What you've discovered is that it's not really Rails or Sinatra that's
creating the Tempfile -- it's Rack:
https://github.com/rack/rack/blob/master/lib/rack/utils.rb#L483
I think you'll need to dig down to that web server - app interface
level if you want to amend this.
Chris
Sorry, badly worded. I meant that it's happening at the interface between the web server and your app; in this case that's where Rack lives.
Chris