[tor-bugs] #20269 [Core Tor/Tor]: bridge users ignore their cached consensus file on startup

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#20269: bridge users ignore their cached consensus file on startup
------------------------------+------------------------------
     Reporter:  arma          |      Owner:
         Type:  defect        |     Status:  new
     Priority:  Medium        |  Milestone:  Tor: unspecified
    Component:  Core Tor/Tor  |    Version:
     Severity:  Normal        |   Keywords:  029-proposed
Actual Points:                |  Parent ID:
       Points:                |   Reviewer:
      Sponsor:                |
------------------------------+------------------------------
 When a client has UseBridges set to 1, and it has a cached microdesc
 consensus in its datadir, when it starts up it loads that consensus file
 from disk, and calls {{{networkstatus_set_current_consensus()}}} on it.

 That function checks
 {{{
   if (flav != usable_consensus_flavor() &&
       !directory_caches_dir_info(options)) {
     /* This consensus is totally boring to us: we won't use it, and we
 won't
      * serve it.  Drop it. */
     goto done;
   }
 }}}

 and in this case, {{{usable_consensus_flavor()}}} checks
 {{{we_use_microdescriptors_for_circuits()}}} which decides
 {{{
     /* If we are configured to use bridges and none of our bridges
      * know what a microdescriptor is, the answer is no. */
     if (options->UseBridges && !any_bridge_supports_microdescriptors())
       return 0;
 }}}

 That is, if you have bridges but you haven't marked any of them up yet,
 then you default to using the old-flavor consensus, so when you read your
 microdesc-consensus from disk, you quietly discard it. This bug results in
 bridge users always fetching a new consensus at start, even when they
 don't need to.

 (Bug reported by skruffy's owner.)

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/20269>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
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