code: func (bi *blockIndex) LookupNode(hash *chainhash.Hash) *blockNode {
  	bi.RLock()
  	node := bi.index[*hash]
  	bi.RUnlock()
  	return node
  }
docs: // LookupNode returns the block node identified by the provided hash.  It will
  // return nil if there is no entry for the hash.
  //
  // This function is safe for concurrent access.