Merge pull request bitcoinjs#509 from bitcoinjs/pow

Add Block proof-of-work validation function

Author: dcousens

package.json

@@ -62,6 +62,7 @@
     "bigi": "^1.4.0",
     "bip66": "^1.1.0",
     "bs58check": "^1.0.5",
+    "buffer-compare": "^1.1.0",
     "buffer-equals": "^1.0.3",
     "buffer-reverse": "^1.0.0",
     "create-hash": "^1.1.0",

src/block.js

@@ -1,5 +1,6 @@
 var bufferutils = require('./bufferutils')
 var bcrypto = require('./crypto')
+var compare = require('buffer-compare')
 
 var Transaction = require('./transaction')
 
@@ -115,4 +116,27 @@ Block.prototype.toHex = function (headersOnly) {
   return this.toBuffer(headersOnly).toString('hex')
 }
 
+Block.calculateTarget = function (bits) {
+  var exponent = ((bits & 0xff000000) >> 24) - 3
+  var mantissa = bits & 0x007fffff
+  var i = 31 - exponent
+
+  var target = new Buffer(32)
+  target.fill(0)
+
+  target[i] = mantissa & 0xff
+  target[i - 1] = mantissa >> 8
+  target[i - 2] = mantissa >> 16
+  target[i - 3] = mantissa >> 24
+
+  return target
+}
+
+Block.prototype.checkProofOfWork = function () {
+  var hash = [].reverse.call(this.getHash())
+  var target = Block.calculateTarget(this.bits)
+
+  return compare(hash, target) <= 0
+}
+
 module.exports = Block

test/block.js

@@ -1,12 +1,21 @@
 /* global describe, it, beforeEach */
 
 var assert = require('assert')
-
 var Block = require('../src/block')
 
 var fixtures = require('./fixtures/block')
 
 describe('Block', function () {
+  describe('calculateTarget', function () {
+    fixtures.targets.forEach(function (f) {
+      it('returns ' + f.expected + ' for 0x' + f.bits, function () {
+        var bits = parseInt(f.bits, 16)
+
+        assert.equal(Block.calculateTarget(bits).toString('hex'), f.expected)
+      })
+    })
+  })
+
   describe('fromBuffer/fromHex', function () {
     fixtures.valid.forEach(function (f) {
       it('imports the block: ' + f.description + ' correctly', function () {
@@ -52,7 +61,7 @@ describe('Block', function () {
         block = Block.fromHex(f.hex)
       })
 
-      it('calculates ' + f.hash + ' for the block: ' + f.description, function () {
+      it('returns ' + f.hash + ' for the block: ' + f.description, function () {
         assert.strictEqual(block.getHash().toString('hex'), f.hash)
       })
     })
@@ -66,7 +75,7 @@ describe('Block', function () {
         block = Block.fromHex(f.hex)
       })
 
-      it('calculates ' + f.id + ' for the block: ' + f.description, function () {
+      it('returns ' + f.id + ' for the block: ' + f.description, function () {
         assert.strictEqual(block.getId(), f.id)
       })
     })
@@ -87,4 +96,18 @@ describe('Block', function () {
       })
     })
   })
+
+  describe('checkProofOfWork', function () {
+    fixtures.valid.forEach(function (f) {
+      var block
+
+      beforeEach(function () {
+        block = Block.fromHex(f.hex)
+      })
+
+      it('returns ' + f.valid + ' for ' + f.id, function () {
+        assert.strictEqual(block.checkProofOfWork(), f.valid)
+      })
+    })
+  })
 })