Ruby JSON Schema Validator

This library is intended to provide Ruby with an interface for validating JSON objects against a JSON schema conforming to JSON Schema Draft 4. Legacy support for JSON Schema Draft 3, JSON Schema Draft 2, and JSON Schema Draft 1 is also included.

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Please be aware that the upgrade to version 2.0.0 will use Draft-04 by default, so schemas that do not declare a validator using the $schema keyword will use Draft-04 now instead of Draft-03. This is the reason for the major version upgrade.

From rubygems.org:

gem install json-schema

From the git repo:

$ gem build json-schema.gemspec
$ gem install json-schema-2.5.0.gem

Three base validation methods exist: validate, validate!, and fully_validate. The first returns a boolean on whether a validation attempt passes and the second will throw a JSON::Schema::ValidationError with an appropriate message/trace on where the validation failed. The third validation method does not immediately fail upon a validation error and instead builds an array of validation errors return when validation is complete.

All methods take two arguments, which can be either a JSON string, a file containing JSON, or a Ruby object representing JSON data. The first argument to these methods is always the schema, the second is always the data to validate. An optional third options argument is also accepted; available options are used in the examples below.

By default, the validator uses the JSON Schema Draft 4 specification for validation; however, the user is free to specify additional specifications or extend existing ones. Legacy support for Draft 1, Draft 2, and Draft 3 is included by either passing an optional :version parameter to the validate method (set either as :draft1 or draft2), or by declaring the $schema attribute in the schema and referencing the appropriate specification URI. Note that the $schema attribute takes precedence over the :version option during parsing and validation.

For further information on json schema itself refer to Understanding JSON Schema.

require 'rubygems'
require 'json-schema'

schema = {
  "type" => "object",
  "required" => ["a"],
  "properties" => {
    "a" => {"type" => "integer"}
  }
}

data = {
  "a" => 5
}

JSON::Validator.validate(schema, data)

require 'rubygems'
require 'json-schema'

JSON::Validator.validate('schema.json', '{"a" : 5}')

require 'rubygems'
require 'json-schema'

data = ['user','user','user']
JSON::Validator.validate('user.json', data, :list => true)

With the :strict option, validation fails when an object contains properties that are not defined in the schema’s property list or doesn’t match the additionalProperties property. Furthermore, all properties are treated as required by default.

require 'rubygems'
require 'json-schema'

schema = {
  "type" => "object",
  "properties" => {
    "a" => {"type" => "integer"},
    "b" => {"type" => "integer"}
  }
}

JSON::Validator.validate(schema, {"a" => 1, "b" => 2}, :strict => true)            # ==> true
JSON::Validator.validate(schema, {"a" => 1, "b" => 2, "c" => 3}, :strict => true)  # ==> false
JSON::Validator.validate(schema, {"a" => 1}, :strict => true)                      # ==> false

require 'rubygems'
require 'json-schema'

schema = {
  "type" => "object",
  "required" => ["a"],
  "properties" => {
    "a" => {"type" => "integer"}
  }
}

data = {
  "a" => "taco"
}

begin
  JSON::Validator.validate!(schema, data)
rescue JSON::Schema::ValidationError
  puts $!.message
end

require 'rubygems'
require 'json-schema'

schema = {
  "type" => "object",
  "required" => ["a","b"],
  "properties" => {
    "a" => {"type" => "integer"},
    "b" => {"type" => "string"}
  }
}

data = {
  "a" => "taco"
}

errors = JSON::Validator.fully_validate(schema, data)

# ["The property '#/a' of type String did not match the following type: integer in schema 03179a21-197e-5414-9611-e9f63e8324cd#", "The property '#/' did not contain a required property of 'b' in schema 03179a21-197e-5414-9611-e9f63e8324cd#"]

require 'rubygems'
require 'json-schema'

schema = {
  "type" => "object",
  "required" => ["a","b"],
  "properties" => {
    "a" => {"type" => "integer"},
    "b" => {"type" => "string"}
  }
}

data = {
  "a" => "taco"
}

errors = JSON::Validator.fully_validate(schema, data, :errors_as_objects => true)

# [{:message=>"The property '#/a' of type String did not match the following type: integer in schema 03179a21-197e-5414-9611-e9f63e8324cd#", :schema=>#<URI::Generic:0x103a76198 URL:03179a21-197e-5414-9611-e9f63e8324cd#>, :failed_attribute=>"Type", :fragment=>"#/a"}, {:message=>"The property '#/' did not contain a required property of 'b' in schema 03179a21-197e-5414-9611-e9f63e8324cd#", :schema=>#<URI::Generic:0x103a76198 URL:03179a21-197e-5414-9611-e9f63e8324cd#>, :failed_attribute=>"Properties", :fragment=>"#/"}]

  require 'rubygems'
  require 'json-schema'

  schema = {
    "type" => "object",
    "required" => ["a","b"],
    "properties" => {
      "a" => {"type" => "integer"},
      "b" => {"type" => "string"},
      "c" => {
        "type" => "object",
        "properties" => {
          "z" => {"type" => "integer"}
        }
      }
    }
  }

  data = {
    "z" => 1
  }

  JSON::Validator.validate(schema, data, :fragment => "#/properties/c")

require 'rubygems'
require 'json-schema'

schema = {
  "type" => "object",
  "required" => ["a"],
  "properties" => {
    "a" => {"type" => "integer"}  # This will fail schema validation!
  }
}

data = {
  "a" => 5
}

JSON::Validator.validate(schema, data, :validate_schema => true)

With the :insert_defaults option set to true any missing property that has a
default value specified in the schema will be inserted into the validated data. The inserted default value is validated hence catching a schema that specifies an invalid default value.

require 'rubygems'
require 'json-schema'

schema = {
  "type" => "object",
  "required" => ["a"],
  "properties" => {
    "a" => {"type" => "integer", "default" => 42},
    "b" => {"type" => "integer"}
  }
}

# Would not normally validate because "a" is missing and required by schema,
# but "default" option allows insertion of valid default.
data = {
  "b" => 5
}

JSON::Validator.validate(schema, data)
# false

JSON::Validator.validate(schema, data, :insert_defaults => true)
# true
# data = {
#   "a" => 42,
#   "b" => 5
# }

require 'rubygems'
require 'json-schema'

schema = {
  "type" => "object",
  "properties" => {
    "a" => {"type" => "integer", "optional" => true}
  }
}

data = {
  "a" => 5
}

JSON::Validator.validate(schema, data, :version => :draft2)

By default, json-schema accepts a variety of different types for the data parameter, and it will try to work out what to do with it dynamically. You can pass it a string uri (in which case it will download the json from that location before validating), a string of JSON text, or simply a ruby object (such as an array or hash representing parsed json). However, sometimes the nature of the data is ambiguous (for example, is “http://github.com” just a string, or is it a uri?). In other situations, you have already parsed your JSON, and you don’t need to re-parse it.

If you want to be explict about what kind of data is being parsed, JSON schema supports a number of options:

require 'rubygems'
require 'json-schema'

schema = {
  "type" => "string"
}

# examines the data, determines it's a uri, then tries to load data from it
JSON::Validator.validate(schema, 'https://api.github.com') # returns false

# data is already parsed json - just accept it as-is
JSON::Validator.validate(schema, 'https://api.github.com', :parse_data => false) # returns true

# data is parsed to a json string
JSON::Validator.validate(schema, '"https://api.github.com"', :json => true) # returns true

# loads data from the uri
JSON::Validator.validate(schema, 'https://api.github.com', :uri => true) # returns false

For this example, we are going to extend the JSON Schema Draft 3 specification by adding a ‘bitwise-and’ property for validation.

require 'rubygems'
require 'json-schema'

class BitwiseAndAttribute < JSON::Schema::Attribute
  def self.validate(current_schema, data, fragments, processor, validator, options = {})
    if data.is_a?(Integer) && data & current_schema.schema['bitwise-and'].to_i == 0
      message = "The property '#{build_fragment(fragments)}' did not evaluate  to true when bitwise-AND'd with  #{current_schema.schema['bitwise-or']}"
      raise JSON::Schema::ValidationError.new(message, fragments, current_schema)
    end
  end
end

class ExtendedSchema < JSON::Schema::Validator
  def initialize
    super
    extend_schema_definition("http://json-schema.org/draft-03/schema#")
    @attributes["bitwise-and"] = BitwiseAndAttribute
    @uri = URI.parse("http://test.com/test.json")
  end

  JSON::Validator.register_validator(self.new)
end

schema = {
  "$schema" => "http://test.com/test.json",
  "properties" => {
    "a" => {
      "bitwise-and" => 1
    },
    "b" => {
      "type" => "string"
    }
  }
}

data = {
  "a" => 0
}

data = {"a" => 1, "b" => "taco"}
JSON::Validator.validate(schema,data) # => true
data = {"a" => 1, "b" => 5}
JSON::Validator.validate(schema,data) # => false
data = {"a" => 0, "b" => "taco"}
JSON::Validator.validate(schema,data) # => false

The JSON schema standard allows custom formats in schema definitions which should be ignored by validators that do not support them. JSON::Schema allows registering procs as custom format validators which receive the value to be checked as parameter and must raise a JSON::Schema::CustomFormatError to indicate a format violation. The error message will be prepended by the property name, e.g. “The property ‘#a’”:

require 'rubygems'
require 'json-schema'

format_proc = -> value {
  raise JSON::Schema::CustomFormatError.new("must be 42") unless value == "42"
}

# register the proc for format 'the-answer' for draft4 schema
JSON::Validator.register_format_validator("the-answer", format_proc, ["draft4"])

# omitting the version parameter uses ["draft1", "draft2", "draft3", "draft4"] as default
JSON::Validator.register_format_validator("the-answer", format_proc)

# deregistering the custom validator
# (also ["draft1", "draft2", "draft3", "draft4"] as default version)
JSON::Validator.deregister_format_validator('the-answer', ["draft4"])

# shortcut to restore the default formats for validators (same default as before)
JSON::Validator.restore_default_formats(["draft4"])

# with the validator registered as above, the following results in
# ["The property '#a' must be 42"] as returned errors
schema = {
  "$schema" => "http://json-schema.org/draft-04/schema#",
  "properties" => {
    "a" => {
      "type" => "string",
      "format" => "the-answer",
    }
  }
}
errors = JSON::Validator.fully_validate(schema, {"a" => "23"})

In some cases, you may wish to prevent the JSON Schema library from making HTTP calls or reading local files in order to resolve $ref schemas. If you fully control all schemas which should be used by validation, this could be accomplished by registering all referenced schemas with the validator in advance:

schema = JSON::Schema.new(some_schema_definition, Addressable::URI.parse('http://example.com/my-schema'))
JSON::Validator.add_schema(schema)

If more extensive control is necessary, the JSON::Schema::Reader instance used can be configured in a few ways:

# Change the default schema reader used
JSON::Validator.schema_reader = JSON::Schema::Reader.new(:accept_uri => true, :accept_file => false)

# For this validation call, use a reader which only accepts URIs from my-website.com
schema_reader = JSON::Schema::Reader.new(
  :accept_uri => proc { |uri| uri.host == 'my-website.com' }
)
JSON::Validator.validate(some_schema, some_object, :schema_reader => schema_reader)

The JSON::Schema::Reader interface requires only an object which responds to read(string) and returns a JSON::Schema instance. See the API documentation for more information.

The JSON Schema library currently supports the json and yajl-ruby backend JSON parsers. If either of these libraries are installed, they will be automatically loaded and used to parse any JSON strings supplied by the user.

If more than one of the supported JSON backends are installed, the yajl-ruby parser is used by default. This can be changed by issuing the following before validation:

JSON::Validator.json_backend = :json

Optionally, the JSON Schema library supports using the MultiJSON library for selecting JSON backends. If the MultiJSON library is installed, it will be autoloaded.

The ‘format’ attribute is only validated for the following values:

• date-time
• date
• time
• ip-address (IPv4 address in draft1, draft2 and draft3)
• ipv4 (IPv4 address in draft4)
• ipv6
• uri

All other ‘format’ attribute values are simply checked to ensure the instance value is of the correct datatype (e.g., an instance value is validated to be an integer or a float in the case of ‘utc-millisec’).

Additionally, JSON::Validator does not handle any json hyperschema attributes.