Unmanaged memory leak in WindowsHidApiService.GetHidCapabilities

[VerusMaya]

Describe the issue
I observed an ongoing unmanaged memory leak when regularly polling for connected devices. I reproduced it with a minimal CLI .exe and narrowed it down to WindowsHidApiService.GetHidCapabilities. To resolve the leak, change the HidD_FreePreparsedData pointerToPreparsedData parameter to not be ref.

The HidD_GetPreparsedData documentation shows a *PreparsedData parameter. This matches with the out parameter option used.
https://docs.microsoft.com/en-us/windows-hardware/drivers/ddi/hidsdi/nf-hidsdi-hidd_getpreparseddata

The HidD_FreePreparsedData documentation shows a PreparsedData parameter with no dereference. I believe it should therefore be called without ref.
https://docs.microsoft.com/en-us/windows-hardware/drivers/ddi/hidsdi/nf-hidsdi-hidd_freepreparseddata

Relevant call stack -
WindowsHidApiService.GetHidCapabilities
WindowsHidApiService.GetDeviceDefinition
WindowsHidDeviceFactoryExtensions.GetDeviceDefinition
WindowsDeviceEnumerator.GetConnectedDeviceDefinitionsAsync

Screenshots
Memory profiler running for one minute. Notice the bottom-right section for unmanaged memory breakdown by module.

without fix

with fix

Your Code
The memory leak can be reproduced easily.

static async Task Main(string[] args) {
	IDeviceFactory factory = new FilterDeviceDefinition(0x1234, 0x5678).CreateWindowsHidDeviceFactory();
	while (true) {
		_ = await factory.GetConnectedDeviceDefinitionsAsync();
		await Task.Delay(TimeSpan.FromMilliseconds(100));
	}
}

The leak can be resolved with two changes.

Device.Net/src/Hid.Net/Windows/WindowsHidApiService.cs

Line 61 in 417330e

private static extern bool HidD_FreePreparsedData(ref IntPtr pointerToPreparsedData);

private static extern bool HidD_FreePreparsedData(IntPtr pointerToPreparsedData);

Device.Net/src/Hid.Net/Windows/WindowsHidApiService.cs

Line 117 in 417330e

isSuccess = HidD_FreePreparsedData(ref pointerToPreParsedData);

isSuccess = HidD_FreePreparsedData(pointerToPreParsedData);

Log / Stack Trace
No relevant logging or stack trace.

Info

• Platform: Windows 10
• Device Type: HID
• Version: 4.2.1
• .NET: 5.0

PR coming soon.

[VerusMaya]

Following up since it has been a bit.

Have you had a chance to look into this?

It would be great to get an updated nuget package with the memory leak resolved.

Thank you!

[Resonanz]

?

[HossamElwahsh]

Great work finding this. 💯 forked and fixed. until this gets merged into main branch.