Passing in a fragment with an even number of tokens can lead to undefined method `validate' for #<Hash...>

[ckundo]

We're seeing an exception when validating a json response from a Rails controller. It seems to fail on every other token in the JSON fragment path:

schema_options = {
  fragment: "#/schemas/v1.reports.index.response/purchases",
  strict: true
}
data = JSON.parse(response.body)

JSON::Validator.fully_validate(
  "schema.json",
  data,
  schema_options,
)

Raises:

# => ...undefined method `validate' for #<Hash...>

But for example, this fragment does not raise the exception:

"#/schemas/v1.reports.index.response/purchases/items"

We have monkey-patched this as follows:

module JSON
  class Validator
    def schema_from_fragment(base_schema, fragment)
      # ...

      fragments.each do |f|
        if base_schema.is_a?(JSON::Schema) #test if fragment is a JSON:Schema instance
          if !base_schema.schema.has_key?(f)
            raise JSON::Schema::SchemaError.new("Invalid fragment resolution for :fragment option")
          end

          # HERE:
          if base_schema.schema[f].is_a? Hash
            base_schema = JSON::Schema.new(base_schema.schema[f], schema_uri, @options[:version])
          else
            base_schema = base_schema.schema[f]
          end
        elsif base_schema.is_a?(Hash)
          # ...

That is, this line https://github.com/ruby-json-schema/json-schema/blob/master/lib/json-schema/validator.rb#L91 should always create a new JSON::Schema.

[rickreilly]

+1

[RST-J]

Would you please provide a test case, example schema and data which fails (I don't doubt your bug report)?

[jrgns]

I'm seeing the same issue, but it's not due to the number of tokens. It happens when the second last token points to a proper schema, and the last token points to a Hash.

The bug exists because the resulting base_schema get's converted into a JSON::Schema in all the if clauses except the first one: https://github.com/jrgns/json-schema/blob/master/lib/json-schema/validator.rb#L89

[jrgns]

This might be by design, though, since you can use the fragment to point to something that is not a schema like a property or a required array.

The reason I ran across it is that I'm trying to validate both the input and the output of an API call using the hyper-schema:

JSON::Validator.validate!('schema.json', input, strict: true, fragment: '#/definitions/users/links/0/schema')
JSON::Validator.validate!('schema.json', output, strict: true, fragment: '#/definitions/users/links/0/targetSchema')

My schema looks like the ones described here

[jrgns]

Probably also related to #217

[jrgns]

PR #217 will fix this issue.

[aledalgrande]

Just got into this today. Getting same error when an array is used in the fragment (which is every test if you follow a prmd schema style).

+1

[iainbeeston]

I'll try to sort this out once and for all tomorrow...

[iainbeeston]

Just a quick update on this. At the moment we're maintaining two different code paths for resolving fragments: one for the :fragment option and one for $ref properties. I'm investigating whether I can refactor so that the :fragment option reuses the code for handling $ref properties (which is more tested and I'd argue more robust). Unfortunately it's more work than just fixing :fragment but I believe it's the right choice for the long-term