qrscanner: nicer error messages

electrum/qrscanner.py

@@ -27,6 +27,8 @@ import os
 import sys
 import ctypes
 
+from .util import UserFacingException
+from .i18n import _
 from .logging import get_logger
 
 
@@ -53,7 +55,7 @@ except BaseException as e1:
 
 def scan_barcode_ctypes(device='', timeout=-1, display=True, threaded=False):
     if libzbar is None:
-        raise RuntimeError("Cannot start QR scanner; zbar not available.")
+        raise UserFacingException("Cannot start QR scanner: zbar not available.")
     libzbar.zbar_symbol_get_data.restype = ctypes.c_char_p
     libzbar.zbar_processor_create.restype = ctypes.POINTER(ctypes.c_int)
     libzbar.zbar_processor_get_results.restype = ctypes.POINTER(ctypes.c_int)
@@ -62,7 +64,9 @@ def scan_barcode_ctypes(device='', timeout=-1, display=True, threaded=False):
     proc = libzbar.zbar_processor_create(threaded)
     libzbar.zbar_processor_request_size(proc, 640, 480)
     if libzbar.zbar_processor_init(proc, device.encode('utf-8'), display) != 0:
-        raise RuntimeError("Can not start QR scanner; initialization failed.")
+        raise UserFacingException(
+            _("Cannot start QR scanner: initialization failed.") + "\n" +
+            _("Make sure you have a camera connected and enabled."))
     libzbar.zbar_processor_set_visible(proc)
     if libzbar.zbar_process_one(proc, timeout):
         symbols = libzbar.zbar_processor_get_results(proc)
@@ -85,7 +89,7 @@ def scan_barcode_osx(*args_ignored, **kwargs_ignored):
     root_ec_dir = os.path.abspath(os.path.dirname(__file__) + "/../")
     prog = root_ec_dir + "/" + "contrib/osx/CalinsQRReader/build/Release/CalinsQRReader.app/Contents/MacOS/CalinsQRReader"
     if not os.path.exists(prog):
-        raise RuntimeError("Cannot start QR scanner; helper app not found.")
+        raise UserFacingException("Cannot start QR scanner: helper app not found.")
     data = ''
     try:
         # This will run the "CalinsQRReader" helper app (which also gets bundled with the built .app)
@@ -96,7 +100,7 @@ def scan_barcode_osx(*args_ignored, **kwargs_ignored):
             data = p.stdout.read().decode('utf-8').strip()
         return data
     except OSError as e:
-        raise RuntimeError("Cannot start camera helper app; {}".format(e.strerror))
+        raise UserFacingException("Cannot start camera helper app: {}".format(e.strerror))
 
 scan_barcode = scan_barcode_osx if sys.platform == 'darwin' else scan_barcode_ctypes