Merge pull request #81 from pnagurny/feature/blockchain-cache

Cache blockchain data for fast startup time

lib/blockchain.js

@@ -18,6 +18,7 @@ function BlockChain() {
   };
   this.next = {};
   this.prev = {};
+  this.cache = [];
 }
 
 BlockChain.NULL = NULL;
@@ -112,6 +113,7 @@ BlockChain.prototype.confirm = function(hash) {
   this.next[prevHash] = hash;
   this.hashByHeight[height] = hash;
   this.height[hash] = height;
+  this.cache.push(this.getCachedDataForHash(hash));
 };
 
 BlockChain.prototype.unconfirm = function(hash) {
@@ -123,6 +125,7 @@ BlockChain.prototype.unconfirm = function(hash) {
   delete this.next[prevHash];
   delete this.hashByHeight[height];
   delete this.height[hash];
+  this.cache.pop();
 };
 
 BlockChain.prototype.hasData = function(hash) {
@@ -178,4 +181,24 @@ BlockChain.prototype.getCurrentHeight = function() {
   return this.height[this.tip];
 };
 
+BlockChain.prototype.loadFromCache = function(cache) {
+  for(var i = 0; i < cache.length; i++) {
+    this.prev[cache[i].hash] = cache[i].prevHash;
+    this.work[cache[i].hash] = cache[i].work;
+    this.confirm(cache[i].hash);
+  }
+};
+
+BlockChain.prototype.getCache = function() {
+  return this.cache;
+};
+
+BlockChain.prototype.getCachedDataForHash = function(hash) {
+  return {
+    hash: hash,
+    prevHash: this.prev[hash],
+    work: this.work[hash]
+  };
+};
+
 module.exports = BlockChain;

lib/node.js

@@ -128,6 +128,12 @@ BitcoreNode.prototype.initialize = function() {
           delete self.blockCache[deleteHash];
         }
       })
+      .then(function() {
+        // Update header cache every 100 blocks
+        if(block.height % 100 === 0) {
+          return self.blockService.saveBlockchainCache(self.blockchain.getCache());
+        }
+      })
       .catch(function(error) {
         self.stop(error);
       });

lib/services/block.js

@@ -38,7 +38,8 @@ var Index = {
   height: 'bh-', // bh-<hash> -> height (-1 means disconnected)
   tip: 'tip', // tip -> { hash: hex, height: int }, the latest tip
   work: 'wk-', // wk-<hash> -> amount of work for block
-  header: 'header-' // header-<hash> -> JSON for block header
+  header: 'header-', // header-<hash> -> JSON for block header
+  blockchain: 'bc-'
 };
 _.extend(Index, {
   getNextBlock: helper(Index.next),
@@ -466,39 +467,61 @@ BlockService.prototype.getBlockchain = function() {
   var blockchain = new BlockChain();
   var headers = [];
 
-  console.log('Fetching headers from db...');
-  var fetchHeader = function(blockHash) {
-    if (blockHash === BlockChain.NULL) {
-      console.log('All headers fetched, total =', headers.length);
-      return;
-    }
-    var headerKey = Index.getBlockHeader(blockHash);
-    return self.database.getAsync(headerKey)
-      .then(function(json) {
-        return bitcore.Block.BlockHeader.fromJSON(json);
-      })
-      .then(function(header) {
-        headers.push(header);
-        return fetchHeader(BufferUtil.reverse(header.prevHash).toString('hex'));
-      });
-  };
+  console.log('Fetching hashes from db...');
 
-  return self._getLatestHash()
-    .then(function(tip) {
-      if (!tip) {
-        console.log('No tip found, syncing blockchain from genesis block');
-        return null;
+  return self.database.getAsync(Index.blockchain, {valueEncoding: 'json'})
+    .catch(function(err) {
+      if(err instanceof LevelUp.errors.NotFoundError) {
+        return [];
       }
-      console.log('Tip is', tip);
-      return fetchHeader(tip)
-        .then(function() {
-          while (headers.length !== 0) {
-            var header = headers.pop();
-            blockchain.proposeNewHeader(header);
+      throw err;
+    })
+    .then(function(blockchainCache) {
+      console.log(blockchainCache.length + ' headers cached');
+
+      var fetchHeader = function(blockHash) {
+        if (blockHash === BlockChain.NULL) {
+          console.log('All headers fetched, total =', headers.length);
+          return Promise.resolve();
+        } else if(blockchainCache.length && blockchainCache[blockchainCache.length - 1].hash === blockHash) {
+          console.log(headers.length + ' non-cached headers loaded');
+          return Promise.resolve();
+        }
+        var headerKey = Index.getBlockHeader(blockHash);
+        return self.database.getAsync(headerKey)
+          .then(function(json) {
+            return bitcore.Block.BlockHeader.fromJSON(json);
+          })
+          .then(function(header) {
+            headers.push(header);
+            return fetchHeader(BufferUtil.reverse(header.prevHash).toString('hex'));
+          });
+      };
+
+      return self._getLatestHash()
+        .then(function(tip) {
+          if (!tip) {
+            console.log('No tip found, syncing blockchain from genesis block');
+            return null;
           }
-          return blockchain;
-        });
+          console.log('Tip is', tip);
+
+          return fetchHeader(tip)
+            .then(function() {
+              blockchain.loadFromCache(blockchainCache);
+
+              while (headers.length !== 0) {
+                var header = headers.pop();
+                blockchain.proposeNewHeader(header);
+              }
+              return blockchain;
+            });
+        })
     });
 };
 
+BlockService.prototype.saveBlockchainCache = function(cache) {
+  return this.database.putAsync(Index.blockchain, JSON.stringify(cache));
+}
+
 module.exports = BlockService;