This is the extension of https://github.com/ooni/probe-cli/pull/431, and my final deliverable for GSoC 2021.
The diff introduces:
1) The new `testhelper` which supports testing multiple IP endpoints per domain and introduces HTTP/3 control measurements. The specification of the `testhelper` can be found at https://github.com/ooni/spec/pull/219. The `testhelper` algorithm consists of three main steps:
* `InitialChecks` verifies that the input URL can be parsed, has an expected scheme, and contains a valid domain name.
* `Explore` enumerates all the URLs that it discovers by redirection from the original URL, or by detecting h3 support at the target host.
* `Generate` performs a step-by-step measurement of each discovered URL.
2) A prototype of the corresponding new experiment `websteps` which uses the control measurement of the `testhelper` to know which URLs to measure, and what to expect. The prototype does not yet have:
* unit and integration tests,
* an analysis tool to compare the control and the probe measurement.
This PR is my final deliverable as it is the outcome of the trials, considerations and efforts of my GSoC weeks at OONI.
It fully integrates HTTP/3 (QUIC) support which has been only used in the `urlgetter` experiment until now.
Related issues: https://github.com/ooni/probe/issues/1729 and https://github.com/ooni/probe/issues/1733.
* refactor(netxlite): make sure we always use netmocks
While there, improve logging and make sure we test 100% of the
package with unit tests only. (We don't need to have integration
testing in this package because it's fairly simple/obvious.)
Part of https://github.com/ooni/probe/issues/1505
* further improve logs
What do I mean by pivoting? Netx is currently organized by row:
```
| dialer | quicdialer | resolver | ...
saving | | | | ...
errorwrapping | | | | ...
logging | | | | ...
mocking/sys | | | | ...
```
Every row needs to implement saving, errorwrapping, logging, mocking (or
adapting to the system or to some underlying library).
This causes cross package dependencies and, in turn, complexity. For
example, we need the `trace` package for supporting saving.
And `dialer`, `quickdialer`, et al. need to depend on such a package.
The same goes for errorwrapping.
This arrangement further complicates testing. For example, I am
currently working on https://github.com/ooni/probe/issues/1505 and
I realize it need to repeat integration tests in multiple places.
Let's say instead we pivot the above matrix as follows:
```
| saving | errorwrapping | logging | ...
dialer | | | | ...
quicdialer | | | | ...
logging | | | | ...
mocking/sys | | | | ...
...
```
In this way, now every row contains everything related to a specific
action to perform. We can now share code without relying on extra
support packages. What's more, we can write tests and, judding from
the way in which things are made, it seems we only need integration
testing in `errorwrapping` because it's where data quality matters
whereas, in all other cases, unit testing is fine.
I am going, therefore, to proceed with these changes and "pivot"
`netx`. Hopefully, it won't be too painful.
