store after each branch derivation to save progress

lib/server.js

@@ -1143,8 +1143,6 @@ WalletService.prototype.scan = function(opts, cb) {
 
   opts = opts || {};
 
-  var allAddresses = [];
-
   function deriveAddresses(size, derivator, cb) {
     async.mapSeries(_.range(size), function(i, next) {
       setTimeout(function() {
@@ -1160,6 +1158,7 @@ WalletService.prototype.scan = function(opts, cb) {
 
   function scanBranch(derivator, cb) {
     var activity = true;
+    var allAddresses = [];
     async.whilst(function() {
       return activity;
     }, function(next) {
@@ -1172,7 +1171,9 @@ WalletService.prototype.scan = function(opts, cb) {
           next();
         });
       });
-    }, cb);
+    }, function(err) {
+      return cb(err, _.flatten(allAddresses));
+    });
   };
 
 
@@ -1193,13 +1194,11 @@ WalletService.prototype.scan = function(opts, cb) {
       });
 
       async.eachSeries(derivators, function(derivator, next) {
-        scanBranch(derivator, next);
-      }, function(err) {
-        if (err) return cb(err);
-        self.storage.storeAddressAndWallet(wallet, _.flatten(allAddresses), function(err) {
-          return cb(err);
+        scanBranch(derivator, function(err, addresses) {
+          if (err) return next(err);
+          self.storage.storeAddressAndWallet(wallet, addresses, next);
         });
-      });
+      }, cb);
     });
   });