The DNSClient type existed because the Resolver type did not include CloseIdleConnections in its signature. Now that Resolver includes CloseIdleConnections, the DNSClient type has become unnecessary and can be safely removed. See https://github.com/ooni/probe/issues/1956.
Directory github.com/ooni/probe-cli/internal
This directory contains private Go packages.
As a reminder, you can always check the Go documentation of a package by using
go doc -all ./internal/$package
where $package
is the name of the package.
Some notable packages: