[metrics-bugs] #33421 [Metrics/Onionperf]: Track which Guard is used for experimental measurements

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#33421: Track which Guard is used for experimental measurements
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 Reporter:  acute                      |          Owner:  metrics-team
     Type:  enhancement                |         Status:  needs_information
 Priority:  Medium                     |      Milestone:
Component:  Metrics/Onionperf          |        Version:
 Severity:  Normal                     |     Resolution:
 Keywords:  metrics-team-roadmap-2020  |  Actual Points:
Parent ID:  #33321                     |         Points:  3
 Reviewer:                             |        Sponsor:  Sponsor59-must
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Comment (by karsten):

 Thanks for the clarification!

 So, we already track which relays are being used in a circuit, including
 the entry guard in first position. What we do not yet track is whether the
 first relay in that circuit was selected as guard at the time of launching
 the circuit.

 I wonder if we can use Tor's `GUARD` event in the same way as we're using
 the `BUILDTIMEOUT_SET` event. That means, when parsing through the log of
 controller events, we maintain the set of current guards that we update
 whenever we see a new `GUARD` event. And when we parse a `CIRC` event we
 compare that set to the first relay in the circuit and include that
 information in the parsed circuit object. Would that solve the issue?

 Next question (to acute and/or myself): Why do I not see any `GUARD`
 events in the current controller logs? Even the test instance that I just
 started that doesn't use `UseEntryGuards 0` doesn't emit them. Hmm.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/33421#comment:9>
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