GATT Notification not sending

GATT Notification not sending

[Nathan Jozwiak]

Hi all,

I'm trying to send a notification to a client when a characteristic 
value is updated by the server.

Here is the characteristics creation in the GATT server:

     /* Notification characteristic */
     bt_uuid16_create(&uuid, GATT_CHARAC_UUID);
     atval[0] = GATT_CHR_PROP_READ | GATT_CHR_PROP_NOTIFY;
     put_le16(h + 1, &atval[1]);
     put_le16(UUID_NOTIFY, &atval[3]);
     attrib_db_add(adapter->adapter, h++, &uuid, ATT_NONE, 
ATT_NOT_PERMITTED, atval, 5);

     /* Notification value */
     bt_uuid16_create(&uuid, UUID_NOTIFY);
     ekey_valid_handle = h;
     atval[0] = 0x00;
     attrib_db_add(adapter->adapter, h++, &uuid, ATT_NONE, 
ATT_NOT_PERMITTED, atval, 1);

     /* Notification Client Characteristic Config (CCC) */
     bt_uuid16_create(&uuid, GATT_CLIENT_CHARAC_CFG_UUID);
     atval[0] = 0x00;
     attrib_db_add(adapter->adapter, h++, &uuid, ATT_NONE, ATT_NONE, 
atval, 1);

I am connecting to the GATT server using the gatttool on another Linux 
system.

	[CON][00:02:72:C9:5E:0F][LE]> char-desc 0x18
	handle: 0x0018, uuid: 2803
	handle: 0x0019, uuid: f005
	handle: 0x001a, uuid: 2902
	[CON][00:02:72:C9:5E:0F][LE]> char-read-hnd 0x1a
	Characteristic value/descriptor: 00 01
	[CON][00:02:72:C9:5E:0F][LE]> char-read-hnd 0x19
	Characteristic value/descriptor: 00

Should the CCC init to 0x01? That doesn't make sense to me. Wouldn't 
that indicate the client was already setup for notifications?

I have an application that communicates with bluetoothd over TCP 
sockets. So when I send bluetoothd a command it will forward it, my 
application will process it, and respond to bluetoothd which will then 
update the Notification characteristic value depending on the 
success/failure of processing. I then need to notify the client of the 
change so it can reread the value to see if the command was successful.

	[CON][00:02:72:C9:5E:0F][LE]> char-write-cmd 0x000b 0x1234567890
	[CON][00:02:72:C9:5E:0F][LE]> char-read-hnd 0x19
	Characteristic value/descriptor: ff

The update of the characteristic value worked fine. But I am using btmon 
to monitor traffic between the two devices and I see no messages going 
out from the server to the client.


Thanks,
Nate

Re: GATT Notification not sending

[Nathan Jozwiak]

Update: I downloaded the LightBlue app from the Apple Store. The app 
allows you to connect to a GATT server and select available services to 
interact with. My notification characteristic showed up properly with an 
initial value of 0x00 and a CCC value of 0. But when attempted to 
register with the notification I saw this error from my bluetoothd output:

bluetoothd[8754]: Refusing storage path for private addressed device 
/org/bluez/hci0/dev_59_F2_63_47_1D_90
bluetoothd[8754]: Unable to get ccc storage path for device
bluetoothd[8754]: attrib/gattrib.c:g_attrib_ref() 0xa073bd8: ref=3
bluetoothd[8754]: attrib/gattrib.c:g_attrib_unref() 0xa073bd8: ref=2

Unfortunately, I do not know the command LightBlue was sending to set 
the CCC, but I figured this might be a clue for someone.

Am I not properly setting up the notification characteristic? I followed 
the same logic as the power level characteristic setup in 
profiles/proximity/reporter.c register_tx_power().

Thanks
Nate

On 10/14/14 11:54 AM, Nathan Jozwiak wrote:
> Hi all,
>
> I'm trying to send a notification to a client when a characteristic
> value is updated by the server.
>
> Here is the characteristics creation in the GATT server:
>
>      /* Notification characteristic */
>      bt_uuid16_create(&uuid, GATT_CHARAC_UUID);
>      atval[0] = GATT_CHR_PROP_READ | GATT_CHR_PROP_NOTIFY;
>      put_le16(h + 1, &atval[1]);
>      put_le16(UUID_NOTIFY, &atval[3]);
>      attrib_db_add(adapter->adapter, h++, &uuid, ATT_NONE,
> ATT_NOT_PERMITTED, atval, 5);
>
>      /* Notification value */
>      bt_uuid16_create(&uuid, UUID_NOTIFY);
>      ekey_valid_handle = h;
>      atval[0] = 0x00;
>      attrib_db_add(adapter->adapter, h++, &uuid, ATT_NONE,
> ATT_NOT_PERMITTED, atval, 1);
>
>      /* Notification Client Characteristic Config (CCC) */
>      bt_uuid16_create(&uuid, GATT_CLIENT_CHARAC_CFG_UUID);
>      atval[0] = 0x00;
>      attrib_db_add(adapter->adapter, h++, &uuid, ATT_NONE, ATT_NONE,
> atval, 1);
>
> I am connecting to the GATT server using the gatttool on another Linux
> system.
>
>      [CON][00:02:72:C9:5E:0F][LE]> char-desc 0x18
>      handle: 0x0018, uuid: 2803
>      handle: 0x0019, uuid: f005
>      handle: 0x001a, uuid: 2902
>      [CON][00:02:72:C9:5E:0F][LE]> char-read-hnd 0x1a
>      Characteristic value/descriptor: 00 01
>      [CON][00:02:72:C9:5E:0F][LE]> char-read-hnd 0x19
>      Characteristic value/descriptor: 00
>
> Should the CCC init to 0x01? That doesn't make sense to me. Wouldn't
> that indicate the client was already setup for notifications?
>
> I have an application that communicates with bluetoothd over TCP
> sockets. So when I send bluetoothd a command it will forward it, my
> application will process it, and respond to bluetoothd which will then
> update the Notification characteristic value depending on the
> success/failure of processing. I then need to notify the client of the
> change so it can reread the value to see if the command was successful.
>
>      [CON][00:02:72:C9:5E:0F][LE]> char-write-cmd 0x000b 0x1234567890
>      [CON][00:02:72:C9:5E:0F][LE]> char-read-hnd 0x19
>      Characteristic value/descriptor: ff
>
> The update of the characteristic value worked fine. But I am using btmon
> to monitor traffic between the two devices and I see no messages going
> out from the server to the client.
>
>
> Thanks,
> Nate
> --
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-- 
Nathan Jozwiak
MapleLeaf Software, Inc.
858-598-4814

Re: GATT Notification not sending

[Johan Hedberg]

Hi Nathan,

On Tue, Oct 14, 2014, Nathan Jozwiak wrote:
> Update: I downloaded the LightBlue app from the Apple Store. The app allows
> you to connect to a GATT server and select available services to interact
> with. My notification characteristic showed up properly with an initial
> value of 0x00 and a CCC value of 0. But when attempted to register with the
> notification I saw this error from my bluetoothd output:
> 
> bluetoothd[8754]: Refusing storage path for private addressed device
> /org/bluez/hci0/dev_59_F2_63_47_1D_90
> bluetoothd[8754]: Unable to get ccc storage path for device
> bluetoothd[8754]: attrib/gattrib.c:g_attrib_ref() 0xa073bd8: ref=3
> bluetoothd[8754]: attrib/gattrib.c:g_attrib_unref() 0xa073bd8: ref=2
> 
> Unfortunately, I do not know the command LightBlue was sending to set the
> CCC, but I figured this might be a clue for someone.

Unfortunately this isn't related to your main issue. It just means that
you're running a kernel version that doesn't support LE Privacy. Because
of this the kernel has not been able to notify user space of the
Identity Address of the remote device so that information about it could
be stored persistently (iOS is one of the few implementations out there
actively using Random Private Addresses).

Johan