Second part for #137

The `FragmentTree` does not follow orignal code hashing.
A fragment leaf consists of `value`, `slot` and `byteLength`.
`byteLength` is the orignal length of any given bytes.

test/utils/FragmentTree.js

@@ -0,0 +1,34 @@
+const assert = require('assert');
+const { randomFillSync } = require('crypto');
+
+const { FragmentTree } = require('./../../utils');
+
+function randomString (size) {
+  return `0x${randomFillSync(Buffer.alloc(size)).toString('hex')}`;
+}
+
+describe('FragmentTree', function () {
+  for (let i = 1; i < 1024; i++) {
+    it(`Loop #${i}`, () => {
+      const bytecode = randomString(i);
+      const byteLength = (bytecode.length - 2) / 2;
+      const tree = new FragmentTree().run(bytecode);
+      const slots = ~~((i + 31) / 32);
+
+      for (let x = 0; x < slots; x++) {
+        const leaf = tree.leaves[x];
+        const startOffset = (x * 64) + 2;
+        const value = bytecode.substring(startOffset, startOffset + 64).padEnd(64, '0');
+
+        assert.equal(leaf.slot, x, 'slot should match');
+        assert.equal(leaf.byteLength, byteLength, 'byteLength should match');
+        assert.equal(leaf.value, `0x${value}`, 'value should match');
+      }
+
+      assert.equal(tree.leaves.length, slots + slots % 2, 'number of leaves should match');
+
+      const proof = tree.calculateProof(slots - 1);
+      assert.ok(tree.verifyProof(tree.leaves[slots - 1], proof), 'verifyProof');
+    });
+  }
+});

utils/AbstractMerkleTree.js

@@ -86,7 +86,7 @@ module.exports = class AbstractMerkleTree {
       let last = this.tree[level - 1];
       let cur = [];
 
-      if (last.length === 1) {
+      if (last.length <= 1 && level > 1) {
         // done
         break;
       }
@@ -125,8 +125,8 @@ module.exports = class AbstractMerkleTree {
       for (let y = 0; y < row.length; y++) {
         const e = row[y];
         const h = e.hash.substring(2, 6);
-        const hl = e.left.hash.substring(2, 6);
-        const hr = e.right.hash.substring(2, 6);
+        const hl = e.left ? e.left.hash.substring(2, 6) : '?';
+        const hr = e.right ? e.right.hash.substring(2, 6) : '?';
 
         res += ` [ ${h} (l:${hl} r:${hr}) ] `;
       }

utils/FragmentTree.js

@@ -0,0 +1,68 @@
+const ethers = require('ethers');
+
+const AbstractMerkleTree = require('./AbstractMerkleTree');
+
+// We should support compressed proofs in the future,
+// means re-using hashes if we construct a proof for more than 1 slot.
+module.exports = class FragmentTree extends AbstractMerkleTree {
+  /// @dev return hash proof for `slot`,
+  /// `slot` is position in `this.leaves`.
+  /// @return proof - array of 32 bytes hex-string (hashes)
+  calculateProof (slot) {
+    const proof = [];
+    const len = this.depth - 1;
+
+    for (let i = 0; i < len; i++) {
+      proof.push(this.tree[i][slot ^ 1].hash);
+      slot >>= 1;
+    }
+    return proof;
+  }
+
+  /// @dev verify if given `proofs` and `leaf` match `this.root.hash`
+  verifyProof (leaf, proofs) {
+    const len = proofs.length;
+    let hash = leaf.hash;
+    let slot = leaf.slot;
+
+    for (let i = 0; i < len; i++) {
+      const proof = proofs[i];
+
+      if (slot % 2 === 0) {
+        hash = this.constructor.hash(hash, proof);
+      } else {
+        hash = this.constructor.hash(proof, hash);
+      }
+      slot >>= 1;
+    }
+
+    return hash === this.root.hash;
+  }
+
+  /// @notice build the tree for the given hex-string `data`.
+  /// @dev `data` will be splited into fragments and padded to one word (32 bytes).
+  run (data) {
+    data = data.replace('0x', '');
+
+    this.tree = [[]];
+
+    const leaves = this.tree[0];
+    const byteLength = data.length / 2;
+    const len = data.length;
+    let slot = 0;
+
+    for (let i = 0; i < len;) {
+      const value = '0x' + data.substring(i, i += 64).padEnd(64, '0');
+      const hash = ethers.utils.solidityKeccak256(
+        ['bytes32', 'uint256', 'uint256'],
+        [value, slot, byteLength]
+      );
+
+      slot = leaves.push({ hash, value, slot, byteLength });
+    }
+
+    this.recal(0);
+
+    return this;
+  }
+};

utils/index.js

@@ -4,6 +4,7 @@ const OffchainStepper = require('./OffchainStepper.js');
 const Merkelizer = require('./Merkelizer.js');
 const ProofHelper = require('./ProofHelper.js');
 const ExecutionPoker = require('./ExecutionPoker.js');
+const FragmentTree = require('./FragmentTree.js');
 
 module.exports = {
   Constants,
@@ -12,4 +13,5 @@ module.exports = {
   Merkelizer,
   ProofHelper,
   ExecutionPoker,
+  FragmentTree,
 };