[tor-bugs] #20533 [Core Tor/Tor]: Each download request should only increment the failure count once

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#20533: Each download request should only increment the failure count once
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     Reporter:  teor          |      Owner:
         Type:  defect        |     Status:  new
     Priority:  Medium        |  Milestone:  Tor: 0.2.9.x-final
    Component:  Core Tor/Tor  |    Version:
     Severity:  Normal        |   Keywords:  regression
Actual Points:                |  Parent ID:
       Points:  1             |   Reviewer:
      Sponsor:                |
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 From #20499:

 At startup (or reload) the relay fetches the microdesc consensus

 1 minute later it tries to fetch it again
 (update_consensus_networkstatus_downloads() is called) and receives a 304
 response as it hasn't been modified

 download_status_increment_failure() gets called with a status_code of 304

 update_consensus_networkstatus_downloads() gets called again, this time it
 stops at the call to connection_dir_count_by_purpose_and_resource() which
 returns 1 (equal to max_in_progress_conns)

 download_status_increment_failure() gets called again, this time with a
 status_code of 0 (as a result each 304 response results in the fail count
 being increased by 2)

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/20533>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
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