function fails and it returns NULL

we can compare if non-NULL elsewhere

if a connection is tunneled through a proxy. A tunnel is done with CONNECT,
either when using HTTPS or FTPS, or if explicitly enabled by the app.

idea (not really new, but its better to have it mentioned in here)

both with older libidn versions without idn_free() and with libidn versions
that gets installed without idn-free.h

versions

interface is used

the curl_easy_strerror() function to provide one