@nidomiro/relation-tuple-parser

This library can parse a string representation of a Relation tuple to an object structure in typescript.

Relation tuples are used to evaluate permissions in "Zanzibar: Google's Consistent, Global Authorization System".

The BNF of a valid Relation tuple is as follows:

<relation-tuple> ::= <object>'#'relation'@'<subject> | <object>'#'relation'@('<subject>')'
<object> ::= namespace':'object_id
<subject> ::= subject_id | <subject_set>
<subject_set> ::= <object>'#'relation

Examples of valid strings:

namespace:object#relation@subjectId
namespace:object#relation@(subjectId)
namespace:object#relation@subjectNamespace:subjectObject#subjectRelation
namespace:object#relation@(subjectNamespace:subjectObject#subjectRelation)

The different parts of the Relation tuple can contain any character but :#@().

A Relation tuple can easily be verbalised: The Relation tuple sharedFiles:a.txt#access@(dirs:b#access) can be verbalised as "Anyone with access to dirs:b has access to sharedFiles:a.txt".

After Parsing you get an object in the format:

interface SubjectSet {
	namespace: string
	object: string
	relation: string
}

interface RelationTuple {
	namespace: string
	object: string
	relation: string
	subjectIdOrSet: string | SubjectSet
}

Usage

import { parseRelationTuple } from '@nidomiro/relation-tuple-parser'

const result = parseRelationTuple('sharedFiles:a.txt#access@(dirs:b#access)')
const value = result.unwrapOrThrow()
/* value = {
				namespace: 'sharedFiles',
				object: 'a.txt',
				relation: 'access',
				subjectIdOrSet: {
					namespace: 'dirs',
					object: 'b',
					relation: 'access',
				},
			}
 */

With replacements

It is also possible to parse the Relation tuple in a structure where different placeholders can be replaced. This is especially useful if you define a Guard via Decorators but require som dynamic replacements e.g. for the id of the current user.

Usage

import { parseRelationTupleWithReplacements } from '@nidomiro/relation-tuple-parser'

const result = parseRelationTupleWithReplacements(({ userId }) => `groups:admin#member@${userId}`)

/**
 * Contains the "Template" of the Relation tuple with the replacements defined above.
 * Calculate this once and use it on every evaluation.
 */
const valueWithreplacements = result.unwrapOrThrow()

/**
 * Execute this at evaluation time (e.g. every incomming Request) to get the actual Relation tuple to evaluate against.
 */
const relationTuple = applyReplacements(valueWithreplacements, {
	userId: 'my_user_id',
})

/*	relationTuple = {
						namespace: 'groups',
						object: 'admin',
						relation: 'member',
						subjectIdOrSet: 'my_user_id',
					}
 */

Development

Building

Run nx build typescript to build the library.

Running unit tests

Run nx test typescript to execute the unit tests.

Publish

Make sure you are logged into npm.

Run nx publish typescript --tag latest --ver x.x.x to publish to npm.