BLE Features - non-blocking connects, char presentation format

[semireg]

After working on adding a callback on characteristic subscription I've got a few more feature requests for the BLE API. I might attempt these myself... but first I'm looking to make sure that they are achievable given other's knowledge of the underlying ESP-32 API.

1. ✅ Read a characteristic's presentation format descriptor. I created a pull request for this feature. However, it could use a second pair of eyes to make sure this is a good approach for future extensibility.

2. ✅ Non-blocking connect with configurable timeout. I've got this working. Looks like "background auto connection" is a red herring. I can't find any documentation on it, and setting is_direct to false never connects. A quick repl paste below shows how it works. I created a pull request that needs review, testing, etc.

3. ✅ Making sure scan response data is available in the advertisement. Looking into this possibly related issue and associated ESP-idf pull request. Update: I have confirmed that the current WiPy firmware is affected by this issue. Implementing sizeof instead of ESP_BLE_ADV_DATA_LEN_MAX allows for the parsing of the full scan response. I created a pull request for this fix.

As you may have gathered, these are on the GATTC side of the API.

#2 REPL paste...

Vanilla async_connect:

paste mode; Ctrl-C to cancel, Ctrl-D to finish
=== from network import Bluetooth
=== ble = Bluetooth()
=== import binascii
=== 
=== def conn_cb (bt_o):
===     print('conn_cb events {}'.format(bt_o.events()))
=== 
=== ble.callback(trigger=Bluetooth.SERVER_ASYNC_CONNECTED, handler=conn_cb)
=== 
=== ble.start_scan(-1)
=== c = ble.async_connect(binascii.unhexlify('12345678ABCD'))
=== 
bt_async_connect: creating connection object
>>> 
>>> 
>>> c.isconnected()
False
>>> c.isconnected()
False
>>> 
>>> 
>>> 
>>> 
>>> gattc_events_handler: ESP_GATTC_CONNECT_EVT
gattc_events_handler: loop 
gattc_events_handler: found match
gattc_events_handler: async_disconnect false: sending callback
conn_cb events 262

>>> c.isconnected()
True
>>> 
>>> 
>>> c.disconnect()
>>> c.isconnected()
False

Then, immediately afterwards in the same REPL, a demonstration of cancelling a connection.

>>> c = ble.async_connect(binascii.unhexlify('12345678ABCD'))
bt_async_connect: creating connection object
>>> c.disconnect()
>>> c.isconnected()
False
>>> 
>>> 
>>> 
>>> close_connection: async_disconnect: truegattc_events_handler: ESP_GATTC_CONNECT_EVT
gattc_events_handler: loop 
gattc_events_handler: found match
gattc_events_handler: async_disconnect true: closing

>>> 
>>> c.isconnected()
False

This works for my use case. I couldn't find a better way to effectively cancel esp_ble_gattc_open. Again, check out the pull request.

Here's a version that's easily pastable via ctrl-e:

from network import Bluetooth
ble = Bluetooth()
import binascii

def conn_cb (bt_o):
	print('--- conn_cb events {}'.format(bt_o.events()))

ble.callback(trigger=Bluetooth.SERVER_ASYNC_CONNECTED, handler=conn_cb)

ble.start_scan(-1)
c = ble.async_connect(binascii.unhexlify('12345678ABCD'))