Add node methods

node.go

@@ -0,0 +1,143 @@
+package merkletree
+
+import (
+	"fmt"
+	"math/big"
+)
+
+// NodeType defines the type of node in the MT.
+type NodeType byte
+
+const (
+	// NodeTypeMiddle indicates the type of middle Node that has children.
+	NodeTypeMiddle NodeType = 0
+	// NodeTypeLeaf indicates the type of a leaf Node that contains a claim.
+	NodeTypeLeaf NodeType = 1
+	// NodeTypeEmpty indicates the type of an empty Node.
+	NodeTypeEmpty NodeType = 2
+
+	// DBEntryTypeRoot indicates the type of a DB entry that indicates the current Root of a MerkleTree
+	DBEntryTypeRoot NodeType = 3
+)
+
+// Node is the struct that represents a node in the MT. The node should not be
+// modified after creation because the cached key won't be updated.
+type Node struct {
+	// Type is the type of node in the tree.
+	Type NodeType
+	// ChildL is the left child of a middle node.
+	ChildL *Hash
+	// ChildR is the right child of a middle node.
+	ChildR *Hash
+	// Entry is the data stored in a leaf node.
+	Entry [2]*Hash
+	// key is a cache used to avoid recalculating key
+	key *Hash
+}
+
+// NewNodeLeaf creates a new leaf node.
+func NewNodeLeaf(k, v *Hash) *Node {
+	return &Node{Type: NodeTypeLeaf, Entry: [2]*Hash{k, v}}
+}
+
+// NewNodeMiddle creates a new middle node.
+func NewNodeMiddle(childL *Hash, childR *Hash) *Node {
+	return &Node{Type: NodeTypeMiddle, ChildL: childL, ChildR: childR}
+}
+
+// NewNodeEmpty creates a new empty node.
+func NewNodeEmpty() *Node {
+	return &Node{Type: NodeTypeEmpty}
+}
+
+// NewNodeFromBytes creates a new node by parsing the input []byte.
+func NewNodeFromBytes(b []byte) (*Node, error) {
+	if len(b) < 1 {
+		return nil, ErrNodeDataBadSize
+	}
+	n := Node{Type: NodeType(b[0])}
+	b = b[1:]
+	switch n.Type {
+	case NodeTypeMiddle:
+		if len(b) != 2*ElemBytesLen {
+			return nil, ErrNodeDataBadSize
+		}
+		n.ChildL, n.ChildR = &Hash{}, &Hash{}
+		copy(n.ChildL[:], b[:ElemBytesLen])
+		copy(n.ChildR[:], b[ElemBytesLen:ElemBytesLen*2])
+	case NodeTypeLeaf:
+		if len(b) != 2*ElemBytesLen {
+			return nil, ErrNodeDataBadSize
+		}
+		n.Entry = [2]*Hash{&Hash{}, &Hash{}}
+		copy(n.Entry[0][:], b[0:32])
+		copy(n.Entry[1][:], b[32:64])
+	case NodeTypeEmpty:
+		break
+	default:
+		return nil, ErrInvalidNodeFound
+	}
+	return &n, nil
+}
+
+// LeafKey computes the key of a leaf node given the hIndex and hValue of the
+// entry of the leaf.
+func LeafKey(k, v *Hash) (*Hash, error) {
+	return HashElemsKey(big.NewInt(1), k.BigInt(), v.BigInt())
+}
+
+// Key computes the key of the node by hashing the content in a specific way
+// for each type of node.  This key is used as the hash of the merklee tree for
+// each node.
+func (n *Node) Key() (*Hash, error) {
+	if n.key == nil { // Cache the key to avoid repeated hash computations.
+		// NOTE: We are not using the type to calculate the hash!
+		switch n.Type {
+		case NodeTypeMiddle: // H(ChildL || ChildR)
+			var err error
+			n.key, err = HashElems(n.ChildL.BigInt(), n.ChildR.BigInt())
+			if err != nil {
+				return nil, err
+			}
+		case NodeTypeLeaf:
+			var err error
+			n.key, err = LeafKey(n.Entry[0], n.Entry[1])
+			if err != nil {
+				return nil, err
+			}
+		case NodeTypeEmpty: // Zero
+			n.key = &HashZero
+		default:
+			n.key = &HashZero
+		}
+	}
+	return n.key, nil
+}
+
+// Value returns the value of the node.  This is the content that is stored in the backend database.
+func (n *Node) Value() []byte {
+	switch n.Type {
+	case NodeTypeMiddle: // {Type || ChildL || ChildR}
+		return append([]byte{byte(n.Type)}, append(n.ChildL[:], n.ChildR[:]...)...)
+	case NodeTypeLeaf: // {Type || Data...}
+		return append([]byte{byte(n.Type)}, append(n.Entry[0][:], n.Entry[1][:]...)...)
+	case NodeTypeEmpty: // {}
+		return []byte{}
+	default:
+		return []byte{}
+	}
+}
+
+// String outputs a string representation of a node (different for each type).
+func (n *Node) String() string {
+	switch n.Type {
+	case NodeTypeMiddle: // {Type || ChildL || ChildR}
+		return fmt.Sprintf("Middle L:%s R:%s", n.ChildL, n.ChildR)
+	case NodeTypeLeaf: // {Type || Data...}
+		return fmt.Sprintf("Leaf I:%v D:%v", n.Entry[0], n.Entry[1])
+	case NodeTypeEmpty: // {}
+		return "Empty"
+	default:
+		return "Invalid Node"
+	}
+}