draft-ietf-httpbis-header-structure-08.txt   draft-ietf-httpbis-header-structure-09.txt 
HTTP 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: April 26, 2019 The Varnish Cache Project Expires: June 4, 2019 The Varnish Cache Project
October 23, 2018 December 1, 2018
Structured Headers for HTTP Structured Headers for HTTP
draft-ietf-httpbis-header-structure-08 draft-ietf-httpbis-header-structure-09
Abstract Abstract
This document describes a set of data types and algorithms associated This document describes a set of data types and algorithms associated
with them that are intended to make it easier and safer to define and with them that are intended to make it easier and safer to define and
handle HTTP header fields. It is intended for use by new handle HTTP header fields. It is intended for use by new
specifications of HTTP header fields as well as revisions of existing specifications of HTTP header fields as well as revisions of existing
header field specifications when doing so does not cause header field specifications when doing so does not cause
interoperability issues. interoperability issues.
skipping to change at page 2, line 10 skipping to change at page 2, line 10
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 April 26, 2019. This Internet-Draft will expire on June 4, 2019.
Copyright Notice Copyright Notice
Copyright (c) 2018 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.
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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. Notational Conventions . . . . . . . . . . . . . . . . . 4 1.1. Intentionally Strict Processing . . . . . . . . . . . . . 4
2. Defining New Structured Headers . . . . . . . . . . . . . . . 4 1.2. Notational Conventions . . . . . . . . . . . . . . . . . 4
2. Defining New Structured Headers . . . . . . . . . . . . . . . 5
3. Structured Header Data Types . . . . . . . . . . . . . . . . 7 3. Structured Header Data Types . . . . . . . . . . . . . . . . 7
3.1. Dictionaries . . . . . . . . . . . . . . . . . . . . . . 7 3.1. Dictionaries . . . . . . . . . . . . . . . . . . . . . . 7
3.2. Lists . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.2. Lists . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.3. Parameterised Lists . . . . . . . . . . . . . . . . . . . 8 3.3. Lists of Lists . . . . . . . . . . . . . . . . . . . . . 8
3.4. Items . . . . . . . . . . . . . . . . . . . . . . . . . . 8 3.4. Parameterised Lists . . . . . . . . . . . . . . . . . . . 8
3.5. Integers . . . . . . . . . . . . . . . . . . . . . . . . 9 3.5. Items . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.6. Floats . . . . . . . . . . . . . . . . . . . . . . . . . 9 3.6. Integers . . . . . . . . . . . . . . . . . . . . . . . . 9
3.7. Strings . . . . . . . . . . . . . . . . . . . . . . . . . 9 3.7. Floats . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.8. Identifiers . . . . . . . . . . . . . . . . . . . . . . . 10 3.8. Strings . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.9. Byte Sequences . . . . . . . . . . . . . . . . . . . . . 10 3.9. Tokens . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.10. Booleans . . . . . . . . . . . . . . . . . . . . . . . . 11 3.10. Byte Sequences . . . . . . . . . . . . . . . . . . . . . 11
4. Structured Headers in HTTP/1 . . . . . . . . . . . . . . . . 11 3.11. Booleans . . . . . . . . . . . . . . . . . . . . . . . . 11
4.1. Serialising Structured Headers into HTTP/1 . . . . . . . 11 4. Structured Headers in HTTP/1 . . . . . . . . . . . . . . . . 12
4.2. Parsing HTTP/1 Header Fields into Structured Headers . . 16 4.1. Serialising Structured Headers into HTTP/1 . . . . . . . 12
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24 4.2. Parsing HTTP/1 Header Fields into Structured Headers . . 18
6. Security Considerations . . . . . . . . . . . . . . . . . . . 24 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 25 6. Security Considerations . . . . . . . . . . . . . . . . . . . 27
7.1. Normative References . . . . . . . . . . . . . . . . . . 25 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 28
7.2. Informative References . . . . . . . . . . . . . . . . . 25 7.1. Normative References . . . . . . . . . . . . . . . . . . 28
7.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 26 7.2. Informative References . . . . . . . . . . . . . . . . . 28
Appendix A. Frequently Asked Questions . . . . . . . . . . . . . 26 7.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 29
A.1. Why not JSON? . . . . . . . . . . . . . . . . . . . . . . 26 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 29
A.2. Structured Headers don't "fit" my data. . . . . . . . . . 27 Appendix B. Frequently Asked Questions . . . . . . . . . . . . . 29
Appendix B. Changes . . . . . . . . . . . . . . . . . . . . . . 28 B.1. Why not JSON? . . . . . . . . . . . . . . . . . . . . . . 30
B.1. Since draft-ietf-httpbis-header-structure-07 . . . . . . 28 B.2. Structured Headers don't "fit" my data. . . . . . . . . . 30
B.2. Since draft-ietf-httpbis-header-structure-06 . . . . . . 28 B.3. What should generic Structured Headers implementations
B.3. Since draft-ietf-httpbis-header-structure-05 . . . . . . 28 expose? . . . . . . . . . . . . . . . . . . . . . . . . . 31
B.4. Since draft-ietf-httpbis-header-structure-04 . . . . . . 28 Appendix C. Changes . . . . . . . . . . . . . . . . . . . . . . 31
B.5. Since draft-ietf-httpbis-header-structure-03 . . . . . . 29 C.1. Since draft-ietf-httpbis-header-structure-08 . . . . . . 31
B.6. Since draft-ietf-httpbis-header-structure-02 . . . . . . 29 C.2. Since draft-ietf-httpbis-header-structure-07 . . . . . . 32
B.7. Since draft-ietf-httpbis-header-structure-01 . . . . . . 29 C.3. Since draft-ietf-httpbis-header-structure-06 . . . . . . 32
B.8. Since draft-ietf-httpbis-header-structure-00 . . . . . . 29 C.4. Since draft-ietf-httpbis-header-structure-05 . . . . . . 32
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 29 C.5. Since draft-ietf-httpbis-header-structure-04 . . . . . . 33
C.6. Since draft-ietf-httpbis-header-structure-03 . . . . . . 33
C.7. Since draft-ietf-httpbis-header-structure-02 . . . . . . 33
C.8. Since draft-ietf-httpbis-header-structure-01 . . . . . . 33
C.9. Since draft-ietf-httpbis-header-structure-00 . . . . . . 33
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 34
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.
Once a header field is defined, bespoke parsers and serialisers often Once a header field is defined, bespoke parsers and serialisers 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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To specify a header field that is a Structured Header, see Section 2. To specify a header field that is a Structured Header, see Section 2.
Section 3 defines a number of abstract data types that can be used in Section 3 defines a number of abstract data types that can be used in
Structured Headers. Structured Headers.
Those abstract types can be serialised into and parsed from textual Those abstract types can be serialised into and parsed from textual
headers - such as those used in HTTP/1 - using the algorithms headers - such as those used in HTTP/1 - using the algorithms
described in Section 4. described in Section 4.
1.1. Notational Conventions 1.1. Intentionally Strict Processing
This specification intentionally defines strict parsing and
serialisation behaviours using step-by-step algorithms; the only
error handling defined is to fail the operation altogether.
This is designed to encourage faithful implementation and therefore
good interoperability. Therefore, implementations that try to be
"helpful" by being more tolerant of input are doing a disservice to
the overall community, since it will encourage other implementations
to implement similar (but likely subtly different) workarounds.
In other words, strict processing is an intentional feature of this
specification; it allows non-conformant input to be discovered and
corrected early, and avoids both interoperability and security issues
that might otherwise result.
Note that as a result of this strictness, if a header field is
appended to by multiple parties (e.g., intermediaries, or different
components in the sender), it could be that an error in one party's
value causes the entire header field to fail parsing.
1.2. Notational Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in 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 VCHAR, SP, DIGIT, ALPHA and DQUOTE rules [RFC5234], including the VCHAR, SP, DIGIT, ALPHA and DQUOTE rules
from that document. It also includes the OWS rule from [RFC7230]. from that document. It also includes the OWS rule from [RFC7230].
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o Specify any additional constraints upon the syntax of the o Specify any additional constraints upon the syntax of the
structured used, as well as the consequences when those structured used, as well as the consequences when those
constraints are violated. When Structured Headers parsing fails, constraints are violated. When Structured Headers parsing fails,
the header is discarded (see Section 4.2); in most situations, the header is discarded (see Section 4.2); in most situations,
header-specific constraints should do likewise. header-specific constraints should do likewise.
Note that a header field definition cannot relax the requirements of Note that a header field definition cannot relax the requirements of
a structure or its processing because doing so would preclude a structure or its processing because doing so would preclude
handling by generic software; they can only add additional handling by generic software; they can only add additional
constraints. constraints. Likewise, header field definitions should use
Structured Headers for the entire header field value, not a portion
thereof.
For example: For example:
# Foo-Example Header # Foo-Example Header
The Foo-Example HTTP header field conveys information about how The Foo-Example HTTP header field conveys information about how
much Foo the message has. much Foo the message has.
Foo-Example is a Structured Header [RFCxxxx]. Its value MUST be a Foo-Example is a Structured Header [RFCxxxx]. Its value MUST be a
dictionary ([RFCxxxx], Section Y.Y). Its ABNF is: dictionary ([RFCxxxx], Section Y.Y). Its ABNF is:
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3. Structured Header Data Types 3. 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. The ABNF provided represents the on-wire into Structured Headers. The ABNF provided represents the on-wire
format in HTTP/1. format in HTTP/1.
3.1. Dictionaries 3.1. Dictionaries
Dictionaries are ordered maps of key-value pairs, where the keys are Dictionaries are ordered maps of key-value pairs, where the keys are
identifiers (Section 3.8) and the values are items (Section 3.4). short, textual strings and the values are items (Section 3.5). There
There can be one or more members, and keys are required to be unique. can be one or more members, and keys are required to be unique.
Implementations MUST provide access to dictionaries both by index and Implementations MUST provide access to dictionaries both by index and
by key. Specifications MAY use either means of accessing the by key. Specifications MAY use either means of accessing the
members. members.
The ABNF for dictionaries in HTTP/1 headers is: The ABNF for dictionaries in HTTP/1 headers is:
sh-dictionary = dict-member *( OWS "," OWS dict-member ) sh-dictionary = dict-member *( OWS "," OWS dict-member )
dict-member = member-name "=" member-value dict-member = member-name "=" member-value
member-name = sh-identifier member-name = key
member-value = sh-item member-value = sh-item
key = lcalpha *( lcalpha / DIGIT / "_" / "-" )
lcalpha = %x61-7A ; a-z
In HTTP/1, keys and values are separated by "=" (without whitespace), In HTTP/1, keys and values are separated by "=" (without whitespace),
and key/value pairs are separated by a comma with optional and key/value pairs are separated by a comma with optional
whitespace. For example: whitespace. For example:
Example-DictHeader: en="Applepie", da=*w4ZibGV0w6ZydGU=* Example-DictHeader: en="Applepie", da=*w4ZibGV0w6ZydGU=*
Typically, a header field specification will define the semantics of Typically, a header field specification will define the semantics of
individual keys, as well as whether their presence is required or individual keys, as well as whether their presence is required or
optional. Recipients MUST ignore keys that are undefined or unknown, optional. Recipients MUST ignore keys that are undefined or unknown,
unless the header field's specification specifically disallows them. unless the header field's specification specifically disallows them.
Parsers MUST support dictionaries containing at least 1024 key/value Parsers MUST support dictionaries containing at least 1024 key/value
pairs. pairs, and dictionary keys with at least 64 characters.
3.2. Lists 3.2. Lists
Lists are arrays of items (Section 3.4) with one or more members. Lists are arrays of items (Section 3.5) with one or more members.
The ABNF for lists in HTTP/1 headers is: The ABNF for lists in HTTP/1 headers is:
sh-list = list-member *( OWS "," OWS list-member ) sh-list = list-member *( OWS "," OWS list-member )
list-member = sh-item list-member = sh-item
In HTTP/1, each member is separated by a comma and optional In HTTP/1, 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."
Header specifications can constrain the types of individual values if Header specifications can constrain the types of individual values if
necessary. necessary.
Parsers MUST support lists containing at least 1024 members. Parsers MUST support lists containing at least 1024 members.
3.3. Parameterised Lists 3.3. Lists of Lists
Parameterised Lists are arrays of a parameterised identifiers. Lists of Lists are arrays of arrays containing items (Section 3.5).
A parameterised identifier is an identifier (Section 3.8) with an The ABNF for lists of lists in HTTP/1 headers is:
optional set of parameters, each parameter having an identifier and
an optional value that is an item (Section 3.4). Ordering between sh-listlist = inner-list *( OWS "," OWS inner-list )
inner-list = list-member *( OWS ";" OWS list-member )
In HTTP/1, each inner-list is separated by a comma and optional
whitespace, and members of the inner-list are separated by semicolons
and optional whitespace. For example, a header field whose value is
defined as a list of lists of strings could look like:
Example-StrListListHeader: "foo";"bar", "baz", "bat"; "one"
Header specifications can constrain the types of individual inner-
list values if necessary.
Parsers MUST support lists of lists containing at least 1024 members,
and inner-lists containing at least 256 members.
3.4. Parameterised Lists
Parameterised Lists are arrays of parameterised identifier with one
or more members.
A parameterised identifier is a token (Section 3.9}) with an optional
set of parameters, each parameter having a textual name and an
optional value that is an item (Section 3.5). Ordering between
parameters is not significant, and duplicate parameters MUST cause parameters is not significant, and duplicate parameters MUST cause
parsing to fail. parsing to fail.
The ABNF for parameterised lists in HTTP/1 headers is: The ABNF for parameterised lists in HTTP/1 headers is:
sh-param-list = param-id *( OWS "," OWS param-id ) sh-param-list = param-item *( OWS "," OWS param-item )
param-id = sh-identifier *parameter param-item = primary-id *parameter
primary-id = sh-token
parameter = OWS ";" OWS param-name [ "=" param-value ] parameter = OWS ";" OWS param-name [ "=" param-value ]
param-name = sh-identifier param-name = key
param-value = sh-item param-value = sh-item
In HTTP/1, each param-id is separated by a comma and optional In HTTP/1, each param-id is separated by a comma and optional
whitespace (as in Lists), and the parameters are separated by whitespace (as in Lists), and the parameters are separated by
semicolons. For example: semicolons. For example:
Example-ParamListHeader: abc_123;a=1;b=2; cdef_456, ghi;q="9";r="w" Example-ParamListHeader: abc_123;a=1;b=2; cdef_456, ghi;q="9";r="w"
Parsers MUST support parameterised lists containing at least 1024 Parsers MUST support parameterised lists containing at least 1024
members, and support members with at least 256 parameters. members, support members with at least 256 parameters, and support
parameter keys with at least 64 characters.
3.4. Items 3.5. Items
An item is can be a integer (Section 3.5), float (Section 3.6), An item is can be a integer (Section 3.6), float (Section 3.7),
string (Section 3.7), identifier (Section 3.8), byte sequence string (Section 3.8), token (Section 3.9}), byte sequence
(Section 3.9), or Boolean (Section 3.10). (Section 3.10), or Boolean (Section 3.11).
The ABNF for items in HTTP/1 headers is: The ABNF for items in HTTP/1 headers is:
sh-item = sh-integer / sh-float / sh-string / sh-identifier / sh-binary sh-item = sh-integer / sh-float / sh-string / sh-token / sh-binary
/ sh-boolean / sh-boolean
3.5. Integers 3.6. Integers
Integers have a range of -9,223,372,036,854,775,808 to 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). 9,223,372,036,854,775,807 inclusive (i.e., a 64-bit signed integer).
The ABNF for integers in HTTP/1 headers is: The ABNF for integers in HTTP/1 headers is:
sh-integer = ["-"] 1*19DIGIT sh-integer = ["-"] 1*19DIGIT
For example: For example:
Example-IntegerHeader: 42 Example-IntegerHeader: 42
3.6. Floats 3.7. Floats
Floats are integers with a fractional part, that can be stored as Floats are integers with a fractional part, that can be stored as
IEEE 754 double precision numbers (binary64) ([IEEE754]). IEEE 754 double precision numbers (binary64) ([IEEE754]).
The ABNF for floats in HTTP/1 headers is: The ABNF for floats in HTTP/1 headers is:
sh-float = ["-"] ( sh-float = ["-"] (
DIGIT "." 1*14DIGIT / DIGIT "." 1*14DIGIT /
2DIGIT "." 1*13DIGIT / 2DIGIT "." 1*13DIGIT /
3DIGIT "." 1*12DIGIT / 3DIGIT "." 1*12DIGIT /
skipping to change at page 9, line 46 skipping to change at page 10, line 26
11DIGIT "." 1*4DIGIT / 11DIGIT "." 1*4DIGIT /
12DIGIT "." 1*3DIGIT / 12DIGIT "." 1*3DIGIT /
13DIGIT "." 1*2DIGIT / 13DIGIT "." 1*2DIGIT /
14DIGIT "." 1DIGIT ) 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 float could look
like: like:
Example-FloatHeader: 4.5 Example-FloatHeader: 4.5
3.7. Strings 3.8. 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 0x20 to 0x7E). Note that this excludes tabs, newlines, the range 0x20 to 0x7E). Note that this excludes tabs, newlines,
carriage returns, etc. carriage returns, etc.
The ABNF for strings in HTTP/1 headers is: The ABNF for strings in HTTP/1 headers is:
sh-string = DQUOTE *(chr) DQUOTE sh-string = DQUOTE *(chr) DQUOTE
chr = unescaped / escaped chr = unescaped / escaped
unescaped = %x20-21 / %x23-5B / %x5D-7E unescaped = %x20-21 / %x23-5B / %x5D-7E
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Note that strings only use DQUOTE as a delimiter; single quotes do Note that strings only use DQUOTE as a delimiter; single quotes do
not delimit strings. Furthermore, only DQUOTE and "\" can be not delimit strings. Furthermore, only DQUOTE and "\" can be
escaped; other sequences MUST cause parsing to fail. escaped; other sequences MUST cause parsing to fail.
Unicode is not directly supported in this document, because it causes Unicode is not directly supported in this document, because it causes
a number of interoperability issues, and - with few exceptions - a number of interoperability issues, and - with few exceptions -
header values do not require it. header values do not require it.
When it is necessary for a field value to convey non-ASCII string When it is necessary for a field value to convey non-ASCII string
content, a byte sequence (Section 3.9) SHOULD be specified, along content, a byte sequence (Section 3.10) SHOULD be specified, along
with a character encoding (preferably UTF-8). with a character encoding (preferably UTF-8).
Parsers MUST support strings with at least 1024 characters. Parsers MUST support strings with at least 1024 characters.
3.8. Identifiers 3.9. Tokens
Identifiers are short textual identifiers; their abstract model is Tokens are short textual words; their abstract model is identical to
identical to their expression in the textual HTTP serialisation. their expression in the textual HTTP serialisation.
Parsers MUST support identifiers with at least 64 characters.
The ABNF for identifiers in HTTP/1 headers is: The ABNF for tokens in HTTP/1 headers is:
sh-identifier = lcalpha *( lcalpha / DIGIT / "_" / "-"/ "*" / "/" ) sh-token = ALPHA *( ALPHA / DIGIT / "_" / "-" / "." / ":" / "%" / "*" / "/" )
lcalpha = %x61-7A ; a-z
Note that identifiers can only contain lowercase letters. Parsers MUST support tokens with at least 512 characters.
3.9. Byte Sequences 3.10. 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/1 headers is: The ABNF for a byte sequence in HTTP/1 headers is:
sh-binary = "*" *(base64) "*" sh-binary = "*" *(base64) "*"
base64 = ALPHA / DIGIT / "+" / "/" / "=" base64 = ALPHA / DIGIT / "+" / "/" / "="
In HTTP/1 headers, a byte sequence is delimited with asterisks and In HTTP/1 headers, a byte sequence is delimited with asterisks and
encoded using base64 ([RFC4648], Section 4). For example: encoded 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.
3.10. Booleans 3.11. Booleans
Boolean values can be conveyed in Structured Headers. Boolean values can be conveyed in Structured Headers.
The ABNF for a Boolean in HTTP/1 headers is: The ABNF for a Boolean in HTTP/1 headers is:
sh-boolean = "!" boolean sh-boolean = "?" boolean
boolean = "T" / "F" boolean = %54 / %46 ; capital "T" or "F"
In HTTP/1 headers, a byte sequence is delimited with a "!" character. In HTTP/1 headers, a byte sequence is indicated with a leading "?"
For example: character. For example:
Example-BoolHdr: !T Example-BoolHdr: ?T
4. Structured Headers in HTTP/1 4. Structured Headers in HTTP/1
This section defines how to serialise and parse Structured Headers in This section defines how to serialise and parse Structured Headers in
HTTP/1 textual header fields, and protocols compatible with them HTTP/1 textual header fields, and protocols compatible with them
(e.g., in HTTP/2 [RFC7540] before HPACK [RFC7541] is applied). (e.g., in HTTP/2 [RFC7540] before HPACK [RFC7541] is applied).
4.1. Serialising Structured Headers into HTTP/1 4.1. Serialising Structured Headers into HTTP/1
Given a structured defined in this specification: Given a structured defined in this specification:
1. If the structure is a dictionary, return the result of 1. If the structure is a dictionary, return the result of
Serialising a Dictionary {#ser-dictionary}. Serialising a Dictionary (Section 4.1.1).
2. If the structure is a list, return the result of Serialising a 2. If the structure is a parameterised list, return the result of
List {#ser-list}. Serialising a Parameterised List (Section 4.1.4).
3. If the structure is a parameterised list, return the result of 3. If the structure is a list of lists, return the result of
Serialising a Parameterised List {#ser-param-list}. Serialising a List of Lists ({ser-listlist}).
4. If the structure is an item, return the result of Serialising an 4. If the structure is a list, return the result of Serialising a
Item {#ser-item}. List Section 4.1.2.
5. Otherwise, fail serialisation. 5. If the structure is an item, return the result of Serialising an
Item (Section 4.1.5).
6. Otherwise, fail serialisation.
4.1.1. Serialising a Dictionary 4.1.1. Serialising a Dictionary
Given a dictionary as input: Given a dictionary as input_dictionary:
1. Let output be an empty string. 1. Let output be an empty string.
2. For each member mem of input: 2. For each member mem of input_dictionary:
1. Let name be the result of applying Serialising an Identifier 1. Let name be the result of applying Serialising an Key
Section 4.1.8 to mem's member-name. (Section 4.1.1.1) to mem's member-name.
2. Append name to output. 2. Append name to output.
3. Append "=" to output. 3. Append "=" to output.
4. Let value be the result of applying Serialising an Item 4. Let value be the result of applying Serialising an Item
Section 4.1.4 to mem's member-value. (Section 4.1.5) to mem's member-value.
5. Append value to output. 5. Append value to output.
6. If more members remain in input: 6. If more members remain in input_dictionary:
1. Append a COMMA to output. 1. Append a COMMA to output.
2. Append a single WS to output. 2. Append a single WS to output.
3. Return output. 3. Return output.
4.1.1.1. Serialising a Key
Given a key as input_key:
1. If input_key is not a sequence of characters, or contains
characters not allowed in the ABNF for key, fail serialisation.
2. Let output be an empty string.
3. Append input_key to output, using ASCII encoding [RFC0020].
4. Return output.
4.1.2. Serialising a List 4.1.2. Serialising a List
Given a list as input: Given a list as input_list:
1. Let output be an empty string. 1. Let output be an empty string.
2. For each member mem of input: 2. For each member mem of input_list:
1. Let value be the result of applying Serialising an Item 1. Let value be the result of applying Serialising an Item
Section 4.1.4 to mem. (Section 4.1.5) to mem.
2. Append value to output. 2. Append value to output.
3. If more members remain in input: 3. If more members 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 WS to output.
3. Return output. 3. Return output.
4.1.3. Serialising a Parameterised List 4.1.3. Serialising a List of Lists
Given a parameterised list as input: Given a list of lists of items as input_list:
1. Let output be an empty string. 1. Let output be an empty string.
2. For each member mem of input: 2. For each member inner_list of input_list:
1. Let id be the result of applying Serialising an Identifier 1. If inner_list is not a list, fail serialisation.
Section 4.1.8 to mem's identifier.
2. If inner_list is empty, fail serialisation.
3. For each inner_mem of inner_list:
1. Let value be the result of applying Serialising an Item
(Section 4.1.5) to inner_mem.
2. Append value to output.
3. If more members remain in inner_list:
1. Append a ";" to output.
2. Append a single WS to output.
4. If more members remain in input_list:
1. Append a COMMA to output.
2. Append a single WS to output.
3. Return output.
4.1.4. Serialising a Parameterised List
Given a parameterised list as input_plist:
1. Let output be an empty string.
2. For each member mem of input_plist:
1. Let id be the result of applying Serialising a Token
(Section 4.1.9) to mem's token.
2. Append id to output. 2. Append id to output.
3. For each parameter in mem's parameters: 3. For each parameter in mem's parameters:
1. Append ";" to output. 1. Append ";" to output.
2. Let name be the result of applying Serialising an 2. Let name be the result of applying Serialising a Key
Identifier Section 4.1.8 to parameter's param-name. (Section 4.1.1.1) to parameter's param-name.
3. Append name to output. 3. Append name to output.
4. If parameter has a param-value: 4. If parameter has a param-value:
1. Let value be the result of applying Serialising an 1. Let value be the result of applying Serialising an
Item Section 4.1.4 to parameter's param-value. Item (Section 4.1.5) to parameter's param-value.
2. Append "=" to output. 2. Append "=" to output.
3. Append value to output. 3. Append value to output.
4. If more members remain in input: 4. If more members remain in input_plist:
1. Append a COMMA to output. 1. Append a COMMA to output.
2. Append a single WS to output. 2. Append a single WS to output.
3. Return output. 3. Return output.
4.1.4. Serialising an Item 4.1.5. Serialising an Item
Given an item as input: Given an item as input_item:
1. If input is a type other than an integer, float, string, 1. If input_item is an integer, return the result of applying
identifier, byte sequence, or Boolean, fail serialisation. Serialising an Integer (Section 4.1.6) to input_item.
2. If input is an integer, return the result of applying Serialising 2. If input_item is a float, return the result of applying
an Integer Section 4.1.5 to input. Serialising a Float (Section 4.1.7) to input_item.
3. If input is a float, return the result of applying Serialising a 3. If input_item is a string, return the result of applying
Float Section 4.1.6 to input. Serialising a String (Section 4.1.8) to input_item.
4. If input is a string, return the result of applying Serialising a 4. If input_item is a token, return the result of Serialising a
String Section 4.1.7 to input. Token (Section 4.1.9) to input_item.
5. If input is an identifier, return the result of Serialising an 5. If input_item is a Boolean, return the result of applying
Identifier {#ser-identifier}. Serialising a Boolean (Section 4.1.11) to input_item.
6. If input is a Boolean, return the result of applying Serialising 6. If input_item is a byte sequence, return the result of applying
a Boolean Section 4.1.10 to input. Serialising a Byte Sequence (Section 4.1.10) to input_item.
7. Otherwise, return the result of applying Serialising a Byte 7. Otherwise, fail serialisation.
Sequence Section 4.1.9 to input.
4.1.5. Serialising an Integer 4.1.6. Serialising an Integer
Given an integer as input: Given an integer as input_integer:
1. If input is not an integer in the range of 1. If input_integer is not an integer in the range of
-9,223,372,036,854,775,808 to 9,223,372,036,854,775,807 -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807
inclusive, fail serialisation. inclusive, fail serialisation.
2. Let output be an empty string. 2. Let output be an empty string.
3. If input is less than (but not equal to) 0, append "-" to output. 3. If input_integer is less than (but not equal to) 0, append "-" to
output.
4. Append input's numeric value represented in base 10 using only 4. Append input_integer's numeric value represented in base 10 using
decimal digits to output. only decimal digits to output.
5. Return output. 5. Return output.
4.1.6. Serialising a Float 4.1.7. Serialising a Float
Given a float as input: Given a float as input_float:
1. If input is not a IEEE 754 double precision number, fail 1. If input_float is not a IEEE 754 double precision number, fail
serialisation. serialisation.
2. Let output be an empty string. 2. Let output be an empty string.
3. If input is less than (but not equal to) 0, append "-" to output. 3. If input_float is less than (but not equal to) 0, append "-" to
output.
4. Append input's integer component represented in base 10 using 4. Append input_float's integer component represented in base 10
only decimal digits to output; if it is zero, append "0". using only decimal digits to output; if it is zero, append "0".
5. Append "." to output. 5. Append "." to output.
6. Append input's decimal component represented in base 10 using 6. Append input_float's decimal component represented in base 10
only decimal digits to output; if it is zero, append "0". using only decimal digits to output; if it is zero, append "0".
7. Return output. 7. Return output.
4.1.7. Serialising a String 4.1.8. Serialising a String
Given a string as input: Given a string as input_string:
1. If input is not a sequence of characters, or contains characters 1. If input_string is not a sequence of characters, or contains
outside the range allowed by VCHAR or SP, fail serialisation. characters outside the range allowed by VCHAR or SP, fail
serialisation.
2. Let output be an empty string. 2. Let output be an empty string.
3. Append DQUOTE to output. 3. Append DQUOTE to output.
4. For each character char in input: 4. For each character char in input_string:
1. If char is "\" or DQUOTE: 1. If char is "\" or DQUOTE:
1. Append "\" to output. 1. Append "\" to output.
2. Append char to output, using ASCII encoding [RFC0020]. 2. Append char to output, using ASCII encoding [RFC0020].
5. Append DQUOTE to output. 5. Append DQUOTE to output.
6. Return output. 6. Return output.
4.1.8. Serialising an Identifier 4.1.9. Serialising a Token
Given an identifier as input: Given a token as input_token:
1. If input is not a sequence of characters, or contains characters 1. If input_token is not a sequence of characters, or contains
not allowed in Section 3.8, fail serialisation. characters not allowed in Section 3.9}, fail serialisation.
2. Let output be an empty string. 2. Let output be an empty string.
3. Append input to output, using ASCII encoding [RFC0020]. 3. Append input_token to output, using ASCII encoding [RFC0020].
4. Return output. 4. Return output.
4.1.9. Serialising a Byte Sequence 4.1.10. Serialising a Byte Sequence
Given a byte sequence as input: Given a byte sequence as input_bytes:
1. If input 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 as per [RFC4648], 4. Append the result of base64-encoding input_bytes as per
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.
4.1.10. Serialising a Boolean 4.1.11. Serialising a Boolean
Given a Boolean as input: Given a Boolean as input_boolean:
1. If input is not a boolean, fail serialisation. 1. If input_boolean is not a boolean, 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. If input is true, append "T" to output. 4. If input_boolean is true, append "T" to output.
5. If input is false, append "F" to output. 5. If input_boolean is false, append "F" to output.
6. Return output. 6. Return output.
4.2. Parsing HTTP/1 Header Fields into Structured Headers 4.2. Parsing HTTP/1 Header Fields 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, and header_type, one of "dictionary", "list", header's field-value, and header_type, one of "dictionary", "list",
"param-list", or "item", return the parsed header value. "list-list", "param-list", or "item", return the parsed header value.
1. Discard any leading OWS from input_string. 1. Discard any leading OWS from input_string.
2. If header_type is "dictionary", let output be the result of 2. If header_type is "dictionary", let output be the result of
Parsing a Dictionary from Text (Section 4.2.1). Parsing a Dictionary from Text (Section 4.2.1).
3. If header_type is "list", let output be the result of Parsing a 3. If header_type is "list", let output be the result of Parsing a
List from Text (Section 4.2.2). List from Text (Section 4.2.3).
4. If header_type is "param-list", let output be the result of 4. If header_type is "list-list", let output be the result of
Parsing a Parameterised List from Text (Section 4.2.3). Parsing a List of Lists from Text (Section 4.2.4).
5. Otherwise, let output be the result of Parsing an Item from Text 5. If header_type is "param-list", let output be the result of
(Section 4.2.5). Parsing a Parameterised List from Text (Section 4.2.5).
6. Discard any leading OWS from input_string. 6. If header_type is "item", let output be the result of Parsing an
Item from Text (Section 4.2.7).
7. If input_string is not empty, fail parsing. 7. Discard any leading OWS from input_string.
8. Otherwise, return output. 8. If input_string is not empty, fail parsing.
9. Otherwise, return output.
When generating input_string, parsers MUST combine all instances of When generating input_string, 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.
For Lists, Parameterised Lists and Dictionaries, this has the effect For Lists, Lists of Lists, Parameterised Lists and Dictionaries, this
of correctly concatenating all instances of the header field. has the effect of correctly concatenating all instances of the header
field, as long as individual individual members of the top-level data
structure are not 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 serialiser or the parser. results are not under the control of the serialiser or the parser.
Integers, Floats and Byte Sequences cannot be split across multiple Integers, Floats and Byte Sequences cannot be split across multiple
headers because the inserted commas will cause parsing to fail. headers because the inserted commas will cause parsing to 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 discarded. This is intentionally entire header field's value MUST be discarded. This is intentionally
strict, to improve interoperability and safety, and specifications strict, to improve interoperability and safety, and specifications
referencing this document cannot loosen this requirement. referencing this document cannot loosen this requirement.
Note that this has the effect of discarding any header field with Note that this has the effect of discarding any header field with
non-ASCII characters in input_string. non-ASCII characters in input_string.
4.2.1. Parsing a Dictionary from Text 4.2.1. Parsing a Dictionary from Text
Given an ASCII string input_string, return an ordered map of Given an ASCII string input_string, return an ordered map of (key,
(identifier, item). input_string is modified to remove the parsed item). input_string is modified to remove the parsed value.
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 Parse Identifier from 1. Let this_key be the result of running Parse a Key from Text
Text (Section 4.2.8) with input_string. (Section 4.2.2) with input_string.
2. If dictionary already contains this_key, fail parsing. 2. If dictionary already contains this_key, fail parsing.
3. Consume the first character of input_string; if it is not 3. Consume the first character of input_string; if it is not
"=", fail parsing. "=", fail parsing.
4. Let this_value be the result of running Parse Item from Text 4. Let this_value be the result of running Parse Item from Text
(Section 4.2.5) with input_string. (Section 4.2.7) with input_string.
5. Add key this_key with value this_value to dictionary. 5. Add key this_key with value this_value to dictionary.
6. Discard any leading OWS from input_string. 6. Discard any leading OWS from input_string.
7. If input_string is empty, return dictionary. 7. If input_string is empty, return dictionary.
8. Consume the first character of input_string; if it is not 8. Consume the first character of input_string; if it is not
COMMA, fail parsing. COMMA, fail parsing.
9. Discard any leading OWS from input_string. 9. Discard any leading OWS from input_string.
10. If input_string is empty, fail parsing. 10. If input_string is empty, fail parsing.
3. No structured data has been found; fail parsing. 3. No structured data has been found; fail parsing.
4.2.2. Parsing a List from Text 4.2.2. Parsing a Key from Text
Given an ASCII string input_string, return a key. input_string is
modified to remove the parsed value.
1. If the first character of input_string is not lcalpha, fail
parsing.
2. Let output_string be an empty string.
3. While input_string is not empty:
1. Let char be the result of removing the first character of
input_string.
2. If char is not one of lcalpha, DIGIT, "_", or "-":
1. Prepend char to input_string.
2. Return output_string.
3. Append char to output_string.
4. Return output_string.
4.2.3. Parsing a List from Text
Given an ASCII string input_string, return a list of items. Given an ASCII string input_string, return a list of items.
input_string is modified to remove the parsed value. input_string is modified to remove the parsed value.
1. Let items be an empty array. 1. Let items be an empty array.
2. While input_string is not empty: 2. While input_string is not empty:
1. Let item be the result of running Parse Item from Text 1. Let item be the result of running Parse Item from Text
(Section 4.2.5) with input_string. (Section 4.2.7) with input_string.
2. Append item to items. 2. Append item to items.
3. Discard any leading OWS from input_string. 3. Discard any leading OWS from input_string.
4. If input_string is empty, return items. 4. If input_string is empty, return items.
5. Consume the first character of input_string; if it is not 5. Consume the first character of input_string; if it is not
COMMA, fail parsing. COMMA, fail parsing.
6. Discard any leading OWS from input_string. 6. Discard any leading OWS from input_string.
7. If input_string is empty, fail parsing. 7. If input_string is empty, fail parsing.
3. No structured data has been found; fail parsing. 3. No structured data has been found; fail parsing.
4.2.3. Parsing a Parameterised List from Text 4.2.4. Parsing a List of Lists from Text
Given an ASCII string input_string, return a list of lists of items.
input_string is modified to remove the parsed value.
1. let top_list be an empty array.
2. Let inner_list be an empty array.
3. While input_string is not empty:
1. Let item be the result of running Parse Item from Text
(Section 4.2.7) with input_string.
2. Append item to inner_list.
3. Discard any leading OWS from input_string.
4. If input_string is empty, append inner_list to top_list and
return top_list.
5. Let char be the result of consuming the first character of
input_string.
6. If char is COMMA:
1. Append inner_list to top_list.
2. Let inner_list be an empty array.
7. Else if char is not ";", fail parsing.
8. Discard any leading OWS from input_string.
9. If input_string is empty, fail parsing.
4. No structured data has been found; fail parsing.
4.2.5. Parsing a Parameterised List from Text
Given an ASCII string input_string, return a list of parameterised Given an ASCII string input_string, return a list of parameterised
identifiers. input_string is modified to remove the parsed value. identifiers. input_string is modified to remove the parsed value.
1. Let items be an empty array. 1. Let items be an empty array.
2. While input_string is not empty: 2. While input_string is not empty:
1. Let item be the result of running Parse Parameterised 1. Let item be the result of running Parse Parameterised
Identifier from Text (Section 4.2.4) with input_string. Identifier from Text (Section 4.2.6) with input_string.
2. Append item to items. 2. Append item to items.
3. Discard any leading OWS from input_string. 3. Discard any leading OWS from input_string.
4. If input_string is empty, return items. 4. If input_string is empty, return items.
5. Consume the first character of input_string; if it is not 5. Consume the first character of input_string; if it is not
COMMA, fail parsing. COMMA, fail parsing.
6. Discard any leading OWS from input_string. 6. Discard any leading OWS from input_string.
7. If input_string is empty, fail parsing. 7. If input_string is empty, fail parsing.
3. No structured data has been found; fail parsing. 3. No structured data has been found; fail parsing.
4.2.4. Parsing a Parameterised Identifier from Text 4.2.6. Parsing a Parameterised Identifier from Text
Given an ASCII string input_string, return an identifier with an Given an ASCII string input_string, return an token with an unordered
unordered map of parameters. input_string is modified to remove the map of parameters. input_string is modified to remove the parsed
parsed value. value.
1. Let primary_identifier be the result of Parsing an Identifier 1. Let primary_identifier be the result of Parsing a Token from Text
from Text (Section 4.2.8) from input_string. (Section 4.2.10) from input_string.
2. Let parameters be an empty, unordered map. 2. Let parameters be an empty, unordered map.
3. In a loop: 3. In a loop:
1. If the first character of input_string is not ";", exit the 1. Discard any leading OWS from input_string.
2. If the first character of input_string is not ";", exit the
loop. loop.
2. Consume a ";" character from the beginning of input_string. 3. Consume a ";" character from the beginning of input_string.
3. Discard any leading OWS from input_string. 4. Discard any leading OWS from input_string.
4. let param_name be the result of Parsing an Identifier from 5. let param_name be the result of Parsing a key from Text
Text (Section 4.2.8) from input_string. (Section 4.2.2) from input_string.
5. If param_name is already present in parameters, fail parsing. 6. If param_name is already present in parameters, fail parsing.
6. Let param_value be a null value. 7. Let param_value be a null value.
7. 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
Text (Section 4.2.5) from input_string. Text (Section 4.2.7) from input_string.
8. Insert (param_name, param_value) into parameters. 9. Add key param_name with value param_value to parameters.
4. Return the tuple (primary_identifier, parameters). 4. Return the tuple (primary_identifier, parameters).
4.2.5. Parsing an Item from Text 4.2.7. Parsing an Item from Text
Given an ASCII string input_string, return an item. input_string is Given an ASCII string input_string, return an item. input_string is
modified to remove the parsed value. modified to remove the parsed value.
1. Discard any leading OWS from input_string. 1. If the first character of input_string is a "-" or a DIGIT,
process input_string as a number (Section 4.2.8) and return the
2. If the first character of input_string is a "-" or a DIGIT,
process input_string as a number (Section 4.2.6) and return the
result. result.
3. If the first character of input_string is a DQUOTE, process 2. If the first character of input_string is a DQUOTE, process
input_string as a string (Section 4.2.7) and return the result. input_string as a string (Section 4.2.9) and return the result.
4. If the first character of input_string is "*", process 3. If the first character of input_string is "*", process
input_string as a byte sequence (Section 4.2.9) and return the input_string as a byte sequence (Section 4.2.11) and return the
result. result.
5. If the first character of input_string is "!", process 4. If the first character of input_string is "?", process
input_string as a Boolean (Section 4.2.10) and return the result. input_string as a Boolean (Section 4.2.12) and return the result.
6. If the first character of input_string is a lcalpha, process 5. If the first character of input_string is an ALPHA, process
input_string as an identifier (Section 4.2.8) and return the input_string as a token (Section 4.2.10) and return the result.
result.
7. Otherwise, fail parsing. 6. Otherwise, fail parsing.
4.2.6. Parsing a Number from Text 4.2.8. Parsing a Number from Text
NOTE: This algorithm parses both Integers Section 3.5 and Floats Given an ASCII string input_string, return a number. input_string is
Section 3.6, and returns the corresponding structure. modified to remove the parsed value.
NOTE: This algorithm parses both Integers Section 3.6 and Floats
Section 3.7, 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 "-", remove it from 4. If the first character of input_string is "-", remove it from
input_string and set sign to -1. input_string and set sign to -1.
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6. If type is "float" and input_number contains more than 16 6. If type is "float" 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 defined in
Section 3.5, fail parsing. Section 3.6, 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. Parse input_number as a float and let output_number be the 2. Parse input_number as a float and let output_number be the
product of the result and sign. product of the result and sign.
10. Return output_number. 10. Return output_number.
4.2.7. Parsing a String from Text 4.2.9. Parsing a String from Text
Given an ASCII string input_string, return an unquoted string. Given an ASCII string 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.
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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.
4.2.8. Parsing an Identifier from Text 4.2.10. Parsing a Token from Text
Given an ASCII string input_string, return an identifier. Given an ASCII string input_string, return a token. input_string is
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 ALPHA, 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. Let char be the result of removing the first character of 1. Let char be the result of removing the first character of
input_string. input_string.
2. If char is not one of lcalpha, DIGIT, "_", "-", "*" or "/": 2. If char is not one of ALPHA, DIGIT, "_", "-", ".", ":", "%",
"*" or "/":
1. Prepend char to input_string. 1. Prepend char to input_string.
2. Return output_string. 2. Return output_string.
3. Append char to output_string. 3. Append char to output_string.
4. Return output_string. 4. Return output_string.
4.2.9. Parsing a Byte Sequence from Text 4.2.11. Parsing a Byte Sequence from Text
Given an ASCII string input_string, return a byte sequence. Given an ASCII string 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. Let b64_content be the result of removing content of input_string 3. If there is not a "*" character before the end 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,
fail parsing. fail parsing.
4. Consume the "*" character at the beginning of input_string. 4. Let b64_content be the result of removing content of input_string
up to but not including the first instance of the character "*".
5. If b64_content contains a character not included in ALPHA, DIGIT, 5. Consume the "*" character at the beginning of input_string.
6. If b64_content contains a character not included in ALPHA, DIGIT,
"+", "/" and "=", fail parsing. "+", "/" and "=", fail parsing.
6. 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, synthesising padding if necessary (note the b64_content, synthesising padding if necessary (note the
requirements about recipient behaviour below). requirements about recipient behaviour below).
7. Return binary_content. 8. Return binary_content.
Because some implementations of base64 do not allow reject of encoded Because some implementations of base64 do not allow reject of encoded
data that is not properly "=" padded (see [RFC4648], Section 3.2), data that is not properly "=" padded (see [RFC4648], Section 3.2),
parsers SHOULD NOT fail when it is not present, unless they cannot be parsers SHOULD NOT fail when it is not present, unless they cannot be
configured to do so. configured to do so.
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.
4.2.10. Parsing a Boolean from Text 4.2.12. Parsing a Boolean from Text
Given an ASCII string input_string, return a Boolean. input_string is Given an ASCII string input_string, return a Boolean. 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 "!", 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 case-sensitively matches 3. If the first character of input_string case-sensitively matches
"T", discard the first character, and return true. "T", discard the first character, and return true.
4. If the first character of input_string case-sensitively matches 4. If the first character of input_string case-sensitively matches
"F", discard the first character, and return false. "F", discard the first character, and return false.
5. No value has matched; fail parsing. 5. No value has matched; fail parsing.
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[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
[4] https://github.com/httpwg/structured-header-tests [4] https://github.com/httpwg/structured-header-tests
[5] https://github.com/httpwg/wiki/wiki/Structured-Headers [5] https://github.com/httpwg/wiki/wiki/Structured-Headers
Appendix A. Frequently Asked Questions [6] https://github.com/httpwg/structured-header-tests
A.1. Why not JSON? Appendix A. Acknowledgements
Many thanks to Matthew Kerwin for his detailed feedback and careful
consideration during the development of this specification.
Appendix B. Frequently Asked Questions
B.1. Why not JSON?
Earlier proposals for structured headers were based upon JSON Earlier proposals for structured headers were based upon JSON
[RFC8259]. However, constraining its use to make it suitable for [RFC8259]. However, constraining its use to make it suitable for
HTTP header fields required senders and recipients to implement HTTP header fields required senders and recipients to implement
specific additional handling. specific additional handling.
For example, JSON has specification issues around large numbers and For example, JSON has specification issues around large numbers and
objects with duplicate members. Although advice for avoiding these objects with duplicate members. Although advice for avoiding these
issues is available (e.g., [RFC7493]), it cannot be relied upon. issues is available (e.g., [RFC7493]), it cannot be relied upon.
skipping to change at page 27, line 25 skipping to change at page 30, line 40
some deployments would fail to enforce them, thereby harming some deployments would fail to enforce them, thereby harming
interoperability. interoperability.
Since a major goal for Structured Headers is to improve Since a major goal for Structured Headers is to improve
interoperability and simplify implementation, these concerns led to a interoperability and simplify implementation, these concerns led to a
format that requires a dedicated parser and serialiser. format that requires a dedicated parser and serialiser.
Additionally, there were widely shared feelings that JSON doesn't Additionally, there were widely shared feelings that JSON doesn't
"look right" in HTTP headers. "look right" in HTTP headers.
A.2. Structured Headers don't "fit" my data. B.2. Structured Headers don't "fit" my data.
Structured headers intentionally limits the complexity of data Structured headers intentionally limits the complexity of data
structures, to assure that it can be processed in a performant manner structures, to assure that it can be processed in a performant manner
with little overhead. This means that work is necessary to fit some with little overhead. This means that work is necessary to fit some
data types into them. data types into them.
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 a list of key/value pairs, we use a Since the description contains a list of key/value pairs, we use a
Parameterised List to represent them, with the identifier for each Parameterised List to represent them, with the token for each item in
item in the list used to identify it in the "descriptions" member of the list used to identify it in the "descriptions" member of the
the Example-Thing header. Example-Thing 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 B. Changes B.3. What should generic Structured Headers implementations expose?
A generic implementation should expose the top-level parse
(Section 4.2) and serialise (Section 4.1) functions. They need not
be functions; for example, it could be implemented as an object, with
methods for each of the different top-level types.
For interoperability, it's important that generic implementations be
complete and follow the algorithms closely; see Section 1.1. To aid
this, a common test suite is being maintained by the community; see
https://github.com/httpwg/structured-header-tests [7].
Appendix C. Changes
_RFC Editor: Please remove this section before publication._ _RFC Editor: Please remove this section before publication._
B.1. Since draft-ietf-httpbis-header-structure-07 C.1. Since draft-ietf-httpbis-header-structure-08
o Disallow whitespace before items properly (#703).
o Created "key" for use in dictionaries and parameters, rather than
relying on identifier (#702). Identifiers have a separate minimum
supported size.
o Expanded the range of special characters allowed in identifier to
include all of ALPHA, ".", ":", and "%" (#702).
o Use "?" instead of "!" to indicate a Boolean (#719).
o Added "Intentionally Strict Processing" (#684).
o Gave better names for referring specs to use in Parameterised
Lists (#720).
o Added Lists of Lists (#721).
o Rename Identifier to Token (#725).
o Add implementation guidance (#727).
C.2. 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).
B.2. Since draft-ietf-httpbis-header-structure-06 C.3. 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.
B.3. Since draft-ietf-httpbis-header-structure-05 C.4. 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.
B.4. Since draft-ietf-httpbis-header-structure-04 C.5. 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.
B.5. Since draft-ietf-httpbis-header-structure-03 C.6. Since draft-ietf-httpbis-header-structure-03
o Strengthen language around failure handling. o Strengthen language around failure handling.
B.6. Since draft-ietf-httpbis-header-structure-02 C.7. 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.
B.7. Since draft-ietf-httpbis-header-structure-01 C.8. Since draft-ietf-httpbis-header-structure-01
o Replaced with draft-nottingham-structured-headers. o Replaced with draft-nottingham-structured-headers.
B.8. Since draft-ietf-httpbis-header-structure-00 C.9. 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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