Hyperjump - JSON Schema Core
JSON Schema Core (JSC) is a framework for building JSON Schema based validators
and other tools.
It includes tools for:
- Working with schemas (
$id
, $schema
, $ref
, etc) - Working with instances
- Building custom keywords
- Building custom vocabularies
- Standard output formats
- Custom output formats
- Compiling schemas for validating multiple instances
Install
JSC is designed to run in a vanilla node.js environment, but has no dependencies
on node.js specific libraries so it can be bundled for the browser. No
compilers, preprocessors, or bundlers are used.
Node.js
npm install @hyperjump/json-schema-core
Browser
When in a browser context, JSC is designed to use the browser's fetch
implementation instead of a node.js fetch clone. The Webpack bundler does this
properly without any extra configuration, but if you are using the Rollup
bundler you will need to include the browser: true
option in your Rollup
configuration.
plugins: [
resolve({
browser: true
}),
commonjs()
]
Schema
A Schema Document (SDoc) is a structure that includes the schema, the id, and a
JSON Pointer. The "value" of an SDoc is the portion of the schema that the JSON
pointer points to. This allows an SDoc to represent any value in the schema
while maintaining enough context to follow $ref
s and track the position in the
document.
-
Schema.add: (schema: object, url?: URI, schemaVersion?: string) => undefined
Load a schema. See the "$id" and "$schema" sections for more details
-
Schema.get: (url: URI, contextDoc?: SDoc) => Promise
Fetch a schema. Schemas can come from an HTTP request, a file, or a schema
that was added with Schema.add
.
-
Schema.uri: (doc: SDoc) => URI
Returns a URI including the id and JSON Pointer that represents a value
within the schema.
-
Schema.getAnchorPointer: (doc: SDoc, anchor: string) => any
Get a JSON Pointer for the location in the schema that the anchor refers to.
-
Schema.value: (doc: SDoc) => any
The portion of the schema the document's JSON Pointer points to.
-
Schema.typeOf: (doc: SDoc, type: string) => boolean
Determines if the JSON type of the given doc matches the given type
-
Schema.has: (key: string, doc: SDoc) => Promise
Similar to key in schema
.
-
Schema.step: (key: string, doc: SDoc) => Promise
Similar to schema[key]
, but returns an SDoc.
-
Schema.entries: (doc: SDoc) => Promise<[[string, SDoc]]>
Similar to Object.entries
, but returns SDocs for values.
-
Schema.keys: (doc: SDoc) => [string]
Similar to Object.keys
.
-
Schema.map: (fn: (item: Promise, index: integer) => T, doc: SDoc) => Promise<[T]>
A map
function for an SDoc whose value is an array.
-
Schema.length: (doc: SDoc) => number
Similar to Array.prototype.length
.
Schema Identification
JSC requires that all schemas are identified by at least one URI. There are two
types of schema identifiers, internal and external. An internal identifier is an
identifier that is specified within the schema using $id
. An external
identifier is an identifier that is specified outside of the schema. In JSC, an
external identifier can be either the URL a schema is retrieved with, or the
identifier specified when using Schema.add
to load a schema.
JSC can fetch schemas from the web or from the file system, but when fetching
from the file system, there are limitations for security reasons. If
your schema has an identifier with an http scheme (http://example.com), it's
not allowed to reference schemas with a file scheme
(file:///path/to/my/schemas).
Internal identifiers ($id
s) are resolved against the external identifier of
the schema (if one exists) and the resulting URI is used to identify the schema.
All identifiers must be absolute URIs. External identifiers are required to be
absolute URIs and internal identifiers must resolve to absolute URIs.
const { Core, Schema } = require("@hyperjump/json-schema-core");
const schemaJson = {
"$schema": "https://json-schema.org/draft/2019-09/schema",
"type": "string"
}
Schema.add(schemaJson, "http://example.com/schemas/string");
const schema = await Schema.get("http://example.com/schemas/string");
const schemaJson = {
"$schema": "https://json-schema.org/draft/2019-09/schema",
"$id": "http://example.com/schemas/string",
"type": "string"
}
Schema.add(schemaJson);
const schema = await Schema.get("http://example.com/schemas/string");
const schemaJson = {
"$schema": "https://json-schema.org/draft/2019-09/schema",
"type": "string"
}
Schema.add(schemaJson);
const schema = await Schema.get("http://example.com/schemas/string");
const schema = await Schema.get("http://example.com/schemas/foo");
const schema = await Schema.get("http://example.com/schemas/string");
const schema = await Schema.get("file:///path/to/my/schemas/string.schema.json");
const schema = await Schema.get("http://example.com/schemas/baz");
await Core.validate(schema);
$schema
JSC is designed to support multiple drafts of JSON Schema and it makes no
assumption about what draft your schema uses. You need to specify it in some
way. The preferred way is to the use $schema
in all of your schemas, but you
can also specify what draft to use when adding a schema using Schema.add
. If a
draft is specified in Schema.add
and the schema has a $schema
, the
$schema
will be used. If no draft is specified, you will get an error.
const schemaJSON = {
"$schema": "https://json-schema.org/draft/2019-09/schema",
"$id": "http://example.com/schemas/string",
"type": "string"
};
Schema.add(schemaJSON);
const schemaJSON = {
"type": "string"
};
Schema.add(schemaJSON, "http://example.com/schemas/string", "https://json-schema.org/draft/2019-09/schema");
const schemaJSON = {
"$id": "http://example.com/schemas/string",
"type": "string"
};
Schema.add(schemaJSON);
const schema = Schema.get("http://example.com/schemas/string");
Instance
An Instance Document (IDoc) is like a Schema Document (SDoc) except with much
more limited functionality.
-
Instance.cons: (instance: any) => IDoc
Construct a IDoc from a value.
-
Instance.get: (url: URI, contextDoc: IDoc) => IDoc
Apply a same-resource reference to a IDoc.
-
Instance.uri: (doc: IDoc) => URI
Returns a URI including the id and JSON Pointer that represents a value
within the instance.
-
Instance.value: (doc: IDoc) => any
The portion of the instance that the document's JSON Pointer points to.
-
Instance.has: (key: string, doc: IDoc) => any
Similar to key in instance
.
-
Instance.typeOf: (doc: IDoc, type: string) => boolean
Determines if the JSON type of the given doc matches the given type.
-
Instance.step: (key: string, doc: IDoc) => IDoc
Similar to schema[key]
, but returns a IDoc.
-
Instance.entries: (doc: IDoc) => [string, IDoc]
Similar to Object.entries
, but returns IDocs for values.
-
Instance.keys: (doc: IDoc) => [string]
Similar to Object.keys
.
-
Instance.map: (fn: (item: IDoc, index: integer) => T, doc: IDoc) => [T]
A map
function for a IDoc whose value is an array.
-
Instance.reduce: (fn: (accumulator: T, item: IDoc, index: integer) => T, initial: T, doc: IDoc) => T
A reduce
function for a IDoc whose value is an array.
-
Instance.every: (fn: (doc: IDoc, index: integer) => boolean, doc: IDoc) => boolean
An every
function for a IDoc whose value is an array.
-
Instance.some: (fn: (doc: IDoc, index: integer) => boolean, doc: IDoc) => boolean
A some
function for a IDoc whose value is an array.
-
Instance.length: (doc: IDoc) => number
Similar to Array.prototype.length
.
Validation
Some helper functions are provided to assist in building validation functions.
-
Core.validate: (schema: SDoc, value: any, outputFormat: OutputFormat = Core.FLAG) => Promise
A curried function that validates a JavaScript value against a schema.
-
Core.compile: (schema: SDoc) => Promise
Compile a schema to be used interpreted later. A compiled schema is a JSON
serializable structure that can be serialized an restored for later use.
-
Core.interpret: (schema: CompiledSchema, instance: Instance, outputFormat = Core.FLAG) =>
A curried function for validating an instance against a compiled schema.
const { Core, Schema } = require("@hyperjump/json-schema-core");
Schema.add({
"$id": "http://example.com/schemas/string",
"$schema": "https://json-schema.org/draft/2019-09/schema",
"type": "string"
});
const schema = await Schema.get("http://example.com/schemas/string");
const isString = await Core.validate(schema);
const result = await Core.validate(schema, "foo");
const compiledSchema = await Core.compile(schema);
const isString = Core.interpret(compiledSchema);
const result = Core.interpret(compiledSchema, Instance.cons("foo"));
Output
JSC supports all of the standard output formats specified for JSON Schema
draft-2019-09 and is separately configurable for instance validation and
meta-validtion.
This implementation does not include the suggested keywordLocation
property in
the output unit. I think absoluteKeywordLocation
+instanceLocation
is
sufficient for debugging and it's awkward for the output to produce JSON
Pointers that potentially won't resolve because they cross schema boundaries.
This implementation includes an extra property in the output unit called
keyword
. This is an identifier (URI) for the keyword that was validated. With
the standard output unit fields, we can see what keyword was validated by
inspecting the last segment of the absoluteKeywordLocation
property. But,
since JSC can support multiple JSON Schema versions, we would have to pull up
the actual schema to find what draft was used. The schema
property gives us
enough information to not have to go back to the schema to know what draft is
being used.
By default JSC will validate all schemas against their meta-schema. However, the
only time you really need this is when developing schemas. When JSC is running
in a production environment or you are working with third-party schemas that you
trust to be correct, you can turn off meta-validation to boost performance.
-
Core.setMetaOutputFormat: (outputFormat: OutputFormat) => undefined
Set the output format used for schema validation. Default Core.DETAILED
-
Core.setShouldMetaValidate: (shouldMetaValidate: boolean) => undefined
Turn schema validation on or off. Default true
-
OutputFormat: An enum of available output formats
- Core.FLAG - Default for instance validation
- Core.BASIC
- Core.DETAILED - Default for meta-validation
- Core.VERBOSE
const { Core, Schema } = require("@hyperjump/json-schema-core");
Schema.add({
"$schema": "https://json-schema.org/draft/2019-09/schema",
"$id": "http://example.com/schemas/string",
"type": "string"
});
const schema = await Schema.get("http://example.com/schemas/string");
const isString = await Core.validate(schema);
const output = isString(42, Core.BASIC);
Schema.add({
"$schema": "https://json-schema.org/draft/2019-09/schema",
"$id": "http://example.com/schemas/foo",
"type": "this-is-not-a-valid-type"
});
Core.setMetaOutputFormat(Core.BASIC);
const schema = await Schema.get("http://example.com/schemas/foo");
const isString = await Core.validate(schema);
Core.setShouldMetaValidate(false);
const schema = await Schema.get("http://example.com/schemas/foo");
const isString = await Core.validate(schema);
PubSub
JSC emits events that you can subscribe to and work with however your
application needs. For now, the only event is the "result"
event that emits
output units every time a keyword is validated. Internally, JSC uses these
events to build standard output formats. Other events can be added when
use-cases are identified for them.
const PubSub = require("pubsub-js");
const { Core, Schema } = require("@hyperjump/json-schema-core");
Schema.add({
"$schema": "https://json-schema.org/draft/2019-09/schema",
"$id": "http://example.com/schemas/string",
"type": "string"
});
const schema = await Schema.get("http://example.com/schemas/string");
const isString = await Core.validate(schema);
const results = [];
const subscriptionToken = PubSub.subscribe("result", (message, result) => {
results.push(result);
});
isString(42);
PubSub.unsubscribe(subscriptionToken);
results;
Customize
JSC uses a micro-kernel architecture, so it's highly customizable. Everything
is a plugin, even the validation logic. This allows you to use JSC as a
framework for building other types of JSON Schema based tools such as code
generators or form generators.
In addition to this documentation you should be able to look at the
JSV code to see an
example of how to add your custom plugins because it's all implemented the same
way.
-
Schema.setConfig: (schemaVersion: string, configName: string, configValue: string) => undefined
Set a configuration value for a schemaVersion.
-
Schema.getConfig: (schemaVersion: string, configName: string) => any
Get a configuration value for a schemaVersion.
References
The $ref
keyword has changed a couple times over the last several drafts. JSC
allows you to configure which version(s) of $ref
s you want to support. There
are several types of references.
-
JSON Reference: (draft-04/06/07) In draft-04, references were defined in
a separate spec from JSON Schema. The JSON Schema spec only constrained $ref
in how URIs are resolved with respect to id
. Then in draft-06/07, JSON
Schema absorbed the JSON Reference spec and further constrained $ref
to only
be allowed where schemas are allowed. JSC doesn't support this constraint
because it can't be done in a keyword agnostic way.
-
JSON Schema Reference: (draft-2019-09+) In draft 2019-09, a reference
was changed from being an object with a $ref
property to the value of a
$ref
keyword. This allowed $ref
to behave more like a keyword.
-
Dynamic JSON Schema Reference: (draft-2019-09+) In draft 2019-09, the
concept of a dynamic scope reference was added to make it easier to extend
recursive schemas. This was added to support building custom meta-schemas.
Draft-04/6/7 style references are configured via dialect configuration using
Schema.setConfig
. Draft-2019-09+ style references are just keywords and can be
added as part of a vocabulary.
const { Schema } = require("@hyperjump/json-schema-core");
Schema.setConfig("http://json-schema.org/draft-04/schema", "jrefToken", "$ref");
Core.defineVocabulary("https://example.com/draft/custom/vocab/core", {
"$ref": Keywords.ref,
"$dynamicRef": Keywords.dynamicRef,
...
});
Identifiers
The $id
keyword has seen it's fair share of churn as well. Although the spec
around this keyword was rewritten and clarified many times, the vast majority of
changes have simply been name changes. JSC allows you to configure which version
you want to support.
-
id: (draft-04) A base URI used to resolve reference URIs.
-
$id: (draft-06/07) Same as id
, just a different name.
-
$id: (draft-2019-09) Same as $id
except with same-document reference
support split out into $anchor
.
-
$anchor: (draft-2019-09) Same-document reference.
-
$recursiveAnchor: (draft-2019-09) Dynamic scope same-document reference.
Value is a boolean that is only allowed at the root of a schema.
-
$dynamicAnchor: (draft-2019-09) Dynamic scope same-document reference.
Value is a string and works like $anchor
.
In draft-2019-09, $id
was redefined from being a resolution scope modifier to
being an inlined reference. This means that JSON Pointers can not cross into
schemas with $id
s. So far, JSC only supports these bounded $id
s. If I come
up with a way to relax this constraint for old draft implementations, I will,
but since there is no sensible reason to want such a thing, it's a low priority.
In JSON Schema, properties called $id
are only considered identifiers if they
appear in a schema. JSC is keyword agnostic, so it doesn't know what is a schema
and what isn't. Therefore, an $id
might be treated as an identifier in places
it's not expected to. This is unlikely, but not impossible.
const { Schema } = require("@hyperjump/json-schema-core");
Schema.setConfig("https://json-schema.org/draft/2019-09/schema", "baseToken", "$id");
Schema.setConfig("https://json-schema.org/draft/2019-09/schema", "embeddedToken", "$id");
Schema.setConfig("https://json-schema.org/draft/2019-09/schema", "anchorToken", "$anchor");
Schema.setConfig("https://json-schema.org/draft/2019-09/schema", "recursiveAnchorToken", "$recursiveAnchor");
Schema.setConfig("http://json-schema.org/draft-04/schema", "baseToken", "$id");
Schema.setConfig("http://json-schema.org/draft-04/schema", "embeddedToken", "$id");
Schema.setConfig("http://json-schema.org/draft-04/schema", "anchorToken", "$id");
Schema.setConfig("http://json-schema.org/draft-04/schema", "baseToken", "id");
Schema.setConfig("http://json-schema.org/draft-04/schema", "embeddedToken", "id");
Schema.setConfig("http://json-schema.org/draft-04/schema", "anchorToken", "id");
Custom Meta-Schemas
Let's say you want to use a custom meta-schema that does stricter validation
than the standard meta-schema. Once you have your custom meta-schema ready, it's
just a couple lines of code to start using it.
const { Core, Schema } = require("@hyperjump/json-schema-core");
Schema.add({
"$id": "https://example.com/draft/2019-09-strict/schema",
"$schema": "https://json-schema.org/draft/2019-09/schema",
"$vocabulary": {
"https://json-schema.org/draft/2019-09/vocab/core": true,
"https://json-schema.org/draft/2019-09/vocab/applicator": true,
"https://json-schema.org/draft/2019-09/vocab/validation": true,
"https://json-schema.org/draft/2019-09/vocab/meta-data": true,
"https://json-schema.org/draft/2019-09/vocab/format": false,
"https://json-schema.org/draft/2019-09/vocab/content": true
},
...
});
Schema.add({
"$id": "http://example.com/schemas/string",
"$schema": "http://example.com/draft/2019-09-strict/schema",
"type": "string"
});
const schema = await Schema.get("http://example.com/schemas/string");
await Core.validate(schema, "foo");
Keywords
A keyword implementation is a module with at least the functions: compile
and
interpret
. In the compile
step, you can do any processing steps necessary to
do the actual validation in the interpret
step. The most common things to do
in the compile
step is to follow references and compile sub-schemas. The
interpret
step takes the result of the compile
step and returns a boolean
value indicating whether validation has passed or failed.
If your custom keyword is an applicator and your dialect supports
unevaluatedProperties
and unevaluatedItems
, you'll also need to provide the
collectEvaluatedProperties
and collectEvaluatedItems
functions.
You can Use the JSV
keyword implementations as examples when creating your own keywords.
-
Core.getKeyword: (keywordId: string) => Keyword
Retreive a keyword by it's identifier.
-
Core.hasKeyword: (keywordId: string) => boolean
Query whether a keyword implementation exists.
-
Core.compileSchema: (schema: SDoc, ast: AST) => undefined
Compile a schema.
-
Core.interpretSchmea: (schemaUri: string, instance: Instance, ast: AST, dynamicAnchors: Map[anchor: String, uri: String]) => boolean
Finds the compiled schema in the ast for the schemaUri and validates the
instance against the it. The result is a boolean indicating if the keyword
passes validation.
-
Core.collectEvaluatedProperties: (schemaUri: string, instance: Instance, ast: AST, dynamicAnchors: Map[anchor: String, uri: String]) => string[]
Walk a schema and collect any property names that are evaluated by the
schemas it finds. A property is not considered evaluated if the schema
containing it is not valid.
-
Core.collectEvaluatedItems: (schemaUri: string, instance: Instance, ast: AST, dynamicAnchors: Map[anchor: String, uri: String]) => number
Walk a schema and collect maximum number of items that are evaluated by the
schemas it finds. An item is not considered evaluated if the schema
containing it is not valid.
This example implements an if
/then
/else
-like keyword called cond
.
cond
is an array of schemas where the first is the if
schema, the second is
the then
schema, and the third is the else
schema.
const { Core, Schema } = require("@hyperjump/json-schema-core");
const compile = async (schema, ast, parentSchema) => {
const schemas = Schema.map((schema) => Core.compileSchema(schema, ast), cond);
return Promise.all(schemas);
};
const interpret = (cond, instance, ast, dynamicAnchors) => {
return Core.interpretSchema(cond[0], instance, ast, dynamicAnchors)
? (conditional[1] ? Core.interpretSchema(cond[1], instance, ast, dynamicAnchors) : true)
: (conditional[2] ? Core.interpretSchema(cond[2], instance, ast, dynamicAnchors) : true);
};
const collectEvaluatedProperties = (cond, instance, ast, dynamicAnchors) => {
const propertyNames = Core.collectEvaluatedProperties(conditional[0], instance, ast, dynamicAnchors);
const branch = propertyNames ? 1 : 2;
if (conditional[branch]) {
const branchPropertyNames = Core.collectEvaluatedProperties(conditional[branch], instance, ast, dynamicAnchors);
return branchPropertyNames && (propertyNames || []).concat(branchPropertyNames);
} else {
return propertyNames || [];
}
};
const collectEvaluatedItems = (cond, instance, ast, dynamicAnchors) => {
const tupleLength = Core.collectEvaluatedItems(cond[0], instance, ast, dynamicAnchors);
const branch = typeof tupleLength === "number" ? 1 : 2;
if (conditional[branch]) {
const branchTupleLength = Core.collectEvaluatedItems(conditional[branch], instance, ast, dynamicAnchors);
return branchTupleLength !== false && Math.max(tupleLength, branchTupleLength);
} else {
return tupleLength || 0;
}
};
module.exports = { compile, interpret, collectEvaluatedProperties, collectEvaluatedItems };
In order to use an keyword in an implementation, you need to add it to a
vocabulary.
Vocabularies
A vocabulary is just a named collection of keywords.
-
Core.defineVocabulary: (vocabularyId: string, keywords: { [keywordId]: Keyword }) => undefined
Define a vocabulary giving it an identifier and an object that maps keyword
identifiers to keyword implementations.
const { Core, Schema } = require("@hyperjump/json-schema-core");
const cond = require("./keywords/cond");
Core.defineVocabulary("https://example.com/draft/custom/vocab/conditionals", {
cond: cond
});
Schema.add({
"$id": "https://example.com/draft/custom/schema",
"$schema": "https://json-schema.org/draft/2019-09/schema",
"$vocabulary": {
...
"https://example.com/draft/custom/vocab/conditionals": true
},
...
});
Schema.add({
"$id": "http://example.com/schemas/cond-example",
"$schema": "https://example.com/draft/custom/schema",
"type": "integer",
"cond": [
{ "minimum": 10 },
{ "multipleOf": 3 },
{ "multipleOf": 2 }
]
});
const schema = await Schema.get("http://example.com/schemas/cond-example");
await Core.validate(schema, 42);
Contributing
Tests
Run the tests
npm test
Run the tests with a continuous test runner
npm test -- --watch