Look up txt records
#include <dns.h>
int dns_txt(stralloc* out,stralloc* fqdn);
dns_txt looks up TXT records for the fully-qualified domain name in fqdn. It puts the concatenation of the TXT records into out and returns 0. If the domain does not exist in DNS, or has no TXT records, out will be empty.
If dns_txt has trouble with the DNS lookup or runs out of memory, it returns -1, setting errno appropriately. It may or may not change out.