This function is called after the init and all the curl_easy_setopt(3)
calls are made, and will perform the transfer as described in the options. It
must be called with the same
as input as the curl_easy_init call returned.
You can do any amount of calls to curl_easy_perform(3) while using the
same handle. If you intend to transfer more than one file, you are even
encouraged to do so. libcurl will then attempt to re-use the same connection
for the following transfers, thus making the operations faster, less CPU
intense and using less network resources. Just note that you will have to use
curl_easy_setopt(3) between the invokes to set options for the following
You must never call this function simultaneously from two places using the
same handle. Let the function return first before invoking it another time. If
you want parallel transfers, you must use several curl handles.
0 means everything was ok, non-zero means an error occurred as
defines. If the CURLOPT_ERRORBUFFER was set with
there will be a readable error message in the error buffer when non-zero is