Get amount of free disk space using Go

Question

Basically I want the output of df -h, which includes both the free space and the total size of the volume. The solution needs to work on Windows, Linux, and Mac and be written in Go.

I have looked through the os and syscall Go documentation and haven't found anything. On Windows, even command line utils are either awkward (dir C:\) or need elevated privileges (fsutil volume diskfree C:\). Surely there is a way to do this that I haven't found yet...

UPDATE:
Per nemo's answer and invitation, I have provided a cross-platform Go package that does this.

Answer 1

On POSIX systems you can use syscall.Statfs.
Example of printing free space in bytes of current working directory:

import "syscall"
import "os"

var stat syscall.Statfs_t

wd, err := os.Getwd()

syscall.Statfs(wd, &stat)

// Available blocks * size per block = available space in bytes
fmt.Println(stat.Bavail * uint64(stat.Bsize))

For Windows you need to go the syscall route as well. Example (source):

h := syscall.MustLoadDLL("kernel32.dll")
c := h.MustFindProc("GetDiskFreeSpaceExW")

var freeBytes int64

_, _, err := c.Call(uintptr(unsafe.Pointer(syscall.StringToUTF16Ptr(wd))),
    uintptr(unsafe.Pointer(&freeBytes)), nil, nil)

Feel free to write a package that provides the functionality cross-platform. On how to implement something cross-platform, see the build tool help page.