Add ActionController::Live::Buffer#writeln the write a line to the stream with a newline included (rails#41501)

David Heinemeier Hansson · web-flow · commit b90875ebd9fe · 2021-02-20T10:02:49.000+01:00
* Add ActionController::Live::Buffer#writeln to write a line to the stream with a newline included

* Don't add newlines to strings that already have them
diff --git a/actionpack/CHANGELOG.md b/actionpack/CHANGELOG.md
@@ -2,16 +2,20 @@
 
     ```ruby
     send_stream(filename: "subscribers.csv") do |stream|
-      stream.write "email_address,updated_at\n"
+      stream.writeln "email_address,updated_at"
     
       @subscribers.find_each do |subscriber|
-        stream.write "#{subscriber.email_address},#{subscriber.updated_at}\n"
+        stream.writeln [ subscriber.email_address, subscriber.updated_at ].join(",")
       end
     end
     ```
     
     *DHH*
 
+*   Add `ActionController::Live::Buffer#writeln` to write a line to the stream with a newline included.
+
+    *DHH*
+
 *   `ActionDispatch::Request#content_type` now returned Content-Type header as it is.
 
     Previously, `ActionDispatch::Request#content_type` returned value does NOT contain charset part.
diff --git a/actionpack/lib/action_controller/metal/live.rb b/actionpack/lib/action_controller/metal/live.rb
@@ -163,6 +163,11 @@ def write(string)
         end
       end
 
+      # Same as +write+ but automatically include a newline at the end of the string.
+      def writeln(string)
+        write string.end_with?("\n") ? string : "#{string}\n"
+      end
+
       # Write a 'close' event to the buffer; the producer/writing thread
       # uses this to notify us that it's finished supplying content.
       #
diff --git a/actionpack/test/controller/live_stream_test.rb b/actionpack/test/controller/live_stream_test.rb
@@ -131,6 +131,12 @@ def render_text
         render plain: "zomg"
       end
 
+      def write_lines
+        response.stream.writeln "hello\n"
+        response.stream.writeln "world"
+        response.stream.close
+      end
+
       def default_header
         response.stream.write "<html><body>hi</body></html>"
         response.stream.close
@@ -312,6 +318,11 @@ def test_write_to_stream
       assert_equal "text/event-stream", @response.headers["Content-Type"]
     end
 
+    def test_write_lines_to_stream
+      get :write_lines
+      assert_equal "hello\nworld\n", @response.body
+    end
+
     def test_send_stream
       get :basic_send_stream
       assert_equal "name,age\ndavid,41", @response.body
