// only waste 9 bytes anyway.
	const maxFrameSize = 16384

	first := true
	for len(headerBlock) > 0 {
		frag := headerBlock
		if len(frag) > maxFrameSize {
			frag = frag[:maxFrameSize]
		}
		headerBlock = headerBlock[len(frag):]
		if err := fn(ctx, frag, first, len(headerBlock) == 0); err != nil {
			return err
		}
		first = false
	}
	return nil
}