We define "coming back online" as happening when a guard attempt
succeeds, if that attempt that was launched when we seemed to be
offline.
We define "seeming to be offline" as having all of our primary
guards marked unreachable, and having received no incoming network
traffic in a while.
Closes#216.
This is based on @eta's patches for !118 and !119: Since we already
have an unbounded channel, we don't need to use an elaborate mess of
one-shot senders. We can just use the unbounded_send() method,
which also lets us enqueue a message without having to await.
Closes#219.
Instead of putting a fully qualified name in the text, in most cases
we should just use the short name of the type or function we're
referring to.
In other words, instead of saying [`crate::module::Foo`], we should
typically say [`Foo`](crate::module::Foo).
The Futureproof<T> type lets you serialize and deserialize types whose
representations might change (most useful for enums that might grow
additional variants). It uses #[serde(untagged)] to accomplish this.
This gets used in order to make the `disabled` field of `Guard` more
robust against future guard disablement reasons being added.
A test was also added to verify correct behaviour of the new type.
As per arti#175, we'd like to be able to handle newer Arti versions
storing additional state in the persisted state files, without dropping
this data on the floor when we write out changes to these files.
Use the #[serde(flatten)] mechanism to achieve this, by adding catch-all
HashMap<String, JsonValue> fields to all structs that are at risk of
this happening to them.
We must not apply our new path-bias behavior (where we blame a guard
if it gives us too many indeterminate circuit failures) if the path
was not chosen at random. If too many random paths fail, we know
that's suspicious, since the other relays are a random sample. But
if a bunch of user-provided paths fail, that could simply be because
the user's chosen exit is down.
We now track, for every guard: the total number of successful
circuits we've built through it, along with the total number of
"indeterminate" circuits.
Recall that a circuit's status is "indeterminate" if it has failed
for a reason that _might_ be the guard's fault, or might not be the
guard's fault. For example, if extending to the second hop of the
circuit fails, we have no way to know whether the guard deliberately
refused to connect there, or whether the second hop is just offline.
But we don't want to forgive all indeterminate circuit failures: if
we did, then a malicious guard could simply reject any second hops
that it didn't like, thereby filtering the client into a chosen
set of circuits.
As a stopgap solution, this patch now makes guards become
permanently disabled if the fraction of their circuit failures
becomes too high.
See also general-purpose path bias selection (arti#65), and Mike's
idea for changing the guard reachability definition (torspec#67).
This patch doesn't do either of those.
Closes#185.
The `get_relay` function was confusing, since it would return None if
the relay was present, but wasn't actually a guard. We only used it
in one place, and in that one place we used it wrong, leading to a
panic bug.
Fixes#193.
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.
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.
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.
Nick Mathewson
eta