feat(Blockchain): allow custom BlockHeader constructor

This can be used for blockchains that have a different block format, for example the alpha sidechain.

Author: mappum

lib/blockStore.js

@@ -26,6 +26,8 @@ var BlockStore = module.exports = function (opts, cb) {
   }
   opts = opts || {}
 
+  this.BlockHeader = opts.BlockHeader || bitcore.BlockHeader
+
   this.store = opts.store || u.createStore({
     path: opts.path,
     db: opts.db,
@@ -44,7 +46,7 @@ BlockStore.prototype.put = function (block, opts, cb) {
   }
   if (block.height == null) return cb(new Error('Must specify height'))
   if (block.header == null) return cb(new Error('Must specify header'))
-  if (!(block.header instanceof bitcore.BlockHeader)) {
+  if (!(block.header instanceof this.BlockHeader)) {
     return cb(new Error('Header must be instance of BlockHeader'))
   }
   if (opts.tip) opts.best = true
@@ -81,10 +83,11 @@ BlockStore.prototype.get = function (hash, cb) {
     return cb(err)
   }
 
+  var self = this
   this.store.get(key, function (err, block) {
     if (err) return cb(err)
     var header = new Buffer(block.header, 'base64')
-    block.header = bitcore.BlockHeader.fromBuffer(header)
+    block.header = self.BlockHeader.fromBuffer(header)
     cb(null, block)
   })
 }

lib/blockchain.js

@@ -30,6 +30,8 @@ var Blockchain = module.exports = function (opts) {
     header: genesisHeader
   }
 
+  this.BlockHeader = genesisHeader.constructor
+
   if (opts.checkpoint) {
     this.checkpoint = opts.checkpoint
     this.checkpoint.hash = u.toHash(this.checkpoint.header.hash)
@@ -39,7 +41,10 @@ var Blockchain = module.exports = function (opts) {
   this.initialized = false
   this.closed = false
 
-  this.store = opts.store || new BlockStore({ path: opts.path })
+  this.store = opts.store || new BlockStore({
+    path: opts.path,
+    BlockHeader: this.BlockHeader
+  })
   this._initStore(function (err) {
     if (err && err !== storeClosedError) return self._error(err)
     else if (err && err === storeClosedError) return
@@ -358,8 +363,8 @@ Blockchain.prototype._listenForUpdates = function () {
   var self = this
   this.peerGroup.on('inv', function (peer, message) {
     message.inventory.forEach(function (item) {
-      if (item.type === Inventory.TYPE.BLOCK
-      || item.type === Inventory.TYPE.FILTERED_BLOCK) {
+      if (item.type === Inventory.TYPE.BLOCK ||
+      item.type === Inventory.TYPE.FILTERED_BLOCK) {
         if (self.lastInv && self.lastInv.compare(item.hash) === 0) return
         self.lastInv = item.hash
         self._getHeaders()
@@ -444,18 +449,18 @@ Blockchain.prototype.processHeader = function (prev, header, cb) {
     return cb(new Error('Block does not connect to previous'), block)
   }
   // TODO: testnet difficulty rules (for now we are just not verifying testnet block difficulty)
-  if (this.network !== bitcore.Networks.testnet
-  && !self.shouldRetarget(height)
-  && header.bits !== prev.header.bits) {
+  if (this.network !== bitcore.Networks.testnet &&
+  !self.shouldRetarget(height) &&
+  header.bits !== prev.header.bits) {
     return cb(new Error('Unexpected difficulty change'), block)
   }
   if (!header.validProofOfWork()) {
     return cb(new Error('Invalid proof of work'), block)
   }
   // TODO: other checks (timestamp, version)
-  if (self.shouldRetarget(height)
+  if (self.shouldRetarget(height) &&
   // don't verify retarget if it requires checking before our checkpoint
-  && !(this.checkpoint && height - this.checkpoint.height < this.interval)) {
+  !(this.checkpoint && height - this.checkpoint.height < this.interval)) {
     return self.calculateTarget(block, function (err, target) {
       if (err) return cb(err, block)