trezor: don't let bridge transport failing block all other transports

[trezor] connecting to device at bridge:hid...
[trezor] connected to device at bridge:hid...
Traceback (most recent call last):
  File "...\electrum\electrum\base_wizard.py", line 255, in choose_hw_device
    u = devmgr.unpaired_device_infos(None, plugin, devices=scanned_devices)
  File "...\electrum\electrum\plugin.py", line 501, in unpaired_device_infos
    client = self.create_client(device, handler, plugin)
  File "...\electrum\electrum\plugin.py", line 374, in create_client
    client = plugin.create_client(device, handler)
  File "...\electrum\electrum\plugins\trezor\trezor.py", line 124, in create_client
    client = self.client_class(transport, handler, self)
  File "...\electrum\electrum\plugins\trezor\client.py", line 7, in __init__
    ProtocolMixin.__init__(self, transport=transport)
  File "...\Python36-32\lib\site-packages\trezorlib\client.py", line 444, in __init__
    self.init_device()
  File "...\Python36-32\lib\site-packages\trezorlib\client.py", line 454, in init_device
    self.features = expect(proto.Features)(self.call)(init_msg)
  File "...\Python36-32\lib\site-packages\trezorlib\client.py", line 115, in wrapped_f
    ret = f(*args, **kwargs)
  File "...\Python36-32\lib\site-packages\trezorlib\client.py", line 129, in wrapped_f
    client.transport.session_begin()
  File "...\Python36-32\lib\site-packages\trezorlib\transport\__init__.py", line 42, in session_begin
    self.open()
  File "...\Python36-32\lib\site-packages\trezorlib\transport\bridge.py", line 69, in open
    raise TransportException('trezord: Could not acquire session' + get_error(r))
trezorlib.transport.TransportException: trezord: Could not acquire session (error=400 str=wrong previous session)
[DeviceMgr] error getting device infos for trezor: trezord: Could not acquire session (error=400 str=wrong previous session)

electrum/base_wizard.py

@@ -27,6 +27,7 @@ import os
 import sys
 import traceback
 from functools import partial
+from typing import List, TYPE_CHECKING, Tuple
 
 from . import bitcoin
 from . import keystore
@@ -41,6 +42,9 @@ from .util import UserCancelled, InvalidPassword, WalletFileException
 from .simple_config import SimpleConfig
 from .plugin import Plugins
 
+if TYPE_CHECKING:
+    from .plugin import DeviceInfo
+
 
 # hardware device setup purpose
 HWD_SETUP_NEW_WALLET, HWD_SETUP_DECRYPT_WALLET = range(0, 2)
@@ -230,7 +234,7 @@ class BaseWizard(object):
         # check available plugins
         supported_plugins = self.plugins.get_hardware_support()
         # scan devices
-        devices = []
+        devices = []  # type: List[Tuple[str, DeviceInfo]]
         devmgr = self.plugins.device_manager
         try:
             scanned_devices = devmgr.scan_devices()
@@ -254,6 +258,7 @@ class BaseWizard(object):
                     # FIXME: side-effect: unpaired_device_info sets client.handler
                     u = devmgr.unpaired_device_infos(None, plugin, devices=scanned_devices)
                 except BaseException as e:
+                    traceback.print_exc()
                     devmgr.print_error(f'error getting device infos for {name}: {e}')
                     indented_error_msg = '    '.join([''] + str(e).splitlines(keepends=True))
                     debug_msg += f'  {name}: (error getting device infos)\n{indented_error_msg}\n'
@@ -278,7 +283,8 @@ class BaseWizard(object):
         for name, info in devices:
             state = _("initialized") if info.initialized else _("wiped")
             label = info.label or _("An unnamed {}").format(name)
-            descr = "%s [%s, %s]" % (label, name, state)
+            descr = f"{label} [{name}, {state}]"
+            # TODO maybe expose info.device.path (mainly for transport type)
             choices.append(((name, info), descr))
         msg = _('Select a device') + ':'
         self.choice_dialog(title=title, message=msg, choices=choices, run_next= lambda *args: self.on_device(*args, purpose=purpose))

electrum/plugin.py

@@ -485,7 +485,7 @@ class DeviceMgr(ThreadJob, PrintError):
               'its seed (and passphrase, if any).  Otherwise all bitcoins you '
               'receive will be unspendable.').format(plugin.device))
 
-    def unpaired_device_infos(self, handler, plugin, devices=None):
+    def unpaired_device_infos(self, handler, plugin: 'HW_PluginBase', devices=None):
         '''Returns a list of DeviceInfo objects: one for each connected,
         unpaired device accepted by the plugin.'''
         if not plugin.libraries_available:
@@ -498,7 +498,11 @@ class DeviceMgr(ThreadJob, PrintError):
         for device in devices:
             if device.product_key not in plugin.DEVICE_IDS:
                 continue
-            client = self.create_client(device, handler, plugin)
+            try:
+                client = self.create_client(device, handler, plugin)
+            except BaseException as e:
+                self.print_error(f'failed to create client for {plugin.name} at {device.path}: {repr(e)}')
+                continue
             if not client:
                 continue
             infos.append(DeviceInfo(device, client.label(), client.is_initialized()))

electrum/plugins/trezor/trezor.py

@@ -121,6 +121,7 @@ class TrezorPlugin(HW_PluginBase):
             return
 
         self.print_error("connected to device at", device.path)
+        # note that this call can still raise!
         client = self.client_class(transport, handler, self)
 
         # Try a ping for device sanity