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Mix this module in to your controller, and all actions in that controller will be able to stream data to the client as it's written.

class MyController < ActionController::Base
  include ActionController::Live

  def stream
    response.headers['Content-Type'] = 'text/event-stream'
    100.times {
      response.stream.write "hello world\n"
      sleep 1
    }
  ensure
    response.stream.close
  end
end

There are a few caveats with this use. You cannot write headers after the response has been committed (Response#committed? will return truthy). Calling write or close on the response stream will cause the response object to be committed. Make sure all headers are set before calling write or close on your stream.

You must call close on your stream when you're finished, otherwise the socket may be left open forever.

The final caveat is that your actions are executed in a separate thread than the main thread. Make sure your actions are thread safe, and this shouldn't be a problem (don't share state across threads, etc).

Namespace
Methods
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P
R
S
Instance Public methods
log_error(exception)
# File actionpack/lib/action_controller/metal/live.rb, line 302
def log_error(exception)
  logger = ActionController::Base.logger
  return unless logger

  logger.fatal do
    message = "\n#{exception.class} (#{exception.message}):\n"
    message << exception.annoted_source_code.to_s if exception.respond_to?(:annoted_source_code)
    message << "  " << exception.backtrace.join("\n  ")
    "#{message}\n\n"
  end
end
process(name)
# File actionpack/lib/action_controller/metal/live.rb, line 261
def process(name)
  t1 = Thread.current
  locals = t1.keys.map { |key| [key, t1[key]] }

  error = nil
  # This processes the action in a child thread. It lets us return the
  # response code and headers back up the rack stack, and still process
  # the body in parallel with sending data to the client
  Thread.new {
    t2 = Thread.current
    t2.abort_on_exception = true

    # Since we're processing the view in a different thread, copy the
    # thread locals from the main thread to the child thread. :'(
    locals.each { |k,v| t2[k] = v }

    begin
      super(name)
    rescue => e
      if @_response.committed?
        begin
          @_response.stream.write(ActionView::Base.streaming_completion_on_exception) if request.format == :html
          @_response.stream.call_on_error
        rescue => exception
          log_error(exception)
        ensure
          log_error(e)
          @_response.stream.close
        end
      else
        error = e
      end
    ensure
      @_response.commit!
    end
  }

  @_response.await_commit
  raise error if error
end
response_body=(body)
# File actionpack/lib/action_controller/metal/live.rb, line 314
def response_body=(body)
  super
  response.close if response
end
set_response!(request)
# File actionpack/lib/action_controller/metal/live.rb, line 319
def set_response!(request)
  if request.env["HTTP_VERSION"] == "HTTP/1.0"
    super
  else
    @_response         = Live::Response.new
    @_response.request = request
  end
end