Archive for the ‘Rants’ Category

DBUS api

Saturday, July 4th, 2009

Some days ago i wrote a post about avahi, here is the second part of it, the rant about the API it provides.

import dbus, gobject, avahi
from dbus import DBusException
from dbus.mainloop.glib import DBusGMainLoop
 
# Looks for iTunes shares
 
TYPE = '_daap._tcp'
 
def service_resolved(*args):
    print 'service resolved'
    print 'name:', args[2]
    print 'address:', args[7]
    print 'port:', args[8]
 
def print_error(*args):
    print 'error_handler'
    print args[0]
 
def myhandler(interface, protocol, name, stype, domain, flags):
    print "Found service '%s' type '%s' domain '%s' " % (name, stype, domain)
 
    if flags & avahi.LOOKUP_RESULT_LOCAL:
            # local service, skip
            pass
 
    server.ResolveService(interface, protocol, name, stype,
        domain, avahi.PROTO_UNSPEC, dbus.UInt32(0),
        reply_handler=service_resolved, error_handler=print_error)
 
loop = DBusGMainLoop()
 
bus = dbus.SystemBus(mainloop=loop)
 
server = dbus.Interface( bus.get_object(avahi.DBUS_NAME, '/'),
        'org.freedesktop.Avahi.Server')
 
sbrowser = dbus.Interface(bus.get_object(avahi.DBUS_NAME,
        server.ServiceBrowserNew(avahi.IF_UNSPEC,
            avahi.PROTO_UNSPEC, TYPE, 'local', dbus.UInt32(0))),
        avahi.DBUS_INTERFACE_SERVICE_BROWSER)
 
sbrowser.connect_to_signal("ItemNew", myhandler)
 
gobject.MainLoop().run()

This is the example i cited in my earlier post as well. Let’s play a little game, whoever spots most retarded things in there wins ;) .

  • Requires event loop too to scan network
  • Depends on glib
  • Requires the definition of 3 new objects (bus, server, sbrowser) and 2 functions (ignoring the error reporting one) before you can get the most basic “client” functionality!
  • service_resolved get’s in a tuple (btw, it has 11 elements), leaving you without an idea what might be in there
  • you pass one interface into another, WTF?!!?

But remember that is just “client” side, you’ll get to call lots of overcomplicated functions on the publish side as well!

Remeber the *args from above? It surely must make sense once you see it’s content, right? Guess again.

(dbus.Int32(4), dbus.Int32(0), dbus.String(u'b00'), dbus.String(u'_pydra._tcp'), dbus.String(u'local'), dbus.String(u'b00.local'), dbus.Int32(0), dbus.String(u'75.17.116.98'), dbus.UInt16(11890), dbus.Array([dbus.Array([dbus.Byte(102)], signature=dbus.Signature('y')), dbus.Array([dbus.Byte(116)], signature=dbus.Signature('y')), dbus.Array([dbus.Byte(119)], signature=dbus.Signature('y'))], signature=dbus.Signature('ay')), dbus.UInt32(13L))

Let’s play the same game as above with this piece of code :-)

  • it has very lousy integration with python types
  • the TXT record is an array of arrays of bytes, just so that you can send a string (notice how avahi core developer says: “Yes indeed, python-dbus is a large pile of bugs. “) :/
  • notice the dbus.Array([dbus.Array([dbus.Byte(102)], i dared to send a normal string and all i got was the last character!
  • there must be a bright side? You can practice your function defining skills so that you can send strings!
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