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Differences from draft-newton-json-content-rules-05.txt
Network Working Group A. Newton
Internet-Draft ARIN
Intended status: Standards Track P. Cordell
Expires: September 22, 2016 Codalogic
March 21, 2016
A Language for Rules Describing JSON Content
draft-newton-json-content-rules-06
Abstract
This document describes a language for specifying and testing the
expected content of JSON structures found in JSON-using protocols,
software, and processes.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 22, 2016.
Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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1. Introduction
This document describes JSON Content Rules (JCR), a language for
specifying and testing the interchange of data in JSON [RFC7159]
format used by computer protocols and processes. The syntax of JCR
is not JSON but is "JSON-like", possessing the conciseness and
utility that has made JSON popular.
1.1. A First Example: Specifying Content
The following JSON data describes a JSON object with two members,
"line-count" and "word-count", each containing an integer.
{ "line-count" : 3426, "word-count" : 27886 }
This is also JCR that describes a JSON object with a member named
"line-count" that is an integer that is exactly 3426 and a member
named "word-count" that is an integer that is exactly 27886.
For a protocol specification, it is probably more useful to specify
that each member is any integer and not specific, exact integers:
{ "line-count" : integer, "word-count" : integer }
Since line counts and word counts should be either zero or a positive
integer, the specification may be further narrowed:
{ "line-count" : 0.. , "word-count" : 0.. }
1.2. A Second Example: Testing Content
Building on the first example, this second example describes the same
object but with the addition of another member, "file-name".
{
"file-name" : "rfc7159.txt",
"line-count" : 3426,
"word-count" : 27886
}
The following JCR describes objects like it.
{
"file-name" : string,
"line-count" : 0..,
"word-count" : 0..
}
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For the purposes of writing a protocol specification, JCR may be
broken down into named rules to reduce complexity and to enable re-
use. The following example takes the JCR from above and rewrites the
members as named rules.
{
fn,
lc,
wc
}
fn "file-name" : string
lc "line-count" : 0..
wc "word-count" : 0..
With each member specified as a named rule, software testers can
override them locally for specific test cases. In the following
example, the named rules are locally overridden for the test case
where the file name is "rfc4627.txt".
fn "file-name" : "rfc4627.txt"
lc "line-count" : 2102
wc "word-count" : 16714
In this example, the protocol specification describes the JSON object
in general and an implementation overrides the rules for testing
specific cases.
2. Overview of the Language
JCR is composed of rules (as the name suggests). A collection of
rules that is processed together is a ruleset. There are five types
of rules: value rules, member rules, array rules, object rules, and
group rules. The first four types describe corresponding aspects of
JSON, respectively.
Except for an optional root rule, each rule has two components, a
rule name and a rule definition:
<rule name> <rule definition>
Rule definitions may in turn contain child rule definitions or
reference other rules by their rule name.
This is an example of a value rule:
v1 : 0..3
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It specifies a rule named "v1" that has a definition of ": 0..3"
(value rule definitions begin with a ':' character). This defines
values of type "v1" to be integers in the range 0 to 3 (minimum value
of 0, maximum value of 3). Value rules can define the limits of JSON
values, such as stating that numbers must fall into a certain range
or that strings must be formatted according to certain patterns or
standards (i.e. URIs, IP addresses, etc...).
Member rules specify JSON object members. The following example
member rule states that the rule's name is 'm1' with a value defined
by the rule named 'v1':
m1 "m1name" v1
Since rule names are substituted by rule definitions, this member
rule can also be written as follows (to define a member rule named m1
for JSON member named "m1name" that has a value that is an integer
between 0 and 3):
m1 "m1name" : 0..3
Object rules are composed of member rules, since JSON objects are
composed of members. Object rules can specify members that are
mandatory, optional, and even choices between members. In this
example, the rule 'o1' defines an object that must contain a member
as defined by member rule 'm1' and optionally a member defined by the
rule 'm2':
o1 { m1, ?m2 }
Array rules are composed of value, object, and other array rules.
Like object rules, array rules can specify the cardinality of the
contents of an array. The following array rule defines an array that
must contain value rule 'v1' and zero or more objects as defined by
rule 'o1':
a1 [ v1, *o1 ]
Finally, group rules designate a collection of rules.
Putting it all together, Figure 2 describes the JSON in Figure 1.
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Example JSON shamelessly lifted from RFC 4627
{
"Image": {
"Width": 800,
"Height": 600,
"Title": "View from 15th Floor",
"Thumbnail": {
"Url": "http://www.example.com/image/481989943",
"Height": 125,
"Width": "100"
},
"IDs": [116, 943, 234, 38793]
}
}
Figure 1
Rules describing Figure 1
{ image }
image "Image" {
width,
height,
"Title" : string,
thumbnail,
"IDs" [ *: integer ]
}
width "Width" width_v
height "Height" height_v
width_v : 0..1280
height_v : 0..1024
thumbnail "Thumbnail" {
width, height, "Url" : uri
}
Figure 2
The rules from Figure 2 can be written more compactly (see Figure 3).
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Compact rules describing Figure 1
{
"Image" {
width,
height,
"Title" :string,
"Thumbnail" {
width, height, "Url" :uri
},
"IDs" [ *:integer ]
}
}
width "Width" : 0..1280
height "Height" : 0..1024
Figure 3
3. Lines and Comments
There is no statement terminator and therefore no need for a line
continuation syntax. Rules may be defined across line boundaries.
Blank lines are allowed.
Comments are very similar to comments in ABNF [RFC4234]. They start
with a semi-colon (';') and continue to the end of the line or
another semi-colon.
4. Rules
Rules are composed of two parts, a rule name and a rule definition:
<rule name> <rule definition>
Rule names allow a rule to be identified by a name. A rule
definition describes the constraints upon which the content is to be
assessed. Rule definitions can use rule names to refer to other
rules.
4.1. Rule Names
Rule names must start with an alphabetic character (a-z,A-Z) and must
contain only alphabetic characters, numeric characters, the hyphen
character ('-') and the underscore character ('_').
Rule names are case sensitive. Rule names identifying rule
definitions must be unique within a ruleset.
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4.2. Rule Definitions
The syntax of each type of rule definition varies depending on the
type:
: string
; value rules start with a colon
"member_name" target_rule_name
; member rules start by defining the member name
{ mem1, mem2 }
; object rules start and end with "curly braces", like JSON objects
[ item1, item2 ]
; array rules start and end with square brackets, like JSON arrays
( rule1, rule2 )
; group rules start and end with parenthesis
A rule definition may embed other rule definitions, either explicitly
or by referencing a rule name that identifies a rule definition.
4.3. Annotations
Rule definitions may start with zero or more annotations. Each
annotation begins with the character sequence "@{" and ends with "}".
The following is an example of a rule definition with the root
annotation (explained in the next section):
@{root} [ nuts, bolts ]
This specification defines the annotations "root", "reject", and
"unordered", but other annotations may be defined.
4.4. Starting Points and Root Rules
Careful readers will have noticed that although rules have been
defined as having rule names and rule definitions, examples from the
introduction have one rule without a rule name. Within each ruleset,
a name on the first rule is optional. When the first rule is defined
without a name, it is considered a root rule.
Root rules are a starting point for the evaluation of JSON against a
ruleset. Or in other words, a root rule is the first rule processed.
Rules may also be declared a root rule with the @{root} annotation.
A ruleset may have more than one root rule, in which case the root
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rule to use for validating JSON should be explicitly specified
locally.
4.5. Value Rules
Value rules define content for JSON values. JSON allows values to be
objects, arrays, numbers, booleans, strings, and null. Arrays and
objects are handled by the array and object rules, and the value
rules define the rest.
4.5.1. Numbers, Booleans and Null
The rules for booleans and null are the simplest and take the
following forms:
rule_name : true
rule_name : false
rule_name : boolean
rule_name : null
Rules for numbers can specify the number be either an integer or
floating point number:
rule_name : integer
rule_name : float
Numbers may also be specified as an absolute value or a range of
possible values, where a range may be specified using a minimum,
maximum, or both:
rule_name : n
rule_name : n..m
rule_name : ..m
rule_name : n..
rule_name : n.f..m.f
rule_name : ..m.f
rule_name : n.f..
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When specifying a minimum and a maximum, both must either be an
integer or a floating point number. Thus to specify a floating point
number between zero and ten a definition of the following form is
used:
: 0.0..10.0
4.5.2. Strings
String values may be specified generically as:
rule_name : string
However, the content of strings can be narrowed in the following
ways:
A quoted string: A rule can specify that the value must be a
specific string:
rule_name : "a constant string"
Regular Expression: A rule can state that a string must match a
regular expression by giving the regular expression:
rule_name : /regex/
URIs and URI templates: A rule can state that a string must be a
URI [RFC3986]:
rule_name : uri
URIs may be further scoped to a specific URI pattern by using a
URI template [RFC6570]:
rule_name : uri..http://{stuff}
rule_name : uri..http://{authority}/{thing1}?q={thing2}
When using URI templates, the variable names are ignored for
pattern matching, but they should be provided for construction of
a valid URI template. Providing the variable names also aids in
the description of what is to be matched.
IP Addresses: Narrowing the content of strings down to IP addresses
can be done with either the 'ip4' (see [RFC1166]) or 'ip6' (see
[RFC5952]) literals:
rule_name : ip4
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rule_name : ip6
Domain Names: Fully qualified A-label and U-label domain names can
be specified with the 'fqdn' and 'idn' literals:
rule_name : fqdn
rule_name : idn
Dates and Times: Dates and times are specified using the ABNF rules
from RFC 3339 [RFC3339] as literals:
rule_name : date-time
rule_name : full-date
rule_name : full-time
Email Addresses: A string can be scoped to the syntax of email
addresses using the literal 'email':
rule_name : email
Email addresses must conform to the syntax of RFC 5322 [RFC5322].
Phone Numbers: Strings conforming to E.123 phone number format can
be specified as follows:
rule_name : phone
Base 64: Strings containing base 64 data, as described by RFC 4648
[RFC4648], can be specified as follows:
rule_name : base64
4.5.3. Any Value
It is possible to specify that a value can be of any type allowable
by JSON using the 'any' value rule. This is done with the 'any'
literal in a value rule:
rule_name : any
However, unlike other value rules which define primitive data types,
this rule defines a value of any kind, either primitive (null,
boolean, number, and string), object, or array.
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4.6. Member Rules
Member rules define members of JSON objects. Member rules follow the
format:
rule_name member_name type
where rule_name is the name of the rule being defined, member_name is
the name of the JSON object member, and type is a value rule, array
rule, or object rule or a reference to a value rule, array rule, or
object rule specifying the allowable content of the JSON object
member.
Member names may be specified either explicitly as a quoted string:
some_member_rule "some_member_name" some_member_target
or a family of member names may be specified as a regular expression:
some_member_rule /some\.[a-z]+\.names/ some_member_target
Member rules may also be written in this form:
rule_name "member_rule" target_rule_definition
The following are examples:
location_uri "locationURI" : uri
iface_mappings /eth[0-9]/ :ip4
Member rules cannot be used as a root rule.
4.7. Object Rules
Object rules define the allowable members of a JSON object, and their
rule definitions contain the member rules of the object. They take
the following form:
rule_name { member_rule_1, member_rule_2 }
The following rule example defines an object composed of two member
rules:
response { location_uri, status_code }
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Given that where a rule name is found a rule definition of an
appropriate type may be used, the above example might also be written
as:
response { "locationUri" : uri, "statusCode" : integer }
Rules given in the rule definition of an object rule do not imply
order. Given the example object rule above both
{ "locationUri" : "http://example.com", "statusCode" : 200 }
and
{ "statusCode" : 200, "locationUri" : "http://example.com" }
are JSON objects that match the rule.
Each member rule of an object rule is evaluated in the order in which
they appear in the object rule. Thus where there is potential
conflict between rule names defined using regular expressions, the
rules with the most constrained name should be defined first.
Otherwise, for example, a rule definition of:
{ /p\d+/ : int, "p0" : string }
would fail to match the JSON object:
{ "p1" : 12, "p0" : "Fred" }
because the "p0" member name would match the regular expression
despite the presence of the subsequently defined "p0" member rule.
4.8. Array Rules
Array rules define the allowable content of JSON arrays. Their rule
definitions are composed of the other rule types with the exception
of member rules and have the following form:
rulename [ rule_1, rule_2 ]
The following example defines an array where the first element is
defined by the width_value rule and the second element is defined by
the height_value rule:
size [ width_value, height_value ]
By default, unlike object rules, order is implied by the array rule
definition. That is, the first rule referenced or defined within an
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array rule specifies that the first element of the array will match
that rule, the second rule given with the array rule specifies that
the second element of the array will match that rule, and so on.
Take for example the following array rule definition:
person [ : string, : integer ]
This JSON array matches the above rule:
[ "Bob Smurd", 24 ]
while this one does not:
[ 24, "Bob Smurd" ]
Finally, if an array has more elements than can be matched from the
array rule, the array does not match the array rule. Or stated
differently, an array with unmatched elements does not validate.
Using the example array rule above, the following array does not
match because the last element of the array does not match any rule
contained in the array rule:
[ "Bob Smurd", 24, "http://example.com/bob-smurd" ]
4.8.1. Unordered Array Rules
Array rules can be made to behave in a similar fashion to object
rules with regard to the order of matching with the @{unordered}
annotation:
person @{unordered} [ :string, :integer ]
This rule matches both of theses JSON arrays.
[ "Bob Smurd", 24 ]
[ 24, "Bob Smurd" ]
Like ordered array rules, the rules contained in an unordered array
rule are evaluated in the order they are specified. The difference
is that they need not match an element of the array in the same
position as given in the array rule.
Like ordered array rules, unordered array rules also require that all
elements of the array be matched by a subordinate rule. If the array
has more elements than can be matched, the array rule does not match
the array.
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4.9. Group Rules
Unlike the other types of rules, group rules have no direct tie with
JSON syntax. Group rules simply group together other rules. They
take the form:
rule_name ( target_rule_1, target_rule_2 )
Group rule definitions and any nesting of group rule definitions,
must conform to the allowable set of rules of the rule containing
them. A group rule referenced inside of an array rule may not
contain a member rule since member rules are not allowed in array
rules directly. Likewise, a group rule referenced inside an object
rule must only contain member rules.
The following is an example of a group rule:
the_bradys [ parents, children ]
children ( :"Greg", :"Marsha", :"Bobby", :"Jan" )
parents ( :"Mike", :"Carol" )
Like the subordinate rules of array and object rules, the subordinate
rules of a group rule are evaluated in the order they appear.
4.10. Ordered and Unordered Groups in Arrays
Section 4.8.1 specifies that arrays can be evaluated by the order of
the items in the array or can be evaluated without order.
Section 4.9 specifies that arrays may have group rules as
subordinates.
The evaluation of a group rule inside an array rule inherits the
ordering property of the array rule. If the array rule is unordered,
then the items of the group rule are also considered to be unordered.
And if the array rule is ordered, then the items of the group rule
are also considered to be ordered.
4.11. Sequence and Choice Combinations in Array, Object, and Group
Rules
Combinations of subordinate rules in array, object, and group rules
can be specified as either a sequence ("and") or a choice ("or"). A
sequence is a rule followed by the comma character (',') followed by
another rule.
[ this, that ]
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A choice is a rule followed by a pipe character ('|') followed by
another rule.
[ this | that ]
Sequence and choice combinations cannot be mixed, and group rules
must be used to explicitly declare precedence between a sequence and
a choice. Therefore, the following is illegal:
[ this, that | the_other ]
The example above should be expressed as:
[ this, ( that | the_other ) ]
4.12. Repetition in Array, Object, and Group Rules
Evaluation of subordinate rules in array, object, and group rules may
be preceded by a repetition expression denoting how many times the
subordinate rule should be evaluated.
Repetition is expressed as a minimum number of repetitions and a
maximum number of repetitions. When no repetition expression is
present, both the minimum and maximum are 1.
A minimum and maximum can be expressed by giving the minimum followed
by an asterisk ('*') character followed by the maximum: min*max.
[ 1*13 name_servers ] ; 1 to 13 name servers
If the minimum is not given, it is assumed to be zero.
{ *99 /eth.*/ mac_addr }; 0 to 99 ethernet addresses
If the maximum is not given, it is assumed to be infinity.
[ 2* octets ] ; two or more bytes
If neither the minimum nor the maximum are given with the asterisk,
this denotes "zero or more".
error_set ( * error ) ; zero or more errors
Repetition may also be expressed with a question mark character ('?')
or a plus character ('+'). '?' is equivalent to '0*1'.
{ name, ?age } ; age is optional
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'+' is equivalent to '1*'
[ + status ] ; 1 or more status values
4.13. Rejecting Rules
The evaluation of a rule can be changed with the @{reject}
annotation. With this annotation, a rule that would otherwise match
does not, and a rule that would not have matched does.
not_two @{reject} : 2
; match anything that isn't the integer 2
@{reject} @{unordered} [ :"fail", *:string ]
; error if one of the status values is "fail"
4.14. Repetitions, Annotations, and Target Rules
With regard to syntax, repetition expressions are part of the syntax
of array, object, and group rules with respect to the embedding of
subordinate rules, whereas annotations are a component of every type
of rule definition. Every type of rule definition may begin with a
series of annotations.
The significance is the placement of repetition expressions with
respect to annotations: repetition expressions precede annotations.
The following is correct:
[ * @{unordered} [ foo ] ]
The following is not:
[ @{unordered} * [ foo ] ]
5. Directives
Directives modify the processing of a ruleset. There are two forms
of the directive, the single line directive and the multi-line
directive.
Single line directives appear on their own line in a ruleset, begin
with a hash character ('#') and are terminated by the end of the
line. They take the following form:
# directive_name optional_directive_parameters
Directives may have other qualifiers after the directive name.
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Multi-line directives also appear on their own lines, but may span
multiple lines. The being with the character sequence "#{" and ends
with "}". The take the following form:
#{ directive_name
directive_parameter_1 directive_paramter_2
directive_parameter_3
...
}
This specification defines the directives "jcr-version", "ruleset-
id", and "import", but other directives may be defined.
5.1. jcr-version
This directive declares that the ruleset complies with a specific
version of this standard. The version is expressed as a major
integer followed by a period followed by a minor integer.
# jcr-version 0.6
The major.minor number signifying compliance with this document is
"0.6". Upon publication of this specification as an IETF proposed
standard, it will be "1.0".
# jcr-version 1.0
Ruleset authors are advised to place this directive as the first line
of a ruleset.
5.2. ruleset-id
This directive identifies a ruleset to rule processors. It takes the
form:
# ruleset-id identifier
An identifier can be a URL (e.g. http://example.com/foo), an inverted
domain name (e.g. com.example.foo) or any other form that conforms to
the JCR ABNF syntax that a ruleset author deems appropriate. To a
JCR processor the identifier is treated as an opague, case-sensitive
string.
5.3. import
The import directive specifies that another ruleset is to have its
rules evaluated in addition to the ruleset where the directive
appears.
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This directive has the following form:
# import identifier as alias
The following is an example:
# import http://example.com/rfc9999 as rfc9999
The rule names of the ruleset to be imported may be referenced by
prepending the alias followed by a period character ('.') followed by
the rule name (i.e. "alias.name"). To continue the example above, if
the ruleset at http://example.com/rfc9999 were to have a rule named
'encoding', rules in the ruleset importing it can refer to that rule
as 'rfc9999.encoding'.
6. Tips and Tricks
6.1. Any Member with Any Value
Because member names may be specified with regular expressions, it is
possible to construct a member rule that matches any member name:
rule_name /.*/ target_rule_name
As an example, the following defines an object member with any name
that has a value that is a string:
user_data /.*/ : string
Constructing an object member of any name with any type would
therefore take the form:
rule_name /.*/ : any
6.2. Restricting Objects
By default, members of objects which do not match a rule are ignored.
The reason for this validation model is due to the nature of the
typical access model to JSON objects in many programming languages,
where members of the object are obtained by referencing the member
name. Therefore extra members may exist without harm.
However, some specifications may need to restrict the members of a
JSON object to a known set. To construct an object rule specifying
that no extra members are expected, the @{reject} annotation may be
used with a regular expression as the last subordinate rule of the
object rule.
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{ member1, member2, + @{reject} /.*/ : any }
This works because subordinate rules are evaluated in the order they
appear in the object rule, and the last rule accepts any member with
any type but fails to validate if one ore more of those rules are
found due to the @{reject} annotation.
6.3. Unrestricting Arrays
Unlike object validation, array rules will not validate items of an
array that do not match a subordinate rule of the array rule. This
processing model is due to the nature of the typical access pattern
of JSON arrays in many programming languages, which is to iterate
over the array. Processes iterating over an array would need to take
special steps for extra items of the array that are not specified,
especially if the items were of a different type than those that are
expected.
Like object rules, the subordinate rules of an array rule are
evaluated in the order they appear. To allow an array to contain any
value after guaranteeing that it contains the necessary items, the
last subordinate rule of the array rule should accept any item:
[ item1, item2, * :any ]
6.4. Groups of Values
In addition to specific primitive data types, value rules may contain
a value choice rule. The value choice rule, and any subordinate rule
within it, must evaluate to a single primitive data type.
The following is an example of a value choice rule embedded in a
value rule:
address : ( :ip4 | :ip6 )
6.5. Groups in Arrays
Groups may also be a subordinate rule of array rules:
[ ( :ip4 | :ip6 ), :integer ]
Unlike value rules, subordinate group rules in array rules may have
sequence combinations and contain any rule type with the exception of
member rules.
[ ( first_name, ? middle_name, last_name ), age ]
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Of course, the above is better written as:
[ name, age ]
name ( first_name, ? middle_name, last_name )
6.6. Groups in Objects
Groups may also be a subordinate rule of object rules:
{ ( title, date, author ), + paragraph }
Subordinate group rules in object rules may have sequence
combinations but must only contain member rules.
{ front_matter, + paragraph }
front_matter ( title, date, author )
title "title" :string
date "date" : full-date
author "author" [ *:string ]
paragraph /p[0-9]*/ :string
6.7. Group Rules as Macros
The syntax for group rules accommodates one ore more subordinate
rules and a repetition expression for each. Other than grouping
multiple rules, a group rule can be used as a macro definition for a
single rule.
paragraphs ( + /p[0-9]*/ : string )
6.8. Comment Separated Rules
Rules may be placed on the same line, but because they have no
termination syntax this style of writing rules can be confusing to
some readers:
first_name "first name" :string last_name "last name" :string
An empty comment can serve as a visual cue to denote the separation
of the two rules:
first_name "first name" :string ;; last_name "last name" :string
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6.9. Object Mixins
Group rules can be used to create object mixins, a pattern for
writing data models similar in style to object derivation in some
programming languages. In the example in Figure 4, both obj1 and
obj2 have a members "foo" and "fob" with obj1 having the additional
member "bar" and obj2 having the additional member "baz".
mixin_group ( "foo" : integer, "fob" : uri )
obj1 { mixin_group, "bar" : string }
obj2 { mixin_group, "baz" : string }
Figure 4
6.10. Subordinate Rule Dependencies
In object and array rules, there may be situations in which it is
necessary to condition the existence of a subordinate rule on the
existence of a sibling subordinate rule. In other words,
example_rule_two should only be evaluated if example_rule_one
evaluates positively. Or put another way, a member of an object or
an item of an array may be present only on the condition that another
member of item is present.
In the following example, the referrer_uri member can only be present
if the location_uri member is present.
response { ?( location_uri, ?referrer_uri ) }
6.11. Multiple Root Styles
As stated in Section 4.4, the first rule in a ruleset is a root rule
when it is unnamed. Group rules can be used as the root rule, such
as in the following example:
( { "foo" : string } | { "bar" : string } )
This is the equivalent of the following:
foo @{root} { "foo" : string }
bar @{root} { "bar" : string }
Either style is valid. However, explicitly naming root rules has the
advantage of explicitly validating a JSON message against a specific
rule.
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6.12. JSON-like Object and Array Definitions
JCR allows an optional colon character (":") to precede object and
array rule definitions to give these definitions more of a JSON-like
appearance. Consider the following example.
{
"foo" {
"fuzz" : string
},
"bar" [
"baz"
]
}
To appear more JSON-like, this may also be given as follows:
{
"foo" : {
"fuzz" : string
},
"bar" : [
"baz"
]
}
7. ABNF Syntax
The following ABNF describes the syntax for JSON Content Rules.
jcr = *( sp-cmt / directive ) [ root-rule ]
*( sp-cmt / directive / rule )
sp-cmt = spaces / comment
spaces = 1*( WSP / CR / LF )
comment = ";" *( "\;" / comment-char ) comment-end-char
comment-char = HTAB / %x20-3A / %x3C-10FFFF
; Any char other than ";" / CR / LF
comment-end-char = CR / LF / ";"
directive = "#" (one-line-directive / multi-line-directive)
one-line-directive = [ spaces ]
(directive-def / one-line-tbd-directive-d) *WSP eol
multi-line-directive = "{" *sp-cmt
(directive-def / multi-line-tbd-directive-d) *sp-cmt "}"
directive-def = jcr-version-d / ruleset-id-d / import-d
jcr-version-d = jcr-version-kw spaces major-version "." minor-version
major-version = p-integer
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minor-version = p-integer
ruleset-id-d = ruleset-id-kw spaces ruleset-id
import-d = import-kw spaces ruleset-id
[ spaces as-kw spaces ruleset-id-alias ]
ruleset-id = ALPHA *not-space
not-space = %x21-10FFFF
ruleset-id-alias = name
one-line-tbd-directive-d = directive-name [ WSP one-line-directive-parameters ]
directive-name = name
one-line-directive-parameters = *not-eol
not-eol = HTAB / %x20-10FFFF
eol = CR / LF
multi-line-tbd-directive-d = directive-name
[ spaces multi-line-directive-parameters ]
multi-line-directive-parameters = multi-line-parameters
multi-line-parameters = *(comment / q-string / regex /
not-multi-line-special)
not-multi-line-special = spaces / %x21 / %x23-2E / %x30-3A / %x3C-7C /
%x7E-10FFFF ; not ", /, ; or }
root-rule = value-rule / group-rule
rule = rule-name *sp-cmt rule-def
rule-name = name
target-rule-name = annotations [ ruleset-id-alias "." ] rule-name
name = ALPHA *( ALPHA / DIGIT / "-" / "-" )
rule-def = type-rule / member-rule / group-rule
type-rule = value-rule / type-choice-rule / target-rule-name
value-rule = primitive-rule / array-rule / object-rule
member-rule = annotations
member-name-spec *sp-cmt type-rule
member-name-spec = regex / q-string
type-choice-rule = ":" *sp-cmt type-choice
type-choice = annotations "(" type-choice-items
*( choice-combiner type-choice-items ) ")"
type-choice-items = *sp-cmt ( type-choice / type-rule ) *sp-cmt
annotations = *( "@{" *sp-cmt annotation-set *sp-cmt "}" *sp-cmt )
annotation-set = reject-annotation / unordered-annotation /
root-annotation / tbd-annotation
reject-annotation = reject-kw
unordered-annotation = unordered-kw
root-annotation = root-kw
tbd-annotation = annotation-name [ spaces annotation-parameters ]
annotation-name = name
annotation-parameters = multi-line-parameters
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primitive-rule = annotations ":" *sp-cmt primimitive-def
primimitive-def = null-type / boolean-type / true-value / false-value /
string-type / string-range / string-value /
float-type / float-range / float-value /
integer-type / integer-range / integer-value /
ip4-type / ip6-type / fqdn-type / idn-type /
uri-range / uri-type / phone-type / email-type /
full-date-type / full-time-type / date-time-type /
base64-type / any
null-type = null-kw
boolean-type = boolean-kw
true-value = true-kw
false-value = false-kw
string-type = string-kw
string-value = q-string
string-range = regex
float-type = float-kw
float-range = float-min ".." [ float-max ] / ".." float-max
float-min = float
float-max = float
float-value = float
integer-type = integer-kw
integer-range = integer-min ".." [ integer-max ] / ".." integer-max
integer-min = integer
integer-max = integer
integer-value = integer
ip4-type = ip4-kw
ip6-type = ip6-kw
fqdn-type = fqdn-kw
idn-type = idn-kw
uri-range = uri-dotdot-kw uri-template
uri-type = uri-kw
phone-type = phone-kw
email-type = email-kw
full-date-type = full-date-kw
full-time-type = full-time-kw
date-time-type = date-time-kw
base64-type = base64-kw
any = any-kw
object-rule = annotations [ ":" *sp-cmt ] "{" *sp-cmt [ object-items *sp-cmt ] "}"
object-items = object-item (*( sequence-combiner object-item ) /
*( choice-combiner object-item ) )
object-item = [ repetition *sp-cmt ] object-item-types
object-item-types = member-rule / target-rule-name / object-group
object-group = "(" *sp-cmt [ object-items *sp-cmt ] ")"
array-rule = annotations [ ":" *sp-cmt ] "[" *sp-cmt [ array-items *sp-cmt ] "]"
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array-items = array-item (*( sequence-combiner array-item ) /
*( choice-combiner array-item ) )
array-item = [ repetition ] *sp-cmt array-item-types
array-item-types = type-rule / array-group
array-group = "(" *sp-cmt [ array-items *sp-cmt ] ")"
group-rule = annotations "(" *sp-cmt [ group-items *sp-cmt ] ")"
group-items = group-item (*( sequence-combiner group-item ) /
*( choice-combiner group-item ) )
group-item = [ repetition ] *sp-cmt group-item-types
group-item-types = type-rule / member-rule / group-group
group-group = group-rule
sequence-combiner = *sp-cmt "," *sp-cmt
choice-combiner = *sp-cmt "|" *sp-cmt
repetition = optional / one-or-more / min-max-repetition /
min-repetition / max-repetition /
zero-or-more / specific-repetition
optional = "?"
one-or-more = "+"
zero-or-more = "*"
min-max-repetition = min-repeat *sp-cmt "*" *sp-cmt max-repeat
min-repetition = min-repeat *sp-cmt "*"
max-repetition = "*" *sp-cmt max-repeat
min-repeat = p-integer
max-repeat = p-integer
specific-repetition = p-integer
integer = ["-"] 1*DIGIT
p-integer = 1*DIGIT
float = [ minus ] int frac [ exp ]
; From RFC 7159 except 'frac' required
minus = %x2D ; -
plus = %x2B ; +
int = zero / ( digit1-9 *DIGIT )
digit1-9 = %x31-39 ; 1-9
frac = decimal-point 1*DIGIT
decimal-point = %x2E ; .
exp = e [ minus / plus ] 1*DIGIT
e = %x65 / %x45 ; e E
zero = %x30 ; 0
q-string = quotation-mark *char quotation-mark
; From RFC 7159
char = unescaped /
escape (
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%x22 / ; " quotation mark U+0022
%x5C / ; \ reverse solidus U+005C
%x2F / ; / solidus U+002F
%x62 / ; b backspace U+0008
%x66 / ; f form feed U+000C
%x6E / ; n line feed U+000A
%x72 / ; r carriage return U+000D
%x74 / ; t tab U+0009
%x75 4HEXDIG ) ; uXXXX U+XXXX
escape = %x5C ; \
quotation-mark = %x22 ; "
unescaped = %x20-21 / %x23-5B / %x5D-10FFFF
regex = "/" *( escape "/" / not-slash ) "/" [ regex-modifiers ]
not-slash = HTAB / CR / LF / %x20-2E / %x30-10FFFF
; Any char except "/"
regex-modifiers = *( "i" / "s" / "x" )
uri-template = 1*ALPHA ":" 1*not-space
;; Keywords
any-kw = %x61.6E.79 ; "any"
as-kw = %x61.73 ; "as"
base64-kw = %x62.61.73.65.36.34 ; "base64"
boolean-kw = %x62.6F.6F.6C.65.61.6E ; "boolean"
date-time-kw = %x64.61.74.65.2D.74.69.6D.65 ; "date-time"
email-kw = %x65.6D.61.69.6C ; "email"
false-kw = %x66.61.6C.73.65 ; "false"
float-kw = %x66.6C.6F.61.74 ; "float"
fqdn-kw = %x66.71.64.6E ; "fqdn"
full-date-kw = %x66.75.6C.6C.2D.64.61.74.65 ; "full-date"
full-time-kw = %x66.75.6C.6C.2D.74.69.6D.65 ; "full-time"
idn-kw = %x69.64.6E ; "idn"
import-kw = %x69.6D.70.6F.72.74 ; "import"
integer-kw = %x69.6E.74.65.67.65.72 ; "integer"
ip4-kw = %x69.70.34 ; "ip4"
ip6-kw = %x69.70.36 ; "ip6"
jcr-version-kw = %x6A.63.72.2D.76.65.72.73.69.6F.6E ; "jcr-version"
null-kw = %x6E.75.6C.6C ; "null"
phone-kw = %x70.68.6F.6E.65 ; "phone"
reject-kw = %x72.65.6A.65.63.74 ; "reject"
root-kw = %x72.6F.6F.74 ; "root"
ruleset-id-kw = %x72.75.6C.65.73.65.74.2D.69.64 ; "ruleset-id"
string-kw = %x73.74.72.69.6E.67 ; "string"
true-kw = %x74.72.75.65 ; "true"
unordered-kw = %x75.6E.6F.72.64.65.72.65.64 ; "unordered"
uri-dotdot-kw = %x75.72.69.2E.2E ; "uri.."
uri-kw = %x75.72.69 ; "uri"
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;; Referenced RFC 5234 Core Rules
ALPHA = %x41-5A / %x61-7A ; A-Z / a-z
CR = %x0D ; carriage return
DIGIT = %x30-39 ; 0-9
HEXDIG = DIGIT / "A" / "B" / "C" / "D" / "E" / "F"
HTAB = %x09 ; horizontal tab
LF = %x0A ; linefeed
SP = %x20 ; space
WSP = SP / HTAB ; white space
JSON Content Rules ABNF
8. Acknowledgements
Andrew Biggs and Paul Jones provided feedback and suggestions which
led to many changes in the syntax.
9. References
9.1. Normative References
[RFC1166] Kirkpatrick, S., Stahl, M., and M. Recker, "Internet
numbers", RFC 1166, DOI 10.17487/RFC1166, July 1990,
<http://www.rfc-editor.org/info/rfc1166>.
[RFC3339] Klyne, G. and C. Newman, "Date and Time on the Internet:
Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002,
<http://www.rfc-editor.org/info/rfc3339>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<http://www.rfc-editor.org/info/rfc3986>.
[RFC4234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 4234, DOI 10.17487/RFC4234,
October 2005, <http://www.rfc-editor.org/info/rfc4234>.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
<http://www.rfc-editor.org/info/rfc4648>.
[RFC5322] Resnick, P., Ed., "Internet Message Format", RFC 5322,
DOI 10.17487/RFC5322, October 2008,
<http://www.rfc-editor.org/info/rfc5322>.
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[RFC5952] Kawamura, S. and M. Kawashima, "A Recommendation for IPv6
Address Text Representation", RFC 5952,
DOI 10.17487/RFC5952, August 2010,
<http://www.rfc-editor.org/info/rfc5952>.
[RFC6570] Gregorio, J., Fielding, R., Hadley, M., Nottingham, M.,
and D. Orchard, "URI Template", RFC 6570,
DOI 10.17487/RFC6570, March 2012,
<http://www.rfc-editor.org/info/rfc6570>.
[RFC7159] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
2014, <http://www.rfc-editor.org/info/rfc7159>.
9.2. Infomative References
[I-D.cordell-jcr-co-constraints]
Cordell, P. and A. Newton, "Co-Constraints for JSON
Content Rules", draft-cordell-jcr-co-constraints-00 (work
in progress), March 2016.
[ARIN_JCR_VALIDATOR]
American Registry for Internet Numbers, "JSON Content
Rules Validator (Work In Progress)",
<https://github.com/arineng/jcrvalidator>.
[CODALOGIC_JCR_VALIDATOR]
Codalogic, "cl-jcr-parser (Work In Progress)",
<https://github.com/codalogic/cl-jcr-parser>.
Appendix A. Co-Constraints
This specification defines a small set of annotations and directives
for JCR, yet the syntax is extensible allowing for other annotations
and directives. [I-D.cordell-jcr-co-constraints] ("Co-Constraints
for JCR") defines further annotations and directives which define
more detailed constraints on JSON messages, including co-constraints
(constraining parts of JSON message based on another part of a JSON
message).
Appendix B. Testing Against JSON Content Rules
One aspect of JCR that differentiates it from other format schema
languages are the mechanisms helpful to developers for taking a
formal specification, such as that found in an RFC, and evolving it
into unit tests, which are essential to producing quality protocol
implementations.
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B.1. Locally Overriding Rules
As mentioned in the introduction, one tool for testing would be the
ability to locally override named rules. As an example, consider the
following rule which defines an array of strings.
statuses [ * :string ]
Consider the specification where this rule is found does not define
the values but references an IANA registry for extensibility
purposes.
If a software developer desired to test a specific situation in which
the array must at least contain the status "accepted", the rules from
the specification could be used and the statuses rule could be
explicitly overridden locally as:
statuses @{unordered} [ :"accepted", * :string ]
Alternatively, the developer may need to ensure that the status
"denied" should not be present in the array:
statuses @{unordered} [ ? @{reject} :"denied", * :string ]
B.2. Rule Callbacks
In many testing scenarios, the evaluation of rules may become more
complex than that which can be expressed in JCR, sometimes involving
variables and interdependencies which can only be expressed in a
programming language.
A JCR processor may provide a mechanism for the execution of local
functions or methods based on the name of a rule being evaluated.
Such a mechanism could pass to the function the data to be evaluated,
and that function could return to the processor the result of
evaluating the data in the function.
Appendix C. Combining Multiple Rulesets (Experimental)
This section is experimental and subject to further development.
Many work items within the IETF are defined by a core specification
which is later enhanced by extension specifications. JCR supports
this pattern of working by using the (@augments) annotation.
The parameters of the @{augments} annotation are a list of one or
more target-rule-names that identify rules to be augmented. The
augmentation process consists of logically adding a reference to the
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rule name of the rule that contains the @{augments} annotation into
each of the rules identified by the target-rule-names in the
@{augments} annotation.
As an example, assume we have a core specification that contains the
following JCR:
#ruleset-id com.example.core
core { core-item1, core-item2 }
more { core-item3, core-item4 }
...
And a subsequently defined extension with the following JCR:
#ruleset-id com.example.extension
#import com.example.core as core
extension @{augments core.core core.more} ext-item1
The resultant core specification is treated as:
#ruleset-id com.example.core
core { core-item1, core-item2, __alias1.extension }
more { core-item3, core-item4, __alias1.extension }
...
where '__alias1' is conceptually an automatically created alias that
aliases 'com.example.extension'.
Because multiple @{augments} annotations may specify the same target-
rule-name, there can be no control over the order the augmentations
are given in the target rule. Hence the specified target-rule-names
are only allowed to correspond to (unordered) objects, unordered
arrays, and value choices.
If the non-nested rules in the target rule are all combined using the
choice combiner, then the augmenting rule is also combined using the
choice combiner. If the non-nested rules in the target rule are all
combined using the sequence combiner, then the augmenting rule is
also combined using the sequence combiner. If the non-nested rules
in the target rule use a combination of the choice combiner and
sequence combiner, then the existing rules within the target group
are logically nested within a group and the augmenting rule is
combined using the sequence combiner. For example, a target rule
initially containing the following definition:
core { core-item1, core-item2 | core-item3 }
would be treated as follows after being augmented:
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core { (core-item1, core-item2 | core-item3), __alias1.extension }
If it is desired to add more than one rule to a target rule then the
augmenting rule can specify a group, for example:
extension @{augments core.core core.more} (ext-item1, ext-item2)
Appendix D. JCR Implementations
The following implementations, [ARIN_JCR_VALIDATOR] and
[CODALOGIC_JCR_VALIDATOR] have influenced the development of this
document.
Authors' Addresses
Andrew Lee Newton
American Registry for Internet Numbers
3635 Concorde Parkway
Chantilly, VA 20151
US
Email: andy@arin.net
URI: http://www.arin.net
Pete Cordell
Codalogic
PO Box 30
Ipswich IP5 2WY
UK
Email: pete.cordell@codalogic.com
URI: http://www.codalogic.com
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