int (*func)(void *, const char *)
Declares the function to be used by a libopendkim instance when it needs to
pass arbitrary configuration information to an active DNS resolver.
The function will be passed the following arguments:
The function is expected to return one of the following:
- A pointer to a handle that refers to the instantiated
resolver service, via a prior call to to the initialization
function defined by
- A pointer to a NULL-terminated string that includes configuration
information to be used by the referenced resolver. The content of string
is passed directly to the underlying resolver's configuration
function and is not used by this library.
- DKIM_DNS_SUCCESS -- query was successfully canceled
- DKIM_DNS_ERROR -- an error occurred