Issue #37: Client-side workarounds.

See also https://trac.torproject.org/projects/tor/ticket/29927

src/vanguards/bandguards.py

@@ -251,6 +251,17 @@ def circ_event(self, event):
         self.circs[event.id].dropped_cells_allowed = 1
       else:
         self.circs[event.id].dropped_cells_allowed = 0
+    # Workaround for Tor bug #29927 (see also
+    # https://github.com/mikeperry-tor/vanguards/issues/37).
+    # Class 4: Mysterious client-side cases of dropped cells
+    # and protocol errors.
+    elif event.purpose == "HS_CLIENT_REND" or event.purpose == "GENERAL":
+      self.circs[event.id].dropped_cells_allowed = 1
+    elif event.purpose == "HS_CLIENT_INTRO":
+      if event.hs_state == "HSCI_DONE":
+        self.circs[event.id].dropped_cells_allowed = 1
+      else:
+        self.circs[event.id].dropped_cells_allowed = 0
 
     # Consider all BUILT circs that have a specific HS purpose
     # to be "in_use".
@@ -324,15 +335,26 @@ def circ_minor_event(self, event):
         if event.old_purpose == "HS_CLIENT_INTRO" \
            and event.old_hs_state != "HSCI_DONE":
           self.circs[event.id].dropped_cells_allowed = 1
-
       # Workaround for Tor bug #29700 (see also
       # https://github.com/mikeperry-tor/vanguards/issues/37).
       # Class 3: Service rend circs can sometimes fail ntor handshake on extend
-      if event.purpose == "HS_SERVICE_REND":
+      elif event.purpose == "HS_SERVICE_REND":
         if event.hs_state == "HSSR_CONNECTING":
           self.circs[event.id].dropped_cells_allowed = 1
         else:
           self.circs[event.id].dropped_cells_allowed = 0
+      # Workaround for Tor bug #29927 (see also
+      # https://github.com/mikeperry-tor/vanguards/issues/37).
+      # Class 4: Mysterious client-side cases of dropped cells
+      # and protocol errors.
+      elif event.purpose == "HS_CLIENT_REND":
+        self.circs[event.id].dropped_cells_allowed = 1
+      elif event.purpose == "HS_CLIENT_INTRO":
+        if event.hs_state == "HSCI_DONE":
+          self.circs[event.id].dropped_cells_allowed = 1
+        else:
+          self.circs[event.id].dropped_cells_allowed = 0
+
 
     plog("DEBUG", event.raw_content())
 
@@ -464,6 +486,11 @@ def check_circuit_limits(self, circ):
                        +"(in state %s %s; old state %s %s).", circ.circ_id,
                        str(circ.purpose), str(circ.hs_state),
                        str(circ.old_purpose), str(circ.old_hs_state))
+      else:
+        plog("INFO", "Tor bug #29927: Got a dropped cell on circ %s "\
+                       +"(in state %s %s; old state %s %s).", circ.circ_id,
+                       str(circ.purpose), str(circ.hs_state),
+                       str(circ.old_purpose), str(circ.old_hs_state))
 
     if CIRC_MAX_MEGABYTES > 0 and \
        circ.total_bytes() > CIRC_MAX_MEGABYTES*_BYTES_PER_MB:

tests/test_bandguards.py

@@ -278,6 +278,8 @@ def test_bwstats():
                                              "HS_CLIENT_REND",
                                              "PATH_BIAS_TESTING"))
   check_dropped_bytes(state, controller, circ_id, 0, 1)
+  assert controller.closed_circ == None
+  check_dropped_bytes(state, controller, circ_id, 0, 1)
   assert controller.closed_circ == str(circ_id)
 
   # Test that no dropped cells are allowed on not-built circ.
@@ -301,6 +303,8 @@ def test_bwstats():
   controller.closed_circ = None
   state.circ_event(built_general_circ(circ_id))
   check_dropped_bytes(state, controller, circ_id, 1000, 1)
+  assert controller.closed_circ == None
+  check_dropped_bytes(state, controller, circ_id, 1000, 1)
   assert controller.closed_circ == str(circ_id)
 
   # Test that with #25573, no dropped cell is allowed
@@ -317,6 +321,8 @@ def test_bwstats():
   state.tor_has_25573 = True
   state.circ_event(built_general_circ(circ_id))
   check_dropped_bytes(state, controller, circ_id, 1000, 1)
+  assert controller.closed_circ == None
+  check_dropped_bytes(state, controller, circ_id, 1000, 1)
   assert controller.closed_circ == str(circ_id)