Reading a Characteristic whose value is null crashes the app

Hi,

We try to access a characteristic in our BLE device. The characteristic’s value is ‘null’. So, when we try to access, we should get null right? Following is the piece of code we used.

`public async Task<byte[]> Read(ICharacteristic characteristic) { byte[] data = {}; try { data = await characteristic.ReadAsync(); } catch (InvalidOperationException ex) { Debug.WriteLine("InvalidOperationException reading the characteristics value: " + ex.Message); } catch (CharacteristicReadException ex) { Debug.WriteLine("CharacteristicReadException reading the characteristics value: " + ex.Message); } catch (ArgumentNullException ex) { Debug.WriteLine("Excpetion in reading the characteristic " + characteristic.Id); } catch(Exception ex) { Debug.WriteLine(ex.Message); } return data; }

`

Steps to reproduce

1. Used the above mentioned to read a characteristic value (which is null in BLE device)

2. App crashes

Expected behavior

byte[] data = await characteristic.ReadAsync(); - ReadAsync() method should return null. So, datashould have the value as null. Ideally, app should not crash here.

Actual behavior

App crashes. Exception handling is done for reading the characteristic. But, the control does not come under any of the catch blocks which we have used. It crashes in Plugin.BLE.iOS.Characteristic line 71.

Crashlog

Nov 24 16:15:13 Audi-iPhone-5S RRCiOS[222] <Warning>: Characteristic.ReadAsync Nov 24 16:15:27 Audi-iPhone-5S RRCiOS[222] <Warning>: Unhandled Exception: System.ArgumentNullException: Value cannot be null. Parameter name: src at (wrapper managed-to-native) System.Runtime.InteropServices.Marshal:copy_from_unmanaged (intptr,int,System.Array,int) at System.Runtime.InteropServices.Marshal.Copy (System.IntPtr source, System.Byte[] destination, System.Int32 startIndex, System.Int32 length) [0x00000] in /Users/builder/data/lanes/3818/3983064a/source/xamarin-macios/_ios-build/Library/Frameworks/Xamarin.iOS.framework/Versions/git/src/mono/mcs/class/corlib/System.Runtime.InteropServices/Marshal.cs:152 at Foundation.NSData.ToArray () [0x00012] in /Users/builder/data/lanes/3818/3983064a/source/xamarin-macios/src/Foundation/NSData.cs:50 at Plugin.BLE.iOS.Characteristic.get_Value () [0x00000] in C:\Projects\xamarin-bluetooth-le\Source\Plugin.BLE.iOS\Characteristic.cs:25 at Plugin.BLE.iOS.Characteristic+<>c__DisplayClass15_0.<ReadNativeAsync>b__2 (System.Object sender, CoreBluetooth.CBCharacteristicEventArgs args) [0x00051] in C:\Projects\xamarin-bluetooth-le\Source\Plugin.BLE.iOS\Characteristic.cs:71 at CoreBluetooth.CBPeripheral+_CBPeripheralDelegate.UpdatedCharacterteristicValue (CoreBluetooth.CBPeripheral peripheral, CoreBluetooth.CBCharacteristic characteristic, Foundation.NSError error) [0x00015] in /Users/builder/data/lanes/3818/3983064a/source/xamarin-macios/src/build/ios/native/CoreBluetooth/CBPeripheral.g.cs:496 at (wrapper managed-to-native) UIKit.UIApplication:UIApplicationMain (int,string[],intptr,intptr) at UIKit.UIApplication.Main (System.String[] args, System.IntPtr principal, System.IntPtr delegate) [0x00005] in /Users/builder/data/lanes/3818/3983064a/source/xamarin-macios/src/UIKit/UIApplication.cs:79 at UIKit.UIApplication.Main (System.String[] args, System.String principalClassName, System.String delegateClassName) [0x00038] in /Users/builder/data/lanes/3818/3983064a/source/xamarin-macios/src/UIKit/UIApplication.cs:63 at RRC.iOS.Application.Main (System.String[] args) [0x00008] in /Users/audiologymacbook/Documents/AudiApps/TFSWS/CoffeeWorkspace/Feat/Coffee_Dev/RCApps/Source/RRC.iOS/Main.cs:17

We downloaded plugin’s source code and used it to read that particular characteristic. Below is the screenshot of crash.

Configuration

Version: 9.3.1

Platform: iOS

Device: iPhone 5S

We want to handle this crash in our app. How should we do it? Please help.

Thanks, Leela

[leelatoo]

@smstuebe Thanks 👍 It works.

[xabre]

@smstuebe agreed