add derivation delay

lib/server.js

@@ -1045,7 +1045,8 @@ WalletService.prototype.getTxHistory = function(opts, cb) {
 
 
 WalletService.scanConfig = {
-  SCAN_WINDOW: 10,
+  SCAN_WINDOW: 20,
+  DERIVATION_DELAY: 10, // in milliseconds
 };
 
 /**
@@ -1063,7 +1064,9 @@ WalletService.prototype.scan = function(opts, cb) {
 
   function deriveAddresses(size, isChange, derivator, cb) {
     async.map(_.range(size), function(i, next) {
-      next(null, derivator(isChange));
+      setTimeout(function() {
+        next(null, derivator(isChange));
+      }, WalletService.scanConfig.DERIVATION_DELAY)
     }, cb);
   };
 

test/integration/server.js

@@ -2481,12 +2481,13 @@ describe('Wallet service', function() {
   });
 
   describe('#scan', function() {
-    var scanWindowOld = WalletService.scanConfig.SCAN_WINDOW;
+    var scanConfigOld = WalletService.scanConfig;
     beforeEach(function() {
       WalletService.scanConfig.SCAN_WINDOW = 2;
+      WalletService.scanConfig.DERIVATION_DELAY = 0;
     });
     afterEach(function() {
-      WalletService.scanConfig.SCAN_WINDOW = scanWindowOld;
+      WalletService.scanConfig = scanConfigOld;
     });
 
     it('should scan main addresses', function(done) {