| Network Working Group | A. Newton |
| Internet-Draft | ARIN |
| Intended status: Standards Track | P. Cordell |
| Expires: April 21, 2016 | Codalogic |
| October 19, 2015 |
A Language for Rules Describing JSON Content
draft-newton-json-content-rules-05
This document describes a language for specifying and testing the expected content of JSON structures found in JSON-using protocols, software, and processes.
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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.
The following JSON data describes a JSON object with two members, "line-count" and "word-count", each containing an integer.
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:
Since line counts and word counts should be either zero or a positive integer, the specification may be further narrowed:
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..
}
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.
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.
Each rule has two components, a rule name and a 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:
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':
Since rule names can be 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):
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':
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':
Finally, group rules designate a collection of rules.
Putting it all together, Figure 2 describes the JSON in Figure 1.
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 ]
}
thumbnail "Thumbnail" {
width, height, "Url" : uri
}
width "Width" width_v
height "Height" height_v
width_v : 0..1280
height_v : 0..1024
Figure 2
The rules from Figure 2 can be written more compactly (see Figure 3).
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
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.
Rules are composed of two parts, a rule name and a 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.
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.
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.
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):
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 rule to use for validating JSON should be explicitly specified locally.
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.
The rules for booleans and null are the simplest and take the following forms:
Rules for numbers can specify the number be either an integer or floating point number:
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:
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:
String values may be specified generically as:
However, the content of strings can be narrowed in the following ways:
URIs may be further scoped to a specific URI pattern by using a
URI template [RFC6570]:
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.
Email addresses must conform to the syntax of
RFC 5322 [RFC5322].
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:
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.
Member rules define members of JSON objects. Member rules follow the format:
where rule_name is the name of the rule being defined, member_name is the name of the JSON object member, and target_rule_name is 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:
or a family of member names may be specified as a regular expression:
Since rule names in rule definitions may be replaced by rule definitions, member rules may also be written in this form:
The following are examples:
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:
The following rule example defines an object composed of two member rules:
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:
Rules given in the rule definition of an object rule do not imply order. Given the example object rule above both
and
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:
would fail to match the JSON object:
because the "p0" member name would match the regular expression despite the presence of the subsequently defined "p0" member rule.
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:
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:
By default, unlike object rules, order is implied by the array rule definition. That is, the first rule referenced or defined within an 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:
This JSON array matches the above rule:
while this one does not:
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:
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:
This rule matches both of theses JSON arrays.
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.
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:
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.
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.
A choice is a rule followed by a pipe character ('|') followed by another rule.
Sequence and choice combinations maybe mixed, with evaluation occurring in the order the rules are specified (i.e. right to left).
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.
If the minimum is not given, it is assumed to be zero.
If the maximum is not given, it is assumed to be infinity.
If neither the minimum nor the maximum are given with the asterisk, this denotes "zero or more".
Repetition may also be expressed with a question mark character ('?') or a plus character ('+'). '?' is equivalent to '0*1'.
'+' is equivalent to '1*'
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"
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.
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:
The following is not:
Additionally, annotations may not decorate references to rules (target rule names). The following is not correct:
Directives modify the processing of a ruleset. They 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:
Directives may have other qualifiers after the directive name.
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.
The major.minor number signifying compliance with this document is "0.5". Upon publication of this specification as an IETF proposed standard, it will be "1.0".
Ruleset authors are advised to place this directive as the first line of a ruleset.
This directive identifies a ruleset to rule processors. It takes the form:
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.
The import directive specifies that another ruleset is to have its rules evaluated in addition to the ruleset where the directive appears.
This directive has the following form:
The following is an example:
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'.
Because member names may be specified with regular expressions, it is possible to construct a member rule that matches any member name:
As an example, the following defines an object member with any name that has a value that is a string:
Constructing an object member of any name with any type would therefore take the form:
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.
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.
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:
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:
Groups may also be a subordinate rule of array rules:
Unlike value rules, subordinate group rules in array rules may have sequence combinations and contain any rule type with the exception of member rules.
Of course, the above is better written as:
Groups may also be a subordinate rule of object rules:
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
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.
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:
An empty comment can serve as a visual cue to denote the separation of the two rules:
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
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.
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 = "#" [ spaces ] directive-def eol
directive-def = jcr-version-d / ruleset-id-d / import-d /
tbd-directive-d
jcr-version-d = jcr-version-kw spaces major-version "." minor-version
major-version = integer
minor-version = integer
ruleset-id-d = ruleset-id-kw spaces ruleset-id
import-d = import-kw spaces ruleset-id
[ spaces as-kw ruleset-id-alias ]
ruleset-id = ALPHA *not-space
not-space = %x21-10FFFF
ruleset-id-alias = name
tbd-directive-d = directive-name [ spaces directive-parameters ]
directive-name = name
directive-parameters = not-eol
not-eol = HTAB / %x20-10FFFF
eol = CR / LF
root-rule = value-rule / array-rule / object-rule /
member-rule / group-rule
rule = rule-name *sp-cmt rule-def
rule-name = name
target-rule-name = [ ruleset-id-alias "." ] rule-name
name = ALPHA *( ALPHA / DIGIT / "-" / "-" )
rule-def = type-rule / member-rule / group-rule
type-rule = value-rule / array-rule / object-rule /
target-rule-name
member-rule = annotations
member-name-spec *sp-cmt (type-rule / type-choice)
member-name-spec = regex / q-string
type-choice = "(" 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 = *( spaces / %x21-28 / %x2A-10FFFF )
; Not close bracket - ")"
value-rule = annotations ":" *sp-cmt ( value-choice / value-def )
value-choice = annotations
"(" *sp-cmt value-choice-items *sp-cmt ")"
value-choice-items = value-choice-item
*( choice-combiner value-choice-item )
value-choice-item = ":" *sp-cmt
value-def / value-choice / target-rule-name
value-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-type / uri-range / 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-type = uri-kw
uri-range = uri-template
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 [ object-items *sp-cmt ] "}"
object-items = object-item *( sequence-or-choice 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 [ array-items *sp-cmt ] "]"
array-items = array-item *( sequence-or-choice 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-or-choice group-item )
group-item = [ repetition ] *sp-cmt group-item-types
group-item-types = type-rule / member-rule / group-group
group-group = group-rule
sequence-or-choice = sequence-combiner / choice-combiner
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 (
%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 ) "/"
not-slash = HTAB / CR / LF / %x20-2E / %x30-10FFFF
; Any char except ";"
uri-template = 1*ALPHA ":" 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-kw = %x75.72.69 ; "uri"
;; 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
Andrew Biggs and Paul Jones provided feedback and suggestions which led to many changes in the syntax.
| [RFC1166] | Kirkpatrick, S., Stahl, M. and M. Recker, "Internet numbers", RFC 1166, DOI 10.17487/RFC1166, July 1990. |
| [RFC3339] | Klyne, G. and C. Newman, "Date and Time on the Internet: Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002. |
| [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. |
| [RFC4234] | Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", RFC 4234, DOI 10.17487/RFC4234, October 2005. |
| [RFC4648] | Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006. |
| [RFC5322] | Resnick, P., "Internet Message Format", RFC 5322, DOI 10.17487/RFC5322, October 2008. |
| [RFC5952] | Kawamura, S. and M. Kawashima, "A Recommendation for IPv6 Address Text Representation", RFC 5952, DOI 10.17487/RFC5952, August 2010. |
| [RFC6570] | Gregorio, J., Fielding, R., Hadley, M., Nottingham, M. and D. Orchard, "URI Template", RFC 6570, DOI 10.17487/RFC6570, March 2012. |
| [RFC7159] | Bray, T., "The JavaScript Object Notation (JSON) Data Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March 2014. |
| [ARIN_JCR_VALIDATOR] | American Registry for Internet Numbers, "JSON Content Rules Validator (Work In Progress)" |
| [CODALOGIC_JCR_VALIDATOR] | Codalogic, "cl-jcr-parser (Work In Progress)" |
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.
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.
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:
Alternatively, the developer may need to ensure that the status "denied" should not be present in the array:
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.
Another method still under evaluation by the authors maybe to annotate rules with references to code directly embedded in a ruleset.
odd_int @(check-code my_code) : integer
# code my_code(ruby-2.0)
## def my_def data
## return data % 2
## end
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 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.
#ruleset-id com.example.core
core { core-item1, core-item2 }
more { core-item3, core-item4 }
...
As an example, assume we have a core specification that contains the following JCR:
#ruleset-id com.example.extension
#import com.example.core as core
extension @(augments core.core core.more) ext-item1
And a subsequently defined extension with the following JCR:
#ruleset-id com.example.core
core { core-item1, core-item2, __alias1.extension }
more { core-item3, core-item4, __alias1.extension }
...
The resultant core specification is treated as:
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:
would be treated as follows after being augmented:
If it is desired to add more than one rule to a target rule then the augmenting rule can specify a group, for example:
The following implementations, [ARIN_JCR_VALIDATOR] and [CODALOGIC_JCR_VALIDATOR] have influenced the development of this document.