code: func (db *nodeDB) node(id NodeID) *Node {
  	var node Node
  	if err := db.fetchRLP(makeKey(id, nodeDBDiscoverRoot), &node); err != nil {
  		return nil
  	}
  	node.sha = crypto.Keccak256Hash(node.ID[:])
  	return &node
  }
docs: // node retrieves a node with a given id from the database.