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openapi-runtime-expression

Runtime Expressions allow defining values based on information that will only be available within the HTTP message in an actual API call. This mechanism is used by Link Objects and Callback Objects of OpenAPI specification.

openapi-runtime-expression is a parser and validator for OpenAPI Runtime Expressions. It supports Runtime Expressions defined in following OpenAPI specification versions:

Table of Contents

Getting started

Installation

You can install openapi-runtime-expression using npm:

 $ npm install openapi-runtime-expression

Given that openapi-runtime-expression is a pure ESM package you can also install it directly from GitHub.

 $ npm install github:char0n/openapi-runtime-expression

Usage

openapi-runtime-expression currently supports extraction, parsing and validation. Both parser and validator are based on a superset of ABNF (SABNF) and use apg-js parser generator.

Extraction

OpenAPI embeds Runtime Expressions into string values surrounded with {} curly braces. To extract Runtime Expressions from this embedded form, use the extract function. Extracted Runtime Expression can be used for further parsing of validation.

import { extract, test, parse } from 'openapi-runtime-expression';

const expression = extract('{$request.header.accept}'); // => '$request.header.accept'

test(expression); // => true
parse(expression); // => { result, ast }

Parsing

Parsing a Runtime Expression is as simple as importing the parse function and calling it.

import { parse } from 'openapi-runtime-expression';

const parseResult = parse('$request.header.accept');

parseResult variable has the following shape:

{
  result: {
    success: true,
    state: 101,
    length: 22,
    matched: 22,
    maxMatched: 22,
    maxTreeDepth: 14,
    nodeHits: 152,
    inputLength: 22,
    subBegin: 0,
    subEnd: 22,
    subLength: 22
  },
  ast: exportsAst {
    callbacks: [
      expression: [Function: expression],
      source: [Function: source],
      'header-reference': [Function: headerReference],
      'query-reference': [Function: queryReference],
      'path-reference': [Function: pathReference],
      'body-reference': [Function: bodyReference],
      'json-pointer': [Function: jsonPointer],
      'reference-token': [Function: referenceToken],
      name: [Function: name],
      token: [Function: token]
    ],
    astObject: 'astObject',
    init: [Function: init],
    ruleDefined: [Function: ruleDefined],
    udtDefined: [Function: udtDefined],
    down: [Function: down],
    up: [Function: up],
    translate: [Function: translate],
    setLength: [Function: setLength],
    getLength: [Function: getLength],
    toXml: [Function: toSml],
    phrases: [Function: phrases]
  }
}
Interpreting AST as list of entries
import { parse } from 'openapi-runtime-expression';

const parseResult = parse('$request.header.accept');
const parts = [];

parseResult.ast.translate(parts);

After running the above code, parts variable has the following shape:

[
  ['expression', '$request.query.queryUrl' ],
  ['source', 'query.queryUrl'],
  ['query-reference', 'query.queryUrl'],
  ['name', 'queryUrl'],
]
Interpreting AST as XML
import { parse } from 'openapi-runtime-expression';

const parseResult = parse('$request.header.accept');
const xml = parseResult.ast.toXml();

After running the above code, xml variable has the following content:

<?xml version="1.0" encoding="utf-8"?>
<root nodes="4" characters="23">
<!-- input string, decimal integer character codes -->
  36,114,101,113,117,101,115,116,46,113,117,101,114,121,46,113,117,101,114,121,85,114,108
 <node name="expression" index="0" length="23">
   36,114,101,113,117,101,115,116,46,113,117,101,114,121,46,113,117,101,114,121,85,114,108
  <node name="source" index="9" length="14">
    113,117,101,114,121,46,113,117,101,114,121,85,114,108
   <node name="query-reference" index="9" length="14">
     113,117,101,114,121,46,113,117,101,114,121,85,114,108
    <node name="name" index="15" length="8">
      113,117,101,114,121,85,114,108
    </node><!-- name="name" -->
   </node><!-- name="query-reference" -->
  </node><!-- name="source" -->
 </node><!-- name="expression" -->
</root>

NOTE: AST can also be traversed in classical way using depth first traversal. For more information about this option please refer to apg-js and apg-js-examples.

Validation

Validating a Runtime Expression is as simple as importing the test function and calling it.

import { test } from 'openapi-runtime-expression';

test('$request.header.accept'); // => true
test('nonsensical string'); // => false

Grammar

New grammar instance can be created in following way:

import { Grammar } from 'openapi-runtime-expression';

const grammar = new Grammar();

To obtain original ABNF (SABNF) grammar as a string:

import { Grammar } from 'openapi-runtime-expression';

const grammar = new Grammar();

grammar.toString();
// or
String(grammar);

More about OpenAPI runtime expressions

The runtime expression is defined by the following ABNF syntax

expression = ( "$url" / "$method" / "$statusCode" / "$request." source / "$response." source )
source = ( header-reference / query-reference / path-reference / body-reference )
header-reference = "header." token
query-reference = "query." name
path-reference = "path." name
body-reference = "body" ["#" json-pointer ]
json-pointer    = *( "/" reference-token )
reference-token = *( unescaped / escaped )
unescaped       = %x00-2E / %x30-7D / %x7F-10FFFF
   ; %x2F ('/') and %x7E ('~') are excluded from 'unescaped'
escaped         = "~" ( "0" / "1" )
  ; representing '~' and '/', respectively
name = *( CHAR )
token = 1*tchar
tchar = "!" / "#" / "$" / "%" / "&" / "'" / "*" / "+" / "-" / "." /
  "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA

Here, json-pointer is taken from RFC6901, char from RFC7159 and token from RFC7230.

The name identifier is case-sensitive, whereas token is not.

The table below provides examples of runtime expressions and examples of their use in a value:

Examples
Source Location example expression notes
HTTP Method $method The allowable values for the $method will be those for the HTTP operation.
Requested media type $request.header.accept
Request parameter $request.path.id Request parameters MUST be declared in the parameters section of the parent operation or they cannot be evaluated. This includes request headers.
Request body property $request.body#/user/uuid In operations which accept payloads, references may be made to portions of the requestBody or the entire body.
Request URL $url
Response value $response.body#/status In operations which return payloads, references may be made to portions of the response body or the entire body.
Response header $response.header.Server Single header values only are available

Runtime expressions preserve the type of the referenced value. Expressions can be embedded into string values by surrounding the expression with {} curly braces.

License

openapi-runtime-expression is licensed under Apache 2.0 license. openapi-runtime-expression comes with an explicit NOTICE file containing additional legal notices and information.

Software Bill Of Materials (SBOM)

Software Bill Of materials is available in sbom.spdx.yaml using SPDX language.