[tor-bugs] #28141 [Core Tor/sbws]: Catch DNS-related unhandled exception

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#28141: Catch DNS-related unhandled exception
-------------------------------+---------------------------------
     Reporter:  pastly         |      Owner:  (none)
         Type:  defect         |     Status:  new
     Priority:  Medium         |  Milestone:  sbws 1.0 (MVP must)
    Component:  Core Tor/sbws  |    Version:
     Severity:  Critical       |   Keywords:
Actual Points:                 |  Parent ID:
       Points:                 |   Reviewer:
      Sponsor:                 |
-------------------------------+---------------------------------
 I've been running sbws for about 5 days without checking on it.

 The first time the following exception appeared in my logs, I went from
 seeing a variety of thread names in the logs to only seeing a couple. This
 indicates to me this is (a/the) exception that has been causing sbws to
 fallback to just one measurement thread. (Later instances of this
 exception don't change anything)

 {{{
 2018-10-21 11:09:45,926 ERROR Thread-6 scanner.py:259 -
 dispatch_worker_thread - Unhandled exception in worker thread
 Traceback (most recent call last):
   File "/home/mtraudt/.pyenv/versions/3.5.6/envs/sbws-
 venv-3.5.6/lib/python3.5/site-packages/sbws/core/scanner.py", line 257, in
 dispatch_worker_thread
     return measure_relay(*a, **kw)
   File "/home/mtraudt/.pyenv/versions/3.5.6/envs/sbws-
 venv-3.5.6/lib/python3.5/site-packages/sbws/core/scanner.py", line 171, in
 measure_relay
     dest = destinations.next()
   File "/home/mtraudt/.pyenv/versions/3.5.6/envs/sbws-
 venv-3.5.6/lib/python3.5/site-packages/sbws/lib/destination.py", line 251,
 in next
     self._perform_usability_test()
   File "/home/mtraudt/.pyenv/versions/3.5.6/envs/sbws-
 venv-3.5.6/lib/python3.5/site-packages/sbws/lib/destination.py", line 182,
 in _perform_usability_test
     possible_exits = [e for e in self._rl.exits
   File "/home/mtraudt/.pyenv/versions/3.5.6/envs/sbws-
 venv-3.5.6/lib/python3.5/site-packages/sbws/lib/destination.py", line 183,
 in <listcomp>
     if e.can_exit_to(dest.hostname, dest.port)]
   File "/home/mtraudt/.pyenv/versions/3.5.6/envs/sbws-
 venv-3.5.6/lib/python3.5/site-packages/sbws/lib/relaylist.py", line 123,
 in can_exit_to
     host = resolve(host)[0]
   File "/home/mtraudt/.pyenv/versions/3.5.6/envs/sbws-
 venv-3.5.6/lib/python3.5/site-packages/sbws/globals.py", line 71, in
 resolve
     for result in socket.getaddrinfo(hostname, 0):
   File "/home/mtraudt/.pyenv/versions/3.5.6/lib/python3.5/socket.py", line
 733, in getaddrinfo
     for res in _socket.getaddrinfo(host, port, family, type, proto,
 flags):
 socket.gaierror: [Errno -2] Name or service not known
 2018-10-21 11:09:45,926 ERROR Thread-10 scanner.py:314 - closure -
 Unhandled exception caught while measuring ViDiSrv: <class
 'socket.gaierror'> [Errno -2] Name or service not known
 }}}

 Branch incoming.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/28141>
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