マークル ツリー マークル ツリー Go 言語の実装

マークル ツリーの実装は多数あります。ここでは、純粋なメモリの実装についてのリファレンスを示します。これは理解に役立ちます。

プロジェクトアドレス https://github.com/cbergoon/merkletree

コア分析

1. 構造

type Content interface {
	CalculateHash() ([]byte, error)
	Equals(other Content) (bool, error)
}

//MerkleTree is the container for the tree. It holds a pointer to the root of the tree,
//a list of pointers to the leaf nodes, and the merkle root.
type MerkleTree struct {
	Root         *Node
	merkleRoot   []byte
	Leafs        []*Node
	hashStrategy func() hash.Hash
}

//Node represents a node, root, or leaf in the tree. It stores pointers to its immediate
//relationships, a hash, the content stored if it is【 a leaf, and other metadata.
type Node struct {
	Tree   *MerkleTree
	Parent *Node
	Left   *Node
	Right  *Node
	leaf   bool
	dup    bool
	Hash   []byte
	C      Content
}

2. コアメソッド

//buildWithContent is a helper function that for a given set of Contents, generates a
//corresponding tree and returns the root node, a list of leaf nodes, and a possible error.
//Returns an error if cs contains no Contents.
// 这里先计算了所有的叶子节点的hash，然后在递归调用 buildIntermediate 来构建整个树
func buildWithContent(cs []Content, t *MerkleTree) (*Node, []*Node, error) {
	if len(cs) == 0 {
		return nil, nil, errors.New("error: cannot construct tree with no content")
	}
	var leafs []*Node
	for _, c := range cs {
		hash, err := c.CalculateHash()
		if err != nil {
			return nil, nil, err
		}

		leafs = append(leafs, &Node{
			Hash: hash,
			C:    c,
			leaf: true,
			Tree: t,
		})
	}
	if len(leafs)%2 == 1 {
		duplicate := &Node{
			Hash: leafs[len(leafs)-1].Hash,
			C:    leafs[len(leafs)-1].C,
			leaf: true,
			dup:  true,
			Tree: t,
		}
		leafs = append(leafs, duplicate)
	}
	root, err := buildIntermediate(leafs, t)
	if err != nil {
		return nil, nil, err
	}

	return root, leafs, nil
}

//buildIntermediate is a helper function that for a given list of leaf nodes, constructs
//the intermediate and root levels of the tree. Returns the resulting root node of the tree.
func buildIntermediate(nl []*Node, t *MerkleTree) (*Node, error) {
	var nodes []*Node
	for i := 0; i < len(nl); i += 2 {
		h := t.hashStrategy()
		var left, right int = i, i + 1
		if i+1 == len(nl) {
			right = i
		}
		chash := append(nl[left].Hash, nl[right].Hash...)
		if _, err := h.Write(chash); err != nil {
			return nil, err
		}
		n := &Node{
			Left:  nl[left],
			Right: nl[right],
			Hash:  h.Sum(nil),
			Tree:  t,
		}
		nodes = append(nodes, n)
		nl[left].Parent = n
		nl[right].Parent = n
		if len(nl) == 2 {
			return n, nil
		}
	}
	return buildIntermediate(nodes, t)
}

他のメソッドについては、ソース コードの実装を参照してください。組織的に考えると比較的わかりやすいです。