hostname to its canonical presentation form; a UTF-8
string in Unicode normalization form C, containing no uppercase
letters, no forbidden characters, and no ASCII-encoded segments,
and not ending with a trailing dot.
Of course if
hostname is not an internationalized hostname, then
the canonical presentation form will be entirely ASCII.
Available since: 2.22
A valid UTF-8 or ASCII hostname.
The data is owned by the caller of the function. The value is a NUL terminated UTF-8 string.