Fixes #23964

  - Adds #each_chunk to ActionDispatch::Response. it's a method which
    will be called by ActionDispatch::Response#each.
  - Make Response#each a proper method instead of delegating to @stream
  - In Live, instead of overriding #each, override #each_chunk.
  - `#each` should just spit out @str_body if it's already set
  - Adds #test_set_header_after_read_body_during_action
    to prove this fixes #23964
  - Adds #test_each_isnt_called_if_str_body_is_written to
    ensure #each_chunk is not called when @str_body is available
  - Call `@response.sent!` in AC::TestCase's #perform so a test response
    acts a bit more like a real response. Makes test that call  `#assert_stream_closed`
    pass again.
  - Additionally assert `#committed?` in `#assert_stream_closed`
  - Make test that was calling @response.stream.each pass again by
    calling @response.each instead.

3 files changed, 36 insertions, 2 deletions

diff --git a/actionpack/test/controller/live_stream_test.rb b/actionpack/test/controller/live_stream_test.rb
index 0c3884cd38..298e12722b 100644
--- a/actionpack/test/controller/live_stream_test.rb
+++ b/actionpack/test/controller/live_stream_test.rb
@@ -246,7 +246,8 @@ module ActionController
 
     def assert_stream_closed
       assert response.stream.closed?, 'stream should be closed'
-      assert response.sent?, 'stream should be sent'
+      assert response.committed?,     'response should be committed'
+      assert response.sent?,          'response should be sent'
     end
 
     def capture_log_output
diff --git a/actionpack/test/dispatch/live_response_test.rb b/actionpack/test/dispatch/live_response_test.rb
index e4475f4233..de57c4be1d 100644
--- a/actionpack/test/dispatch/live_response_test.rb
+++ b/actionpack/test/dispatch/live_response_test.rb
@@ -65,7 +65,7 @@ module ActionController
         latch = Concurrent::CountDownLatch.new
 
         t = Thread.new {
-          @response.stream.each do
+          @response.each do
             latch.count_down
           end
         }
diff --git a/actionpack/test/dispatch/response_test.rb b/actionpack/test/dispatch/response_test.rb
index cd385982d9..b03791e499 100644
--- a/actionpack/test/dispatch/response_test.rb
+++ b/actionpack/test/dispatch/response_test.rb
@@ -37,6 +37,39 @@ class ResponseTest < ActiveSupport::TestCase
     assert_equal "closed stream", e.message
   end
 
+  def test_each_isnt_called_if_str_body_is_written
+    # Controller writes and reads response body
+    each_counter = 0
+    @response.body = Object.new.tap {|o| o.singleton_class.send(:define_method, :each) { |&block| each_counter += 1; block.call 'foo' } }
+    @response['X-Foo'] = @response.body
+
+    assert_equal 1, each_counter, "#each was not called once"
+
+    # Build response
+    status, headers, body = @response.to_a
+
+    assert_equal 200, status
+    assert_equal "foo", headers['X-Foo']
+    assert_equal "foo", body.each.to_a.join
+
+    # Show that #each was not called twice
+    assert_equal 1, each_counter, "#each was not called once"
+  end
+
+  def test_set_header_after_read_body_during_action
+    @response.body
+
+    # set header after the action reads back @response.body
+    @response['x-header'] = "Best of all possible worlds."
+
+    # the response can be built.
+    status, headers, body = @response.to_a
+    assert_equal 200, status
+    assert_equal "", body.body
+
+    assert_equal "Best of all possible worlds.", headers['x-header']
+  end
+
   def test_read_body_during_action
     @response.body = "Hello, World!"