| SYNOPSIS | 
#include <dkim.h>
int dkim_dns_set_trustanchor(
	DKIM_LIB *libopendkim,
        int (*func)(void *, const char *)
);
Declares the function to be used by a libopendkim instance when it needs to
pass trust anchor 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
      dkim_dns_set_init().
  A pointer to a NULL-terminated string that includes trust anchor
      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
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