Call windows function (getting the font directory)

I try to find out the font folder on a windows installation. AFAICS the proposed way is to call SHGetKnownFolderPath in Shell32.dll with KNOWNFOLDERID set to FOLDERID_Fonts.

I have no idea what to pass to the Call function in the code below:

package main

import (
	"syscall"
)

func main() {
	// HRESULT SHGetKnownFolderPath(
	//   _In_      REFKNOWNFOLDERID rfid,
	//   _In_      DWORD dwFlags,
	//   _In_opt_  HANDLE hToken,
	//   _Out_     PWSTR *ppszPath
	// );

	var (
		shell32             = syscall.NewLazyDLL("Shell32.dll")
		shGetKnowFolderPath = shell32.NewProc("SHGetKnownFolderPath")

		// Doesn't work, of course:
		folderId int
		flags    int
		handle   int
		retval   int
	)

	shGetKnowFolderPath.Call(uintptr(folderId), uintptr(flags), uintptr(handle), uintptr(retval))
}

Any idea? (I guess a workaround for now would be to stick to %windir%\Fonts, but I'd like to get a proper solution).

References:

• http://msdn.microsoft.com/en-us/library/windows/desktop/bb762181(v=vs.85).aspx
• http://msdn.microsoft.com/en-us/library/windows/desktop/dd378457(v=vs.85).aspx

For example,

package main

import (
	"fmt"
	"syscall"
	"unsafe"
)

type GUID struct {
	Data1 uint32
	Data2 uint16
	Data3 uint16
	Data4 [8]byte
}

var (
	FOLDERID_Fonts = GUID{0xFD228CB7, 0xAE11, 0x4AE3, [8]byte{0x86, 0x4C, 0x16, 0xF3, 0x91, 0x0A, 0xB8, 0xFE}}
)

var (
	modShell32               = syscall.NewLazyDLL("Shell32.dll")
	modOle32                 = syscall.NewLazyDLL("Ole32.dll")
	procSHGetKnownFolderPath = modShell32.NewProc("SHGetKnownFolderPath")
	procCoTaskMemFree        = modOle32.NewProc("CoTaskMemFree")
)

func SHGetKnownFolderPath(rfid *GUID, dwFlags uint32, hToken syscall.Handle, pszPath *uintptr) (retval error) {
	r0, _, _ := syscall.Syscall6(procSHGetKnownFolderPath.Addr(), 4, uintptr(unsafe.Pointer(rfid)), uintptr(dwFlags), uintptr(hToken), uintptr(unsafe.Pointer(pszPath)), 0, 0)
	if r0 != 0 {
		retval = syscall.Errno(r0)
	}
	return
}

func CoTaskMemFree(pv uintptr) {
	syscall.Syscall(procCoTaskMemFree.Addr(), 1, uintptr(pv), 0, 0)
	return
}

func FontFolder() (string, error) {
	var path uintptr
	err := SHGetKnownFolderPath(&FOLDERID_Fonts, 0, 0, &path)
	if err != nil {
		return "", err
	}
	defer CoTaskMemFree(path)
	folder := syscall.UTF16ToString((*[1 << 16]uint16)(unsafe.Pointer(path))[:])
	return folder, nil
}

func main() {
	folder, err := FontFolder()
	if err != nil {
		fmt.Println(err)
		return
	}
	fmt.Println("Font Folder:", folder)
}

Output:

Font Folder: C:\Windows\Fonts

golang.org/x/sys/windows now has a wrapper for SHGetKnownFolderPath, so this is much easier:

package main

import (
	"fmt"

	"golang.org/x/sys/windows"
)

func main() {
	path, err := windows.KnownFolderPath(windows.FOLDERID_Fonts, 0)
	if err != nil {
		fmt.Println(err)
		return
	}
	fmt.Println(path)
}

Just in case someone needs the folder id for documents in golang format:

Replace this in peterSO's code example:

FOLDERID_Documents = GUID{0xFDD39AD0, 0x238F, 0x46AF, [8]byte{0xAD, 0xB4, 0x6C, 0x85, 0x48, 0x03, 0x69, 0xC7}}

FOLDERID_PublicDocuments = GUID{0xED4824AF, 0xDCE4, 0x45A8, [8]byte{0x81, 0xE2, 0xFC, 0x79, 0x65, 0x08, 0x36, 0x34}}

see

https://msdn.microsoft.com/en-us/library/windows/desktop/dd378457(v=vs.85).aspx

folderId for the fonts directory is {FD228CB7-AE11-4AE3-864C-16F3910AB8FE}

flags can probably be SHGFP_TYPE_DEFAULT

handle can probably be NULL

retval I think should be a bool but I'm not sure.

All answers are from your previously linked SHGetFolderPath function.