In https://github.com/ooni/probe-cli/pull/832's initial diff, I
mentioned it would be cool to flatten oohelperd's hier.
I'm doing this now, and just for the master branch.
This diff is mostly a mechanical refactoring with very light
and apparently rather safe manual changes.
This diff modifies the implementation of oohelperd in the master branch
to always use throw-away HTTPClient, Dialer, and Resolver.
The rationale of this change is to ensure we're not hitting limits of the
HTTPClient regarding the max number of connections per host.
This issue is described at https://github.com/ooni/probe/issues/2182.
While there, it feels more correct to use throw-away Dialer and Resolver.
We have a different patch for the release/3.15 branch because of
netx-related refactorings: https://github.com/ooni/probe-cli/pull/832.
The oohelperd implementation did not actually need using netx because
it was just constructing default types with logging, which is what
netxlite already does. Hence, let's avoid using netx here.
See https://github.com/ooni/probe/issues/2121
This diff addresses another point of https://github.com/ooni/probe/issues/1956:
> - [ ] observe that we're still using a bunch of private interfaces for common interfaces such as the `Dialer`, so we can get rid of these private interfaces and always use the ones in `model`, which allows us to remove a bunch of legacy wrappers
Additional cleanups may still be possible. The more I cleanup, the more I see
there's extra legacy code we can dispose of (which seems good?).
