code: func (p *peer) RequestOneHeader(hash common.Hash) error {
  	p.Log().Debug("Fetching single header", "hash", hash)
  	return p2p.Send(p.rw, GetBlockHeadersMsg, &getBlockHeadersData{Origin: hashOrNumber{Hash: hash}, Amount: uint64(1), Skip: uint64(0), Reverse: false})
  }
docs: // RequestOneHeader is a wrapper around the header query functions to fetch a
  // single header. It is used solely by the fetcher.