[tor-bugs] #31874 [Circumvention]: Automatically test the PTs of bridges

[Tor Bug Tracker & Wiki]

#31874: Automatically test the PTs of bridges
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     Reporter:  phw             |      Owner:  (none)
         Type:  defect          |     Status:  new
     Priority:  Medium          |  Milestone:
    Component:  Circumvention   |    Version:
     Severity:  Normal          |   Keywords:  s30-o23a3
Actual Points:                  |  Parent ID:  #31280
       Points:  10              |   Reviewer:
      Sponsor:  Sponsor30-must  |
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 When a new bridge is set up, our directory authority is testing its OR
 port and assigns it the `Running` flag if the OR port is reachable.
 Nothing however is testing a bridge's PT port(s). This resulted in several
 bridges having an unreachable obfs4 port, e.g., because the operator
 failed to whitelist the obfs4 port in their firewall. Let's fix this by
 testing a bridge's pluggable transport and alerting the operator if the PT
 is unreachable.

 Obfs4proxy has client implementations for most of our currently-deployed
 PTs, so we could start by writing some glue code that takes as input a
 bridge line and makes obfs4proxy (and tor) connect to the given bridge.

 Another question is where we should do the testing from. Our bridge
 authority and BridgeDB are the obvious candidates. Our bridge authority
 currently tests bridges' OR ports but we may not want it to also test PTs.

 Finally, how should we let bridge operators know if their PTs are
 unreachable? We may want to send them an email (if they have contact
 information in their descriptor), and/or make their tor log a warning.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/31874>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
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