/usr/share/system-config-printer/dnssdresolve.py is in system-config-printer-common 1.5.7-3.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 | #!/usr/bin/python3
## Copyright (C) 2010, 2011, 2012, 2013, 2014 Red Hat, Inc.
## Authors:
##  Tim Waugh <twaugh@redhat.com>
## This program is free software; you can redistribute it and/or modify
## it under the terms of the GNU General Public License as published by
## the Free Software Foundation; either version 2 of the License, or
## (at your option) any later version.
## This program is distributed in the hope that it will be useful,
## but WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
## GNU General Public License for more details.
## You should have received a copy of the GNU General Public License
## along with this program; if not, write to the Free Software
## Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
import dbus, re
import urllib.parse
from debug import *
class DNSSDHostNamesResolver:
    def __init__ (self, devices):
        self._devices = devices
        self._unresolved = len (devices)
        self._device_uri_by_name = {}
        debugprint ("+%s" % self)
    def __del__ (self):
        debugprint ("-%s" % self)
    def resolve (self, reply_handler):
        self._reply_handler = reply_handler
        bus = dbus.SystemBus ()
        if not bus:
            reply_handler ([])
            del self._devices
            del self._reply_handler
            return
        for uri, device in self._devices.items ():
            if not uri.startswith ("dnssd://"):
                self._unresolved -= 1
                continue
            # We need to resolve the DNS-SD hostname in order to
            # compare with other network devices.
            result = urllib.parse.urlparse (uri)
            hostname = result.netloc
            elements = hostname.rsplit (".", 3)
            if len (elements) != 4:
                self._resolved ()
                continue
            name, stype, protocol, domain = elements
            name = urllib.parse.unquote (name)
            stype += "." + protocol #  e.g. _printer._tcp
            try:
                obj = bus.get_object ("org.freedesktop.Avahi", "/")
                server = dbus.Interface (obj,
                                         "org.freedesktop.Avahi.Server")
                self._device_uri_by_name[(name, stype, domain)] = uri
                debugprint ("Resolving address for %s" % hostname)
                server.ResolveService (-1, -1,
                                        name, stype, domain,
                                        -1, 0,
                                        reply_handler=self._reply,
                                        error_handler=lambda e:
                                            self._error (uri, e))
            except dbus.DBusException as e:
                debugprint ("Failed to resolve address: %s" % repr (e))
                self._resolved ()
    def _resolved (self):
        self._unresolved -= 1
        if self._unresolved == 0:
            debugprint ("All addresses resolved")
            self._reply_handler (self._devices)
            del self._devices
            del self._reply_handler
    def _reply (self, interface, protocol, name, stype, domain,
                host, aprotocol, address, port, txt, flags):
        uri = self._device_uri_by_name[(name, stype, domain)]
        self._devices[uri].address = address
        hostname = host
        p = hostname.find(".")
        if p != -1:
            hostname = hostname[:p]
        debugprint ("%s is at %s (%s)" % (uri, address, hostname))
        self._devices[uri].hostname = hostname
        self._resolved ()
    def _error (self, uri, error):
        debugprint ("Error resolving %s: %s" % (uri, repr (error)))
        self._resolved ()
if __name__ == '__main__':
    class Device:
        def __repr__ (self):
            try:
                return "<Device @ %s>" % self.address
            except:
                return "<Device>"
    devices = {"dnssd://dlk-08E206-P1._printer._tcp.local/": Device(),
               "dnssd://foo._printer._tcp.local/": Device()}
    from dbus.glib import DBusGMainLoop
    DBusGMainLoop (set_as_default=True)
    class Test:
        def __init__ (self, loop, devices):
            self._loop = loop
            self._devices = devices
        def run (self):
            r = DNSSDHostNamesResolver (self._devices)
            r.resolve (reply_handler=self.reply)
            return False
        def reply (self, *args):
            print(args)
            self._loop.quit ()
    from gi.repository import GObject
    from gi.repository import GLib
    loop = GObject.MainLoop ()
    set_debugging (True)
    GLib.idle_add (Test (loop, devices).run)
    loop.run ()
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