[tor-commits] [sbws/master] Fix assertion if stem can't find a relay

[pastly at torproject.org]

commit 88fae60bc7b420ca7f36f92b482401b8a7adebaf
Author: Matt Traudt <sirmatt at ksu.edu>
Date:   Wed Jun 6 20:43:42 2018 -0400

    Fix assertion if stem can't find a relay
    
    2018-06-06 04:42:03 ERROR Thread-5 scanner.py:225 - dispatch_worker_thread - Unhandled exception in worker thread
    Traceback (most recent call last):
      File "/home/pastly/src/simple-bw-scanner/sbws/core/scanner.py", line 223, in dispatch_worker_thread
        return measure_relay(*a, **kw)
      File "/home/pastly/src/simple-bw-scanner/sbws/core/scanner.py", line 138, in measure_relay
        dest = destinations.next()
      File "/home/pastly/src/simple-bw-scanner/sbws/lib/destination.py", line 222, in next
        self._perform_usability_test()
      File "/home/pastly/src/simple-bw-scanner/sbws/lib/destination.py", line 171, in _perform_usability_test
        circ_id = self._cb.build_circuit([None, exit.fingerprint])
      File "/home/pastly/src/simple-bw-scanner/sbws/lib/circuitbuilder.py", line 175, in build_circuit
        for r in path]
      File "/home/pastly/src/simple-bw-scanner/sbws/lib/circuitbuilder.py", line 175, in <listcomp>
        for r in path]
    AttributeError: 'NoneType' object has no attribute 'fingerprint'
    2018-06-06 04:42:03 ERROR Thread-10 scanner.py:280 - closure - Unhandled exception caught while measuring torbogen: <class 'AttributeError'> 'NoneType' object has no attribute 'fingerprint'
---
 sbws/lib/circuitbuilder.py | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/sbws/lib/circuitbuilder.py b/sbws/lib/circuitbuilder.py
index d7dbe90..ac5603b 100644
--- a/sbws/lib/circuitbuilder.py
+++ b/sbws/lib/circuitbuilder.py
@@ -147,8 +147,20 @@ class GapsCircuitBuilder(CircuitBuilder):
                 continue
             chosen_fps.append(choice)
             black_fps.append(choice)
-        return [stem_utils.fp_or_nick_to_relay(self.controller, fp)
-                for fp in chosen_fps]
+        relays = []
+        for fp in chosen_fps:
+            relay = stem_utils.fp_or_nick_to_relay(self.controller, fp)
+            if not relay:
+                log.warning(
+                    'We\'re selecting a handful of random relays and stem '
+                    'doesn\'t think one of the fingerprints we gave it goes '
+                    'to a relay. Maybe we got a new consensus since the last '
+                    'time we refreshed our list of relays. In any case, we '
+                    'could try to recover. But failing inside '
+                    '_random_sample_relays is easier. Sorry.')
+                return None
+            relays.append(relay)
+        return relays
 
     def build_circuit(self, path):
         ''' <path> is a list of relays and Falsey values. Relays can be