Stop when connected to target server
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_CONNECT_ONLY, long only);
Pass a long. If the parameter equals 1, it tells the library to perform all the required proxy authentication and connection setup, but no data transfer, and then return. This option is implemented for HTTP, SMTP and POP3.
The option can be used to simply test a connection to a server, but is more useful when used with the CURLINFO_LASTSOCKET option to curl_easy_getinfo(3) as the library can set up the connection and then the application can obtain the most recently used socket for special data transfers.
HTTP, SMTP and POP3
Added in 7.15.2
Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.