Sending a single element in an array using XML format fails with the request being invalid

[ramkumar-kr]

Hi,

I have an API which accepts requests using XML. It accepts an array of products. However for a case where there is only one product in the array, validation errors occur.
Sample request -
curl -X POST \ http://localhost:3000/v1/products \ -H 'cache-control: no-cache' \ -H 'content-type: application/xml' \ -d '<?xml version="1.0" encoding="UTF-8" ?> <admin> <product> <id>1</id> <price>100</price> </product> </admin>'

This is because when there is a single element in an array, the product will be parsed to a hash instead of an array of hash objects.
Expected - { admin: { products: [{ id: "1", price: "100" }] } }
Actual - { admin: { products: { id: "1", price: "100" } } }

the parameters are defined as

params do
  requires :admin, type: Hash do
    requires :products, type: Array do
      requires :id, type: String
      requires :price, type: String
    end
  end
end

Currently to overcome this, I run the following before_validation block

before_validation do
  params[:admin][:products] = [params[:admin][:products]] if params[:admin][:products].is_a?(Hash)
end

I was wondering since grape knows the request type (Array or Hash), can it convert the hash to an array before validating (similar to the before_validation block).

Notes:
Using Grape version : 1.0.0
Sample code - https://github.com/ramkumar-kr/grape-xml-error

[dblock]

In your example you send a single product, it cannot guess that it's an array, but maybe you're right and it should infer and coerce it it because of what's in the params block. I say write a spec for this next and lets see if we can implement/fix this.

[ramkumar-kr]

Hi,
Sorry for the late reply.
I have created a Spec and have sent a pull request for it.

[Smeedy]

We also bumped into this one the other day. This is due to the XML parsing of the arrays using the default ActiveSupport::XmlMini. We noticed that Nokogiri handles the XML arrays correctly using some test XML on the irb.

So the less intrusive solution is using MultiXML and Nokogiri as the parser in the project and not rewrite the params in the before hook.

So the use of an initializer like

require 'multi_xml'

# Force all the XML parsing to be handled by Nokogiri
MultiXml.parser = :nokogiri
MultiXml.parser = MultiXml::Parsers::Nokogiri # Same as above

will set the definition. The use of MultiXml will be picked up by the Grape framework and Bob's your uncle.

See: https://github.com/ruby-grape/grape#json-and-xml-processors

[dblock]

@Smeedy Do you think you can turn the spec linked above into a passing one and add some documentation and PR the thing?