/0 (#784).
o Parameters are now ordered maps (#765). o Parameters are now ordered maps (#765).
o Clamp integers to 15 digits (#737). o Clamp integers to 15 digits (#737).
D.6. Since draft-ietf-httpbis-header-structure-08 D.7. Since draft-ietf-httpbis-header-structure-08
o Disallow whitespace before items properly (#703). o Disallow whitespace before items properly (#703).
o Created "key" for use in dictionaries and parameters, rather than o Created "key" for use in dictionaries and parameters, rather than
relying on identifier (#702). Identifiers have a separate minimum relying on identifier (#702). Identifiers have a separate minimum
supported size. supported size.
o Expanded the range of special characters allowed in identifier to o Expanded the range of special characters allowed in identifier to
include all of ALPHA, ".", ":", and "%" (#702). include all of ALPHA, ".", ":", and "%" (#702).
skipping to change at page 35, line 44 skipping to change at page 37, line 29
o Gave better names for referring specs to use in Parameterised o Gave better names for referring specs to use in Parameterised
Lists (#720). Lists (#720).
o Added Lists of Lists (#721). o Added Lists of Lists (#721).
o Rename Identifier to Token (#725). o Rename Identifier to Token (#725).
o Add implementation guidance (#727). o Add implementation guidance (#727).
D.7. Since draft-ietf-httpbis-header-structure-07 D.8. Since draft-ietf-httpbis-header-structure-07
o Make Dictionaries ordered mappings (#659). o Make Dictionaries ordered mappings (#659).
o Changed "binary content" to "byte sequence" to align with Infra o Changed "binary content" to "byte sequence" to align with Infra
specification (#671). specification (#671).
o Changed "mapping" to "map" for #671. o Changed "mapping" to "map" for #671.
o Don't fail if byte sequences aren't "=" padded (#658). o Don't fail if byte sequences aren't "=" padded (#658).
o Add Booleans (#683). o Add Booleans (#683).
o Allow identifiers in items again (#629). o Allow identifiers in items again (#629).
o Disallowed whitespace before items (#703). o Disallowed whitespace before items (#703).
o Explain the consequences of splitting a string across multiple o Explain the consequences of splitting a string across multiple
headers (#686). headers (#686).
D.8. Since draft-ietf-httpbis-header-structure-06 D.9. Since draft-ietf-httpbis-header-structure-06
o Add a FAQ. o Add a FAQ.
o Allow non-zero pad bits. o Allow non-zero pad bits.
o Explicitly check for integers that violate constraints. o Explicitly check for integers that violate constraints.
D.9. Since draft-ietf-httpbis-header-structure-05 D.10. Since draft-ietf-httpbis-header-structure-05
o Reorganise specification to separate parsing out. o Reorganise specification to separate parsing out.
o Allow referencing specs to use ABNF. o Allow referencing specs to use ABNF.
o Define serialisation algorithms. o Define serialisation algorithms.
o Refine relationship between ABNF, parsing and serialisation o Refine relationship between ABNF, parsing and serialisation
algorithms. algorithms.
D.10. Since draft-ietf-httpbis-header-structure-04 D.11. Since draft-ietf-httpbis-header-structure-04
o Remove identifiers from item. o Remove identifiers from item.
o Remove most limits on sizes. o Remove most limits on sizes.
o Refine number parsing. o Refine number parsing.
D.11. Since draft-ietf-httpbis-header-structure-03 D.12. Since draft-ietf-httpbis-header-structure-03
o Strengthen language around failure handling. o Strengthen language around failure handling.
D.12. Since draft-ietf-httpbis-header-structure-02 D.13. Since draft-ietf-httpbis-header-structure-02
o Split Numbers into Integers and Floats. o Split Numbers into Integers and Floats.
o Define number parsing. o Define number parsing.
o Tighten up binary parsing and give it an explicit end delimiter. o Tighten up binary parsing and give it an explicit end delimiter.
o Clarify that mappings are unordered. o Clarify that mappings are unordered.
o Allow zero-length strings. o Allow zero-length strings.
o Improve string parsing algorithm. o Improve string parsing algorithm.
o Improve limits in algorithms. o Improve limits in algorithms.
o Require parsers to combine header fields before processing. o Require parsers to combine header fields before processing.
o Throw an error on trailing garbage. o Throw an error on trailing garbage.
D.13. Since draft-ietf-httpbis-header-structure-01 D.14. Since draft-ietf-httpbis-header-structure-01
o Replaced with draft-nottingham-structured-headers. o Replaced with draft-nottingham-structured-headers.
D.14. Since draft-ietf-httpbis-header-structure-00 D.15. Since draft-ietf-httpbis-header-structure-00
o Added signed 64bit integer type. o Added signed 64bit integer type.
o Drop UTF8, and settle on BCP137 ::EmbeddedUnicodeChar for h1- o Drop UTF8, and settle on BCP137 ::EmbeddedUnicodeChar for h1-
unicode-string. unicode-string.
o Change h1_blob delimiter to ":" since "'" is valid t_char o Change h1_blob delimiter to ":" since "'" is valid t_char
Authors' Addresses Authors' Addresses
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