"Connection: close" and actually close the connection after the
  response-body, libcurl could still have outstanding data to send and it
  would not properly notice this and stop sending. This caused weirdness and
  sad faces. http://curl.haxx.se/bug/view.cgi?id=2080222

  Note that there are still reasons to consider libcurl's behavior when
  getting a >= 400 response code while sending data, as Craig Perras' note
  "http upload: how to stop on error" specifies:
  http://curl.haxx.se/mail/archive-2008-08/0138.html