[tor-bugs] #29500 [Core Tor/Tor]: Broken circuitpadding unittests on appveyor

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#29500: Broken circuitpadding unittests on appveyor
-------------------------------------------------+-------------------------
 Reporter:  asn                                  |          Owner:  (none)
     Type:  defect                               |         Status:
                                                 |  needs_revision
 Priority:  High                                 |      Milestone:  Tor:
                                                 |  0.4.0.x-final
Component:  Core Tor/Tor                         |        Version:
 Severity:  Normal                               |     Resolution:
 Keywords:  wtf-pad, tor-relay, tor-cell,        |  Actual Points:
  padding, 041-proposed, 040-must                |
Parent ID:  #28631                               |         Points:
 Reviewer:                                       |        Sponsor:
-------------------------------------------------+-------------------------
Changes (by teor):

 * status:  needs_review => needs_revision


Comment:

 Replying to [comment:15 mikeperry]:
 > ...
 > Might as well set needs_review. I suppose there could be an argument for
 handling the case where monotime_absolute_usec() might return 0 in the
 wild, but I don't think that is actually possible there (this code only
 runs on relays upon receiving valid onionskins for circuit extension..
 lots of time should have passed since monotime_init() at that point).

 It doesn't matter how much time has passed, the monotime_*diff_*()
 functions can still return zero. So all code that uses the
 monotime_*diff_*() functions needs to handle zero correctly.

 See #29640, in particular:
 {{{
 Zero deltas happen more often:
  *  - on Windows (due to an OS bug),
  *  - when using monotime_coarse, or on systems with low-resolution
 timers,
  *  - on platforms where we emulate monotonic time using wall-clock time,
 and
  *  - when using time units that are larger than nanoseconds (due to
  *    truncation on division).
 }}}

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/29500#comment:17>
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