gattc/sd: copy data in interrupt handler for characteristic notification events to data that was already allocated before entering the handler

Signed-off-by: deadprogram <ron@hybridgroup.com>

adapter_nrf528xx.go

@@ -240,11 +240,10 @@ func handleEvent() {
 				// Find the callback and call it (if there is any).
 				for _, callbackInfo := range gattcNotificationCallbacks {
 					if callbackInfo.valueHandle == hvxEvent.handle && callbackInfo.connectionHandle == gattcEvent.conn_handle {
-						// Create a Go slice from the data, to pass to the
-						// callback.
-						data := (*[255]byte)(unsafe.Pointer(&hvxEvent.data[0]))[:hvxEvent.len:hvxEvent.len]
 						if callbackInfo.callback != nil {
-							callbackInfo.callback(data)
+							// copy to Go slice from the data, to pass to the callback.
+							copy(callbackInfo.data, (*[255]byte)(unsafe.Pointer(&hvxEvent.data[0]))[:hvxEvent.len:hvxEvent.len])
+							callbackInfo.callback(callbackInfo.data[:hvxEvent.len])
 						}
 						break
 					}

gattc_sd.go

@@ -341,6 +341,7 @@ type gattcNotificationCallback struct {
 	connectionHandle uint16
 	valueHandle      uint16 // may be 0 if the slot is empty
 	callback         func([]byte)
+	data             []byte
 }
 
 // List of notification callbacks for the current connection. Some slots may be
@@ -348,6 +349,15 @@ type gattcNotificationCallback struct {
 // notification callbacks.
 var gattcNotificationCallbacks []gattcNotificationCallback
 
+func (c DeviceCharacteristic) newgattcNotificationCallback(cb func([]byte)) gattcNotificationCallback {
+	return gattcNotificationCallback{
+		connectionHandle: c.connectionHandle,
+		valueHandle:      c.valueHandle,
+		data:             make([]byte, 255),
+		callback:         cb,
+	}
+}
+
 // EnableNotifications enables notifications in the Client Characteristic
 // Configuration Descriptor (CCCD). This means that most peripherals will send a
 // notification with a new value every time the value of the characteristic
@@ -376,11 +386,7 @@ func (c DeviceCharacteristic) EnableNotifications(callback func(buf []byte)) err
 		for i, callbackInfo := range gattcNotificationCallbacks {
 			// Check for empty slots.
 			if callbackInfo.valueHandle == 0 {
-				gattcNotificationCallbacks[i] = gattcNotificationCallback{
-					connectionHandle: c.connectionHandle,
-					valueHandle:      c.valueHandle,
-					callback:         callback,
-				}
+				gattcNotificationCallbacks[i] = c.newgattcNotificationCallback(callback)
 				updatedCallback = true
 				break
 			}
@@ -393,11 +399,7 @@ func (c DeviceCharacteristic) EnableNotifications(callback func(buf []byte)) err
 	if !updatedCallback {
 		// The append call is done outside of a cricital section to avoid GC in
 		// a critical section.
-		callbackList := append(gattcNotificationCallbacks, gattcNotificationCallback{
-			connectionHandle: c.connectionHandle,
-			valueHandle:      c.valueHandle,
-			callback:         callback,
-		})
+		callbackList := append(gattcNotificationCallbacks, c.newgattcNotificationCallback(callback))
 		mask := DisableInterrupts()
 		gattcNotificationCallbacks = callbackList
 		RestoreInterrupts(mask)