Optimize block list page to not parse all transactions from a block when

the only data that is interesting is number of transactions. Fixes 100%
CPU while building block list.

lib/blocks.js

@@ -135,16 +135,34 @@ BlockController.prototype.list = function(req, res) {
     async.mapSeries(
       hashes,
       function(hash, next) {
-        self.node.getBlock(hash, function(err, block) {
+        self.node.services.bitcoind.getBlock(hash, function(err, blockBuffer) {
           if(err) {
             return next(err);
           }
+          var br = new bitcore.encoding.BufferReader(blockBuffer);
+          // take a shortcut to get number of transactions and the blocksize.
+          // Also reads the coinbase transaction and only that.
+          // Old code parsed all transactions in every block _and_ then encoded
+          // them all back together to get the binary size of the block.
+          // FIXME: This code might still read the whole block. Fixing that
+          // would require changes in bitcore-node.
+          var header = bitcore.BlockHeader.fromBufferReader(br);
+          var info = {};
+          var txlength = br.readVarintNum();
+          info.transactions = [bitcore.Transaction().fromBufferReader(br)];
 
-          var info = self.node.services.bitcoind.getBlockIndex(hash);
+          var index = self.node.services.bitcoind.getBlockIndex(hash);
-          block.__height = info.height;
+          var block = {
+              height: index.height,
+              size: blockBuffer.length,
+              hash: hash,
+              time: header.time,
+              txlength: txlength,
+              poolInfo: self.getPoolInfo(info)
+          };
 
-          if(moreTs > block.header.timestamp) {
+          if(moreTs > header.timestamp) {
-            moreTs = block.header.timestamp;
+            moreTs = header.timestamp;
           }
 
           return next(null, block);
@@ -156,20 +174,11 @@ BlockController.prototype.list = function(req, res) {
         }
 
         blocks.sort(function(a, b) {
-          return b.__height - a.__height;
+          return b.height - a.height;
         });
 
         var data = {
-          blocks: blocks.map(function(block) {
+          blocks: blocks,
-            return {
-              height: block.__height,
-              size: block.toBuffer().length,
-              hash: block.hash,
-              time: block.header.time,
-              txlength: block.transactions.length,
-              poolInfo: self.getPoolInfo(block)
-            };
-          }),
           length: blocks.length,
           pagination: {
             next: next,