// Len returns the length of a Seeker.
// If s has a Len, Size, or Stat method, one of those will be used. Otherwise,
// Seek will be used to determine the length, before restoring the cursor to its
// previous position.
func Len(s io.Seeker) (int64, error) {
switch s := s.(type) {
case sizer:
return s.Size(), nil
case lener:
return int64(s.Len()), nil
case stater:
info, err := s.Stat()
if err != nil {
return 0, err
}
return info.Size(), nil
}
i, err := s.Seek(0, os.SEEK_CUR)
if err != nil {
return 0, err
}
j, err := s.Seek(0, os.SEEK_END)
if err != nil {
return j, err
}
_, err = s.Seek(i, os.SEEK_SET)
return j, err
}
