read_write example returning -1 at gattlib_read_char_by_uuid in Bluez 5.45

[Buguito]

Hi Olivier and dear devs.. I'm porting a C++ program of my own that was properly working with a RFDuino device also of my own. We were using QTBluetooth, and switched to pure C, so i went ahead and started using this library gattlib for future replacement of RFDuino with some NRF module and do an embedded system.

The LE Scan works just fine, and also the provided example for characteristics discovery (discovery). But when i try to read the value from my LE device (an RFDuino that reads a temp and humidity sensor), i'm getting a ret = -1 from the gattlib_read_char_by_uuid call at read_write.c example.

So i went ahead and tried to trace where the issue was, putting some printf in the gattlib.c at the dbus/ folder and recompiling the examples.

The issue is at org_bluez_gatt_characteristic1_call_read_value_sync(characteristic, &out_value, NULL, &error)

Using the original gatttool i can read properly (don't know if gatttool actually uses DBUS API or not...)

Here are the outputs:

root@gizmo:~/gattlib/build/examples/discover# ./discover D5:A9:88:3E:CA:09 service[0] start_handle:00 end_handle:00 uuid:0x2220 service[1] start_handle:00 end_handle:00 uuid:0x1801 characteristic[0] properties:12 value_handle:0000 uuid:0x2221 characteristic[1] properties:0c value_handle:0000 uuid:0x2223 characteristic[2] properties:2f value_handle:0000 uuid:0x2222 characteristic[3] properties:20 value_handle:0000 uuid:0x2a05

root@gizmo:~/gattlib/build/examples/read_write# ./read_write D5:A9:88:3E:CA:09 read 00002221-0000-1000-8000-00805f9b34fb Connecting.. Connected. UUID: 00002221-0000-1000-8000-00805f9b34fb ERROR AT READ_VALUE_SYNC Error: GDBus.Error:org.freedesktop.DBus.Error.UnknownMethod: Method "ReadValue" with signature "" on interface "org.bluez.GattCharacteristic1" doesn't exist Ret: -1

Now when using gatttool:

root@gizmo:~/gattlib/build/examples/read_write# gatttool -t random -b D5:A9:88:3E:CA:09 --char-read -a 0x000e Characteristic value/descriptor: 49 00 00 88 42 33 33 bb 41 00 00 00 00 00 00 62 00 00 30 00

It reads the characteristic just fine (20 bytes) as intended.

Any thoughts on the "GDBus.Error:org.freedesktop.DBus.Error.UnknownMethod: Method "ReadValue" with signature "" on interface "org.bluez.GattCharacteristic1", error?

It's driving me insane.

Thank you!

[Buguito]

Some extra info. getting the primary services with gatttool:

root@gizmo:~/gattlib/build/examples/read_write# gatttool -t random -b D5:A9:88:3E:CA:09 --primary attr handle = 0x0001, end grp handle = 0x0007 uuid: 00001800-0000-1000-8000-00805f9b34fb attr handle = 0x0008, end grp handle = 0x000b uuid: 00001801-0000-1000-8000-00805f9b34fb attr handle = 0x000c, end grp handle = 0xffff uuid: 00002220-0000-1000-8000-00805f9b34fb

As you can see, there's a 0x000c which is the only service available for read/write at RFDuino propietary GATT Profile.

Characteristics with gatttool:

root@gizmo:~/gattlib/build/examples/read_write# gatttool -t random -b D5:A9:88:3E:CA:09 --characteristics handle = 0x0002, char properties = 0x0a, char value handle = 0x0003, uuid = 00002a00-0000-1000-8000-00805f9b34fb handle = 0x0004, char properties = 0x02, char value handle = 0x0005, uuid = 00002a01-0000-1000-8000-00805f9b34fb handle = 0x0006, char properties = 0x02, char value handle = 0x0007, uuid = 00002a04-0000-1000-8000-00805f9b34fb handle = 0x0009, char properties = 0x20, char value handle = 0x000a, uuid = 00002a05-0000-1000-8000-00805f9b34fb handle = 0x000d, char properties = 0x12, char value handle = 0x000e, uuid = 00002221-0000-1000-8000-00805f9b34fb handle = 0x0010, char properties = 0x0c, char value handle = 0x0011, uuid = 00002222-0000-1000-8000-00805f9b34fb handle = 0x0012, char properties = 0x0c, char value handle = 0x0013, uuid = 00002223-0000-1000-8000-00805f9b34fb

And if i evesdrop on dbus with dbus-monitor --system while using your read_write.c example, i have this:

method call sender=:1.38 -> dest=:1.2 serial=28 path=/org/bluez/hci0/dev_D5_A9_88_3E_CA_09/service000c/char000d; interface=org.bluez.GattCharacteristic1; member=ReadValue error sender=:1.2 -> dest=:1.38 error_name=org.freedesktop.DBus.Error.UnknownMethod reply_serial=28 string "Method "ReadValue" with signature "" on interface "org.bluez.GattCharacteristic1" doesn't exist "

Don't know if that means anything to you.

[Buguito]

Ok, i've installed bluez-5.41, recompiled so no D-BUS API is used, changed the ADDR type to "random" in the examples and it's working now. My device might have been incompatible with the DBUS-API or i failed to change the ADDR type to random previously in the examples but not sure about the latter. Mostly my device was not compatible since it's a RFDuino with old firmware.

[Buguito]

Ok, so i wanted to retry with D-BUS API. From what i understand the problem is that the signature for the call to ReadValue method on the org.bluez.GattCharacteristic1 is wrong. It's "empty", passing in no paraemters, while using d-feet if i send "{}" as input parameter i get the data correctly. If i send nothing, i get the same signature error issue in d-feet dbus debugger.

It expects dict of {string, variant}. I think this line should be left uncommented in the XML for the ReadValue method for the gdbus-codegen:

<arg name="options" type="a{sv}" direction="in"/>

Also, the proper changes should be made for the gattlib.c at the /dbus directory, so it can compile, since we are introducing an extra parameter to the org_bluez_gatt_characteristic1_call_read_value_sync call.

As i see, on previous versions of bluez, like 5.37, the ReadValue method had no parameters and now it has that dict of (string, variant). Using instrospection with d-feet i got the same line that was commented out in the .XML file (with a type="a{sv}" as input parameter).

So if i'm not mistaken, you library won't work with DBUS API on the latest versions since the signature for ReadValue and WriteValue have changed.

Regards, Alan

[Buguito]

Ok i fixed it. Olivier in case you want to change this in future releases to comply with the latest signatures for ReadValue and WriteValue, this as basically the changes i had to make.

First remove the commented lines in the XML's for gdbus-codegen, so there's an input parameter of type="a{sv}".

Then in gattlib.c at /dbus, add the parameter in both read_value and write_value as follows:

GVariant *in_params = g_variant_parse(G_VARIANT_TYPE_VARDICT, "{}", NULL, NULL, NULL); org_bluez_gatt_characteristic1_call_read_value_sync(characteristic, in_params, &out_value, NULL, &error);

Also i guess we must do a g_variant_unref (in_params), so it's memory will get released, but i'm getting an assertion failed for G_OBJECT, as if it was not a G_OBJECT).

That must be added in both read_value calls (there's a async and one withouth it), and also in the write_value corresponding functions. Have not tested the write yet, but the read operation now is working swell in via DBUS API running Bluez 5.45.

Regards, Alan

[oliviermartin]

Thanks a lot @Buguito for the investigation. I created a fix following your comment in this commit c890f64dd9. I have not tested it yet - but it builds... I hope to test it myself soon.

I close the issue for now. Feel free to re-open it.