This is fairly big diff because a number of hickory types moved around
or changed signature.
In particular, the config structs changed in a way that would fan out
and require attention by our users. So the approach I opted to take
here was to define our own types that look like the hickory 0.25
shape and then we have explicit logic to map those to hickory and
also to our unbound resolver crate.
This commit also bumps up the unbound resolver crate because it also
uses hickory's types. I took the opportunity to upgrade the version
of the embedded unbound resolver as part of that work.
This commit does some plumbing work to allow defining alternative
resolvers with different names that can be used to query different
upstream DNS servers.
This is most useful when implement DNSBLs where you might have a custom
DNS server configured with one or more RBL zones that is reserved purely
for RBL lookups.
The plumbing introduces a more regular syntax for defining one of the
various implementations of the Resolver trait, as well as a new
Aggregate resolver impl that can query across multiple Resolvers until a
query is satisfied.
This allows some interesting and powerful configurations, such as
loading a static zone file into memory to query it directly, and/or
blending that together with querying either the system or some other
upstream DNS server as a fallback.
The various lookup functions (except for MX!) have been updated to
accept an optional alternate resolver name, so that they work together
with the above.
A new rbl_lookup function is also provided as a convenience for querying
the most common form of RBLS.
ptr_host and reverse_ip are two string utility functions that are likely
not going to be widely used, but are very convenient to have when you
do have a usecase that requires it!
closes: https://github.com/KumoCorp/kumomta/issues/269
Wez Furlong