push the parameter parsers on to the class

The middleware stack is a singleton in the application (one instance is
shared for the entire application) which means that there was only one
opportunity to set the parameter parsers.  Since there is only one set
of parameter parsers in an app, lets just configure them on the request
class (since that is where they are used).

actionpack/lib/action_dispatch/http/parameters.rb

@@ -3,6 +3,20 @@ module Http
     module Parameters
       PARAMETERS_KEY = 'action_dispatch.request.path_parameters'
 
+      DEFAULT_PARSERS = {
+        Mime::JSON => lambda { |raw_post|
+          data = ActiveSupport::JSON.decode(raw_post)
+          data.is_a?(Hash) ? data : {:_json => data}
+        }
+      }
+
+      def self.included(klass)
+        class << klass
+          attr_accessor :parameter_parsers
+        end
+
+        klass.parameter_parsers = DEFAULT_PARSERS
+      end
       # Returns both GET and POST \parameters in a single hash.
       def parameters
         params = get_header("action_dispatch.request.parameters")
@@ -31,6 +45,27 @@ def path_parameters=(parameters) #:nodoc:
       def path_parameters
         get_header(PARAMETERS_KEY) || {}
       end
+
+      private
+
+      def parse_formatted_parameters(request, parsers)
+        return yield if request.content_length.zero?
+
+        strategy = parsers.fetch(request.content_mime_type) { return yield }
+
+        begin
+          strategy.call(request.raw_post)
+        rescue => e # JSON or Ruby code block errors
+          my_logger = logger || ActiveSupport::Logger.new($stderr)
+          my_logger.debug "Error occurred while parsing request parameters.\nContents:\n\n#{request.raw_post}"
+
+          raise ParamsParser::ParseError.new(e.message, e)
+        end
+      end
+
+      def params_parsers
+        ActionDispatch::Request.parameter_parsers
+      end
     end
   end
 end

actionpack/lib/action_dispatch/http/request.rb

@@ -361,16 +361,6 @@ def POST
     end
     alias :request_parameters :POST
 
-    def params_parsers
-      fetch_header "action_dispatch.request.params_parsers" do
-        {}
-      end
-    end
-
-    def params_parsers= hash
-      set_header "action_dispatch.request.params_parsers", hash
-    end
-
     # Returns the authorization header regardless of whether it was specified directly or through one of the
     # proxy alternatives.
     def authorization
@@ -399,20 +389,5 @@ def check_method(name)
         HTTP_METHOD_LOOKUP[name] || raise(ActionController::UnknownHttpMethod, "#{name}, accepted HTTP methods are #{HTTP_METHODS[0...-1].join(', ')}, and #{HTTP_METHODS[-1]}")
         name
       end
-
-    def parse_formatted_parameters(request, parsers)
-      return yield if request.content_length.zero?
-
-      strategy = parsers.fetch(request.content_mime_type) { return yield }
-
-      begin
-        strategy.call(request.raw_post)
-      rescue => e # JSON or Ruby code block errors
-        my_logger = logger || ActiveSupport::Logger.new($stderr)
-        my_logger.debug "Error occurred while parsing request parameters.\nContents:\n\n#{request.raw_post}"
-
-        raise ParamsParser::ParseError.new(e.message, e)
-      end
-    end
   end
 end

actionpack/lib/action_dispatch/middleware/params_parser.rb

@@ -18,26 +18,16 @@ def initialize(message, original_exception)
       end
     end
 
-    DEFAULT_PARSERS = {
-      Mime::JSON => lambda { |raw_post|
-        data = ActiveSupport::JSON.decode(raw_post)
-        data.is_a?(Hash) ? data : {:_json => data}
-      }
-    }
-
     # Create a new +ParamsParser+ middleware instance.
     #
     # The +parsers+ argument can take Hash of parsers where key is identifying
     # content mime type, and value is a lambda that is going to process data.
     def initialize(app, parsers = {})
-      @app, @parsers = app, DEFAULT_PARSERS.merge(parsers)
+      @app = app
+      ActionDispatch::Request.parameter_parsers = ActionDispatch::Request::DEFAULT_PARSERS.merge(parsers)
     end
 
     def call(env)
-      request = Request.new(env)
-
-      request.params_parsers = @parsers
-
       @app.call(env)
     end
   end