[tor-bugs] #23623 [Core Tor/Tor]: hs: Cache current time period number and SRV start time

[Tor Bug Tracker & Wiki]

#23623: hs: Cache current time period number and SRV start time
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     Reporter:  dgoulet       |      Owner:  (none)
         Type:  enhancement   |     Status:  new
     Priority:  Medium        |  Milestone:  Tor: 0.3.2.x-final
    Component:  Core Tor/Tor  |    Version:
     Severity:  Normal        |   Keywords:  tor-hs, tor-sr
Actual Points:                |  Parent ID:
       Points:                |   Reviewer:
      Sponsor:                |
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 For each node in the consensus, we call `node_set_hsdir_index()` which
 gets the time period and srv start time to learn if we are in between TP
 and SRV or not.

 These calls ultimately call `get_voting_schedule()` which allocates memory
 and prints a debug log everytime.

 All of this is actually pretty heavy and they are values we can cache
 because they are all based on the timings of a new consensus (valid_after,
 valid_until, fresh_until).

 It is also called every second by a tor with a hidden service.

 Caching those and updating when we get a new consensus seems a light
 refactoring for a good performance improvement.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/23623>
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