DBUS api

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 &amp; 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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Tags: Application programming interface, dbus, rant

This entry was posted on Saturday, July 4th, 2009 at 10:19 am and is filed under Rants. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.