Re: Notify on succeeds while no apparent descriptor

Thank you Luiz, I'm not sure what are most OSes there because macOS
and Android don't allow register characteristics without a CCC.

I'll ping armansito@ and let you know ;)

On Thu, Jun 30, 2016 at 1:36 PM, Luiz Augusto von Dentz
[off-list ref] wrote:

Hi François,

On Wed, Jun 29, 2016 at 10:24 AM, François Beaufort
[off-list ref] wrote:

quoted

I have a bogus BLE device which exposes "badly" a characteristic
notification. Even though it doesn't find a characteristic descriptor,
I'm still able to start notifications and even receive value changed
events.

For info, Android and macOS raise an exception when trying to start
notifications. See
https://github.com/WebBluetoothCG/ble-test-peripheral-android/issues/63

See logs:

< ACL Data TX: Handle 32 flags 0x00 dlen 9
                                                   [hci0] 403.621325
      ATT: Find Information Request (0x04) len 4
        Handle range: 0x002b-0xffff

quoted

HCI Event: Number of Completed Packets (0x13) plen 5                                                                    [hci0] 403.689256

        Num handles: 1
        Handle: 32
        Count: 1

quoted

ACL Data RX: Handle 32 flags 0x02 dlen 9                                                                                [hci0] 403.755926

      ATT: Error Response (0x01) len 4
        Find Information Request (0x04)
        Handle: 0x002b
        Error: Attribute Not Found (0x0a)

---

[Nexus 5X]# list-attributes
Primary Service
        /org/bluez/hci0/dev_46_EE_57_93_31_08/service0001
        Generic Attribute Profile
Characteristic
        /org/bluez/hci0/dev_46_EE_57_93_31_08/service0001/char0002
        Service Changed
Primary Service
        /org/bluez/hci0/dev_46_EE_57_93_31_08/service0028
        Battery Service
Characteristic
        /org/bluez/hci0/dev_46_EE_57_93_31_08/service0028/char0029
        Battery Level
[Nexus 5X]# select-attribute
/org/bluez/hci0/dev_46_EE_57_93_31_08/service0028/char0029
[Nexus 5X:/service0028/char0029]# notify on
[CHG] Attribute
/org/bluez/hci0/dev_46_EE_57_93_31_08/service0028/char0029 Notifying:
yes
Notify started
[CHG] Attribute
/org/bluez/hci0/dev_46_EE_57_93_31_08/service0028/char0029 Value: 0x32
[Nexus 5X:/service0028/char0029]# notify off
[CHG] Attribute
/org/bluez/hci0/dev_46_EE_57_93_31_08/service0028/char0029 Notifying:
no
Notify stopped
--

Just to make it public what I have stated in the irc, currently we
allow enabling notification even without CCC (out of the spect
unsolicited notification):

commit 46aad83687251bef0fa0ac60583e5898170b0f10
Author: Arman Uguray [off-list ref]
Date:   Tue Feb 3 19:58:22 2015 -0800
    shared/gatt: Allow register_notify without CCC

    Most OSes allow to register characteristics without a CCC even if they
    do support notification/indication, this is not according to the
    specification and may not even work in practice since there is no way
    to enable notifications/indications without a CCC to write to but there
    has been some applications that do that anyway.

Perhaps Arman had it exactly for these broken application that don't
register a CCC which Im guessing is because the GATT API don't do it
by default (Android?) leaving it up to the app which can screw up we
can observe here.


--
Luiz Augusto von Dentz