Now that we have properly refactored the caching resolvers we can
move them into netxlite as optional resolvers created using the
proper abstract factories we just added.
This diff reduces the complexity and the code size of netx.
See https://github.com/ooni/probe/issues/2121.
For testability, replace most if-based construction logic with
calls to well-tested factories living in other packages.
While there, acknowledge that a bunch of types could now be private
and make them private, modifying the code to call the public
factories allowing to construct said types instead.
Part of https://github.com/ooni/probe/issues/2121
This diff modifies netx to stop using most netxlite resolver internals
but the internal function that creates a new, unwrapped system resolver,
which will be dealt with in a subsequent pull request.
See https://github.com/ooni/probe/issues/2121
This diff has been extracted and adapted from 8848c8c516
The reason to prefer composition over embedding is that we want the
build to break if we add new methods to interfaces we define. If the build
does not break, we may forget about wrapping methods we should
actually be wrapping. I noticed this issue inside netxlite when I was working
on websteps-illustrated and I added support for NS and PTR queries.
See https://github.com/ooni/probe/issues/2096
While there, perform comprehensive netxlite code review
and apply minor changes and improve the docs.
