From d58e09a3a7eabc0ab6f137d2b184f52de5d1aa34 Mon Sep 17 00:00:00 2001
From: Daniel Cousens <github@dcousens.com>
Date: Thu, 5 May 2016 00:42:05 +1000
Subject: [PATCH] Block: add checkMerkleRoot

---
 src/block.js             | 30 ++++++++++++++++++++++++++++++
 test/block.js            | 38 ++++++++++++++++++++++++++++++++++++++
 test/fixtures/block.json | 14 ++++++++++++++
 3 files changed, 82 insertions(+)

diff --git a/src/block.js b/src/block.js
index 75a7980..9356c89 100644
--- a/src/block.js
+++ b/src/block.js
@@ -1,3 +1,4 @@
+var createHash = require('create-hash')
 var bufferutils = require('./bufferutils')
 var bcrypto = require('./crypto')
 var bufferCompare = require('buffer-compare')
@@ -133,6 +134,35 @@ Block.calculateTarget = function (bits) {
   return target
 }
 
+Block.calculateMerkleRoot = function (transactions) {
+  var length = transactions.length
+  if (length === 0) throw TypeError('Cannot compute merkle root for zero transactions')
+
+  var hashes = transactions.map(function (transaction) { return transaction.getHash() })
+
+  while (length > 1) {
+    var j = 0
+
+    for (var i = 0; i < length; i += 2, ++j) {
+      var hasher = createHash('sha256')
+      hasher.update(hashes[i])
+      hasher.update(i + 1 !== length ? hashes[i + 1] : hashes[i])
+      hashes[j] = bcrypto.sha256(hasher.digest())
+    }
+
+    length = j
+  }
+
+  return hashes[0]
+}
+
+Block.prototype.checkMerkleRoot = function () {
+  if (!this.transactions) return false
+
+  var actualMerkleRoot = Block.calculateMerkleRoot(this.transactions)
+  return bufferCompare(this.merkleRoot, actualMerkleRoot) === 0
+}
+
 Block.prototype.checkProofOfWork = function () {
   var hash = bufferReverse(this.getHash())
   var target = Block.calculateTarget(this.bits)
diff --git a/test/block.js b/test/block.js
index 7dd653f..97cb700 100644
--- a/test/block.js
+++ b/test/block.js
@@ -97,6 +97,44 @@ describe('Block', function () {
     })
   })
 
+  describe('calculateMerkleRoot', function () {
+    it('should throw on zero-length transaction array', function () {
+      assert.throws(function () {
+        Block.calculateMerkleRoot([])
+      }, /Cannot compute merkle root for zero transactions/)
+    })
+
+    fixtures.valid.forEach(function (f) {
+      if (f.hex.length === 160) return
+
+      var block
+
+      beforeEach(function () {
+        block = Block.fromHex(f.hex)
+      })
+
+      it('returns ' + f.merkleRoot + ' for ' + f.id, function () {
+        assert.strictEqual(Block.calculateMerkleRoot(block.transactions).toString('hex'), f.merkleRoot)
+      })
+    })
+  })
+
+  describe('checkMerkleRoot', function () {
+    fixtures.valid.forEach(function (f) {
+      if (f.hex.length === 160) return
+
+      var block
+
+      beforeEach(function () {
+        block = Block.fromHex(f.hex)
+      })
+
+      it('returns ' + f.valid + ' for ' + f.id, function () {
+        assert.strictEqual(block.checkMerkleRoot(), true)
+      })
+    })
+  })
+
   describe('checkProofOfWork', function () {
     fixtures.valid.forEach(function (f) {
       var block
diff --git a/test/fixtures/block.json b/test/fixtures/block.json
index a18fca5..c7aa5f7 100644
--- a/test/fixtures/block.json
+++ b/test/fixtures/block.json
@@ -101,6 +101,20 @@
       "timestamp": 1439710609,
       "valid": false,
       "version": 3
+    },
+    {
+      "description": "Genesis Block",
+      "bits": 486604799,
+      "hash": "6fe28c0ab6f1b372c1a6a246ae63f74f931e8365e15a089c68d6190000000000",
+      "height": 0,
+      "hex": "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",
+      "id": "000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f",
+      "merkleRoot": "3ba3edfd7a7b12b27ac72c3e67768f617fc81bc3888a51323a9fb8aa4b1e5e4a",
+      "nonce": 2083236893,
+      "prevHash": "0000000000000000000000000000000000000000000000000000000000000000",
+      "timestamp": 1231006505,
+      "valid": true,
+      "version": 1
     }
   ],
   "invalid": [