sliceForAppend takes a slice and a requested number of bytes. It returns a // slice with the contents of the given slice followed by that many bytes and a // second slice that aliases into it and contains only the extra bytes. If the // original slice has sufficient capacity then no allocation is performed. func sliceForAppend(in []byte, n int) (head, tail []byte) { if total := len(in) + n; cap(in) >= total { head = in[:total] } else { head = make([]byte, total) copy(head, in) } tail = head[len(in):] return...