BLE: Add "service change attribute"

src/ble.rs

@@ -39,11 +39,69 @@ pub enum BleSendable {
     SpatemRaw(io::msg::RawMsgRx),
 }
 
-#[gatt_server]
-struct Server {
+// GAP + 4 GATT attributes + our service(s)
+const _ATTRIBUTE_TABLE_SIZE: usize = GAP_SERVICE_ATTRIBUTE_COUNT + 4 + CITSEvents::ATTRIBUTE_COUNT;
+
+pub struct Server<'values> {
+    server: AttributeServer<
+        'values,
+        embassy_sync::blocking_mutex::raw::NoopRawMutex,
+        DefaultPacketPool,
+        _ATTRIBUTE_TABLE_SIZE,
+        1,
+        CONNECTIONS_MAX,
+    >,
     c_its_events: CITSEvents,
 }
 
+impl<'values> Server<'values> {
+    // we implement this ourselves to add the "SERVICE_CHANGED" GATT characteristic,
+    // otherwise client devices won't update the service's characteristics when they change.
+    fn new_with_config(config: PeripheralConfig<'values>) -> Result<Self, &'static str> {
+        let mut table: AttributeTable<
+            '_,
+            embassy_sync::blocking_mutex::raw::NoopRawMutex,
+            _ATTRIBUTE_TABLE_SIZE,
+        > = AttributeTable::new();
+
+        // manual implementation of: gap.build(&mut table)?;
+        if !config.name.is_ascii() || config.name.len() > 22 {
+            return Err("Device name is too long. Max length is 22 bytes");
+        }
+
+        let mut gap_builder = table.add_service(Service::new(service::GAP));
+        gap_builder.add_characteristic_ro(characteristic::DEVICE_NAME, config.name.as_bytes());
+        gap_builder.add_characteristic_ro(characteristic::APPEARANCE, config.appearance);
+        gap_builder.build();
+
+        // add custom GATT service
+        let mut gatt_builder = table.add_service(Service::new(service::GATT));
+        gatt_builder.add_characteristic_ro(characteristic::SERVICE_CHANGED, &[1, 0, 255, 255]); // [0x0001, 0xFFFF] in little-endian
+        gatt_builder.build();
+
+        let c_its_events = CITSEvents::new(&mut table);
+
+        Ok(Self {
+            server: AttributeServer::new(table),
+            c_its_events,
+        })
+    }
+}
+
+impl<'values> core::ops::Deref for Server<'values> {
+    type Target = AttributeServer<
+        'values,
+        embassy_sync::blocking_mutex::raw::NoopRawMutex,
+        DefaultPacketPool,
+        _ATTRIBUTE_TABLE_SIZE,
+        1,
+        CONNECTIONS_MAX,
+    >;
+    fn deref(&self) -> &Self::Target {
+        &self.server
+    }
+}
+
 #[gatt_service(uuid = "c0b70000-d4f4-4000-ada8-f99a02ee315c")]
 struct CITSEvents {
     #[descriptor(uuid = descriptors::MEASUREMENT_DESCRIPTION, name = "Position", read, value = "PositionState proto msg", type = &'static str)]
@@ -135,10 +193,10 @@ pub async fn run(
         "Starting advertising and GATT service for {}",
         features.join(",")
     );
-    let server = Server::new_with_config(GapConfig::Peripheral(PeripheralConfig {
+    let server = Server::new_with_config(PeripheralConfig {
         name: &name,
         appearance: &appearance::UNKNOWN,
-    }))
+    })
     .unwrap();
 
     let _ = embassy_futures::join::join(ble_task(runner), async {