Check config on Windows (#292)

* add in a basic Windows config check script

* feedback from wbamberg

native-messaging/README.md

@@ -21,6 +21,8 @@ To get this working, there's a little setup to do.
 3. Edit "ping_pong_win.bat" to refer to the location of "ping_pong.py" on your computer.
 4. Add a registry key containing the path to "ping_pong.json" on your computer. See [App manifest location ](https://developer.mozilla.org/en-US/Add-ons/WebExtensions/Native_messaging#App_manifest_location) to find details of the registry key to add.
 
+To assist in troubleshooting on Windows, there is a script called `check_config_win.py`. Running this from the command line should give you an idea of any problems.
+
 ## Testing the example ##
 
 Then just install the add-on as usual, by visiting about:debugging, clicking "Load Temporary Add-on", and selecting the add-on's "manifest.json".
@@ -29,5 +31,5 @@ You should see a new browser action icon in the toolbar. Open the console ("Tool
 
     Sending: ping
     Received: pong
-    
+
 If you don't see this output, see the [Troubleshooting guide](https://developer.mozilla.org/en-US/Add-ons/WebExtensions/Native_messaging#Troubleshooting) for ideas.

native-messaging/check_config_win.py

@@ -0,0 +1,64 @@
+'''
+A Python script that attempts to check that the configuration of your
+nativeMessaging app is set up correctly
+
+Currently requires Python 3.
+
+If you find more issues with setting this up, let's see if we can add to this
+script.
+'''
+import json
+import os
+import re
+import winreg
+
+key_path = 'Software\\Mozilla\\NativeMessagingHosts\\ping_pong'
+# Assuming current user overrides local machine.
+key_roots = ['HKEY_CURRENT_USER', 'HKEY_LOCAL_MACHINE']
+
+found_key = False
+
+for root in key_roots:
+    key = winreg.OpenKey(getattr(winreg, root), key_path)
+    try:
+        print('Checking:', root, key_path)
+        res = winreg.QueryValueEx(key, '')
+    except FileNotFoundError:
+        print('...error finding key')
+        continue
+
+    found_key = True
+    break
+
+if not found_key:
+    raise ValueError('Could not find a registry entry, aborting.')
+
+json_path = res[0]
+print('Path from registry key is:', json_path)
+if not os.path.exists(json_path):
+    raise ValueError('JSON file does not exist:', json_path)
+
+try:
+    bat_data = json.load(open(json_path, 'r'))
+except json.decoder.JSONDecodeError:
+    raise ValueError('Parsing error. Is {} a JSON file?'.format(json_path))
+
+bat_path = bat_data['path']
+print('Path from JSON is:', bat_path)
+if not os.path.exists(bat_path):
+    raise ValueError('.bat does not exist:', bat_path)
+
+py_lines = open(bat_path, 'r').readlines()
+py_path = None
+for line in py_lines:
+    if line.startswith('call python '):
+        py_path = line[12:].replace('\\\\', '\\').strip()
+
+if not py_path:
+    raise ValueError('No python script in the batch file.')
+
+print('Path from batch file is:', py_path)
+if not os.path.exists(py_path):
+    raise ValueError('Python file does not exist:', py_path)
+
+print('Looks good! Give it a try from Firefox.')