From 4d825639606b8db83c8e4c9c46b8e8771499071b Mon Sep 17 00:00:00 2001
From: Alexander Early <alexander.early@gmail.com>
Date: Sun, 6 Mar 2016 15:02:10 -0800
Subject: [PATCH] defend against multiple callbacks.  Fixes #814

---
 lib/auto.js        |  5 +++--
 mocha_test/auto.js | 14 +++++++++++++-
 2 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/lib/auto.js b/lib/auto.js
index 0e9d10867..ae3ecfcf8 100644
--- a/lib/auto.js
+++ b/lib/auto.js
@@ -10,6 +10,7 @@ import okeys from 'lodash/keys';
 import noop from 'lodash/noop';
 import once from 'lodash/once';
 import rest from 'lodash/rest';
+import onlyOnce from './internal/onlyOnce';
 
 import setImmediate from './internal/setImmediate';
 
@@ -60,7 +61,7 @@ export default function (tasks, concurrency, callback) {
     arrayEach(keys, function (k) {
         if (hasError) return;
         var task = isArray(tasks[k]) ? tasks[k]: [tasks[k]];
-        var taskCallback = rest(function(err, args) {
+        var taskCallback = onlyOnce(rest(function(err, args) {
             runningTasks--;
             if (args.length <= 1) {
                 args = args[0];
@@ -80,7 +81,7 @@ export default function (tasks, concurrency, callback) {
                 results[k] = args;
                 setImmediate(taskComplete);
             }
-        });
+        }));
 
         var requires = task.slice(0, task.length - 1);
 
diff --git a/mocha_test/auto.js b/mocha_test/auto.js
index c6b7150ea..6b96be4fc 100644
--- a/mocha_test/auto.js
+++ b/mocha_test/auto.js
@@ -4,7 +4,7 @@ var _ = require('lodash');
 
 describe('auto', function () {
 
-    it('auto', function(done){
+    it('basics', function(done){
         var callOrder = [];
         async.auto({
             task1: ['task2', function(results, callback){
@@ -344,4 +344,16 @@ describe('auto', function () {
         });
     });
 
+    it("does not allow calling callbacks twice", function () {
+        expect(function () {
+            async.auto({
+                bad: function (cb) {
+                    cb();
+                    cb();
+                }
+            }, function () {});
+
+        }).to.throw();
+    });
+
 });