* cleanup: remove UnderlyingNetworkLibrary and TProxy
While there, replace mixture of mocking and real connections inside
quicping with pure mocking of network connections.
Closes https://github.com/ooni/probe/issues/2224
* cleanup: we don't need a SimpleResolver now
This type was only used by UnderlyingNetworkLibrary and all the
rest of the code uses Resolver. So, let's avoid complexity by zapping
the SimpleResolver type and merging it inside Resolver.
After https://github.com/ooni/probe-cli/pull/764, the build for
CGO_ENABLED=0 has been broken for miniooni:
https://github.com/ooni/probe-cli/runs/6636995859?check_suite_focus=true
Likewise, it's not possible to run tests with CGO_ENABLED=0.
To make tests work with `CGO_ENABLED=0`, I needed to sacrifice some
unit tests run for the CGO case. It is not fully clear to me what was happening
here, but basically `getaddrinfo_cgo_test.go` was compiled with CGO
being disabled, even though the ``//go:build cgo` flag was specified.
Additionally, @hellais previously raised a valid point in the review
of https://github.com/ooni/probe-cli/pull/698:
> Another issue we should consider is that, if I understand how
> this works correctly, depending on whether or not we have built
> with CGO_ENABLED=0 on or not, we are going to be measuring
> things in a different way (using our cgo inspired getaddrinfo
> implementation or using netgo). This might present issues when
> analyzing or interpreting the data.
>
> Do we perhaps want to add some field to the output data format that
> gives us an indication of which DNS resolution code was used to
> generate the the metric?
This comment is relevant to the current commit because
https://github.com/ooni/probe-cli/pull/698 is the previous
iteration of https://github.com/ooni/probe-cli/pull/764.
So, while fixing the build and test issues, let us also distinguish
between the CGO_ENABLED=1 and CGO_ENABLED=0 cases.
Before this commit, OONI used "system" to indicate the case where
we were using net.DefaultResolver. This behavior dates back to the
Measurement Kit days. While it is true that ooni/probe-engine and
ooni/probe-cli could have been using netgo in the past when we
said "system" as the resolver, it also seems reasonable to continue
to use "system" top indicate getaddrinfo.
So, the choice here is basically to use "netgo" from now on to
indicate the cases in which we were built with CGO_ENABLED=0.
This change will need to be documented into ooni/spec along with
the introduction of the `android_dns_cache_no_data` error.
## Checklist
- [x] I have read the [contribution guidelines](https://github.com/ooni/probe-cli/blob/master/CONTRIBUTING.md)
- [x] reference issue for this pull request: https://github.com/ooni/probe/issues/2029
- [x] if you changed anything related how experiments work and you need to reflect these changes in the ooni/spec repository, please link to the related ooni/spec pull request: https://github.com/ooni/spec/pull/242
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.
## Checklist
- [x] I have read the [contribution guidelines](https://github.com/ooni/probe-cli/blob/master/CONTRIBUTING.md)
- [x] reference issue for this pull request: https://github.com/ooni/probe/issues/1885
- [x] related ooni/spec pull request: N/A
Location of the issue tracker: https://github.com/ooni/probe
## Description
This PR contains a set of changes to move important interfaces and data types into the `./internal/model` package.
The criteria for including an interface or data type in here is roughly that the type should be important and used by several packages. We are especially interested to move more interfaces here to increase modularity.
An additional side effect is that, by reading this package, one should be able to understand more quickly how different parts of the codebase interact with each other.
This is what I want to move in `internal/model`:
- [x] most important interfaces from `internal/netxlite`
- [x] everything that was previously part of `internal/engine/model`
- [x] mocks from `internal/netxlite/mocks` should also be moved in here as a subpackage
