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node.go
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node.go
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package node
import (
"encoding/hex"
"fmt"
"github.com/onflow/flow-go/ledger"
"github.com/onflow/flow-go/ledger/common/hash"
)
// Node defines an Mtrie node
//
// DEFINITIONS:
// * HEIGHT of a node v in a tree is the number of edges on the longest
// downward path between v and a tree leaf.
//
// Conceptually, an MTrie is a sparse Merkle Trie, which has two node types:
// * INTERIM node: has at least one child (i.e. lChild or rChild is not
// nil). Interim nodes do not store a path and have no payload.
// * LEAF node: has _no_ children.
// Per convention, we also consider nil as a leaf. Formally, nil is the generic
// representative for any empty (sub)-trie (i.e. a trie without allocated
// registers).
//
// Nodes are supposed to be treated as _immutable_ data structures.
// TODO: optimized data structures might be able to reduce memory consumption
type Node struct {
// Implementation Comments:
// Formally, a tree can hold up to 2^maxDepth number of registers. However,
// the current implementation is designed to operate on a sparsely populated
// tree, holding much less than 2^64 registers.
lChild *Node // Left Child
rChild *Node // Right Child
height int // height where the Node is at
path ledger.Path // the storage path (dummy value for interim nodes)
payload *ledger.Payload // the payload this node is storing (leaf nodes only)
hashValue hash.Hash // hash value of node (cached)
}
// NewNode creates a new Node.
// UNCHECKED requirement: combination of values must conform to
// a valid node type (see documentation of `Node` for details)
func NewNode(height int,
lchild,
rchild *Node,
path ledger.Path,
payload *ledger.Payload,
hashValue hash.Hash,
) *Node {
n := &Node{
lChild: lchild,
rChild: rchild,
height: height,
path: path,
hashValue: hashValue,
payload: payload,
}
return n
}
// NewLeaf creates a compact leaf Node.
// UNCHECKED requirement: height must be non-negative
// UNCHECKED requirement: payload is non nil
// UNCHECKED requirement: payload should be deep copied if received from external sources
func NewLeaf(path ledger.Path,
payload *ledger.Payload,
height int,
) *Node {
n := &Node{
lChild: nil,
rChild: nil,
height: height,
path: path,
payload: payload,
}
n.hashValue = n.computeHash()
return n
}
// NewInterimNode creates a new interim Node.
// UNCHECKED requirement:
// * for any child `c` that is non-nil, its height must satisfy: height = c.height + 1
func NewInterimNode(height int, lchild, rchild *Node) *Node {
n := &Node{
lChild: lchild,
rChild: rchild,
height: height,
payload: nil,
}
n.hashValue = n.computeHash()
return n
}
// NewInterimCompactifiedNode creates a new compactified interim Node. For compactification,
// we only consider the immediate children. When starting with a maximally pruned trie and
// creating only InterimCompactifiedNodes during an update, the resulting trie remains maximally
// pruned. Details on compactification:
// * If _both_ immediate children represent completely unallocated sub-tries, then the sub-trie
// with the new interim node is also completely empty. We return nil.
// * If either child is a leaf (i.e. representing a single allocated register) _and_ the other
// child represents a completely unallocated sub-trie, the new interim node also only holds
// a single allocated register. In this case, we return a compactified leaf.
// UNCHECKED requirement:
// * for any child `c` that is non-nil, its height must satisfy: height = c.height + 1
func NewInterimCompactifiedNode(height int, lChild, rChild *Node) *Node {
if lChild.IsDefaultNode() {
lChild = nil
}
if rChild.IsDefaultNode() {
rChild = nil
}
// CASE (a): _both_ children do _not_ contain any allocated registers:
if lChild == nil && rChild == nil {
return nil // return nil representing as completely empty sub-trie
}
// CASE (b): one child is a compactified leaf (single allocated register) _and_ the other child represents
// an empty subtrie => in total we have one allocated register, which we represent as single leaf node
if rChild == nil && lChild.IsLeaf() {
h := hash.HashInterNode(lChild.hashValue, ledger.GetDefaultHashForHeight(lChild.height))
return &Node{height: height, path: lChild.path, payload: lChild.payload, hashValue: h}
}
if lChild == nil && rChild.IsLeaf() {
h := hash.HashInterNode(ledger.GetDefaultHashForHeight(rChild.height), rChild.hashValue)
return &Node{height: height, path: rChild.path, payload: rChild.payload, hashValue: h}
}
// CASE (b): both children contain some allocated registers => we can't compactify; return a full interim leaf
return NewInterimNode(height, lChild, rChild)
}
// IsDefaultNode returns true iff the sub-trie represented by this root node contains
// only unallocated registers. This is the case, if the node is nil or the node's hash
// is equal to the default hash value at the respective height.
func (n *Node) IsDefaultNode() bool {
if n == nil {
return true
}
return n.hashValue == ledger.GetDefaultHashForHeight(n.height)
}
// computeHash returns the hashValue of the node
func (n *Node) computeHash() hash.Hash {
// check for leaf node
if n.lChild == nil && n.rChild == nil {
// if payload is non-nil, compute the hash based on the payload content
if n.payload != nil {
return ledger.ComputeCompactValue(hash.Hash(n.path), n.payload.Value, n.height)
}
// if payload is nil, return the default hash
return ledger.GetDefaultHashForHeight(n.height)
}
// this is an interim node at least one of lChild or rChild is not nil.
var h1, h2 hash.Hash
if n.lChild != nil {
h1 = n.lChild.Hash()
} else {
h1 = ledger.GetDefaultHashForHeight(n.height - 1)
}
if n.rChild != nil {
h2 = n.rChild.Hash()
} else {
h2 = ledger.GetDefaultHashForHeight(n.height - 1)
}
return hash.HashInterNode(h1, h2)
}
// VerifyCachedHash verifies the hash of a node is valid
func verifyCachedHashRecursive(n *Node) bool {
if n == nil {
return true
}
if !verifyCachedHashRecursive(n.lChild) || !verifyCachedHashRecursive(n.rChild) {
return false
}
computedHash := n.computeHash()
return n.hashValue == computedHash
}
// VerifyCachedHash verifies the hash of a node is valid
func (n *Node) VerifyCachedHash() bool {
return verifyCachedHashRecursive(n)
}
// Hash returns the Node's hash value.
// Do NOT MODIFY returned slice!
func (n *Node) Hash() hash.Hash {
return n.hashValue
}
// Height returns the Node's height.
// Per definition, the height of a node v in a tree is the number
// of edges on the longest downward path between v and a tree leaf.
func (n *Node) Height() int {
return n.height
}
// Path returns a pointer to the Node's register storage path.
// If the node is not a leaf, the function returns `nil`.
func (n *Node) Path() *ledger.Path {
if n.IsLeaf() {
return &n.path
}
return nil
}
// Payload returns the the Node's payload.
// Do NOT MODIFY returned slices!
func (n *Node) Payload() *ledger.Payload {
return n.payload
}
// LeftChild returns the the Node's left child.
// Only INTERIM nodes have children.
// Do NOT MODIFY returned Node!
func (n *Node) LeftChild() *Node { return n.lChild }
// RightChild returns the the Node's right child.
// Only INTERIM nodes have children.
// Do NOT MODIFY returned Node!
func (n *Node) RightChild() *Node { return n.rChild }
// IsLeaf returns true if and only if Node is a LEAF.
func (n *Node) IsLeaf() bool {
// Per definition, a node is a leaf if and only it has no children
return n == nil || (n.lChild == nil && n.rChild == nil)
}
// FmtStr provides formatted string representation of the Node and sub tree
func (n *Node) FmtStr(prefix string, subpath string) string {
right := ""
if n.rChild != nil {
right = fmt.Sprintf("\n%v", n.rChild.FmtStr(prefix+"\t", subpath+"1"))
}
left := ""
if n.lChild != nil {
left = fmt.Sprintf("\n%v", n.lChild.FmtStr(prefix+"\t", subpath+"0"))
}
payloadSize := 0
if n.payload != nil {
payloadSize = n.payload.Size()
}
hashStr := hex.EncodeToString(n.hashValue[:])
hashStr = hashStr[:3] + "..." + hashStr[len(hashStr)-3:]
return fmt.Sprintf("%v%v: (path:%v, payloadSize:%d hash:%v)[%s] (obj %p) %v %v ", prefix, n.height, n.path, payloadSize, hashStr, subpath, n, left, right)
}
// AllPayloads returns the payload of this node and all payloads of the subtrie
func (n *Node) AllPayloads() []ledger.Payload {
return n.appendSubtreePayloads([]ledger.Payload{})
}
// appendSubtreePayloads appends the payloads of the subtree with this node as root
// to the provided Payload slice. Follows same pattern as Go's native append method.
func (n *Node) appendSubtreePayloads(result []ledger.Payload) []ledger.Payload {
if n == nil {
return result
}
if n.IsLeaf() {
return append(result, *n.Payload())
}
result = n.lChild.appendSubtreePayloads(result)
result = n.rChild.appendSubtreePayloads(result)
return result
}