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Draft: Implement a retry-after-delay mechanism for FallbackDirs

Closed Draft: Implement a retry-after-delay mechanism for FallbackDirs
nickm/arti:fallback_status into main
Closed Nick Mathewson requested to merge nickm/arti:fallback_status into main
  1. Mar 25, 2022
  3. Mar 23, 2022
    • Nick Mathewson's avatar
      Treat "All fallbacks down" similar to "all guard down". · 26431bc5
      Nick Mathewson authored 
      (Instead of retrying immediately, wait till at least one will be up.)
      26431bc5
    • Nick Mathewson's avatar
      Add and use status reporting APIs for FallbackSet. · d25638cf
      Nick Mathewson authored 
      Internally to the circmgr crate, we use a FallbackMonitor object
with an API similar to the GuardStatusMonitor.  Externally, we have
reporting functions to note success and failure.

With this change, we now notice when fallbacks have failed or given
us useless information, and we mark them as unusable for a while
before we consider retrying them.  This should be sufficient to
solve the problem observed in #406, where some kinds of failures to
connect to (or download from) fallback directories resulted in an
obnoxious busy-loop.
      d25638cf
    • Nick Mathewson's avatar
      circmgr: Add Status information to FallbackSet. · 44556261
      Nick Mathewson authored 
      This field will track when we can retry, and is now used to see
which fallbacks are usable.  (It is not yet set on success or
failure.)

The design here is a bit tricky; I've been through a few iterations
of it, and this is the one that seems like it will give us
reasonable lifetimes and behavior.
      44556261
    • Nick Mathewson's avatar
      Turn "Set of fallback directories" into its own type. · 5747703b
      Nick Mathewson authored 
      We're going to want to add some intelligence here, and having an
opaque type for this object will help us in the long run.
      5747703b
    • Nick Mathewson's avatar
      Move FallbackDir to tor-circmgr. · 310f13fc
      Nick Mathewson authored 
      This movement will help with #406, which requires that we track the
success and failure status of our fallback directories.
      310f13fc