jtd
is a Ruby implementation of JSON Type Definition, a schema language
for JSON. jtd
primarily gives you two things:
- Validating input data against JSON Typedef schemas.
- A Ruby representation of JSON Typedef schemas.
With this package, you can add JSON Typedef-powered validation to your application, or you can build your own tooling on top of JSON Type Definition.
You can install this package with gem
:
gem install jtd
Detailed API documentation is available online at:
https://rubydoc.info/gems/jtd/JTD
For more high-level documentation about JSON Typedef in general, or JSON Typedef in combination with Python in particular, see:
For a more detailed tutorial and guidance on how to integrate
jtd
in your application, see "Validating JSON in Ruby with JSON Typedef" in the JSON Typedef docs.
Here's an example of how you can use this package to validate JSON data against a JSON Typedef schema:
require 'jtd'
schema = JTD::Schema.from_hash({
'properties' => {
'name' => { 'type' => 'string' },
'age' => { 'type' => 'uint32' },
'phones' => {
'elements' => {
'type' => 'string'
}
}
}
})
# JTD::validate returns an array of validation errors. If there were no problems
# with the input, it returns an empty array.
# Outputs: []
p JTD::validate(schema, {
'name' => 'John Doe',
'age' => 43,
'phones' => ['+44 1234567', '+44 2345678'],
})
# This next input has three problems with it:
#
# 1. It's missing "name", which is a required property.
# 2. "age" is a string, but it should be an integer.
# 3. "phones[1]" is a number, but it should be a string.
#
# Each of those errors corresponds to one of the errors returned by validate.
# Outputs:
#
# [
# #<struct JTD::ValidationError
# instance_path=[],
# schema_path=["properties", "name"]
# >,
# #<struct JTD::ValidationError
# instance_path=["age"],
# schema_path=["properties", "age", "type"]
# >,
# #<struct JTD::ValidationError
# instance_path=["phones", "1"],
# schema_path=["properties", "phones", "elements", "type"]
# >
# ]
p JTD::validate(schema, {
'age' => '43',
'phones' => ['+44 1234567', 442345678],
})
By default, JTD::validate
returns every error it finds. If you just care about
whether there are any errors at all, or if you can't show more than some number
of errors, then you can get better performance out of JTD::validate
using the
max_errors
option.
For example, taking the same example from before, but limiting it to 1 error, we get:
# Outputs:
#
# [#<struct JTD::ValidationError instance_path=[], schema_path=["properties", "name"]>]
options = JTD::ValidationOptions.new(max_errors: 1)
p JTD::validate(schema, {
'age' => '43',
'phones' => ['+44 1234567', 442345678],
}, options)
If you want to run jtd
against a schema that you don't trust, then you should:
-
Ensure the schema is well-formed, using the
#verify
method onJTD::Schema
. That will check things like making sure allref
s have corresponding definitions. -
Call
JTD::validate
with themax_depth
option. JSON Typedef lets you write recursive schemas -- if you're evaluating against untrusted schemas, you might go into an infinite loop when evaluating against a malicious input, such as this one:{ "ref": "loop", "definitions": { "loop": { "ref": "loop" } } }
The
max_depth
option tellsJTD::validate
how manyref
s to follow recursively before giving up and raisingJTD::MaxDepthExceededError
.
Here's an example of how you can use jtd
to evaluate data against an untrusted
schema:
require 'jtd'
# validate_untrusted returns true if `data` satisfies `schema`, and false if it
# does not. Throws an error if `schema` is invalid, or if validation goes in an
# infinite loop.
def validate_untrusted(schema, data)
schema.verify()
# You should tune max_depth to be high enough that most legitimate schemas
# evaluate without errors, but low enough that an attacker cannot cause a
# denial of service attack.
options = JTD::ValidationOptions.new(max_depth: 32)
JTD::validate(schema, data, options).empty?
end
# Returns true
validate_untrusted(JTD::Schema.from_hash({ 'type' => 'string' }), 'foo')
# Returns false
validate_untrusted(JTD::Schema.from_hash({ 'type' => 'string' }), nil)
# Raises ArgumentError (invalid type: nonsense)
validate_untrusted(JTD::Schema.from_hash({ 'type' => 'nonsense' }), 'foo')
# Raises JTD::MaxDepthExceededError (max depth exceeded during JTD::validate)
validate_untrusted(JTD::Schema.from_hash({
'definitions' => {
'loop' => { 'ref' => 'loop' },
},
'ref' => 'loop',
}), nil)