The previous code would report all failures to build a circuit as
failures of the guard. But of course that's not right: If we
fail to extend to the second or third hop, that might or might not
be the guard's fault.
Now we use the "pending status" feature of the GuardMonitor type so
that an early failure is attributed to the guard, but a later
failure is attributed as "Indeterminate". Only a complete circuit
is called a success. We use a new "GuardStatusHandle" type here so
that we can report the status early if there is a timeout.
(When we're building a path with a guard, we need to tell the guard
manager whether the path succeeded, and we need to wait to hear
whether the guard is usable.)
The advantage here is that we no longer have to use a futures-aware
Mutex, or a blocking send operation, and therefore can simplify a
bunch of the GuardMgr APIs to no longer be async. That'll avoid
having to propagate the asyncness up the stack.
The disadvantage is that unbounded channels are just that: nothing
in the channel prevents us from overfilling it. Fortunately, the
process that consumes from the channel shouldn't block much, and
the channel only gets filled when we're planning a circuit path.
I tried using -Z minimal-versions to downgrade all first-level
dependencies to their oldest permitted versions, and found that we
were apparently depending on newer features of all three crates.
I'm kind of surprised there were only three.
Also, refactor our message handling to be more like the tor_proto
reactors. The previous code had a bug where, once the stream of
events was exhausted, we wouldn't actually get any more
notifications.
There are some missing parts here (like persistence and tests)
and some incorrect parts (I am 90% sure that the "exploratory
circuit" flag is bogus). Also it is not integrated with the circuit
manager code.
The limitations with toml seemed to be reaching a head, and I wasn't
able to refactor the guardmgr code enough to actually have its state
be serializable as toml. Json's limitations are much narrower.
The affected API (getgrouplist) isn't one that we use, directly or
transitively. We can't just upgrade immediately, since the ctrlc
crate is currently stuck on the older version of nix.
Nick Mathewson
Trinity Pointard
Jani Monoses