implement Fileinfo for Windows and non-Windows

internal/internal_unix.go

@@ -0,0 +1,17 @@
+//go:build !windows
+
+package internal
+
+import (
+	"os"
+	"syscall"
+)
+
+// Fileinfo returns syscall fields from a FileInfo object.
+func Fileinfo(fi os.FileInfo) (uid, gid int) {
+	if fi == nil {
+		return -1, -1
+	}
+	stat := fi.Sys().(*syscall.Stat_t)
+	return int(stat.Uid), int(stat.Gid)
+}