Pass content_types option to Grape::Middleware::Error

[bernd]

This fixes the Content-Type header on error responses with a custom
format. It wasn't able to find the custom format and used the default
of "text/html".

[dblock]

Just to confirm that I understand this correctly.

Errors now return the same content type as the body. Should this really be the case? Aren't errors their own things and can be handled as such? Or am I misunderstanding and the error middleware already does this and looks up the content type, except that it's broken for custom content-types?

[dm1try]

I think, error middleware already does this using Base middleware class implementation:

# lib/grape/middleware/base.rb
def content_types
  ContentTypes.content_types_for(options[:content_types])
end

def content_type
  content_type_for(env['api.format'] || options[:format]) || 'text/html'
end

without options[:content_types], it looks up only predefined content types:

# lib/grape/util/content_types.rb

    CONTENT_TYPES = ActiveSupport::OrderedHash[
      :xml,  'application/xml',
      :serializable_hash, 'application/json',
      :json, 'application/json',
      :jsonapi, 'application/vnd.api+json',
      :atom, 'application/atom+xml',
      :rss,  'application/rss+xml',
      :txt,  'text/plain',
   ]

[bernd]

The error middleware already does this but fails for custom content-types.

An example:

class Api < Grape::API
  content_type :json, 'application/json'
  content_type :xml, 'application/xml'
  content_type :custom, 'application/vnd.custom'

  formatter :custom, ->(obj, _) { "CUSTOM | #{obj[:message]}\n" }
  error_formatter :custom, ->(*a) { "CUSTOM  ERROR | #{a.first[:message]}\n" }

  get '/ok' do
    {message: "hello world"}
  end

  get '/error' do
    error!({message: 'ERROR'})
  end
end

+ curl -i localhost:9292/ok.json
HTTP/1.1 200 OK
Content-Type: application/json
Content-Length: 25

{"message":"hello world"}

+ curl -i localhost:9292/ok.xml
HTTP/1.1 200 OK
Content-Type: application/xml
Content-Length: 87

<?xml version="1.0" encoding="UTF-8"?>
<hash>
  <message>hello world</message>
</hash>

+ curl -i localhost:9292/ok.custom
HTTP/1.1 200 OK
Content-Type: application/vnd.custom
Content-Length: 21

CUSTOM | hello world

+ curl -i localhost:9292/error.json
HTTP/1.1 500 Internal Server Error
Content-Type: application/json
Content-Length: 19

{"message":"ERROR"}

+ curl -i localhost:9292/error.xml
HTTP/1.1 500 Internal Server Error
Content-Type: application/xml
Content-Length: 83

<?xml version="1.0" encoding="UTF-8"?>
<error>
  <message>ERROR</message>
</error>

+ curl -i localhost:9292/error.custom
HTTP/1.1 500 Internal Server Error
Content-Type: text/html
Content-Length: 22

CUSTOM  ERROR | ERROR

With my patch applied, the content-type for the last response changes to application/vnd.custom.

[dblock]

Thanks, merging.