[tor-bugs] #19836 [Metrics/CollecTor]: Prepare relay descriptor downloader for consensuses published at :30 of the hour

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#19836: Prepare relay descriptor downloader for consensuses published at :30 of the
hour
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     Reporter:  karsten            |      Owner:
         Type:  defect             |     Status:  new
     Priority:  Low                |  Milestone:
    Component:  Metrics/CollecTor  |    Version:
     Severity:  Normal             |   Keywords:
Actual Points:                     |  Parent ID:
       Points:                     |   Reviewer:
      Sponsor:                     |
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 Consensuses have always been published once per hour, so with valid-after
 time :00 in the past.  This might change in the future, as has been
 discussed in the context of consensus diffs, but which might also happen
 independent of those.

 However, CollecTor is not ready for such a change, because
 `currentValidAfter` in `RelayDescriptorDownloader` is always initialized
 with :00 of the hour.  This would prevent us from accepting a consensus
 published at :30.  Of course, when we make such a change we should also
 accept other valid-after times that :00 and :30.

 Testing a fix might require setting up a testing network using Chutney and
 archiving network data produced by that.  That is, we could also create a
 testing environment and write unit tests for this, which we should do
 anyway.  But that shouldn't block us here, unless the fix is more complex
 than I currently anticipate.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/19836>
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