[macOS] Added QR scanner facility using platform-native helper app.

electrum/qrscanner.py

@@ -40,7 +40,7 @@ except BaseException:
     libzbar = None
 
 
-def scan_barcode(device='', timeout=-1, display=True, threaded=False, try_again=True):
+def scan_barcode_ctypes(device='', timeout=-1, display=True, threaded=False, try_again=True):
     if libzbar is None:
         raise RuntimeError("Cannot start QR scanner; zbar not available.")
     libzbar.zbar_symbol_get_data.restype = ctypes.c_char_p
@@ -69,6 +69,29 @@ def scan_barcode(device='', timeout=-1, display=True, threaded=False, try_again=
     data = libzbar.zbar_symbol_get_data(symbol)
     return data.decode('utf8')
 
+def scan_barcode_osx(*args_ignored, **kwargs_ignored):
+    import subprocess
+    # NOTE: This code needs to be modified if the positions of this file changes with respect to the helper app!
+    # This assumes the built macOS .app bundle which ends up putting the helper app in
+    # .app/contrib/CalinsQRReader/build/Release/CalinsQRReader.app.
+    root_ec_dir = os.path.abspath(os.path.dirname(__file__) + "/../")
+    prog = root_ec_dir + "/" + "contrib/CalinsQRReader/build/Release/CalinsQRReader.app/Contents/MacOS/CalinsQRReader"
+    if not os.path.exists(prog):
+        raise RuntimeError("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)
+        # Just like the zbar implementation -- the main app will hang until the QR window returns a QR code
+        # (or is closed). Communication with the subprocess is done via stdout.
+        # See contrib/CalinsQRReader for the helper app source code.
+        with subprocess.Popen([prog], stdout=subprocess.PIPE) as p:
+            data = p.stdout.read().decode('utf-8').strip()
+        return data
+    except OSError as e:
+        raise RuntimeError("Cannot start camera helper app; {}".format(e.strerror))
+
+scan_barcode = scan_barcode_osx if sys.platform == 'darwin' else scan_barcode_ctypes
+
 def _find_system_cameras():
     device_root = "/sys/class/video4linux"
     devices = {} # Name -> device