AggregateResolver aggregates the results from multiple
resolver instances.
This is most useful when you want to overlay or otherwise
force in test data to take precedence over real resolver
results. In that situation, you’d push a TestResolver
ahead of the HickoryResolver that you want to use for
real DNS resolution.
A set of resolved IP addresses together with whether the DNS lookup that
produced them was DNSSEC validated (secure). The secure flag is what lets
the delivery path decide DANE eligibility without performing a second
lookup; see ResolvedAddress::is_secure.
Helper to reason about a domain name string.
It can either be name that needs to be resolved, or some kind
of IP literal.
We also allow for an optional port number to be present in
the domain name string.
If the provided parameter ends with :PORT and PORT is a valid u16,
then crack apart and return the LABEL and PORT number portions.
Otherwise, returns None