Testing an ActionController::Live controller leads to a deadlock

[Kjir]

This is a deeper and more correct report of #31200 after some deep investigation of the issue.

Steps to reproduce

In a new rails application generate a controller and implement it like follows:

rails new stream_test
cd stream_test
bin/rails g controller Home index

class HomeController < ApplicationController
  include ActionController::Live

  def index
    11.times { response.stream.write('a') }
    ensure
      response.stream.close
  end
end

Then run the controller test

bin/rails test

Expected behavior

The test should succeed

Actual behavior

The test will just hang forever. This is because under the hood when streaming responses with ActionController::Live we are adding the responses to a SizedQueue with size 10. In a real context, the browser will consume the data as soon as it is generated thus freeing space in the queue; in a rack test context, however, we are expecting the whole response to be returned without actually consuming it as it is processed. So if the test includes more than 10 writes on the stream, the tests will hang forever.

I can see three possible solutions:

• Disable streaming in test environments
• Substitute the SizedQueue with an infinite Queue in test environments
• Consume the response in async.

The third option is arguably the best solution, but it is also the most complex one. I'm also not sure where it should be implemented, it could require changes in the rack-test gem.

Any other thoughts?

System configuration

Rails version:
Lastest master (Rails 5.2.0.beta2) at the time of writing. Commit: a88eb9087260cca256c6faba40bf538d4a0289b3
Ruby version:
ruby 2.4.2p198 (2017-09-14 revision 59899) [x86_64-darwin16]

[rails-bot]

This issue has been automatically marked as stale because it has not been commented on for at least three months.
The resources of the Rails team are limited, and so we are asking for your help.
If you can still reproduce this error on the 5-1-stable branch or on master, please reply with all of the information you have about it in order to keep the issue open.
Thank you for all your contributions.

[zzak]

Fixed by #41609