How to annotate byte* parameter with inexpressible length?

[jevansaks]

We've got a bunch of APIs in the printer space which have pretty funky parameters. The SAL annotations theoretically express the buffer size (

win32metadata/generation/WinSDK/RecompiledIdlHeaders/um/winspool.h

Line 1479 in ad21d24

AddPrinterW(

) but they are not expressible in Win32 metadata today.

Does anyone have a suggestion for how to make sure that a byte* parameter is carried through to the projection as a byte array?

@riverar any thoughts?

[riverar]

So the headers contain:

HANDLE
WINAPI
AddPrinterA(
_In_opt_    LPSTR    pName,
_In_range_(1, 2)
            DWORD      Level,
_When_(Level == 1, _In_reads_bytes_(sizeof(PRINTER_INFO_1)))
_When_(Level == 2, _In_reads_bytes_(sizeof(PRINTER_INFO_2)))
            LPBYTE     pPrinter
);

Currently, the metadata system lacks the capability to indicate that pPrinter can reference either of two different structure types. Developers will need to handle this ambiguity themselves.

Examples

C#:

public static unsafe IntPtr AddPrinter(string? printerName, PRINTER_INFO_2 info)
{
    return AddPrinter(printerName, 2, (byte*)&info);
}

Rust:

pub fn add_printer(name: Option<&str>, info: &PRINTER_INFO_2A) -> Result<HANDLE> {
    unsafe {
        let handle = AddPrinterA(
            name,
            2,
            info as *const _ as *mut u8, // LPBYTE is projected as *const u8
        );
        // ...
    }
}

Errata

• Updated C# example to account for the unusable [In] byte overload and instead use the byte* overload