Respect content type set in superclass before filter

lib/sinatra/base.rb

@@ -998,6 +998,7 @@ def filter!(type, base = settings)
       filter! type, base.superclass if base.superclass.respond_to?(:filters)
       base.filters[type].each do |args|
         result = process_route(*args)
+        @pinned_response = !@response['Content-Type'].nil?
         yield result if block_given?
       end
     end
@@ -1123,9 +1124,7 @@ def dispatch!
 
       invoke do
         static! if settings.static? && (request.get? || request.head?)
-        filter! :before do
-          @pinned_response = !@response['Content-Type'].nil?
-        end
+        filter! :before
         route!
       end
     rescue ::Exception => boom

test/filter_test.rb

@@ -262,6 +262,17 @@ class AfterFilterTest < Minitest::Test
     assert_equal 8, count
   end
 
+  it "respects content type set in superclass filter" do
+    base = Class.new(Sinatra::Base)
+    base.before { content_type :json }
+    mock_app(base) do
+      get('/foo'){ {:foo => :bar}.to_json }
+    end
+
+    get '/foo'
+    assert_equal 'application/json', response.headers['Content-Type']
+  end
+
   it 'does not run after filter when serving static files' do
     ran_filter = false
     mock_app do