Rails + Puma + Transfer-Encoding: chunked response - supported or not?

Configuration

• Rails: 4.2.7.1
• Puma: 3.8.2

--

Transfer-Encoding:  chunked

I've been unable to make this work and unable to find a definitive answer: in the above configuration, I want to stream large amounts of data to the client (in the response) - is this supported?

• If so, what is my responsibility?
  • Should my controller be emitting hexadecimal chunk sizes, \r\n, 0 etc?
• It feels like I want but can't find a simple response API like:
  • write, write, write, flush
  • write, write, write, flush
  • close
• I've read 100 posts about Rack, monkey patching and other insanity
• I've read about Puma and/or Rack mangling the encoding, possibly gzip/deflating in the wrong order
• This seems like a simple feature that should be readily available but I am stumped
• I have created numerous tests, e.g. self.response_body = Enumerator.new and response.stream.write, etc. -- all with similar results (via curl) - Malformed encoding found in chunked-encoding or transfer closed with outstanding read data remaining

Can anyone show me the light?

The ActionController::Live API offers exactly what you describe: response.stream.write and response.stream.close. (write flushes a chunk automatically; you'll need to do your own buffering if that doesn't work for you.)

As long as you include ActionController::Live (and note that affects the behaviour of the entire controller, not just one action), you should then be able to write a streaming response with no further effort: you need not, and should not, set any headers etc related to chunking.

Additional reference: http://tenderlovemaking.com/2012/07/30/is-it-live.html