A clojure library that implements JSON schema validation.

This library is distributed under the MIT license (see LICENSE).

(require '[closchema.core :as schema])
=> nil
(schema/validate {:type "array" :items {:type "string"}} ["1" "2"])
=> true
(schema/validate {:type "array" :items {:type "string"}} ["1" 2])
=> false
(schema/report-errors
  (schema/validate {:type "array" :items {:type "string"}} ["1" 2 {}]))
=> '(.. errors )

This library implements the file-based part of referencing described here (at the end of the post):

http://www.sitepen.com/blog/2008/10/31/json-schema/

Right now, you can only specify filenames (not full URLs), and they must be located in your Java resources directory, as specified on the classpath. There is no ID-based referencing as of this readme.

With this extension, one can specify a reference to a file containing a schema using the key $ref when describing a property:

{
    "type" : "object",
    "properties" : {
        "id" : {"type" : "integer"},
        "address" : {"$ref" : "path/to/file"}
    }
}

Reading is lazy, so the schema is not read until we hit it at validation time. Files are read using slurp and clojure.data.json. Schema references are cached using memoize.

extends is implemented as it is described here:

http://www.sitepen.com/blog/2009/09/02/json-namespacing/

Anything validating as :type "object" can use extends. The value of extends can be any valid schema, or any array of schemas. This specifies that, as part of its validation, this object must validate against the specified schema or schemas.

Thus, the following produces a schema specifying an :id that is an integer, and also specifying that an object must additionally validate against the schema in "file1.json".

{
    "type" : "object",
    "extends" : {"$ref" : "file1.json"},
    "properties" : {
        "id" : {"type" : "integer"}
    }
}

Multiple inheritance also has the expected semantics:

{
    "type" : "object",
    "extends" : [{"$ref" : "file1.json"}, {"$ref" : "file2.json"}],
    "properties" : {
        "id" : {"type" : "integer"}
    }
}

A word of caution: If :additionalProperties false is set in a "child" schema, nothing will validate against it unless the parent schema(s) is/are empty. That is, :additionalProperties takes precedence over :extends.

The entire spec http://tools.ietf.org/html/draft-zyp-json-schema-03 is not implemented yet. We'll gradually support more features as needed.