Internet DRAFT - draft-jonas-json-template-language
draft-jonas-json-template-language
Network Working Group S. Jonas
Internet-Draft ETC Labs Core
Intended status: Informational March 29, 2019
Expires: September 30, 2019
JSON Template Language
draft-jonas-json-template-language-01
Abstract
JSON Template Language is a simple, compact template language to
substitute JSON [1] into a template. It is derived from the template
literals of Javascript, as defined in the ECMAScript Programming
Language Standard, Ninth Edition ECMA-262 [2]. It has uses not
limited to: specifying interfaces, runtime expression mapping, and
other forms of programmatically interacting with JSON and templates.
Status of This Memo
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This Internet-Draft will expire on September 30, 2019.
Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
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include Simplified BSD License text as described in Section 4.e of
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 2
3. Security Considerations . . . . . . . . . . . . . . . . . . . 3
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 3
5. Example Usage . . . . . . . . . . . . . . . . . . . . . . . . 3
5.1. Accessing Array indicies . . . . . . . . . . . . . . . . 3
5.2. Accessing Nested Objects and Arrays . . . . . . . . . . . 4
6. JSON Template Grammar . . . . . . . . . . . . . . . . . . . . 4
6.1. Template literal . . . . . . . . . . . . . . . . . . . . 5
6.2. Identifier . . . . . . . . . . . . . . . . . . . . . . . 5
6.3. Path . . . . . . . . . . . . . . . . . . . . . . . . . . 5
6.4. Array Index . . . . . . . . . . . . . . . . . . . . . . . 5
6.5. Head . . . . . . . . . . . . . . . . . . . . . . . . . . 6
6.6. Tail . . . . . . . . . . . . . . . . . . . . . . . . . . 6
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
7.1. Normative References . . . . . . . . . . . . . . . . . . 6
7.2. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
JSON Template Language provides a mechanism for describing various
parts of a template by using familiar syntax from Javascript and
JSON. By using a familiar syntax we can get interoperability within
the JSON [3] and URI [4] specifications.
The terms "string", "object" and "array" are from the conventions of
Javascript and JSON.
A JSON Template provides a structural description of a template, and
when JSON is provided, machine-readable instructions on how to
construct a string corresponding to those values. A template is
transformed into a string by replacing each of the template literals
with the corresponding JSON values.
2. Conventions and Definitions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
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3. Security Considerations
When considering runtime security of JSON Template Language, the
surface area is only expanding JSON value by key. No loops or
operator grammar is defined and should be avoided in runtime
contexts.
4. IANA Considerations
This document has no IANA actions.
5. Example Usage
for the given JSON:
{
"query": {
"number": 1,
"salad": "potato"
}
}
and the given template:
number${query.number}salad${query.salad}
\__________/ \__________/
| |
| |
For each key in given JSON, substitute it by key into the string.
expansion:
number1saladpotato
5.1. Accessing Array indicies
for the given JSON
{
"query": {
"numbers": [0, 1, 2, 3],
"salads": ["caesar", "potato"]
}
}
and the given template:
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number${query.numbers[1]}salad${query.salads[1]}
\_____________/ \_____________/
| |
| |
For each key in given JSON, substitute it by array index into the string.
expansion:
number1saladpotato
5.2. Accessing Nested Objects and Arrays
for the given JSON
{
"nested": {
"query": {
"number": 1,
"salads": ["caesar", "potato"]
}
}
}
and the given template:
number${query.numbers[1]}salad${query.salads[1]}
\_____________/ \_____________/
| |
| |
For each key in given JSON, substitute it by path first. then array index into the string.
expansion:
number1saladpotato
6. JSON Template Grammar
Language Grammar defined in ABNF [5]
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grammar = *( [head] template-head identifier *["." path] *[array-left array-index array-right] template-tail [tail] )
template-head = "${"
template-tail = "}"
identifier = *( ALPHA / "_" )
path = *( ALPHA / "_" )
array-left = "["
array-right = "]"
array-index = *( DIGIT )
head = *( ALPHA / DIGIT / special-characters )
tail = *( ALPHA / DIGIT / special-characters )
special-characters = *("-" / "_" / "~" / "." / ":" / "/" / "?" / "#" / "[" / "]" / "@" / "!" / "&" / "'" / "(" / ")" / "*" / "+" / "," / ";" / "=")
6.1. Template literal
The contents within the Template literal should be valid a key-value
object mapping or array-index mapping for JSON [6].
grammar = *( [head] template-head identifier *["." path] \
[array-left array-index array-right] template-tail [tail] )
A template literal is represented within a URIs [7] as a pair of
curly braces starting with a "$".
template-head = "${"
template-tail = "}"
6.2. Identifier
An identifier is a valid JSON key.
identifier = *( ALPHA / "_" )
6.3. Path
MUST be a valid nested JSON key that will be resolved with the
identifier.
*["." path]
6.4. Array Index
MUST be a valid index of a JSON array are represented within square
brackets and MUST be a valid number.
*[array-left array-index array-right]
array-left = "["
array-right = "]"
array-index = *( DIGIT )
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6.5. Head
Head represents the characters before template-head, this could be
beginning of the template or the last tail.
head = *( ALPHA / DIGIT / special-characters )
6.6. Tail
Tail represents the characters after the template-tail until the end
of the template or the next instance of a template literal.
tail = *( ALPHA / DIGIT / special-characters )
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
7.2. URIs
[1] https://tools.ietf.org/html/rfc7159
[2] https://www.ecma-international.org/ecma-262/9.0/index.html#sec-
template-literals
[3] https://tools.ietf.org/html/rfc7159, https://www.ecma-
international.org/ecma-262/9.0/index.html#sec-template-literals
[4] https://tools.ietf.org/html/rfc6570
[5] https://tools.ietf.org/html/rfc5234
[6] https://tools.ietf.org/html/rfc7159
[7] https://tools.ietf.org/html/rfc3986
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Author's Address
Shane Jonas
ETC Labs Core
Email: shane.j@etclabs.org
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