Merge pull request rails#48444 from JoeDupuis/keep-headers-mutable

Rack spec requires mutable headers

Author: guilleiguaran

actionpack/lib/action_dispatch/http/response.rb

@@ -462,7 +462,6 @@ def before_sending
       # our last chance.
       commit! unless committed?
 
-      @headers.freeze
       @request.commit_cookie_jar! unless committed?
     end
 

actionpack/test/dispatch/live_response_test.rb

@@ -86,36 +86,6 @@ def test_content_length_is_removed
         @response.stream.write "omg"
         assert_nil @response.headers["Content-Length"]
       end
-
-      def test_headers_cannot_be_written_after_web_server_reads
-        @response.stream.write "omg"
-        latch = Concurrent::CountDownLatch.new
-
-        t = Thread.new {
-          @response.each do
-            latch.count_down
-          end
-        }
-
-        latch.wait
-        assert_predicate @response.headers, :frozen?
-        assert_raises(FrozenError) do
-          @response.headers["Content-Length"] = "zomg"
-        end
-
-        @response.stream.close
-        t.join
-      end
-
-      def test_headers_cannot_be_written_after_close
-        @response.stream.close
-        # we can add data until it's actually written, which happens on `each`
-        @response.each { |x| }
-
-        assert_raises(FrozenError) do
-          @response.headers["Content-Length"] = "zomg"
-        end
-      end
     end
   end
 end