From e9705c820875afb957ef308e81867ea67f259d73 Mon Sep 17 00:00:00 2001
From: Pavol Rusnak <stick@gk2.sk>
Date: Sun, 4 Feb 2018 12:04:34 +0100
Subject: [PATCH] webusb: don't create usb context on WebUsbTransport import

---
 trezorlib/device.py           |  5 +++--
 trezorlib/transport_webusb.py | 29 ++++++++++++++---------------
 2 files changed, 17 insertions(+), 17 deletions(-)

diff --git a/trezorlib/device.py b/trezorlib/device.py
index f1e9d15286..2e3b42b90a 100644
--- a/trezorlib/device.py
+++ b/trezorlib/device.py
@@ -22,6 +22,7 @@ from .transport_hid import HidTransport
 from .transport_udp import UdpTransport
 from .transport_webusb import WebUsbTransport
 
+
 class TrezorDevice(object):
 
     @classmethod
@@ -44,7 +45,7 @@ class TrezorDevice(object):
 
     @classmethod
     def find_by_path(cls, path):
-        if path == None:
+        if path is None:
             try:
                 return cls.enumerate()[0]
             except IndexError:
@@ -61,7 +62,7 @@ class TrezorDevice(object):
         if prefix == WebUsbTransport.PATH_PREFIX:
             return WebUsbTransport.find_by_path(path)
 
-        if prefix ==HidTransport.PATH_PREFIX:
+        if prefix == HidTransport.PATH_PREFIX:
             return HidTransport.find_by_path(path)
 
         raise Exception("Unknown path prefix '%s'" % prefix)
diff --git a/trezorlib/transport_webusb.py b/trezorlib/transport_webusb.py
index 2596747d8c..45a974e0f8 100644
--- a/trezorlib/transport_webusb.py
+++ b/trezorlib/transport_webusb.py
@@ -19,8 +19,9 @@
 from __future__ import absolute_import
 
 import time
-import usb1
 import os
+import atexit
+import usb1
 
 from .protocol_v1 import ProtocolV1
 from .protocol_v2 import ProtocolV2
@@ -35,15 +36,6 @@ ENDPOINT = 1
 DEBUG_INTERFACE = 1
 DEBUG_ENDPOINT = 2
 
-context = usb1.USBContext()
-context.open()
-
-import atexit
-
-def exit_handler():
-    context.close()
-
-atexit.register(exit_handler)
 
 class WebUsbHandle(object):
 
@@ -74,6 +66,7 @@ class WebUsbTransport(Transport):
     '''
 
     PATH_PREFIX = 'webusb'
+    context = None
 
     def __init__(self, device, protocol=None, handle=None, debug=False):
         super(WebUsbTransport, self).__init__()
@@ -97,10 +90,14 @@ class WebUsbTransport(Transport):
     def __str__(self):
         return "%s:%s" % (self.PATH_PREFIX, dev_to_str(self.device))
 
-    @staticmethod
-    def enumerate():
+    @classmethod
+    def enumerate(cls):
+        if cls.context is None:
+            cls.context = usb1.USBContext()
+            cls.context.open()
+            atexit.register(cls.context.close)
         devices = []
-        for dev in context.getDeviceIterator(skip_on_error=True):
+        for dev in cls.context.getDeviceIterator(skip_on_error=True):
             if not (is_trezor1(dev) or is_trezor2(dev) or is_trezor2_bl(dev)):
                 continue
             if not is_vendor_class(dev):
@@ -110,7 +107,7 @@ class WebUsbTransport(Transport):
 
     @classmethod
     def find_by_path(cls, path=None):
-        path = path.replace('%s:' % cls.PATH_PREFIX, '') # Remove prefix from __str__()        
+        path = path.replace('%s:' % cls.PATH_PREFIX, '')  # Remove prefix from __str__()
         for transport in WebUsbTransport.enumerate():
             if path is None or dev_to_str(transport.device) == path:
                 return transport
@@ -177,10 +174,12 @@ def is_trezor2(dev):
 def is_trezor2_bl(dev):
     return (dev.getVendorID(), dev.getProductID()) == DEV_TREZOR2_BL
 
+
 def is_vendor_class(dev):
     configurationId = 0
     altSettingId = 0
     return dev[configurationId][INTERFACE][altSettingId].getClass() == usb1.libusb1.LIBUSB_CLASS_VENDOR_SPEC
 
+
 def dev_to_str(dev):
-    return ':'.join(str(x) for x in ['%03i' % (dev.getBusNumber(), )]  + dev.getPortNumberList())
+    return ':'.join(str(x) for x in ['%03i' % (dev.getBusNumber(), )] + dev.getPortNumberList())