JSON Schema validator

The following example shows how to use the JSON Schema validator.

The following JSON Schema defines the structure of product catalogue. It's saved in the file product.schema.json

{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "$id": "http://example.com/product.schema.json",
  "title": "Product",
  "description": "A product from Acme's catalog",
  "type": "object",
  "properties": {
    "productId": {
      "description": "The unique identifier for a product",
      "type": "integer"
    },
    "productName": {
      "description": "Name of the product",
      "type": "string"
    },
    "price": {
      "description": "The price of the product",
      "type": "number",
      "exclusiveMinimum": 0
    }
  },
  "required": [ "productId", "productName", "price" ]
}

We want to validate the following 2 JSON files whose content are the below:

• valid-product.json

• invalid-product.json

{
  "productId": 1,
  "productName": "A green door",
  "price": 12.50,
  "tags": [ "home", "green" ]
}

{
  "productId": "This must be an integer",
  "productName": 1234,
  "price": -1
}

For the simple validation, you can write the following code:

(import (rnrs)
        (text json)
        (text json schema)
        (text json validator))

(define product-catalogue-schema
  (json-schema->json-validator
   (call-with-input-file "product.schema.json" json-read)))

(define valid-catalogue
  (call-with-input-file "valid-product.json" json-read))

(define invalid-catalogue
  (call-with-input-file "invalid-product.json" json-read))

(values (validate-json product-catalogue-schema valid-catalogue)
        (validate-json product-catalogue-schema invalid-catalogue))

If you want to see the first invalid property, then you can write like this:

(import (rnrs)
        (text json)
        (text json schema)
        (text json validator)
        (srfi :39 parameters))

(define product-catalogue-schema
  (json-schema->json-validator
   (call-with-input-file "product.schema.json" json-read)))

(define valid-catalogue
  (call-with-input-file "valid-product.json" json-read))

(define invalid-catalogue
  (call-with-input-file "invalid-product.json" json-read))

(parameterize ((*json-schema:validator-error-reporter*
                simple-json-schema-error-reporter))
  (validate-json product-catalogue-schema valid-catalogue)
  (validate-json product-catalogue-schema invalid-catalogue))
;; Prints the following
#|
/productId
             object: "This must be an integer"
        schema path: #/$defs/product/properties/productId/type
|#

If you want to run as a lint mode, which goes through entire JSON, you can write like this:

(import (rnrs)
        (text json)
        (text json schema)
        (text json validator)
        (srfi :39 parameters))

(define product-catalogue-schema
  (json-schema->json-validator
   (call-with-input-file "product.schema.json" json-read)))

(define valid-catalogue
  (call-with-input-file "valid-product.json" json-read))

(define invalid-catalogue
  (call-with-input-file "invalid-product.json" json-read))

(parameterize ((*json-schema:validator-error-reporter*
                simple-json-schema-error-reporter)
               (*json-schema:lint-mode?* #t))
  (validate-json product-catalogue-schema valid-catalogue)
  (validate-json product-catalogue-schema invalid-catalogue))
;; Prints the following
#|
/productId
             object: "This must be an integer"
        schema path: #/$defs/product/properties/productId/type
/productName
             object: 1234
        schema path: #/$defs/product/properties/productName/type
/price
             object: -1
        schema path: #/$defs/product/properties/price/exclusiveMinimum
|#

NOTE: On the lint mode, the validation result will always be #t.

Creates JSON validator object of the given JSON Schema schema.

The JSON Schema must be a vector represented S-expression JSON (see JSON parser).

JSON validator is described in JSON validator.

The optional arguments dependencies must be JSON Schema or JSON Schema validators, if it's given, then the procedure uses them as external dependency. This is useful if the *json-schema:resolve-external-schema* parameter is #f or, you don't want to make any socket connection.

Specifying if the validator creation procedure to resolve external reference of schema. e.g. "$ref": "http://json-schema.org/schema#".

The default value is #f.

Specifying the procedure to retrieve extrenal resource. This parameter supersedes the *json-schema:resolve-external-schema?* parameter.

The provided procedure must accept one argument, which is a string representation of external URL, and return Sexp JSON Schema.

Specifying if the validator validates "format" keywords.

The default value is #t.

Specifying error reporter. The error reporter must be a procedure which accepts one argument.

Specifying the port to be used to report error.

The default value is (current-error-port)

Specifying if the validator should act as if it's a linter.

To make this parameter effected, then *json-schema:validator-error-reporter* must also be specified.

The default value is #f.

The pre-defined error repoter for JSON schema validator. This error reporter doesn't show duplicated path, so if a JSON value contains multiple errors, then only one will be shown.