code: func (p *peer) Head() (hash common.Hash, td *big.Int) {
  	p.lock.RLock()
  	defer p.lock.RUnlock()
  
  	copy(hash[:], p.head[:])
  	return hash, new(big.Int).Set(p.td)
  }
docs: // Head retrieves a copy of the current head hash and total difficulty of the
  // peer.