Call windows function (getting the font directory) - winapi

Question

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

Answer 1

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

Answer 2

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)
}

Answer 3

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

Answer 4

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.