[tor-bugs] #20535 [Core Tor/Tor]: A 304 "Not Modified" should update the time to when we next expect a modification

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#20535: A 304 "Not Modified" should update the time to when we next expect a
modification
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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        |     Resolution:
 Keywords:  regression    |  Actual Points:
Parent ID:  #20499        |         Points:  0.5
 Reviewer:                |        Sponsor:
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Comment (by teor):

 Here's my analysis:

 On bootstrap:
 * download_status_increment_attempt increments the schedule for each
 attempt
 * each attempt causes the delay to be increased exponentially (rather than
 using the actual hard-coded Bootstrap schedules)

 After downloading the consensus:
 * download_status_increment_failure doesn't increase the schedule on 503
 (server unavailable), even though it probably should, rather than retrying
 immediately
 * download_status_increment_failure increases the schedule exponentially
 on 304 (not modified), or perhaps doesn't increase the schedule at all
 (see #20499), even though it should probably only increase it up to the
 next time we expect the document to be modified (1 hour)
 * download_status_schedule_get_delay uses the schedule to increase the
 backoff, if the schedule isn't increased, the backoff isn't either (rather
 than using the actual hard-coded Bootstrap schedules)

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/20535#comment:3>
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