stem: disable pad connections

and create function to set options that can fail because they are
not supported by some Tor versions at runtime.

Fixes bug 28692. Bugfix v0.4.0

sbws/globals.py

@@ -8,6 +8,9 @@ from stem import __version__ as stem_version
 from sbws import __version__
 
 
+from collections import OrderedDict
+
+
 log = logging.getLogger(__name__)
 
 RESULT_VERSION = 4
@@ -32,11 +35,22 @@ TORRC_STARTING_POINT = {
     'LogTimeGranularity': '1',
     'ProtocolWarnings': '1',
 }
-
+# Options that need to be set at runtime.
 TORRC_RUNTIME_OPTIONS = {
+    # The scanner builds the circuits to download the data itself,
+    # so do not let Tor to build them.
     '__DisablePredictedCircuits': '1',
+    # The scanner attach the streams to the circuit itself,
+    # so do not let Tor to attache them.
     '__LeaveStreamsUnattached': '1',
 }
+# Options that can be set at runtime and can fail with some Tor versions
+# The ones that fail will be ignored..
+TORRC_OPTIONS_CAN_FAIL = OrderedDict({
+    # Since currently scanner anonymity is not the goal, ConnectionPadding
+    # is disable to do not send extra traffic
+    'ConnectionPadding': '0'
+    })
 
 PKG_DIR = os.path.abspath(os.path.dirname(__file__))
 DEFAULT_CONFIG_PATH = os.path.join(PKG_DIR, 'config.default.ini')

sbws/util/stem.py

@@ -12,7 +12,8 @@ import copy
 import logging
 import os
 from sbws.globals import fail_hard
-from sbws.globals import TORRC_STARTING_POINT, TORRC_RUNTIME_OPTIONS
+from sbws.globals import (TORRC_STARTING_POINT, TORRC_RUNTIME_OPTIONS,
+                          TORRC_OPTIONS_CAN_FAIL)
 
 log = logging.getLogger(__name__)
 stream_building_lock = RLock()
@@ -179,6 +180,22 @@ def set_torrc_runtime_options(controller):
         log.exception(e)
         exit(1)
 
+
+def set_torrc_options_can_fail(controller):
+    """Set options that can fail, at runtime.
+
+    They can be set at launch, but since the may fail because they are not
+    supported in some Tor versions, it's easier to try one by one at runtime
+    and ignore the ones that fail.
+    """
+    for k, v in TORRC_OPTIONS_CAN_FAIL.items():
+        try:
+            controller.set_conf(k, v)
+        except InvalidArguments as error:
+            log.debug('Ignoring option not supported by this Tor version. %s',
+                      error)
+
+
 def launch_tor(conf):
     assert isinstance(conf, ConfigParser)
     os.makedirs(conf.getpath('tor', 'datadir'), mode=0o700, exist_ok=True)
@@ -211,7 +228,9 @@ def launch_tor(conf):
         fail_hard('Error trying to launch tor: %s', e)
     # And return a controller to it
     cont = _init_controller_socket(conf.getpath('tor', 'control_socket'))
-
+    # Set options that can fail at runtime
+    set_torrc_options_can_fail(cont)
+    # Set runtime options
     set_torrc_runtime_options(cont)
 
     log.info('Started and connected to Tor %s via %s', cont.get_version(),

tests/integration/util/test_stem.py

@@ -18,3 +18,11 @@ def test_set_torrc_runtime_invalidrequest_option_fail(persistent_launch_tor):
         controller.set_conf('ControlSocket', '/tmp/dummy')
     except stem_utils.InvalidRequest as e:
         assert "Unable to set option" in e.message
+
+
+def test_set_torrc_options_can_fail_option_fail(persistent_launch_tor):
+    controller = persistent_launch_tor
+    try:
+        controller.set_conf('BadOption', '0')
+    except stem_utils.InvalidArguments as e:
+        assert "Unknown option" in e.message