get file name

getfilename.go

package main

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

var (
	modkernel32 = syscall.NewLazyDLL("kernel32.dll")

	procGetFileInformationByHandleEx = modkernel32.NewProc("GetFileInformationByHandleEx")
)

const (
	FileNameInfo = 2
)

type FileNameInformation struct {
	FileNameLength uint32
	FileName       [1]uint16
}

func GetFileInformationByHandleEx(handle syscall.Handle, infoClass int32, data *byte, buflen uint32) (err error) {
	r1, _, e1 := syscall.Syscall6(procGetFileInformationByHandleEx.Addr(), 4, uintptr(handle), uintptr(infoClass), uintptr(unsafe.Pointer(data)), uintptr(buflen), 0, 0)
	if r1 == 0 {
		if e1 != 0 {
			err = syscall.Errno(e1)
		} else {
			err = syscall.EINVAL
		}
	}
	return
}

func Open(path string) (fd syscall.Handle, err error) {
	if len(path) == 0 {
		return syscall.InvalidHandle, syscall.ERROR_FILE_NOT_FOUND
	}
	pathp, err := syscall.UTF16PtrFromString(path)
	if err != nil {
		return syscall.InvalidHandle, err
	}

	return syscall.CreateFile(pathp, syscall.GENERIC_READ, syscall.FILE_SHARE_READ, nil, syscall.OPEN_EXISTING, syscall.FILE_FLAG_BACKUP_SEMANTICS, 0)
}

func GetFileName(path string) (string, error) {
	fd, err := Open(path)
	if err != nil {
		return "", err
	}
	defer syscall.CloseHandle(fd)

	var buf [syscall.MAX_PATH + 4]byte

	err = GetFileInformationByHandleEx(fd, FileNameInfo, &buf[0], uint32(len(buf)))
	if err != nil {
		return "", err
	}

	nameInfo := (*FileNameInformation)(unsafe.Pointer(&buf[0]))

	p := (*[0xffff]uint16)(unsafe.Pointer(&nameInfo.FileName[0]))

	return syscall.UTF16ToString(p[:nameInfo.FileNameLength/2]), nil
}

func main() {
	if len(os.Args) != 2 {
		fmt.Println("usage: getfilename file")
		os.Exit(1)
	}
	name, err := GetFileName(os.Args[1])
	if err != nil {
		panic(err)
	}
	fmt.Println(name)
}