Add content negotiation middleware + fix response content type.

lib/jsonapi/rails/filter_media_type.rb

@@ -0,0 +1,39 @@
+require 'rack/media_type'
+
+module JSONAPI
+  module Rails
+    class FilterMediaType
+      JSONAPI_MEDIA_TYPE = 'application/vnd.api+json'.freeze
+
+      def initialize(app)
+        @app = app
+      end
+
+      def call(env)
+        return [415, {}, []] unless valid_content_type?(env['CONTENT_TYPE'])
+        return [406, {}, []] unless valid_accept?(env['HTTP_ACCEPT'])
+
+        @app.call(env)
+      end
+
+      private
+
+      def valid_content_type?(content_type)
+        Rack::MediaType.type(content_type) != JSONAPI_MEDIA_TYPE ||
+          Rack::MediaType.params(content_type) == {}
+      end
+
+      def valid_accept?(accept)
+        return true if accept.nil?
+
+        jsonapi_media_types =
+          accept.split(',')
+                .map(&:strip)
+                .select { |m| Rack::MediaType.type(m) == JSONAPI_MEDIA_TYPE }
+
+        jsonapi_media_types.empty? ||
+          jsonapi_media_types.any? { |m| Rack::MediaType.params(m) == {} }
+      end
+    end
+  end
+end

lib/jsonapi/rails/railtie.rb

@@ -1,5 +1,6 @@
 require 'rails/railtie'
 
+require 'jsonapi/rails/filter_media_type'
 require 'jsonapi/rails/log_subscriber'
 require 'jsonapi/rails/renderer'
 
@@ -19,14 +20,16 @@ class Railtie < ::Rails::Railtie
         jsonapi_errors: ErrorsRenderer.new
       }.freeze
 
-      initializer 'jsonapi-rails.init' do
+      initializer 'jsonapi-rails.init' do |app|
         register_mime_type
         register_parameter_parser
         register_renderers
         ActiveSupport.on_load(:action_controller) do
           require 'jsonapi/rails/controller'
           include ::JSONAPI::Rails::Controller
         end
+
+        app.middleware.use FilterMediaType
       end
 
       private
@@ -49,7 +52,7 @@ def register_renderers
           RENDERERS.each do |name, renderer|
             ::ActionController::Renderers.add(name) do |resources, options|
               # Renderer proc is evaluated in the controller context.
-              self.content_type ||= Mime[:jsonapi]
+              headers['Content-Type'] = Mime[:jsonapi].to_s
 
               ActiveSupport::Notifications.instrument('render.jsonapi-rails',
                                                       resources: resources,

spec/content_negotiation_spec.rb

@@ -0,0 +1,17 @@
+require 'rails_helper'
+
+describe ActionController::Base, type: :controller do
+  controller do
+    def index
+      render jsonapi: nil
+    end
+  end
+
+  context 'when sending data' do
+    it 'responds with application/vnd.api+json' do
+      get :index
+
+      expect(response.headers['Content-Type']).to eq('application/vnd.api+json')
+    end
+  end
+end

spec/filter_media_type_spec.rb

@@ -0,0 +1,69 @@
+require 'rails_helper'
+
+describe JSONAPI::Rails::FilterMediaType do
+  let(:app) { ->(_) { [200, {}, ['OK']] } }
+
+  context 'when not receiving JSON API Content-Type' do
+    it 'passes through' do
+      env = { 'CONTENT_TYPE' => 'application/json' }
+
+      expect(described_class.new(app).call(env)[0]).to eq(200)
+    end
+  end
+
+  context 'when receiving JSON API Content-Type without media parameters' do
+    it 'passes through' do
+      env = { 'CONTENT_TYPE' => 'application/vnd.api+json' }
+
+      expect(described_class.new(app).call(env)[0]).to eq(200)
+    end
+  end
+
+  context 'when receiving Content-Type with media parameters' do
+    it 'fails with 415 Unsupported Media Type' do
+      env = { 'CONTENT_TYPE' => 'application/vnd.api+json; charset=utf-8' }
+
+      expect(described_class.new(app).call(env)[0]).to eq(415)
+    end
+  end
+
+  context 'when not receiving JSON API in Accept' do
+    it 'passes through' do
+      env = { 'HTTP_ACCEPT' => 'application/json' }
+
+      expect(described_class.new(app).call(env)[0]).to eq(200)
+    end
+  end
+
+  context 'when receiving JSON API in Accept without media parameters' do
+    it 'passes through' do
+      env = { 'HTTP_ACCEPT' => 'application/vnd.api+json' }
+
+      expect(described_class.new(app).call(env)[0]).to eq(200)
+    end
+  end
+
+  context 'when receiving JSON API in Accept without media parameters among others' do
+    it 'passes through' do
+      env = { 'HTTP_ACCEPT' => 'application/json, application/vnd.api+json' }
+
+      expect(described_class.new(app).call(env)[0]).to eq(200)
+    end
+  end
+
+  context 'when receiving JSON API in Accept with media parameters' do
+    it 'fails with 406 Not Acceptable' do
+      env = { 'HTTP_ACCEPT' => 'application/vnd.api+json; charset=utf-8' }
+
+      expect(described_class.new(app).call(env)[0]).to eq(406)
+    end
+  end
+
+  context 'when receiving JSON API in Accept with media parameters among others' do
+    it 'fails with 406 Not Acceptable' do
+      env = { 'HTTP_ACCEPT' => 'application/json, application/vnd.api+json; charset=utf-8' }
+
+      expect(described_class.new(app).call(env)[0]).to eq(406)
+    end
+  end
+end

spec/railtie_spec.rb

@@ -8,4 +8,10 @@
   it 'registers the params parser for the JSON API MIME type' do
     expect(::ActionDispatch::Request.parameter_parsers[:jsonapi]).not_to be_nil
   end
+
+  it 'registers the FilterMediaType middleware' do
+    expect(
+      Rails.application.middleware.include?(JSONAPI::Rails::FilterMediaType)
+    ).to be true
+  end
 end