This method is not fail-safe and there are occasions where non-successful response codes will slip through, especially when authentication is involved (response codes 401 and 407).
You might get some amounts of headers transferred before this situation is detected, like when a "100-continue" is received as a response to a POST/PUT and a 401 or 407 is received immediately afterwards.
When this option is used and an error is detected, it will cause the
connection to get closed and
#CURLE_HTTP_RETURNED_ERROR is returned.