JSONSkooma – Sugar for your JSONs

JSONSkooma is a Ruby library for validating JSONs against JSON Schemas.

Features

• Supports JSON Schema 2019-09 and 2020-12
• Supports custom dialects, vocabularies, keywords, format validators, output formatters
• Supports custom schema resolvers

Installation

Install the gem and add to the application's Gemfile by executing:

$ bundle add json_skooma

If bundler is not being used to manage dependencies, install the gem by executing:

$ gem install json_skooma

Usage

require "json_skooma"

# Create a registry to store schemas, vocabularies, dialects, etc.
JSONSkooma.create_registry("2020-12", assert_formats: true)

# Load a schema
schema_hash = {
  "$schema" => "https://json-schema.org/draft/2020-12/schema",
  "type" => "object",
  "properties" => {
    "name" => {"type" => "string"},
    "race" => {"enum" => %w[Nord Khajiit Argonian Breton Redguard Dunmer Altmer Bosmer Orc Imperial]},
    "class" => {"type" => "string"},
    "level" => {"type" => "integer", "minimum" => 1},
    "equipment" => {
      "type" => "array",
      "items" => {"type" => "string"}
    }
  },
  "required" => %w[name race class level]
}

schema = JSONSkooma::JSONSchema.new(schema_hash)

data_hash = {
  name: "Matz",
  race: "Human",
  class: "Dragonborn",
  level: 50,
  equipment: %w[Ruby],
}

result = schema.evaluate(data_hash)

result.valid? # => false

result.output(:basic)
# {"valid"=>false,
#  "errors"=>
#    [{"instanceLocation"=>"",
#      "keywordLocation"=>"/properties",
#      "absoluteKeywordLocation"=>"urn:uuid:f477b6ca-7308-4be6-b88c-e848b9002793#/properties",
#      "error"=>"Properties [\"race\"] are invalid"},
#     {"instanceLocation"=>"/race",
#      "keywordLocation"=>"/properties/race/enum",
#      "absoluteKeywordLocation"=>"urn:uuid:f477b6ca-7308-4be6-b88c-e848b9002793#/properties/race/enum",
#      "error"=>
#        "The instance value \"Human\" must be equal to one of the elements in the defined enumeration: [\"Nord\", \"Khajiit\", \"Argonian\", \"Breton\", \"Redguard\", \"Dunmer\", \"Altmer\", \"Bosmer\", \"Orc\", \"Imperial\"]"}]}

Evaluating against a reference

require "json_skooma"

# Create a registry to store schemas, vocabularies, dialects, etc.
JSONSkooma.create_registry("2020-12", assert_formats: true)

# Load a schema
schema_hash = {
  "$schema" => "https://json-schema.org/draft/2020-12/schema",
  "$defs" => {
    "Foo": {
      "type" => "object",
      "properties" => { 
        "foo" => {"enum" => ["baz"]}
      },
    }
  }
}

schema = JSONSkooma::JSONSchema.new(schema_hash)

result = schema.evaluate({foo: "bar"}, ref: "#/$defs/Foo")

result.valid? # => false

result.output(:basic)
# {"valid"=>false,
#  "errors"=>
#   [{"instanceLocation"=>"", "keywordLocation"=>"/properties", "absoluteKeywordLocation"=>"urn:uuid:cb8fb0a0-ce16-416f-b5ba-2a6531992be9#/$defs/Foo/properties", "error"=>"Properties [\"foo\"] are invalid"},
#    {"instanceLocation"=>"/foo",
#     "keywordLocation"=>"/properties/foo/enum",
#     "absoluteKeywordLocation"=>"urn:uuid:cb8fb0a0-ce16-416f-b5ba-2a6531992be9#/$defs/Foo/properties/foo/enum",
#     "error"=>"The instance value \"bar\" must be equal to one of the elements in the defined enumeration: [\"baz\"]"}]}

Handling External $refs in JSON Schemas

In JSONSkooma, you can map $ref identifiers in your JSON schemas to local or remote sources.

This configuration allows JSONSkooma to automatically link $ref URIs to their corresponding schemas from specified sources:

# schema.yml
$schema: https://json-schema.org/draft/2020-12/schema
type: object
properties:
  user:
    $ref: http://local.example/user_definition.yaml
  product:
    $ref: http://remote.example/product_definition.yaml

# Initialize the JSONSkooma registry
schema_registry = JSONSkooma.create_registry("2020-12")

# Add a local source for user definitions
local_schemas_path = File.join(__dir__, "schemas", "local")
schema_registry.add_source(
  "http://local.example/",
  JSONSkooma::Sources::Local.new(local_schemas_path)
)

# Add a remote source for product definitions
schema_registry.add_source(
  "http://remote.example/",
  JSONSkooma::Sources::Remote.new("http://example.com/schemas/")
)

# JSONSkooma now automatically resolves `$refs` to the appropriate schemas:
# - http://local.example/user_definition.yaml -> ./schemas/local/user_definition.yaml
# - http://remote.example/product_definition.yaml -> http://example.com/schemas/product_definition.yaml

Alternatives

• json_schemer – Draft 4, 6, 7, 2019-09 and 2020-12 compliant
• json-schema – Draft 1, 2, 3, 4 and 6 compliant

Feature plans

• Custom error messages
• EcmaScript regexp
• Short circuit errors
• IRI as schema identifiers
• Relative JSONPointer
• More unit tests

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and the created tag, and push the .gem file to rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/skryukov/json_skooma.

License

The gem is available as open source under the terms of the MIT License.