Nordic UART GATT Service for GGK

[krimp]

My little contribution to this amazing project. Implemented the Nordic UART GATT Server Service (to be inserted in the Server.cpp) in the frame of GGK. Tested on RPi3A+, Stretch, Bluez 5.50 and using the Uart Service on the Adafruit Bluefruit APP for IOS.

`

// Nordic UART Service (6e400001-b5a3-f393-e0a9-e50e24dcca9e)
.gattServiceBegin("Nordic_UART_Service", "6e400001-b5a3-f393-e0a9-e50e24dcca9e")

	// Characteristic: String value (custom: 6e400002-b5a3-f393-e0a9-e50e24dcca9e)
	.gattCharacteristicBegin("UART_RX", "6e400002-b5a3-f393-e0a9-e50e24dcca9e", {"write-without-response","write"})

		// Standard characteristic "WriteValue" method call
		.onWriteValue(CHARACTERISTIC_METHOD_CALLBACK_LAMBDA
		{
			// Update the text string value
			GVariant *pAyBuffer = g_variant_get_child_value(pParameters, 0);
			self.setDataPointer("uart_rx", Utils::stringFromGVariantByteArray(pAyBuffer).c_str());

			// Since all of these methods (onReadValue, onWriteValue, onUpdateValue) are all part of the same
			// Characteristic interface (which just so happens to be the same interface passed into our self
			// parameter) we can use that parameter to call our own onUpdatedValue method
			self.callOnUpdatedValue(pConnection, pUserData);

			// Note: Even though the WriteValue method returns void, it's important to return like this, so that a
			// dbus "method_return" is sent, otherwise the client gets an error (ATT error code 0x0e"unlikely").
			// Only "write-without-response" works without this
			self.methodReturnVariant(pInvocation, NULL);
		})

		// Here we use the onUpdatedValue to set a callback that isn't exposed to BlueZ, but rather allows us to manage
		// updates to our value. These updates may have come from our own server or some other source.
		//
		// We can handle updates in any way we wish, but the most common use is to send a change notification.
		.onUpdatedValue(CHARACTERISTIC_UPDATED_VALUE_CALLBACK_LAMBDA
		{
			const char *pTextString = self.getDataPointer<const char *>("uart_rx", "");
			self.sendChangeNotificationValue(pConnection, pTextString);
			return true;
		})

		// GATT Descriptor: Characteristic User Description (0x2901)
		// 
		// See: https://www.bluetooth.com/specifications/gatt/viewer?attributeXmlFile=org.bluetooth.descriptor.gatt.characteristic_user_description.xml
		.gattDescriptorBegin("description", "2901", {"read"})

			// Standard descriptor "ReadValue" method call
			.onReadValue(DESCRIPTOR_METHOD_CALLBACK_LAMBDA
			{
				const char *pDescription = "Nordic UART RX";
				self.methodReturnValue(pInvocation, pDescription, true);
			})

		.gattDescriptorEnd()

	.gattCharacteristicEnd()

	// Characteristic: String value (custom: 6e400003-b5a3-f393-e0a9-e50e24dcca9e)
	.gattCharacteristicBegin("UART_TX", "6e400003-b5a3-f393-e0a9-e50e24dcca9e", {"notify"})

		// Standard characteristic "notify" method call
		.onUpdatedValue(CHARACTERISTIC_UPDATED_VALUE_CALLBACK_LAMBDA
		{
			const char *pTextString = self.getDataPointer<const char *>("uart_tx", "");
			self.sendChangeNotificationValue(pConnection, pTextString);
			return true;
		})

		// GATT Descriptor: Characteristic User Description (0x2901)
		// 
		// See: https://www.bluetooth.com/specifications/gatt/viewer?attributeXmlFile=org.bluetooth.descriptor.gatt.characteristic_user_description.xml
		.gattDescriptorBegin("description", "2901", {"read"})

			// Standard descriptor "ReadValue" method call
			.onReadValue(DESCRIPTOR_METHOD_CALLBACK_LAMBDA
			{
				const char *pDescription = "Nordic UART TX";
				self.methodReturnValue(pInvocation, pDescription, true);
			})

		.gattDescriptorEnd()

	.gattCharacteristicEnd()		
.gattServiceEnd()
`

Transmit data from the server by:

ggkNofifyUpdatedCharacteristic("/com/gobbledegook/Nordic_UART_Service/UART_TX");

Not shown the application specific handlers in the dataGetter for the 'uart_tx' and in the dataSetter for 'uart_rx', but those familiar with the GGK will understand the missing parts...