Automatically connect via DBUS Device API

Automatically connect via DBUS Device API

[Mike Ryan]

It would be useful to have a way to automatically connect to previously
discovered devices via the DBUS Device API.

Current use case: I have BLE devices that become discoverable once they
have a measurement available. Upon connecting, the measurement is
notified/indicated and then the connection drops. Some of the devices
with this behavior support/require pairing, and some do not support
pairing/encryption.

At present, the only options are to manually connect via DBUS or set the
device to auto connect via the management API (using Add Device with
Action set to 2). Since management is root-only, it would be useful to
move this into DBUS.

Possible workflow:

 1. Discover devices as usual using StartDiscovery() on the adapter
 2. Pair (if necessary)
 3. Set new property AutoConnect = true
 4. bluetoothd scans in background, connects when device becomes
    available

One concern: a binary AutoConnect may not be sufficient considering the
management API has three defined actions: background scan (generates an
event, could be handled via a new Connectable property that generates a
ProptertiesChanged event), allow incoming connection (connects on
directed advertising), and auto-connect (connects even on indirect
advertising).

Re: Automatically connect via DBUS Device API

[Luiz Augusto von Dentz]

Hi Mike,

On Tue, Sep 11, 2018 at 8:45 PM, Mike Ryan <mikeryan@lacklustre.net> wrote:
> It would be useful to have a way to automatically connect to previously
> discovered devices via the DBUS Device API.
>
> Current use case: I have BLE devices that become discoverable once they
> have a measurement available. Upon connecting, the measurement is
> notified/indicated and then the connection drops. Some of the devices
> with this behavior support/require pairing, and some do not support
> pairing/encryption.
>
> At present, the only options are to manually connect via DBUS or set the
> device to auto connect via the management API (using Add Device with
> Action set to 2). Since management is root-only, it would be useful to
> move this into DBUS.

Device.Connect should actually set the device to auto connect with use
of Add Device if there is a profile setting the auto_connect flag:

https://git.kernel.org/pub/scm/bluetooth/bluez.git/tree/src/device.c#n4305

Perhaps there is no matching service or you had not registered the
profile with RegisterApplication:

https://git.kernel.org/pub/scm/bluetooth/bluez.git/tree/doc/gatt-api.txt#n355

> Possible workflow:
>
>  1. Discover devices as usual using StartDiscovery() on the adapter
>  2. Pair (if necessary)
>  3. Set new property AutoConnect = true
>  4. bluetoothd scans in background, connects when device becomes
>     available
>
> One concern: a binary AutoConnect may not be sufficient considering the
> management API has three defined actions: background scan (generates an
> event, could be handled via a new Connectable property that generates a
> ProptertiesChanged event), allow incoming connection (connects on
> directed advertising), and auto-connect (connects even on indirect
> advertising).

Is there a use case where you would only connect when it is a directed
advertising vs connectable advertising?

-- 
Luiz Augusto von Dentz