Correctly check content type for custom renderers

this fixes a bug where content type is overwritten to `text/plain` if a custom renderer sets the (default) application-json content type using implicit render

Author: rsamoilov

lib/rage/controller/api.rb

@@ -425,7 +425,7 @@ def prepare_action_params(action_name = nil, **opts, &block)
     end
   end # class << self
 
-  DEFAULT_CONTENT_TYPE = "application/json; charset=utf-8"
+  DEFAULT_CONTENT_TYPE = "application/json; charset=utf-8".dup
   private_constant :DEFAULT_CONTENT_TYPE
 
   # @private
@@ -492,7 +492,7 @@ def render(json: nil, plain: nil, sse: nil, status: nil)
         json.is_a?(String) ? json : json.to_json
       else
         ct = @__headers["content-type"]
-        @__headers["content-type"] = "text/plain; charset=utf-8" if ct.nil? || ct == DEFAULT_CONTENT_TYPE
+        @__headers["content-type"] = "text/plain; charset=utf-8" if ct.nil? || ct.equal?(DEFAULT_CONTENT_TYPE)
         plain.to_s
       end
 

spec/configuration/custom_renderer_spec.rb

@@ -184,5 +184,24 @@ def build_controller(&block)
         [202, { "content-type" => "application/json; charset=utf-8" }, ["{\"message\":\"test\"}"]]
       )
     end
+
+    it "doesn't overwrite default content type for renderers with implicit render" do
+      config.renderer(:jsonld) do |data|
+        headers["content-type"] = "application/json; charset=utf-8"
+        data.merge(:@context => "https://schema.org").to_json
+      end
+
+      config.__finalize
+
+      controller = build_controller do
+        define_method(:index) do
+          render jsonld: { name: "Alice" }
+        end
+      end
+
+      expect(run_action(controller, :index)).to match(
+        [200, { "content-type" =>  "application/json; charset=utf-8" }, [include("Alice")]]
+      )
+    end
   end
 end