Can't get service data to show up in advertising payload

[colececil]

Hello - I'm trying to write a program to broadcast data from my Arduino Nano 33 IoT, using the BTHome standard. I'm trying to use AdvertisementOptions.ServiceData as mentioned/implemented in #241, but it doesn't seem to be doing anything for me.

Here is the relevant part of my code:

btHomeUuid := bluetooth.New16BitUUID(0xFCD2)
deviceInformation := uint8(0x40)
moistureObjectId := uint8(0x2F)

bleAdapter := bluetooth.DefaultAdapter
err := bleAdapter.Enable()
if err != nil {
	panic("Failed to enable BLE adapter")
}

serviceData := make([]byte, 0)
serviceData = append(serviceData, deviceInformation)
serviceData = append(serviceData, moistureObjectId)
serviceData = append(serviceData, uint8(0))
serviceData = append(serviceData, moistureObjectId)
serviceData = append(serviceData, uint8(0))

bleAdvertisement := bleAdapter.DefaultAdvertisement()
err = bleAdvertisement.Configure(bluetooth.AdvertisementOptions{
	LocalName: "automatic-soil-monitor",
	Interval:  bluetooth.NewDuration(5 * time.Second),
	ServiceData: []bluetooth.ServiceDataElement{
		{
			UUID: btHomeUuid,
			Data: serviceData,
		},
	},
})
if err != nil {
	panic("Failed to configure BLE advertisement")
}

err = bleAdvertisement.Start()
if err != nil {
	panic("Failed to start BLE advertisement")
}

And here is the advertisement payload I'm seeing when it's running, as captured by a BLE testing app on my phone:

I'm not sure if I'm doing something wrong, or if I might be running into a bug. Any help would be appreciated!

[deadprogram]

https://github.com/tinygo-org/bluetooth/blob/dev/gap_hci.go#L372

You can add "also service data" to that comment.

[colececil]

Well that explains a lot! 😅 Maybe I'll see if I can figure out how to implement it and create a pull request.

[colececil]

@deadprogram, I sat down this evening to see if I could start to figure out how to implement this, and I was pleasantly surprised to discover you'd already created a pull request for it! Thanks so much!

I tried using the version in your branch, and that has me unblocked again. I'm now getting the service data in the advertisement payload when my program is running on my Arduino Nano 33 IoT. And, now that the payload conforms to the BTHome standard, my Home Assistant server is picking it up and reading in the data! So now I just need to hook up my sensor data to my service data, and my project should be good to go. 😎

(I'm creating a soil moisture sensor device to help me try to keep my deciduous bonsai trees alive when I store them in my garage over the winter. In past winters, I've had trouble keeping them from drying out without overwatering them.)

Thanks for all your hard work developing and supporting this library - it is much appreciated. Even though I ran into a couple bumps along the way, you got them quickly resolved and made it possible for me to implement my project in TinyGo. (I'm so glad I didn't have to do it in C! 😅)

[colececil]

@deadprogram, I ran into one more problem/question here. I'm not sure if this is just me being dumb about pointers and such, but I'm not able to get the service data to update in the advertisement.

Here's a sample snippet of my program:

func main() {
	initialize()
	for {
		readMoistureLevels()
		time.Sleep(time.Second)
	}
}

// initialize initializes the necessary components.
func initialize() {
	bleAdapter = bluetooth.DefaultAdapter
	err := bleAdapter.Enable()
	if err != nil {
		println("Failed to enable BLE adapter:", err)
		restart()
	}

	serviceData = make([]byte, 5)
	serviceData = append(serviceData, deviceInformation)
	serviceData = append(serviceData, moistureObjectId)
	serviceData = append(serviceData, moisturePercentages[0])
	serviceData = append(serviceData, moistureObjectId)
	serviceData = append(serviceData, moisturePercentages[1])

	bleAdvertisement := bleAdapter.DefaultAdvertisement()
	err = bleAdvertisement.Configure(bluetooth.AdvertisementOptions{
		LocalName: "soil-monitor",
		Interval:  bluetooth.NewDuration(5 * time.Second),
		ServiceData: []bluetooth.ServiceDataElement{
			{
				UUID: btHomeUuid,
				Data: serviceData,
			},
		},
	})
	if err != nil {
		println("Failed to configure BLE advertisement:", err)
		restart()
	}

	err = bleAdvertisement.Start()
	if err != nil {
		println("Failed to start BLE advertisement:", err)
		restart()
	}
}

// updateServiceData updates the service data with the current moisture levels.
func updateServiceData() {
	serviceData[2] = moisturePercentages[0]
	serviceData[4] = moisturePercentages[1]
}

// readMoistureLevels reads and reports the moisture levels from the sensors.
func readMoistureLevels() {
	readMoistureLevel(0)
	readMoistureLevel(1)
	updateServiceData()
}

Even after new moisture levels are read from the sensors and updateServiceData is called, the moisture levels still show up as their initial value of 0 in the advertisement payload. Is there a way to update the service data in subsequent broadcasts of the payload, or is this a current limitation of the API? It doesn't look like there's any way to pass in the AdvertisementOptions or anything inside the AdvertisementOptions as a pointer, as far as I can tell.

[deadprogram]

See 7dbb60e

[colececil]

Aha, thanks - I missed that example. I got it working now! Turns out I had two issues with my code:

1. I made a silly mistake and called make([]byte, 5) instead of make([]byte, 0, 5) before using append to add elements to my slice. So instead of a 5-element slice, I got a 10-element slice that was padded by 0s - which I failed to notice.
2. I wasn't calling SetServiceData on my Advertisement after updating the data.