Rather than passing functions to construct complex objects such
as Dialer and QUICDialer, pass interface implementations.
Ensure that a nil implementation does not cause harm.
Make Saver implement the correct interface either directly or
indirectly. We need to implement the correct interface indirectly
for TCP conns (or connected UDP sockets) because we have two
distinct use cases inside netx: observing just the connect event
and observing just the I/O events.
With this change, the construction of composed Dialers and
QUICDialers is greatly simplified and more obvious.
Part of https://github.com/ooni/probe/issues/2121
The code that is now into the tracex package was written a long
time ago, so let's start to make it more in line with the coding
style of packages that were written more recently.
I didn't apply all the changes I'd like to apply in a single diff
and for now I am committing just this diff.
Broadly, what we need to do is:
1. improve documentation
2. ~always use pointer receivers (object receives have the issue
that they are not mutable by accident meaning that you can mutate
them but their state do not change after the call returns, which
is potentially a source of bugs in case you later refactor to use
a pointer receiver, so always use pointer receivers)
3. ~always avoid embedding (let's say we want to avoid embedding
for types we define and it's instead fine to embed types that are
defined in the stdlib: if later we add a new method, we will not
see a broken build and we'll probably forget to add the new method
to all wrappers -- conversely, if we're wrapping rather than
embedding, we'll see a broken build and act accordingly)
4. prefer unit tests and group tests by type being tested rather
than using a flat structure for tests
There's a coverage slippage that I'll compensate in a follow-up diff where I'll focus on unit testing.
Reference issue: https://github.com/ooni/probe/issues/2121
This diff creates a new package under netx called tracex that
contains everything we need to perform measurements using events
tracing and postprocessing (which is the technique with which
we implement most network experiments).
The general idea here is to (1) create a unique package out of
all of these packages; (2) clean up the code a bit (improve tests,
docs, apply more recent code patterns); (3) move the resulting
code as a toplevel package inside of internal.
Once this is done, netx can be further refactored to avoid
subpackages and we can search for more code to salvage/refactor.
See https://github.com/ooni/probe/issues/2121
