Zephyr app with virtual TCP: disconnection callback never fires

[savvn001]

(Using bumble==0.0.212)

I have a setup where I'm running a Zephyr native_sim app, which acts as a peripheral device.
This app is invoked to specify the BT device as a virtual TCP server (like --bt-dev=127.0.0.1:9001).

I have a simple Bumble client interacting with this app via this virtual TCP link, like below:

            transport = "tcp-server:_:9001"
            async with await open_transport_or_link(transport) as (hci_source, hci_sink):

                # Create a local link
                link = LocalLink()

                np_controller = Controller("native_posix_controller", host_source=hci_source, host_sink=hci_sink, link=link)
                self.__logger.debug(f"native_posix_controller obj at {np_controller}")

                # Create a second controller using the same link
                bumble_controller = Controller("bumble_controller", link=link)

                bumble_host = Host()
                bumble_host.controller = bumble_controller

                self.__bumble_device = Device("Bumble", "F0:F1:F2:F3:F4:F5", host=bumble_host)

                self.__logger.debug(f"Virtual TCP opened with {hci_source} {hci_sink}")

Now everything I need seems to work fine, scanning, connecting, GATT writes/reads/notifies etc.
When a disconnect to the device is initiated from the bumble client side, ie via something like peer.connection.disconnect() this works fine, and the disconnect callbacks registered via the various methods get called:

        new_conn = await bumble_device.connect(
            found_device[0].address.to_string(),
            connection_parameters_preferences={
                HCI_LE_1M_PHY: ConnectionParametersPreferences(supervision_timeout=2400),
                HCI_LE_2M_PHY: ConnectionParametersPreferences(supervision_timeout=2400),
            },
            timeout=20,
        )
        new_peer = Peer(new_conn)

        @new_conn.on("disconnection")
        def on_disconnection(reason: int):
            print("***********ON DISCONNECTION**********")
        
        # or like this?
        new_peer.connection.on("disconnection", on_disconnection)

The issue is when the Zephyr app initiates a disconnect, the same callbacks never seem to fire. I can see the app sending HCI commands on disconnect, like 0x0406 but the Bumble client does not seem to be aware of the disconnect on this end at all.

Furthermore, the HCI debug messages from bumble show that the HCI disconnect message is picked up by the bumble controller, but it doesn't seem to go anywhere after that:

2025-07-03 20:27:22,710 - bumble.controller:268 - DEBUG - <<< [native_posix_controller] HOST -> CONTROLLER: HCI_DISCONNECT_COMMAND:
  connection_handle: 0
  reason:            HCI_REMOTE_USER_TERMINATED_CONNECTION_ERROR
2025-07-03 20:27:22,710 - bumble.controller:312 - DEBUG - >>> [native_posix_controller] CONTROLLER -> HOST: HCI_COMMAND_STATUS_EVENT:
  status:                  PENDING
  num_hci_command_packets: 1
  command_opcode:          HCI_DISCONNECT_COMMAND

... nothing more

Is this not implemented yet, or a bug?

[barbibulle]

Thanks for the detailed report. I will try to reproduce this on my end and see what may be going wrong.
In the meantime, I can suggest using an alternative to the LocalLink virtual controller. This controller implementation isn't full featured, and will eventually be deprecated, as there is a much better alternative: the rootcanal project (also on GitHub https://github.com/google/rootcanal) is a much more capable virtual bluetooth controller (though we don't yet use it for all of Bumble's unit tests, because it doesn't run on all platforms yet), so if your host platform is Linux, I would highly recommend trying it out. An easy way to start is to pip install rootcanal, and then python -m rootcanal to start the virtual controller. By default, it accepts HCI connections on port 6402. All clients connected to the same rootcanal instance will be part of a virtual radio medium and can communicate with each other.

[savvn001]

Hi,

Thanks for the response. We use Linux but on aarch64 unfortunately, which I saw Rootcanal does not support yet. Will you ever support ARM64? (Bazel itself does not support ARM64 either it seems, to build it from source).

The Bumble controllers are ok so far for our use cases at least - everything we want is supported except for this small disconnect issue. Last week I was digging into the controller.py source code to try and follow where the issue is, iirc it was something like once the native_posix_controller Controller's object got the disconnect message it could not find the Client in it's dict of current connections. (I think)

[zxzxwu]

Bazel can just cross-compile for different platforms, if we don't need to develop on aarch64.