joi-to-json

Objective

I have been using joi a lot in different Node.js projects to guard the API. It's The most powerful schema description language and data validator for JavaScript. as it said.

Many times, we need to utilize this schema description to produce other output, such as Swagger OpenAPI doc. That is why I build joi-route-to-swagger in the first place.

At the beginning, joi-route-to-swagger relies on joi-to-json-schema which utilizes many joi internal api or properties. Maybe joi did not provide the describe api way before, but I always feel uncomfortable of relying on internal api.

The intention of joi-to-json is to support converting different version's joi schema to JSON Schema using describe api.

The implementation of this JOI to JSON conversion tool is simply a pipeline of two components:

1. Convertors

• Each JOI version has one convertor implementation.
• It converts the joi.describe() output to the baseline format (currently the v16 and v17 one)

2. Parsers

• Each supported output JSON format (e.g. JSON Draft 07, OpenAPI) has one parser implementation.
• All parsers converts the baseline format into its own format

Joi Version Support

• @commercial/joi
  • v12.1.0
• joi
  • 13.7.0
  • 14.3.1
• @hapi/joi
  • 15.1.1
  • 16.1.8
• joi
  • 17.9.2

Although the versions chosen are the latest one for each major version, It should support other minor versions as well.

Installation

npm install joi-to-json

Usage

Only one API parse is available. It's signature is parse(joiObj, type = 'json')

Currently supported output types:

• json - Default. Stands for JSON Schema Draft 07
• open-api - Stands for OpenAPI 3.0 Schema - an extended subset of JSON Schema Specification Wright Draft 00 (aka Draft 5)
• json-draft-04 - Stands for JSON Schema Draft 04
• json-draft-2019-09 - Stands for JSON Schema Draft 2019-09

The output schema format are in outputs under specific folders for different types.

Sample code is as below:

const parse = require('joi-to-json')

const joiSchema = joi.object().keys({
  nickName: joi.string().required().min(3).max(20).example('鹄思乱想').description('Hero Nickname')
    .regex(/^[a-z]+$/, { name: 'alpha', invert: true }),
  avatar: joi.string().required().uri(),
  email: joi.string().email(),
  ip: joi.string().ip({ version: ['ipv4', 'ipv6'] }),
  hostname: joi.string().hostname().insensitive(),
  gender: joi.string().valid('Male', 'Female', '').default('Male'),
  height: joi.number().precision(2).positive().greater(0).less(200),
  birthday: joi.date().iso(),
  birthTime: joi.date().timestamp('unix'),
  skills: joi.array().items(joi.alternatives().try(
    joi.string(),
    joi.object().keys({
      name: joi.string().example('teleport').alphanum().lowercase().required().description('Skill Name'),
      level: joi.number().integer().min(10).max(100).default(50).multiple(10).example(10).description('Skill Level')
    })
  ).required()).min(1).max(3).unique().description('Skills'),
  tags: joi.array().items(joi.string().required()).length(2),
  retired: joi.boolean().truthy('yes').falsy('no').insensitive(false),
  certificate: joi.binary().encoding('base64'),
  notes: joi.any().meta({ 'x-supported-lang': ['zh-CN', 'en-US'], deprecated: true })
})

const jsonSchema = parse(joiSchema)
// Or parsing to OpenAPI schema through:
// const openApiSchema = parse(joiSchema, 'open-api')

Features

Special Joi Operator Support

• Logical Relation Operator

Named Link

Supports named link for schema reuse, such as .link('#person'). For open-api conversion, as the shared schemas are located in #/components/schemas which is not self-contained, the conversion result contains an extra schemas field so that you can extract it when required.

Conditional Expression

Starting from Draft 7, JSON Specification supports If-Then-Else style expression. Before that, we can also use something called Implication using Schema Composition Approach to simulate that.

By default, the If-Then-Else approach is used if the output spec supports it. However, if the joi conditional expression (alternatives or when) is annotated using Meta .meta({ 'if-style': true }), the JSON schema conversion will use the Composition approach using allOf and/or anyOf instead.

Limitation: Currently, if the joi condition definition is referring to another field, the If-Then-Else style output is not supported. Instead, it simply uses the anyOf composing the then and otherwise on the defined field.

YAML File Generation

Most Joi specifications result in the expected OpenAPI schema.

E.g.,

const joi = require('joi')
const { dump } = require('js-yaml')
const { writeFile } = require('fs/promises')

const joiSchema = joi.object().keys({
  uuid: joi.string().uuid({ version: ['uuidv3', 'uuidv5'] }),
  nickName: joi.string().required().example('鹄思乱想').description('Hero Nickname').min(3).max(20).pattern(/^[a-z]+$/, { name: 'alpha', invert: true }),
  avatar: joi.string().required().uri(),
  email: joi.string().email(),
  ip: joi.string().ip({ version: ['ipv4', 'ipv6'] }),
  hostname: joi.string().hostname().insensitive(),
  gender: joi.string().valid('Male', 'Female', '', null).default('Male'),
  isoDateString: joi.string().isoDate(),
  isoDurationString: joi.string().isoDuration(),
  birthday: joi.date().iso(),
  certificate: joi.binary().encoding('base64'),
  tags: joi.array().items(joi.string().required()).length(2),
  nested: joi.object().keys({
    key: joi.string()
  }).unknown(true)
}).unknown(false)

async function writeYAML(targetPath) {
  const openApiSchema = parse(joiSchema, 'open-api')

  const openApiSchemaYAML = dump(openApiSchema, {lineWidth: 120, noCompatMode: true})
  await writeFile(targetPath, openApiSchemaYAML)
}

results in

type: object
required:
  - nickName
  - avatar
properties:
  uuid:
    type: string
    format: uuid
  nickName:
    description: Hero Nickname
    type: string
    pattern: ^[a-z]+$
    minLength: 3,
    maxLength: 20,
    example: 鹄思乱想
  avatar:
    type: string
    format: uri
  email:
    type: string
    format: email
  ip:
    type: string
    oneOf:
      - format: ipv4
      - format: ipv6
  hostname:
    type: string
    format: hostname
  gender:
    type: string
    default: Male
    enum:
      - Male
      - Female
      - ''
      - null
    nullable: true
  isoDateString:
    type: string
    format: date-time
  isoDurationString:
    type: string
    format: duration
  birthday:
    type: string
    format: date-time
  certificate:
    type: string
    format: binary
  tags:
    type: array
    items:
      type: string
    minItems: 2
    maxItems: 2
  nested:
    type: object
    properties:
      key:
        type: string
    additionalProperties: true
additionalProperties: false

Some OpenAPI features are not supported directly in Joi, but Joi schemas can be annotated with joi.any().meta({…}) to get them in the OpenAPI schema:

…

const joiSchema = joi.object().keys({
  deprecatedProperty: joi.string().meta({ deprecated: true }).required(),
  readOnlyProperty: joi.string().meta({ readOnly: true }),
  writeOnlyProperty: joi.string().meta({ writeOnly: true }),
  xMeta: joi.string().meta({ 'x-meta': 42 }),
  unknownMetaProperty: joi.string().meta({ unknownMeta: 42 })
}).unknown(true)

…

begets:

type: object
required:
  - deprecatedProperty
properties:
  deprecatedProperty:
    type: string
    deprecated: true
  readOnlyProperty:
    type: string
    readOnly: true
  writeOnlyProperty:
    type: string
    writeOnly: true
  xMeta:
    type: string
    x-meta: 42
  unknownMetaProperty:
    type: string
    # unknownMeta is not exported
additionalProperties: true

Browser support

For generating JSON Schema in a browser you should use below import syntax for joi library in order to work because the joi browser minimized build does not have describe api which the joi-to-json relies on.

  import Joi from 'joi/lib/index';

TypeScript support

import joi from 'joi';
import * as Joi2Json from 'joi-to-json';
import parse from 'joi-to-json';

const logicalOpParser: Joi2Json.LogicalOpParserOpts = {
  with: function (a) {}
};

parse(joi.string()); // Default call
parse(joi.string(), 'json', {}, { logicalOpParser: false }); // Completely disable Logical Relation Operator
parse(joi.string(), 'open-api', {}, { logicalOpParser }); // Partially override Logical Relation Operator

Test

npm run test

Categories of Test Cases

• JOI Standard Representation Conversion

fixtures-conversion folder stores each JOI version's supported keyword for different data types. In case any data type or keyword is not supported in historical JOI version, we can just create customized file to override the base version, such as v15/link.js.

Standard converted results are stored in outputs-conversion folder.

test/conversion.spec.js Test Spec handles all supported JOI versions' conversion verificaiton.

• JSON output format Conversion

outputs-parsers folder stores different output formats base on the JOI Standard Representation in outputs-conversion folder. The Test Spec under test/parser/ are responsible for these area.

• JSON schema (Draft 07) Validity Unit Test

For special Logical Relation Operator and Conditional Expression, some Unit Tests are created to verify the JOI Spec and corresponding JSON Spec are valid of the same verification intention.

Test Debug Approach

When running conversion.spec.js, below environment variables can be set:

• TEST_CONVERTOR: control which version of joi to test. Example: TEST_CONVERTOR=v17
• TEST_CASE: control which test cases to verify. Name of the test cases is the key of the return object in fixtures-conversion. Example: TEST_CASE=conditional,match_all verifies the case in alternatives.js
• TEST_UPDATE_CONVERSION_BASELINE: control whether writes the baseline file generated from the latest-version convertor (Currently v17). It is activated when setting to true.

When runninng Test Spec under test/parser, below environment variables can be set:

• TEST_CASE: control which test cases to verify. For example, when running json.spec.js, and set TEST_CASE=conditional,match_all, it verifies the corresponding JSON files in outputs-parsers/json/alternatives.
• TEST_UPDATE_PARSER_BASELINE: control whether writes the baseline file for the corresponding parser. It is activated when setting to true. For example, when running json.spec.js, it writes the baseline files under outputs-parsers/json.

Known Limitation

• For object.pattern usage in Joi, pattern parameter can only be a regular expression now as I cannot convert Joi object to regex yet.
• If-Then-Else style output is not applicable for the condition referring to the other field.

License

MIT