curl_easy_duphandle man page
curl_easy_duphandle — Clone a libcurl session handle
CURL *curl_easy_duphandle(CURL *handle);
This function will return a new curl handle, a duplicate, using all the options previously set in the input curl handle. Both handles can subsequently be used independently and they must both be freed with curl_easy_cleanup(3).
All strings that the input handle has been told to point to (as opposed to copy) with previous calls to curl_easy_setopt(3) using char * inputs, will be pointed to by the new handle as well. You must therefore make sure to keep the data around until both handles have been cleaned up.
The new handle will not inherit any state information, no connections, no SSL sessions and no cookies. It also will not inherit any share object states or options (it will be made as if CURLOPT_SHARE(3) was set to NULL).
In multi-threaded programs, this function must be called in a synchronous way, the input handle may not be in use when cloned.
If this function returns NULL, something went wrong and no valid handle was returned.
curl_easy_cleanup(3), curl_easy_reset(3), curl_easy_setopt(3), curl_mime_data_cb(3), libcurl-easy(3), libcurl-tutorial(3).