Hyperjump Validation

Hyperjump Validation is a media type for describing the validation of data. Over the years, I've written a lot of JSON Schemas and helped others in all kinds of domains write their JSON Schemas. Hyperjump Validation is a re-imagining of JSON Schema based on my experiences and knowledge. In part, it's how I would define JSON Schema if given a blank slate, but mostly I'm using this implementation as a sandbox to try out new ideas and approaches to the JSON Schema style.

A Hyperjump Validation document is a JSON Reference (JRef) document and has the content type application/validation+json. To understand Hyperjump Validation, you first need to understand JRef. JRef is similar to $ref in JSON Schema, but it differs in subtle yet important ways.

A Hyperjump Validation document is a declarative set of constraints that a document must conform to in order to be considered valid. The Hyperjump Validation document is parsable into a pure function that can be used to validate a JSON or JRef document in any language.

You can try out Hyperjump Validation in your browser at https://validate.hyperjump.io.

Installation

npm install @hyperjump/validation --save

Usage

GET https://example.com/example1 HTTP/1.1
Accept: application/validation+json

HTTP/1.1 200 OK
Content-Type: application/validation+json

{
  "$meta": { "$href": "https://validation.hyperjump.io/common" },
  "type": "object",
  "properties": {
    "foo": { "type": "string" }
  },
  "required": ["foo"]
}

GET https://example.com/subject1 HTTP/1.1
Accept: application/reference+json

HTTP/1.1 200 OK
Content-Type: application/reference+json

{
  "foo": { "$href": "#/bar" },
  "bar": "abc"
}

GET https://example.com/subject2 HTTP/1.1
Accept: application/json

HTTP/1.1 200 OK
Content-Type: application/reference+json

{ "foo": 123 }

const Hyperjump = require("@hyperjump/browser");
const Validation = require("@hyperjump/validation");

(async function () {
  // Get a validator function from a validation document
  // Throws an exception if the validation document is invalid
  const example1 = Hyperjump.fetch("https://example.com/example1");
  const validate = await Validation.validate(example1);

  // Validate a JRef document
  const subject1 = Hyperjump.fetch("https://example.com/subject1");
  const result1 = validate(subject1);
  Validation.isValid(result1); // => true

  // Validate a JSON Document
  const subject2 = Hyperjump.fetch("https://example.com/subject2");
  const result2 = validate(subject2);
  Validation.isValid(result2); // => false
}());

$meta

Every Hyperjump Validation document should have a $meta property at it's root that defines which validation constraint keywords it uses. For most people, you'll probably just need to put the following line at the top of each Hyperjump Validation document.

{
  "$meta": { "$href": "https://validation.hyperjump.io/common" }
}

The value of $meta is an object whose property names are constraint keywords and property values are URLs pointing to a Hyperjump Validation document that can be used to validate usages of the constraint keyword. This concept is like the JSON Schema meta-schema except there is a meta-schema for each constraint keyword rather than one for the entire document.

Custom Constraint Keywords

You can customize Hyperjump Validation in all kinds of ways with $meta. You can,

• Add a new keyword to the standard vocabulary
• Create a completely custom vocabulary
• Rename an existing keyword
• Combine keywords from different vocabularies to make your own

You can use custom keywords in your keyword validation documents, but if you stick to standard keywords, then implementations that only know the standard keywords can at least validate that your custom keyword is used correctly even if it doesn't know how to apply the constraint when validating a document.

You can add an implementation for a keyword as a plugin using the addKeyword function. All of the standard keywords are implemented as plugins so you can use those as examples for how to create your own.

Standard Vocabulary

I'll fill in documentation for these eventually. For the most part, these are a subset of the JSON Schema keywords.

allOf

anyOf

const

definitions

exclusiveMaximum

exclusiveMinimum

items

maxItems

maxLength

maxProperties

maximum

minItems

minLength

minProperties

minimum

multipleOf

not

oneOf

pattern

patternProperties

properties

required

tupleItems

type

uniqueItems

validation

Contributing

Tests

Run the tests

npm test

Run the tests with a continuous test runner

npm test -- --watch

API

Philosophy and Architectural Constraints

JSON

The standard keywords are designed for validating JSON data. That includes media types that extend JSON such as JRef. However, Hyperjump Validation can validate native JavaScript data as well as Hyperjump documents which can be any media type. When validating non-JSON data, all data is effectively converted to JSON and that value is validated.

This might sound strange, but in order to have interoperability between languages, there needs to be a common set of types. JSON fits that bill as well as anything. Every language knows how to work with JSON.

Client-Server

Hyperjump Validation is designed to be used as part of a client-server architecture. Therefore Hyperjump Validation documents must be identified by a URL and the document must be retrievable from that URL. It's not just an identifier, it's a locator.

Layered System

Hyperjump Validation should be composable at as many levels as possible. There are a set of predefined keywords. New keywords can be defined as a composition of other keywords. (coming soon)

A Hyperjump Validation document is a collection of keywords. Each keyword adds a constraint. An empty Hyperjump Validation document ({}) has no constraints. All JSON documents are valid. Each keyword adds a constraint further narrowing what constitutes a valid document.

Stateless

All keywords are stateless. The result of validating a keyword is dependent only on the value being validated and the keyword value. A keyword can not be dependent on another keyword or any external data.

Cache

The server should define how a Hyperjump Validation document can be cached by the client. This can be done through the standard HTTP cache mechanisms. It's recommended that Hyperjump Validation documents should be immutable and cacheable forever. Once published, they should never change. If they need to change, a new document should be created that is identified by a unique URL.

Uniform Interface

Hyperjump Validation keywords should validate the same way no matter what language the validator is implemented in. The result of validating a JSON document should follow a standardized structure. (coming soon)

TODOs

• More detailed validation results
• $data keyword
• Keyword composition