trezor: use TREZOR_PATH environment variable to specify device path

libagent/device/trezor.py

@@ -106,13 +106,13 @@ class Trezor(interface.Device):
 
     def connect(self):
         """Enumerate and connect to the first available interface."""
-        transports = self._defs.enumerate_transports()
+        transport = self._defs.find_device()
-        if not transports:
+        if not transport:
             raise interface.NotFoundError('{} not connected'.format(self))
 
-        log.debug('transports: %s', transports)
+        log.debug('using transport: %s', transport)
         for _ in range(5):  # Retry a few times in case of PIN failures
-            connection = self._defs.Client(transport=transports[0],
+            connection = self._defs.Client(transport=transport,
                                            state=self.__class__.cached_state)
             self._override_pin_handler(connection)
             self._override_passphrase_handler(connection)

libagent/device/trezor_defs.py

@@ -1,13 +1,27 @@
 """TREZOR-related definitions."""
 
 # pylint: disable=unused-import,import-error
+import os
+import logging
 
 from trezorlib.client import CallException, PinException
 from trezorlib.client import TrezorClient as Client
 from trezorlib.messages import IdentityType, PassphraseAck, PinMatrixAck, PassphraseStateAck
+
+try:
+    from trezorlib.transport import get_transport
+except ImportError:
     from trezorlib.device import TrezorDevice
+    get_transport = TrezorDevice.find_by_path
+
+log = logging.getLogger(__name__)
 
 
-def enumerate_transports():
+def find_device():
-    """Returns all available transports."""
+    """Selects a transport based on `TREZOR_PATH` env variable.
-    return TrezorDevice.enumerate()
+    If unset, picks first connected device.
+    """
+    try:
+        return get_transport(os.environ.get("TREZOR_PATH"))
+    except Exception as e:
+        log.debug("Failed to find a Trezor device: %s", e)