Rack::Lint::Error => a header value must be a String or Array of Strings, but the value of 'content-type' is a NilClass

[ericproulx]

I've been testing Rack::Lint locally and we have a lot of issues in our spec suite. I'll open issues for others but let's start with this one:

Running spec: spec/grape/api_spec.rb:2341.

 Rack::Lint::LintError:
       a header value must be a String or Array of Strings, but the value of 'content-type' is a NilClass

This test is using rack_response directly in a rescue_from like this

subject.rescue_from ApiSpec::APIErrors::ParentError, rescue_subclasses: true do |e|
 rack_response("rescued from #{e.class.name}", 500)
end

Unfortunately, rack_response doesn't act like error! since the last is passing through the formatting part (because of the throw) whereas the rack_response just html escaped if content_type is set totext/html (if content_type is set in the api)

Finally, rack_response is never mentioned in the README but using a plain Rack::Response is. Also, Using rack_response or Rack::Response doesn't pass through the formatting part of the error middleware since its considered a final response.

IMO, there are many ways to solve that but I found an interesting middleware within Rack called [Rack::ContentType] (https://github.com/rack/rack/blob/main/lib/rack/content_type.rb) that will set a default content-type header if needed. Default, is text/html but I think text/plain would be more appropriate since we do not need to escape. I think its a clean way to deal with that issue and we could remove some default behavior in the code.

[ericproulx]

I understand what's happening. Before #1922, content_type was taken from the base middleware which default to txt/plain.

# lib/grape/middleware/base.rb

def content_type
  content_type_for(env[Grape::Env::API_FORMAT] || options[:format]) || TEXT_HTML
end

Now, some test are now using rack_response instead of error! and this method will call content-type from the endpoint which will be nil if not set explicitely from header.

# lib/grape/dsl/inside_route.rb

def content_type(val = nil)
  if val
    header(Rack::CONTENT_TYPE, val)
  else
    header[Rack::CONTENT_TYPE]
  end
end

I don't think anyone is using rack_response in a rescue_from since its never been documented and I think we should
1 - remove the method from inside_route
2 - make the function private in lib/grape/middleware/error.rb, even though its not accessible anymore within rescue_from

[dblock]

Good plan. If no specs break we should be good.