Default callback function

lib/client.js

@@ -119,10 +119,11 @@ Client.prototype.mkdir = function(dir, attrs, callback) {
   if (attrs) {
     attrs.mode = getFolderAttr(process.platform, attrs);
   }
-
+  
   var self = this;
   var dirs = [];
   var exists = false;
+  callback = getCallback(self, callback);
 
   this.sftp(function(err, sftp) {
     if (err) {
@@ -163,6 +164,7 @@ Client.prototype.mkdir = function(dir, attrs, callback) {
 Client.prototype.write = function(options, callback) {
   var destination = options.destination;
   destination = unixy(destination);
+  callback = getCallback(self, callback);
 
   var attrs = options.attrs;
   var content = options.content;
@@ -256,6 +258,8 @@ Client.prototype.upload = function(src, dest, callback) {
   dest = unixy(dest);
 
   var self = this;
+
+  callback = getCallback(self, callback);
 
   async.waterfall([
     function(callback) {
@@ -291,6 +295,8 @@ Client.prototype.upload = function(src, dest, callback) {
 
 Client.prototype.download = function(src, dest, callback) {
   var self = this;
+
+  callback = getCallback(self, callback);
 
   self.sftp(function(err,sftp){
     if (err) {
@@ -332,3 +338,12 @@ function getFolderAttr(platform, attrs) {
     return attrs.mode || DEFAULT_MODE;
   }
 }
+
+function getCallback(self, callback) {
+  if (_.isFunction(callback)) {
+    return callback;
+  }
+  return function defaultCallback(error) {
+    self.emit('error', error);
+  }
+}