getknownfolder.go

// Package winfolder returns the path to known folders on Windows.
// This package will only build on Windows, so make sure that any
// Go file using it is guarded to only build on Windows.
package winfolder

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

var (
	modShell32               = syscall.NewLazyDLL("Shell32.dll")
	procSHGetKnownFolderPath = modShell32.NewProc("SHGetKnownFolderPath")

	modOle32          = syscall.NewLazyDLL("Ole32.dll")
	procCoTaskMemFree = modOle32.NewProc("CoTaskMemFree")

	// {F1B32785-6FBA-4FCF-9D55-7B8E7F157091}
	FOLDERID_LocalAppData = syscall.GUID{0xF1B32785, 0x6FBA, 0x4FCF, [8]byte{0x9D, 0x55, 0x7B, 0x8E, 0x7F, 0x15, 0x70, 0x91}}
)

// Path returns the path to a known folder for Windows.
//
// The folderId argument should be the GUID for the known folder path. Many
// are provided as constants to this package.
func Path(folderId syscall.GUID) (string, error) {
	// Get the path to local app data folder
	var raw *uint16
	ret, _, err := procSHGetKnownFolderPath.Call(
		uintptr(unsafe.Pointer(&folderId)),
		0,
		0,
		uintptr(unsafe.Pointer(&raw)))
	if ret != 0 {
		return "", fmt.Errorf("Failed to read folder: %s", err)
	}

	// Defer freeing memory since this API call is managed
	defer procCoTaskMemFree.Call(uintptr(unsafe.Pointer(raw)))

	// Convert UTF-16 to a Go string
	return syscall.UTF16ToString((*[1 << 16]uint16)(unsafe.Pointer(raw))[:]), nil
}