ActionController::Live with SSE not working properly - ruby-on-rails

Question

I'm trying to use Live Streaming in Rails 4.0.1 in one project but I see problems...
I have this action:
def realtime_push
response.headers['Content-Type'] = 'text/event-stream'
sse = SSE.new(response.stream)
d = Domain.find(params[:domain_id])
begin
loop do
backlinks = d.backlinks.page(params[:page]).per(10)
pagination = render_to_string(:partial => 'backlinks/pagination', :layout => false, :locals => { :backlinks => backlinks })
sse.write({ :html => pagination }, :event => 'pagination')
sleep 1
end
rescue IOError
# When the client disconnects, we'll get an IOError on write
logger.debug "DISCONNECTED"
ensure
sse.close
end
end
When I start Puma and try to get updates:
curl http://localhost:3000/domains/16/backlinks/realtime_push
curl immediately returns with no output.
Curl headers:
HTTP/1.1 200 OK
X-Frame-Options: SAMEORIGIN
X-XSS-Protection: 1; mode=block
X-Content-Type-Options: nosniff
X-UA-Compatible: chrome=1
Content-Type: text/event-stream
Cache-Control: no-cache
X-Request-Id: 1a07be2f-de8d-4ca8-87d0-eee2787ea649
X-Runtime: 0.250782
Transfer-Encoding: chunked
and Puma log shows:
Started GET "/domains/16/backlinks/realtime_push" for 127.0.0.1 at 2013-11-08 12:22:30 +0100
ActiveRecord::SchemaMigration Load (0.7ms) SELECT "schema_migrations".* FROM "schema_migrations"
Processing by BacklinksController#realtime_push as */*
Parameters: {"domain_id"=>"16"}
Domain Load (1.9ms) SELECT "domains".* FROM "domains" WHERE "domains"."id" = $1 LIMIT 1 [["id", "16"]]
(3.3ms) SELECT COUNT(*) FROM "backlinks" WHERE "backlinks"."domain_id" = $1 [["domain_id", 16]]
Rendered backlinks/_pagination.haml (60.6ms)
(0.6ms) SELECT COUNT(*) FROM "backlinks" WHERE "backlinks"."domain_id" = $1 [["domain_id", 16]]
Rendered backlinks/_pagination.haml (36.0ms)
(0.8ms) SELECT COUNT(*) FROM "backlinks" WHERE "backlinks"."domain_id" = $1 [["domain_id", 16]]
Rendered backlinks/_pagination.haml (37.5ms)
(0.8ms) SELECT COUNT(*) FROM "backlinks" WHERE "backlinks"."domain_id" = $1 [["domain_id", 16]]
Rendered backlinks/_pagination.haml (35.6ms)
(0.7ms) SELECT COUNT(*) FROM "backlinks" WHERE "backlinks"."domain_id" = $1 [["domain_id", 16]]
Rendered backlinks/_pagination.haml (38.7ms)
(0.7ms) SELECT COUNT(*) FROM "backlinks" WHERE "backlinks"."domain_id" = $1 [["domain_id", 16]]
Rendered backlinks/_pagination.haml (37.0ms)
So these things are strange:
curl returned no output
log says it rendered pagination 6 times
there was no "DISCONNECT" message in the log
Any ideas? If I comment out the two lines above sse.write and return some text instead of pagination contents, it works...
Here is the SSE class:
class SSE
def initialize io
#io = io
end
def write object, options = {}
options.each do |k,v|
#io.write "#{k}: #{v}\n"
end
#io.write "data: #{JSON.dump(object)}\n\n"
end
def close
#io.close
end
end

Answer 1

This is a bug in render_to_string.
Monkey patch to fix this (that actually doesn't fix the problem - see below):
def render_to_string(*)
orig_stream = response.stream
super
ensure
if orig_stream
response.instance_variable_set(:#stream, orig_stream)
end
end
Source: http://blog.sorah.jp/2013/07/28/render_to_string-in-ac-live
UPDATE: this only appears to fix the problem... although it will cause the controller to actually send the data, the receiving end in JavaScript for some reason still won't get notified of events, see here: SSE (Server-sent events) not working