2 files changed, 24 insertions, 5 deletions
diff --git a/actionpack/lib/action_dispatch/http/mime_negotiation.rb b/actionpack/lib/action_dispatch/http/mime_negotiation.rb
index 68ba1a81b5..980c658ab7 100644
--- a/actionpack/lib/action_dispatch/http/mime_negotiation.rb
+++ b/actionpack/lib/action_dispatch/http/mime_negotiation.rb
@@ -1,6 +1,13 @@
 module ActionDispatch
   module Http
     module MimeNegotiation
+      extend ActiveSupport::Concern
+
+      included do
+        mattr_accessor :ignore_accept_header
+        self.ignore_accept_header = false
+      end
+
       # The MIME type of the HTTP request, such as Mime::XML.
       #
       # For backward compatibility, the post \format is extracted from the
@@ -42,16 +49,14 @@ module ActionDispatch
         formats.first
       end
 
-      BROWSER_LIKE_ACCEPTS = /,\s*\*\/\*|\*\/\*\s*,/
-
       def formats
-        accept = @env['HTTP_ACCEPT']
-
         @env["action_dispatch.request.formats"] ||=
           if parameters[:format]
             Array(Mime[parameters[:format]])
-          elsif xhr? || (accept && accept !~ BROWSER_LIKE_ACCEPTS)
+          elsif use_accept_header && valid_accept_header
             accepts
+          elsif xhr?
+            [Mime::JS]
           else
             [Mime::HTML]
           end
@@ -87,6 +92,18 @@ module ActionDispatch
 
         order.include?(Mime::ALL) ? formats.first : nil
       end
+
+      protected
+
+      BROWSER_LIKE_ACCEPTS = /,\s*\*\/\*|\*\/\*\s*,/
+
+      def valid_accept_header
+        xhr? || (accept && accept !~ BROWSER_LIKE_ACCEPTS)
+      end
+
+      def use_accept_header
+        !self.class.ignore_accept_header
+      end
     end
   end
 end
diff --git a/actionpack/lib/action_dispatch/railtie.rb b/actionpack/lib/action_dispatch/railtie.rb
index 0a3bd5fe40..f51cc3711b 100644
--- a/actionpack/lib/action_dispatch/railtie.rb
+++ b/actionpack/lib/action_dispatch/railtie.rb
@@ -9,10 +9,12 @@ module ActionDispatch
     config.action_dispatch.show_exceptions = true
     config.action_dispatch.best_standards_support = true
     config.action_dispatch.tld_length = 1
+    config.action_dispatch.ignore_accept_header = false
     config.action_dispatch.rack_cache = {:metastore => "rails:/", :entitystore => "rails:/", :verbose => true}
 
     initializer "action_dispatch.configure" do |app|
       ActionDispatch::Http::URL.tld_length = app.config.action_dispatch.tld_length
+      ActionDispatch::Request.ignore_accept_header = app.config.action_dispatch.ignore_accept_header
     end
   end
 end