[Bluetooth] Provide RSSI for discovered Bluetooth device

[andreasf]

In DeviceListener::DeviceDiscovered, please add support for retrieving the Received Signal Strength Indicator (RSSI), delivered by INQUIRY_RESULT_WITH_RSSI and newer HCI events.

BlueZ' D-Bus callback interface always provides it as argument and sets it to some invalid value for the legacy INQUIRY_RESULT.

[andreasf]

Sorry, in DiscoveryListener obviously.

[oruizdorantes]

At the moment as you saw the most standard HCI events and commands are used. I am not sure if the RSSI features are supported by 1.0 or 1.1 dongles. But the kit can find out which version of the specs the device is supporing. So there would be no problem as you comment to use the extended version of those commands. And I am really willing to! showing the signal strench in the preferences will be so nice!

[andreasf]

Replying to oruizdorantes:

I am not sure if the RSSI features are supported by 1.0 or 1.1 dongles.

HCI 1.0/1.1 only support reading the RSSI of a connection. To my knowledge, there are three inquiry modes to date, and the devices I've seen all run in backward compatible mode, so that 1.2, 2.0 and 2.1 can work without this. The inquiry mode would later need to be changed via HCI command, depending on the HCI version read from the device or by trial-and-error.

But the most urgent thing to consider here is the method signature of the listener class. The actual implementation of the data acquisition is not as urgent, since it is hidden from the user.