code: func (s *SimpleAllocator) Alloc(capacity int) []byte {
  	if s.off+capacity < cap(s.arena) {
  		slice := s.arena[s.off : s.off : s.off+capacity]
  		s.off += capacity
  		return slice
  	}
  
  	return make([]byte, 0, capacity)
  }
docs: // Alloc implements Allocator.AllocBytes interface.