GDBus : connection is closed error

[j_arun_mani]

Hi
I tried to establish a Peer to Peer DBus communication by following the C example included in Gio.

server.py

import gi
from gi.repository import Gio, GLib

xml = (
    "<node>"
    "  <interface name='org.gtk.GDBus.TestPeerInterface'>"
    "    <method name='HelloWorld'>"
    "      <arg type='s' name='greeting' direction='in'/>"
    "      <arg type='s' name='response' direction='out'/>"
    "    </method>"
    "  </interface>"
    "</node>"
)

node = Gio.DBusNodeInfo.new_for_xml(xml)
loop = GLib.MainLoop()


def allow_mechanism(observer, mechanism):

    return True


def authorize(observer, stream, client_credentials):

    server_credentials = Gio.Credentials()
    print("Client\n", client_credentials.to_string())
    print("Server\n", server_credentials.to_string())

    if server_credentials.is_same_user(client_credentials):
        print("Connected")
        return True
    return True


def connection_closed(connection, vanished):

    print("Connection closed ", vanished)


def handle_method_call(
    connection, sender, object_path, interface_name, method_name, params, invocation
):

    if method_name == "HelloWorld":
        print("Got a 'HelloWorld'")
        msg = params.unpack()[0]
        greeting = GLib.Variant(
            "(s)", (f"Got message : {msg}",))
        invocation.return_value(greeting)


def new_connection(server, connection):

    credentials = connection.get_peer_credentials()
    caps = connection.get_capabilities()
    print("Credentials\n", credentials.to_string())
    print("Capabilities\n", int(caps))

    connection.connect("closed", connection_closed)
    reg_id = connection.register_object(
        "/org/gtk/GDBus/TestObject", node.interfaces[0], handle_method_call, None, None
    )

    assert reg_id > 0
    return True


address = "unix:abstract=myaddr"
flags = Gio.DBusServerFlags.NONE
guid = Gio.dbus_generate_guid()
observer = Gio.DBusAuthObserver()

observer.connect("allow-mechanism", allow_mechanism)
observer.connect("authorize-authenticated-peer", authorize)

server = Gio.DBusServer.new_sync(address, flags, guid, observer)
server.start()

print("Client addresss ", server.get_client_address())
server.connect("new-connection", new_connection)
try:
    loop.run()
except KeyboardInterrupt:
    loop.quit()

client.py

from gi.repository import Gio, GLib

connection = Gio.DBusConnection.new_for_address_sync("unix:abstract=myaddr",
                                                     Gio.DBusConnectionFlags.AUTHENTICATION_CLIENT,
                                                     None,
                                                     None)
print("Connected")
print(int(connection.get_capabilities()))

var = GLib.Variant("(s)", ("Hi there",))
val = connection.call_sync(
    None,
    "/org/gtk/GDBus/TestObject",
    "org.gtk.GDBus.TestPeerInterface",
    "HelloWorld",
    var,
    GLib.VariantType.new("(s)"),
    Gio.DBusCallFlags.NONE,
    500,
    None
)
print(val)

After launching server, whenever I execute client.py, I get connection is closed error. Why does it happen? Who is closing the connection?

Please help me.

[nielsdg (Niels De Graef)]

Hey @j_arun_mani,

First things first: are you sure that your use case warrants setting up your own D-Bus server? If you just need a client and a server to communicate, it’s better to use the session or system bus (available through g_bus_get(), among others). It’s also much easier to setup.

Next, I’m not terribly familiar with GDBusServer, but if I look at your code I see some strange things:

• You make an observer in server.py, but don’t use it anywhere
• You specify in the client that authentication should be used (Gio.DBusConnectionFlags.AUTHENTICATION_CLIENT), but don’t provide an observer

[j_arun_mani]

Hi there

I’m doing what is said in the C example, just directly without any change. I had the same doubt of implementing custom Connection etc. but seems like there is no other way to design a private bus.

Oh yes, sorry for the strange things, I updated the code but pasted the old one here, let me update it.

[j_arun_mani]

Code updated, same issue.