rj_schema

Fast JSON schema validation with RapidJSON (https://github.com/Tencent/rapidjson)

Usage

require 'rj_schema'

Create an instance of RjSchema::Validator and provide a JSON schema and a JSON document. You can pass a File, Hash, or String:

RjSchema::Validator.new.validate(File.new("schema/my_schema.json"), '{"stuff": 1}')

It is possible to resolve remote schemas by specifying them in the initializer. For example, if your schema contains "$ref": "generic#/definitions/something":

RjSchema::Validator.new(
  'generic' => File.new("definitions/generic.json")
).validate(File.new("schema/my_schema.json"), '{"stuff": 1}')

validate will return an array containing hashes which describe the errors encountered during validation. If the array is empty, the JSON document is valid according to the schema. An ArgumentError exception will be raised if any of the inputs are malformed or missing.

You can also call valid? if you are not interested in the error messages.

Caching

Another feature of rj_schema is the ability to preload schemas. This can boost performance by a lot, especially in applications that routinely perform validations against static schemas, i.e. validations of client inputs inside the endpoints of a web app. Add the schemas to preload into the initializer and pass a Symbol to the validation function:

RjSchema::Validator.new(
  'generic' => File.new("definitions/generic.json"),
  'schema/my_schema.json' => File.new("schema/my_schema.json")
).validate(:"schema/my_schema.json", '{"stuff": 1}')

Limitations

Some limitations apply due to RapidJSON:

• only JSON schema draft-04 is supported
• the format keyword is not supported
• there are a few edge cases with regards to $ref that will cause issues (for more details, see the tests)

Benchmark

The main motivation for this gem was that we needed a faster JSON schema validation for our Ruby apps. We have been using Ruby JSON Schema Validator for a while (https://github.com/ruby-json-schema/json-schema) but some of our endpoints became unacceptably slow.

A benchmark to compare various gem performances can be run with: rake benchmark. These are the results collected on my machine (with g++ (Debian 7.3.0-3) 7.3.0, ruby 2.5.0p0 (2017-12-25 revision 61468) [x86_64-linux]).

report	i/s	x
rj_schema (valid?) (cached)	370.9	1
rj_schema (validate) (cached)	187.5	1.98x slower
json_schemer (valid?) (cached)	135.6	2.73x slower
rj_schema (valid?)	132.7	2.79x slower
rj_schema (validate)	96.9	3.83x slower
json-schema	10.6	34.92x slower
json_schema	3.7	101.26x slower

The error reporting of rj_schema is implemented inefficiently at the time of writing, so in this benchmark environment (based on JSON Schema test suite which includes many failing validations) validate performs significantly worse than valid?. This may not be an issue in production environments though, where failing validations are usually the exception (the overhead is only incurred in case of an error).