@exodus/schemasafe

A code-generating JSON Schema validator that attempts to be reasonably secure.

Supports draft-04/06/07/2019-09/2020-12 and the discriminator OpenAPI keyword.

Features

• Converts schemas to self-contained JavaScript files, can be used in the build process.
  Integrates nicely with bundlers, so one won't need to generate code in runtime, and that works with CSP.
• Optional requireValidation: true mode enforces full validation of the input object.
  Using mode: "strong" is recommended, — it combines that option with additional schema safety checks.
• Does not fail open on unknown or unprocessed keywords — instead throws at build time if schema was not fully understood. That is implemented by tracking processed keywords and ensuring that none remain uncovered.
• Does not fail open on schema problems — instead throws at build time.
  E.g. it will detect mistakes like {type: "array", "maxLength": 2}.
• About 2000 lines of code, non-minified.
• Uses secure code generation approach to prevent data from schema from leaking into the generated code without being JSON-wrapped.
• 0 dependencies
• Very fast
• Supports JSON Schema draft-04/06/07/2019-09/2020-12 and a strict subset of the discriminator OpenAPI keyword.
• Can assign defaults and/or remove additional properties when schema allows to do that safely. Throws at build time if those options are used with schemas that don't allow to do that safely.
• Can be used as a schema linter.

Installation

1npm install --save @exodus/schemasafe

Usage

Simply pass a schema to compile it:

1const { validator } = require('@exodus/schemasafe')
2
3const validate = validator({
4  type: 'object',
5  required: ['hello'],
6  properties: {
7    hello: {
8      type: 'string'
9    }
10  }
11})
12
13console.log('should be valid', validate({ hello: 'world' }))
14console.log('should not be valid', validate({}))

Or use the parser API (running in strong mode by default):

1const { parser } = require('@exodus/schemasafe')
2
3const parse = parser({
4  $schema: 'https://json-schema.org/draft/2019-09/schema',
5  type: 'object',
6  required: ['hello'],
7  properties: {
8    hello: {
9      pattern: '^[a-z]+$',
10      type: 'string'
11    }
12  },
13  additionalProperties: false
14})
15
16console.log(parse('{"hello": "world" }')) // { valid: true, value: { hello: 'world' } }
17console.log(parse('{}')) // { valid: false }

Parser API is recommended, because this way you can avoid handling unvalidated JSON objects in non-string form at all in your code.

Options

See options documentation for the full list of supported options.

Custom formats

@exodus/schemasafe supports the formats specified in JSON schema v4 (such as date-time). If you want to add your own custom formats pass them as the formats options to the validator:

1const validate = validator({
2  type: 'string',
3  format: 'no-foo'
4}, {
5  formats: {
6    'no-foo': (str) => !str.includes('foo'),
7  }
8})
9console.log(validate('test')) // true
10console.log(validate('foo')) // false
11
12const parse = parser({
13  $schema: 'https://json-schema.org/draft/2019-09/schema',
14  type: 'string',
15  format: 'only-a'
16}, {
17  formats: {
18    'only-a': /^a+$/,
19  }
20})
21console.log(parse('"aa"')) // { valid: true, value: 'aa' }
22console.log(parse('"ab"')) // { valid: false }

External schemas

You can pass in external schemas that you reference using the $ref attribute as the schemas option

1const ext = {
2  type: 'string'
3}
4
5const schema = {
6  $ref: 'ext#' // references another schema called ext
7}
8
9// pass the external schemas as an option
10const validate = validator(schema, { schemas: { ext: ext }})
11
12console.log(validate('hello')) // true
13console.log(validate(42)) // false

schemas can be either an object as shown above, a Map, or plain array of schemas (given that those have corresponding $id set at top level inside schemas themselves).

Enabling errors shows information about the source of the error

When the includeErrors option is set to true, @exodus/schemasafe also outputs:

• keywordLocation: a JSON pointer string as an URI fragment indicating which sub-schema failed, e.g. #/properties/item/type
• instanceLocation: a JSON pointer string as an URI fragment indicating which property of the object failed validation, e.g. #/item

1const schema = {
2  type: 'object',
3  required: ['hello'],
4  properties: {
5    hello: {
6      type: 'string'
7    }
8  }
9}
10const validate = validator(schema, { includeErrors: true })
11
12validate({ hello: 100 });
13console.log(validate.errors)
14// [ { keywordLocation: '#/properties/hello/type', instanceLocation: '#/hello' } ]

Or, similarly, with parser API:

1const schema = {
2  $schema: 'https://json-schema.org/draft/2019-09/schema',
3  type: 'object',
4  required: ['hello'],
5  properties: {
6    hello: {
7      type: 'string',
8      pattern: '^[a-z]+$',
9    }
10  },
11  additionalProperties: false,
12}
13const parse = parser(schema, { includeErrors: true })
14
15console.log(parse('{ "hello": 100 }'));
16// { valid: false,
17//   error: 'JSON validation failed for type at #/hello',
18//   errors: [ { keywordLocation: '#/properties/hello/type', instanceLocation: '#/hello' } ]
19// }

Only the first error is reported by default unless allErrors option is also set to true in addition to includeErrors.

See Error handling for more information.

Generate Modules

See the doc/samples directory to see how @exodus/schemasafe compiles supported test suites.

To compile a validator function to an IIFE, call validate.toModule():

1const { validator } = require('@exodus/schemasafe')
2
3const schema = {
4  type: 'string',
5  format: 'hex'
6}
7
8// This works with custom formats as well.
9const formats = {
10  hex: (value) => /^0x[0-9A-Fa-f]*$/.test(value),
11}
12
13const validate = validator(schema, { formats })
14
15console.log(validate.toModule())
16/** Prints:
17 * (function() {
18 * 'use strict'
19 * const format0 = (value) => /^0x[0-9A-Fa-f]*$/.test(value);
20 * return (function validate(data) {
21 *   if (data === undefined) data = null
22 *   if (!(typeof data === "string")) return false
23 *   if (!format0(data)) return false
24 *   return true
25 * })})();
26 */

Performance

@exodus/schemasafe uses code generation to turn a JSON schema into javascript code that is easily optimizeable by v8 and extremely fast.

See Performance for information on options that might affect performance both ways.

Contributing

Get a fully set up development environment with:

1git clone https://github.com/ExodusMovement/schemasafe
2cd schemasafe
3
4git submodule update --init --recursive
5yarn
6yarn lint
7yarn test

Previous work

This is based on a heavily rewritten version of the amazing (but outdated) is-my-json-valid by @mafintosh.

Compared to is-my-json-valid, @exodus/schemasafe adds security-first design, many new features, newer spec versions support, slimmer and more maintainable code, 0 dependencies, self-contained JS module generation, fixes bugs and adds better test coverage, and drops support for outdated Node.js versions.

License

MIT