[tor-bugs] #23817 [Core Tor/Tor]: Tor re-tries directory mirrors that it knows are missing microdescriptors

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#23817: Tor re-tries directory mirrors that it knows are missing microdescriptors
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 Reporter:  teor                                 |          Owner:  (none)
     Type:  defect                               |         Status:
                                                 |  needs_review
 Priority:  Medium                               |      Milestone:  Tor:
                                                 |  0.3.2.x-final
Component:  Core Tor/Tor                         |        Version:
 Severity:  Normal                               |     Resolution:
 Keywords:  tor-guard, tor-hs, prop224,          |  Actual Points:
  032-backport? 031-backport? spec-change        |
Parent ID:  #21969                               |         Points:
 Reviewer:                                       |        Sponsor:
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Comment (by asn):

 Replying to [comment:52 nickm]:
 > So, `num_reachable_filtered_guards()` is O(N) in the total number of
 guard nodes in the network; I don't think we want to re-run it for every
 guard that we check in `guard_obeys_md_dirserver_restriction`, or this
 will be an O(N^2^) computation.

 Thanks for pointing this out. I think my idea of moving the guard-size
 check on restriction enforcing time, instead of keeping it at restriction
 creation time was a bad one.

 The guard restriction is applied on the `circuit_guard_state_t` which gets
 applied on the `dir_connection_t` so everytime we want to fetch new mds we
 will do the guard-size check and create a new restriction, which works
 fine with the current design, so no need to change it.

 I have two new branches with annoying names:
 `bug23817_usable_filtered_033_v2` and `bug23817_usable_filtered_032_v2`
 which should be the minimal change here.

 Let me know how you feel about this one.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/23817#comment:54>
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