LibraryImport fails to Marshal ByValTStr (SYSLIB1051)

[deeprobin]

Description

I just noticed a strange behavior when implementing the Winsock API.

Reproduction Steps

    internal const string Ws2_32 = "ws2_32.dll";
    [StructLayout(LayoutKind.Sequential)]
    internal struct WSAData
    {
        public short wVersion;
        public short wHighVersion;
        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 257)]
        public string szDescription;
        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 129)]
        public string szSystemStatus;
        public short iMaxSockets;
        public short iMaxUdpDg;
        public int lpVendorInfo;
    }
    
    [LibraryImport(Ws2_32, SetLastError = true)]
    internal static partial int WSAStartup(in short wVersionRequested, out WSAData lpWSAData);

Expected behavior

That it works.

Actual behavior

SYSLIB1051

Regression?

No response

Known Workarounds

• Usage of DllImportAttribute instead of LibraryImportAttribute.

Configuration

7.0.100-preview.7.22377.5

Other information

No response

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Issue Details

---

Description

I just noticed a strange behavior when implementing the Winsock API.

Reproduction Steps

    internal const string Ws2_32 = "ws2_32.dll";
    [StructLayout(LayoutKind.Sequential)]
    internal struct WSAData
    {
        public short wVersion;
        public short wHighVersion;
        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 257)]
        public string szDescription;
        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 129)]
        public string szSystemStatus;
        public short iMaxSockets;
        public short iMaxUdpDg;
        public int lpVendorInfo;
    }
    
    [LibraryImport(Ws2_32, SetLastError = true)]
    internal static partial int WSAStartup(in short wVersionRequested, out WSAData lpWSAData);

Expected behavior

That it works.

Actual behavior

SYSLIB1051

Regression?

No response

Known Workarounds

• Usage of DllImportAttribute instead of LibraryImportAttribute.

Configuration

7.0.100-preview.7.22377.5

Other information

No response

Author:	deeprobin
Assignees:	-
Labels:	area-System.Runtime.InteropServices
Milestone:	-

[jkoritzinsky]

This is a known deficiency in the new system. We do not have a source-generator today for generating marshalling information for a user-defined type. You'll need to manually define a marshaller using the new custom type marshaller model if you want to use a non-blittable user-defined type with LibraryImport.

[AaronRobinsonMSFT]

@deeprobin This is by design. See our documentation for this here.