BT GATTS: How to tell when client subscribed to notifications?

[rojer]

My application is a GATT server and it can send notifications in certain cases. However, i would like to know if the client actually subscribed/registered to receive them, as i don't want to waste resources unless client is actually subscribed. I don't see any GATTS event raised when client registers for notifications, so - is there any other way to tell?

[negativekelvin]

It should come as ESP_GATTS_WRITE_EVT for CCCD

[rojer]

i have handlers for all the GATTS events and notification reg/unreg do not seem trigger any of them at present. also - what is CCCD?

[negativekelvin]

A writable descriptor that allows client to configure notifications for that characteristic

https://github.com/espressif/esp-idf/blob/master/examples/bluetooth/gatt_server_service_table/main/gatts_table_creat_demo.c#L170

[rojer]

um... so, as a service, am i supposed to do anything special to receive those events? notifications themselves work fine - when i send them (blindly), the clients receives them just fine. but i don't get any GATTS events when client regs/unregs.

[negativekelvin]

https://github.com/espressif/esp-idf/blob/master/examples/bluetooth/gatt_server/main/gatts_demo.c#L367

[rojer]

that... is not obvious :) but really, i should re-examine the examples again, looks like they've changed a lot.

but i'm definitely not seeing write events, i would've. weird. but i need to verify that my client (BLE Scanner app) actually sends them.

[negativekelvin]

Client will not register if it doesn't discover CCCD

[rojer]

figured it out, thanks!