Post transfer info

Remember how libcurl transfers are associated with an “easy handle”! Each
transfer has such a handle and when a transfer is completed, before the handle
is cleaned or reused for another transfer, it can be used to extract
information from the previous operation.

Your friend for doing this is called curl_easy_getinfo() and you tell it
which specific information you’re interested in and it will return that to you
if it can.

When you use this function, you pass in the easy handle, which information you
want and a pointer to a variable to hold the answer. You must pass in a
pointer to a variable of the correct type or you risk that things will go
side-ways. These information values are designed to be provided after the
transfer is completed.

The data you receive can be a long, a ‘char ‘, a ‘struct curl_slist ‘, a
double or a socket.

This is how you extract the Content-Type: value from the previous HTTP
transfer:

CURLcode res;
char *content_type;
res = curl_easy_getinfo(curl, CURLINFO_CONTENT_TYPE, &content_type);

but if you want to extract the local port number that was used in that
connection:

CURLcode res;
long port_number;
res = curl_easy_getinfo(curl, CURLINFO_LOCAL_PORT, &port_number);

Available information