GATT + DBus API Questions

Discussion:

Ryan Du Bois

2014-10-23 23:41:06 UTC

Hey There,

I've been trying to create a GATT service via the DBus BlueZ API (org.bluez.GattManager1 + org.bluez.GattService1/GattCharacteristic1). I'm currently using dbus-python to do this.

What I have been able to accomplish thus far (with much exploring of the source code, and additional DBG() messages added to illuminate where I had been going wrong) is the following:
- Created proper DBus Proxy objects for GattService1 & GattCharacteristic1
- Each object vends the org.freedesktop.DBus.Properties interface, to allow BlueZ to retrieve the UUID and other properties on each instance.
- Created a proper ObjectManager proxy object to allow BlueZ to retrieve the aforementioned GattService1 and GattCharacteristic1 objects.
- Called GattManager1's RegisterService() method with appropriate arguments.
- Observed that BlueZ's GattManager1 instance calls my ObjectManager's GetManagedObjects() method, and receives the appropriate object paths/handles/properties.
- Observed that BlueZ accomplishes all the internal machinery necessary to register the GATT Service in src/gatt-dbus.c (namely, I get the "Added GATT service /com/kamama/blargh..." printout on the console, when running in debug mode).

What I'm not able to see is the GATT service being listed when I explore the GATT services on my device via a BTLE exploration tool (I'm using LightBlue on Mac OS X to explore this device).

Looking closer at the code, it looks to me like src/gatt-dbus.c is not hooked up to attrib/gatt-service.c, which is probably why my GATT Service and Characteristic are not showing up when exploring the device.

Am I missing something, or is this not yet implemented?

Thanks!
--
+Ryan Du Bois
rdub-jxOQOTJ84wTQT0dZR+***@public.gmane.org

Arman Uguray

2014-10-24 00:00:37 UTC

Permalink

Hi Ryan,

Post by Ryan Du Bois
Hey There,
I've been trying to create a GATT service via the DBus BlueZ API (org.bluez.GattManager1 + org.bluez.GattService1/GattCharacteristic1). I'm currently using dbus-python to do this.
- Created proper DBus Proxy objects for GattService1 & GattCharacteristic1
- Each object vends the org.freedesktop.DBus.Properties interface, to allow BlueZ to retrieve the UUID and other properties on each instance.
- Created a proper ObjectManager proxy object to allow BlueZ to retrieve the aforementioned GattService1 and GattCharacteristic1 objects.
- Called GattManager1's RegisterService() method with appropriate arguments.
- Observed that BlueZ's GattManager1 instance calls my ObjectManager's GetManagedObjects() method, and receives the appropriate object paths/handles/properties.
- Observed that BlueZ accomplishes all the internal machinery necessary to register the GATT Service in src/gatt-dbus.c (namely, I get the "Added GATT service /com/kamama/blargh..." printout on the console, when running in debug mode).
What I'm not able to see is the GATT service being listed when I explore the GATT services on my device via a BTLE exploration tool (I'm using LightBlue on Mac OS X to explore this device).
Looking closer at the code, it looks to me like src/gatt-dbus.c is not hooked up to attrib/gatt-service.c, which is probably why my GATT Service and Characteristic are not showing up when exploring the device.
Am I missing something, or is this not yet implemented?
Thanks!
--
+Ryan Du Bois

As far as I know, gatt-dbus isn't actually wired up to attrib-server
as you said. So it populates an internal linked list of attributes but
then doesn't actually do anything over the listening socket it
creates.

The thing is, we're currently in the process of rewriting all of
bluez's internal GATT/ATT tools and we'll probably entirely rewrite
src/gatt-dbus as well. An experimental implementation should appear
for both GATT client and server roles in the upcoming months, but
until then there's no good way to host GATT services over D-Bus.

Thanks,
Arman

Ryan Du Bois

2014-10-24 00:21:37 UTC

Permalink

Hey Arman,

Post by Arman Uguray
Hi Ryan,

As far as I know, gatt-dbus isn't actually wired up to attrib-server
as you said. So it populates an internal linked list of attributes but
then doesn't actually do anything over the listening socket it
creates.
The thing is, we're currently in the process of rewriting all of
bluez's internal GATT/ATT tools and we'll probably entirely rewrite
src/gatt-dbus as well. An experimental implementation should appear
for both GATT client and server roles in the upcoming months, but
until then there's no good way to host GATT services over D-Bus.
Thanks,
Arman

Okay, that correlates with what I'm seeing. Most examples I've seen online
have been implemented in C, calling gatt_service_add().

In the time between now and a working DBus GATT API, would that
approach be the proper method to host a GATT service with BlueZ?
I'm on 5.21 at the moment, but could easily upgrade to something else
if it's better for GATT services.

Thanks!
--
+Ryan Du Bois
rdub-jxOQOTJ84wTQT0dZR+***@public.gmane.org