ff2mpv.py: Add Python native client (woodruffw#2)

README.md

@@ -15,11 +15,11 @@ well**!
 
 First, install the addon from [AMO](https://addons.mozilla.org/en-US/firefox/addon/ff2mpv/).
 
-Then, copy `ff2mpv` (the Ruby script) to somewhere of your choice. Make sure it's executable.
+Then, copy either `ff2mpv` (the Ruby script) or `ff2mpv.py` (the Python script) to somewhere of your choice. Make sure it's executable.
 
 Finally, copy `ff2mpv.json` (in this repository) into `~/.mozilla/native-messaging-hosts/`. Open
 it in your editor, and change the `path` field to correspond to the path where you saved
-the `ff2mpv` script.
+the script of your choice.
 
 After that, everything should work.
 

ff2mpv.py

@@ -0,0 +1,34 @@
+#!/usr/bin/env python3
+import sys, struct, json
+from subprocess import Popen, DEVNULL
+
+def main():
+    message = get_message()
+    url = message.get('url')
+    args = ['mpv', '--no-terminal', '--', url]
+    Popen(args, stdin=DEVNULL, stdout=DEVNULL, stderr=DEVNULL)
+    # Need to respond something to avoid "Error: An unexpected error occurred"
+    # in Browser Console.
+    send_message('ok')
+
+
+# https://developer.mozilla.org/en-US/Add-ons/WebExtensions/Native_messaging#App_side
+def get_message():
+    raw_length = sys.stdin.buffer.read(4)
+    if not raw_length:
+        return {}
+    length = struct.unpack('@I', raw_length)[0]
+    message = sys.stdin.buffer.read(length).decode('utf-8')
+    return json.loads(message)
+
+
+def send_message(message):
+    content = json.dumps(message).encode('utf-8')
+    length = struct.pack('@I', len(content))
+    sys.stdout.buffer.write(length)
+    sys.stdout.buffer.write(content)
+    sys.stdout.buffer.flush()
+
+
+if __name__ == '__main__':
+    main()