check elements length in constructor

src/FixedMerkleTree.ts

@@ -192,7 +192,7 @@ export default class MerkleTree {
       throw new Error('Element not found')
     }
     const edgePath = this.path(edgeIndex)
-    return { edgePath, edgeElement, edgeIndex }
+    return { edgePath, edgeElement, edgeIndex, edgeElementsCount: this._layers[0].length }
   }
 
   /**
@@ -202,7 +202,7 @@ export default class MerkleTree {
   getTreeSlices(count = 4): { edge: TreeEdge, elements: Element[] }[] {
     const length = this._layers[0].length
     let size = Math.ceil(length / count)
-    size % 2 && size++
+    if (size % 2) size++
     const slices = []
     for (let i = 0; i < length; i += size) {
       const edgeLeft = i

src/PartialMerkleTree.ts

@@ -32,16 +32,16 @@ export class PartialMerkleTree {
     edgePath,
     edgeElement,
     edgeIndex,
+    edgeElementsCount,
   }: TreeEdge, leaves: Element[], { hashFunction, zeroElement }: MerkleTreeOptions = {}) {
-    hashFunction = hashFunction || defaultHash
-    const hashFn = (left, right) => (left !== undefined && right !== undefined) ? hashFunction(left, right) : undefined
+    if (edgeIndex + leaves.length !== edgeElementsCount) throw new Error('Invalid number of elements')
     this._edgeLeafProof = edgePath
     this._initialRoot = edgePath.pathRoot
     this.zeroElement = zeroElement ?? 0
     this._edgeLeaf = { data: edgeElement, index: edgeIndex }
     this._leavesAfterEdge = leaves
     this.levels = levels
-    this._hashFn = hashFn
+    this._hashFn = hashFunction || defaultHash
     this._createProofMap()
     this._buildTree()
   }
@@ -257,9 +257,9 @@ export class PartialMerkleTree {
   serialize(): SerializedPartialTreeState {
     const leaves = this.layers[0].slice(this._edgeLeaf.index)
     return {
-      _initialRoot: this._initialRoot,
       _edgeLeafProof: this._edgeLeafProof,
       _edgeLeaf: this._edgeLeaf,
+      _edgeElementsCount: this._layers[0].length,
       levels: this.levels,
       leaves,
       _zeros: this._zeros,
@@ -271,6 +271,7 @@ export class PartialMerkleTree {
       edgePath: data._edgeLeafProof,
       edgeElement: data._edgeLeaf.data,
       edgeIndex: data._edgeLeaf.index,
+      edgeElementsCount: data._edgeElementsCount,
     }
     return new PartialMerkleTree(data.levels, edge, data.leaves, {
       hashFunction,

src/index.ts

@@ -20,11 +20,11 @@ export type SerializedTreeState = {
 }
 
 export type SerializedPartialTreeState = {
-  levels: number,
+  levels: number
   leaves: Element[]
-  _zeros: Array<Element>,
-  _edgeLeafProof: ProofPath,
-  _initialRoot: Element,
+  _edgeElementsCount: number
+  _zeros: Array<Element>
+  _edgeLeafProof: ProofPath
   _edgeLeaf: LeafWithIndex
 }
 
@@ -38,6 +38,7 @@ export type TreeEdge = {
   edgeElement: Element;
   edgePath: ProofPath;
   edgeIndex: number;
+  edgeElementsCount: number;
 }
 export type LeafWithIndex = { index: number, data: Element }
 

test/fixedMerkleTree.spec.ts

@@ -1,4 +1,4 @@
-import { MerkleTree, TreeEdge } from '../src'
+import { MerkleTree, PartialMerkleTree, TreeEdge } from '../src'
 import { assert, should } from 'chai'
 import { buildMimcSponge } from 'circomlibjs'
 import { createHash } from 'crypto'
@@ -292,6 +292,7 @@ describe('MerkleTree', () => {
         },
         edgeElement: 4,
         edgeIndex: 4,
+        edgeElementsCount: 6,
       }
       const tree = new MerkleTree(4, [0, 1, 2, 3, 4, 5])
       assert.deepEqual(tree.getTreeEdge(4), expectedEdge)
@@ -302,7 +303,38 @@ describe('MerkleTree', () => {
       should().throw(call, 'Element not found')
     })
   })
+  describe('#getTreeSlices', () => {
+    let fullTree: MerkleTree
+    before(() => {
+      const elements = Array.from({ length: 128 }, (_, i) => i)
+      fullTree = new MerkleTree(10, elements)
+    })
+    it('should return correct slices count', () => {
+      const count = 5
+      const slicesCount = fullTree.getTreeSlices(5).length
+      should().equal(count, slicesCount)
+    })
 
+    it('should be able to create partial tree from last slice', () => {
+      const lastSlice = fullTree.getTreeSlices().pop()
+      const partialTree = new PartialMerkleTree(10, lastSlice.edge, lastSlice.elements)
+      should().equal(partialTree.root, fullTree.root)
+    })
+
+    it('should be able to build full tree from slices', () => {
+      const slices = fullTree.getTreeSlices()
+      const lastSlice = slices.pop()
+      const partialTree = new PartialMerkleTree(10, lastSlice.edge, lastSlice.elements)
+      slices.reverse().forEach(({ edge, elements }) => partialTree.shiftEdge(edge, elements))
+      assert.deepEqual(partialTree.layers, fullTree.layers)
+    })
+
+    it('should throw if invalid number of elements', () => {
+      const [firstSlice] = fullTree.getTreeSlices()
+      const call = () => new PartialMerkleTree(10, firstSlice.edge, firstSlice.elements)
+      should().throw(call, 'Invalid number of elements')
+    })
+  })
   describe('#getters', () => {
     const elements = [1, 2, 3, 4, 5]
     const layers = [