Python Autobahn websocket

Question

I am impressed by all the things Python can do. What I like to know is if I can implement a Python script that can call a JavaScript function.

The Python code I use is detecting an NFC card and reads the Unique ID. Currently I use a Java applet to interact with an HTML page. I think Python is much lighter and better for this.

What I tried is a simple autobahn script server.py and an index.html file.

In the server.py script I implemented this code but it is not working..

#! /usr/bin/env python

from sys import stdin, exc_info
from time import sleep

from smartcard.CardMonitoring import CardMonitor, CardObserver
from smartcard.util import *
import sys

from twisted.internet import reactor
from twisted.python import log
from twisted.web.server import Site
from twisted.web.static import File

from autobahn.websocket import WebSocketServerFactory, \
                               WebSocketServerProtocol, \
                               listenWS


class EchoServerProtocol(WebSocketServerProtocol):

   # a simple card observer that prints inserted/removed cards
    class printobserver(CardObserver):
        """A simple card observer that is notified
        when cards are inserted/removed from the system and
        prints the list of cards
        """

        def update(self, observable, (addedcards, removedcards)):
            for card in addedcards:
                print "+Inserted: ", toHexString(card.atr)
        #call javascript function with <toHexString(card.atr)> 
            for card in removedcards:
                print "-Removed: ", toHexString(card.atr)
        #call javascript function with <toHexString(card.atr)> 

    try:
        print "Insert or remove a smartcard in the system."
        print "This program will exit in 10 seconds"
        print ""
        cardmonitor = CardMonitor()
        cardobserver = printobserver()
        cardmonitor.addObserver(cardobserver)

        sleep(10)

        # don't forget to remove observer, or the
        # monitor will poll forever...
        cardmonitor.deleteObserver(cardobserver)

        import sys
        if 'win32' == sys.platform:
            print 'press Enter to continue'
            sys.stdin.read(1)

    except:
        print exc_info()[0], ':', exc_info()[1]


if __name__ == '__main__':

   if len(sys.argv) > 1 and sys.argv[1] == 'debug':
      log.startLogging(sys.stdout)
      debug = True
   else:
      debug = False

   factory = WebSocketServerFactory("ws://localhost:9000",
                                    debug = debug,
                                    debugCodePaths = debug)

   factory.protocol = EchoServerProtocol
   factory.setProtocolOptions(allowHixie76 = True)
   listenWS(factory)

   webdir = File(".")
   web = Site(webdir)
   reactor.listenTCP(8080, web)

   reactor.run()

In the index file there is a JavaScript function

function NFCid(msg) {
  alert(msg);
}

How can I call this function inside server.py

NFCid(toHexString(card.atr))

Answer 1

It would in general be possible to set up a WebSocket connection that ferries data from a Python process running a web(sockets) server to a JavaScript function. However, you'd have to explicitly setup a WebSocket connection from JavaScript and have it connect to the server process. Then, you can pass any data coming in over the WebSocket connection (eg from Python) to any JavaScript function.