Rex::Proto::DNS::Resolver is currently unable to approximate the
host OS' native resolver because:
1. It cannot cache responses and has to go out to its defined NS'
each time to query for the answers,
2. Because it is not aware of the system's hostsfile entries which
can result in leaks/mis-targeted execution, and a bunch of other
unpleasantly nuanced problems.
Address the concern by:
1. Creating a descendant CachedResolver class from
Rex::Proto::DNS::Resolver, with a #send method override which
performs cache query and population.
2. Moving the Cache class up one namespace to Rex::Proto::DNS and
updating the server accordingly.
3. Fixing the MATCH_HOSTNAME regex in Rex::Proto::DNS::Constants to
allow a short-name (vs FQDN) and creating a relevant MATCH_FQDN.
TODO:
1. Deal with adding search domains from the system to short-name
queries and records; if we decide this is a good idea (potential
for leaks).
2. Look at performance optimization for multiple concurrent queries
via singleton/refcounted/other optimized concurrent access patters.
Testing:
1. Pry-level tests of the objects edited/created in this PR. Needs
some runtime testing to QA.
Spencer McIntyre