Error calling HidP_GetButtonCaps routine from C# - interop

Question

I have spent hours and still can't understand why calling the HidP_GetButtonCaps routine (from hid.dll) fails when using Interop in C#.
I am listing devices and trying to get ButtonCaps and so on. But when calling HidP_GetButtonCaps (or HidP_GetValueCaps) the extern function returns an HIDP_STATUS_INVALID_REPORT_TYPE error. And I just don't get it... the report type parameter in this routine is a enum value, how can it fails ???
Here is some code extract. I won't put everything because it is long. Of course if more details need to be put, I'll add it.
There are comments in the code "//REMARK", here is the remarks content:
- Remark 1 : the hidDevice object parameter comes from another method. I know the content of the "DevicePath", "preparsedData" and "ButtonCaps" fields are correct when checking things in debugging mode.
- Remark 2 : here is where I have the problem. I've tried 3 different ways for the argument: with a HIDP_REPORT_TYPE object, directly with HIDP_REPORT_TYPE.HidP_Input or "0", and it does not make any difference...
Thanks so much for your help.
Structures, constants, enum... :
public enum HIDP_REPORT_TYPE : ushort
{
HidP_Input,
HidP_Output,
HidP_Feature
}
public struct ButtonCapsRange
{
public ushort UsageMin;
public ushort UsageMax;
public ushort StringMin;
public ushort StringMax;
public ushort DesignatorMin;
public ushort DesignatorMax;
public ushort DataIndexMin;
public ushort DataIndexMax;
}
public struct ButtonCapsNotRange
{
public ushort Usage;
public ushort Reserved1;
public ushort StringIndex;
public ushort Reserved2;
public ushort DesignatorIndex;
public ushort Reserved3;
public ushort DataIndex;
public ushort Reserved4;
}
[StructLayout(LayoutKind.Explicit)]
public struct HIDP_BUTTON_CAPS
{
[FieldOffset(0)]
public ushort UsagePage;
[FieldOffset(2)]
public byte ReportID;
[FieldOffset(3)]
public bool IsAlias;
[FieldOffset(4)]
public ushort BitField;
[FieldOffset(6)]
public ushort LinkCollection;
[FieldOffset(8)]
public ushort LinkUsage;
[FieldOffset(10)]
public ushort LinkUsagePage;
[FieldOffset(12)]
public bool IsRange;
[FieldOffset(13)]
public bool IsStringRange;
[FieldOffset(14)]
public bool IsDesignatorRange;
[FieldOffset(15)]
public bool IsAbsolute;
[FieldOffset(16)]
public uint[] Reserved;
[FieldOffset(16 + 10 * 4)]
public ButtonCapsRange Range;
[FieldOffset(16 + 10 * 4)]
public ButtonCapsNotRange NotRange;
}
public struct HID_DEVICE
{
public String DevicePath;
public IntPtr pHidDevice; // A file handle to the hid device.
public bool OpenedForRead;
public bool OpenedForWrite;
public bool OpenedOverlapped;
public bool OpenedExclusive;
public IntPtr Ppd; // The opaque parser info describing this device
public HIDP_CAPS Caps; // The Capabilities of this hid device.
public HIDD_ATTRIBUTES Attributes;
public byte[] pInputReportBuffer;
public HID_DATA[] InputData; // array of hid data structures
public ulong InputDataLength; // Num elements in this array.
public HIDP_BUTTON_CAPS[] pInputButtonCaps;
public HIDP_VALUE_CAPS[] pInputValueCaps;
public byte[] pOutputReportBuffer;
public HID_DATA[] pOutputData;
public ulong OutputDataLength;
public HIDP_BUTTON_CAPS[] pOutputButtonCaps;
public HIDP_VALUE_CAPS[] pOutputValueCaps;
public byte[] pFeatureReportBuffer;
public HID_DATA[] pFeatureData;
public ulong FeatureDataLength;
public HIDP_BUTTON_CAPS[] pFeatureButtonCaps;
public HIDP_VALUE_CAPS[] pFeatureValueCaps;
}
external methods:
[DllImport("hid.dll", SetLastError = true)]
[SecurityPermission(SecurityAction.Assert, Unrestricted = true)]
static extern int HidP_GetButtonCaps([MarshalAs(UnmanagedType.U2)] HIDP_REPORT_TYPE ReportType, ref HIDP_BUTTON_CAPS[] ButtonCaps, ref ushort ButtonCapsLength, IntPtr PreparsedData);
Call of the method:
private static bool FillDeviceInfo(ref HID_DEVICE hidDevice)
{
//REMARK 1
ulong numValues;
ushort numCaps;
HIDP_BUTTON_CAPS[] buttonCaps;
HIDP_VALUE_CAPS[] valueCaps;
HID_DATA[] data;
ulong i;
ushort usage;
uint dataIdx;
hidDevice.pInputReportBuffer = new byte[hidDevice.Caps.InputReportByteLength];
buttonCaps = new HIDP_BUTTON_CAPS[hidDevice.Caps.NumberInputButtonCaps];
//for(int a=0;a<buttonCaps.Length ;a++)
// buttonCaps[a].Reserved = new uint[10];
hidDevice.pInputButtonCaps = buttonCaps;
valueCaps = new HIDP_VALUE_CAPS[hidDevice.Caps.NumberInputValueCaps];
hidDevice.pInputValueCaps = valueCaps;
numCaps = hidDevice.Caps.NumberInputButtonCaps;
if (numCaps > 0)
{
//REMARK 2
HIDP_REPORT_TYPE reportType = HIDP_REPORT_TYPE.HidP_Input;
int val = (HidP_GetButtonCaps(reportType, ref buttonCaps, ref numCaps, hidDevice.Ppd));
if (HIDP_STATUS_SUCCESS != val)
{
return false;
}
}
//other stuff and retur true at end
}

Answer 1

OK found the problem... stupid mistake as often.
I solved the problem of the "invalid report type" error by removing the ":ushort" in the enum definition. I thought it was a 2 bytes data in C, but it was a 4 bytes data.
Also, there was a problem with working with tables made in managed memory in HidP_GetButtonCaps.
Instead of using a array of HIDP_BUTTON_CAPS (initialized in managed memory) in HidP_GetButtonCaps, I use a IntPtr refering to an unmanaged memory zone.

Answer 2

I was getting the same kind of exception. I think there's a problem in the CLR trying to automatically marshall data to a struct with a union. Maybe. I wrote my own unpacking method and that seems to have fixed the problem.
public static HidpButtonCaps FromByteArray(byte[] bytes, int offset)
{
var hbc = new HidpButtonCaps()
{
UsagePage = (ushort)(((ushort)bytes[offset+1] << 8) | (ushort)(bytes[offset])),
ReportID = bytes[offset + 2] > 0 ? true : false,
IsAlias = bytes[offset + 3] > 0 ? true : false,
BitField = (ushort)(((ushort)bytes[offset + 5] << 8) | (ushort)(bytes[offset + 4])),
LinkCollection = (ushort)(((ushort)bytes[offset + 7] << 8) | (ushort)(bytes[offset + 6])),
LinkUsage = (ushort)(((ushort)bytes[offset + 9] << 8) | (ushort)(bytes[offset + 8])),
IsRange = bytes[offset + 10] > 0 ? true : false,
IsStringRange = bytes[offset + 11] > 0 ? true : false,
IsDesignatorRange = bytes[offset + 12] > 0 ? true : false,
IsAbsolute = bytes[offset + 13] > 0 ? true : false,
// skip reserved
Range = new HidpButtonCapsRange()
{
UsageMin = (ushort)(((ushort)bytes[offset + 57] << 8) | (ushort)(bytes[offset + 56])),
UsageMax = (ushort)(((ushort)bytes[offset + 59] << 8) | (ushort)(bytes[offset + 58])),
StringMin = (ushort)(((ushort)bytes[offset + 61] << 8) | (ushort)(bytes[offset + 61])),
StringMax = (ushort)(((ushort)bytes[offset + 63] << 8) | (ushort)(bytes[offset + 62])),
DesignatorMin = (ushort)(((ushort)bytes[offset + 65] << 8) | (ushort)(bytes[offset + 64])),
DesignatorMax = (ushort)(((ushort)bytes[offset + 67] << 8) | (ushort)(bytes[offset + 66])),
DataIndexMin = (ushort)(((ushort)bytes[offset + 69] << 8) | (ushort)(bytes[offset + 68])),
DataIndexMax = (ushort)(((ushort)bytes[offset + 71] << 8) | (ushort)(bytes[offset + 70])),
}
};
return hbc;
}
I use it like this
dwSize = hidpcaps.NumberInputButtonCaps;
var bytelength = Marshal.SizeOf(typeof(HidpButtonCaps)) * (int)dwSize;
HidpButtonCaps[] buttonCaps = new HidpButtonCaps[(int)dwSize];
var pbuttoncaps = Marshal.AllocHGlobal(bytelength);
hidpstatus = (HidpStatus)HidP_GetButtonCaps(HidpReportType.HidP_Input, pbuttoncaps, ref dwSize, pPreparsedData);
if (hidpstatus != HidpStatus.HIDP_STATUS_SUCCESS)
{
throw new Win32Exception($"HidP_GetButtonCaps: {hidpstatus.ToString()}");
}
var buttonCapBytes = new byte[bytelength];
Marshal.Copy(pbuttoncaps, buttonCapBytes, 0, bytelength);
for (int i=0; i<(int)hidpcaps.NumberInputButtonCaps; i++)
{
buttonCaps[i] = HidpButtonCaps.FromByteArray(buttonCapBytes, i * Marshal.SizeOf(typeof(HidpButtonCaps)));
}