[99s-extend] Streaming response in cowboy question

[Grzegorz Junka]

I am implementing a proxy on top of Cowboy. Is it possible to stream the 
response back to Cowboy as I receive it from the destination server?

I am thinking about something like specifying a fun instead of Response 
Body when sending the reply so that Cowboy could call it to receive the 
response in chunks (see send_req in 
https://github.com/cmullaparthi/ibrowse/blob/master/src/ibrowse.erl).