This is a very simple example of how to use native messaging to exchange messages between a WebExtension and a native application.

The WebExtension, which can be found under "add-on", connects to the native application and listens to messages from it. It then sends a message to the native application when the user clicks on the WebExtension's browser action. The message payload is just "ping".

The native application, which can be found under "app", listens for messages from the WebExtension. When it receives a message, the native application sends a response message whose payload is just "pong". The native application is written in Python.

Setup

To get this working, there's a little setup to do.

Linux/macOS setup

(macOS) Store this extension in a location other than the Desktop, Documents, or Downloads folders in your home directory. macOS has access restrictions on these directories that prevent the Python script from executing as expected.
Make sure you have Python 3 installed, and your system's PATH environment variable includes the path to Python. You can check by executing this command:
```
> which python3
/usr/local/bin/python3
```
If you don't see the path for Python, install Python 3. See Using Python on Unix platforms (for Linux) or Using Python on a Mac. After making this change, restart Firefox so it picks up the new PATH environment variable.
Make sure that the file permissions for app/ping_pong.py include the execute permission. See this article by RedHat for more information.
Update the "path" field in app/ping_pong.json to be the full path to your app/ping_pong.py file.

For example, if you cloned this repository into /Users/MDN/webextensions-examples/, you would update the file like this:
```
"path": "/Users/MDN/webextensions-examples/native-messaging/app/ping_pong.py"
```
Copy app/ping_pong.json to the correct location on your computer. There are too many options to list here; see the Linux and macOS secitons of App manifest location to find the correct location for your OS and personal preference.

Windows setup

Make sure that you have Python 3 installed and that your system's PATH environment variable includes the path to Python. See Using Python on Windows. After making this change, restart Firefox so it picks up the new PATH environment variable.
Update the "path" field in app\ping_pong.json to use the full path of app\ping_pong_win.bat on your computer. Be aware that you must escape the Windows directory separator (\).

For example, if you cloned this repository into C:\Users\MDN\webextensions-examples\, you update the JSON file like this:
```
"path": "C:\\Users\\MDN\\webextensions-examples\\native-messaging\\app\\ping_pong_win.bat"
```
Update app\ping_pong_win.bat to use the full path of app\ping_pong.py on your computer.
Add a registry key containing the full path of app\ping_pong.json on your computer. See App manifest location to find details of the registry key to add.

To assist in troubleshooting on Windows, there is a script next to this README file named check_config_win.py. Running this in a command shell should help you discover of any problems.

Testing the example

First, install the add-on. Visit about:debugging#/runtime/this-firefox or, from about:debugging click "This Firefox" (or "This Nightly" in the Nightly version of Firefox), click "Load Temporary Add-on", and open the add-on's manifest.json.

Now, open the extension's console using the "Inspect" button. This is where you see communication between the browser and native app.

You should see a new browser action icon in the toolbar. Click it. You should see output like this in the console:

Sending: ping
Received: pong

If you don't see this output, see the Troubleshooting guide for ideas.