fix(auth): address Task 13 deployment review findings

tools/tht/internal/backup/restore_disk_unix.go

@@ -0,0 +1,22 @@
+//go:build !windows
+
+package backup
+
+import (
+	"errors"
+
+	"golang.org/x/sys/unix"
+)
+
+func restoreFreeBytes(target string) (uint64, error) {
+	var statistics unix.Statfs_t
+	if err := unix.Statfs(target, &statistics); err != nil {
+		return 0, errors.New("restore filesystem capacity is unavailable")
+	}
+	blockSize := uint64(statistics.Bsize)
+	available := uint64(statistics.Bavail)
+	if blockSize != 0 && available > ^uint64(0)/blockSize {
+		return 0, errors.New("restore filesystem capacity is invalid")
+	}
+	return blockSize * available, nil
+}