Getting new error using Async with Node 6.2.2 "Callback already called"

What version of async are you using?

3.9.5

Which environment did the issue occur in (Node version/browser version)

Node 6.2.2 and 5.0.71.52

What did you do? Please include a minimal reproducable case illustrating issue.

This app

var fs = require('fs'),
    async = require('async'),
    _dir = './data/';

var writeStream = fs.createWriteStream('./log.txt',
      {'flags' : 'a',
       'encoding' : 'utf8',
       'mode' : 0666});

async.waterfall([
   function readDir(callback) {
      fs.readdir(_dir, function(err, files) {
         callback(err,files);
      });
   },
   function loopFiles(files, callback) {
      files.forEach(function (name) {
         callback (null, name);
      });
   },

   function checkFile(file, callback) {
      fs.stat(_dir + file, function(err, stats) {
         callback(err, stats, file);
      });
   },
   function readData(stats, file, callback) {
      if (stats.isFile())
         fs.readFile(_dir + file, 'utf8', function(err, data){
           callback(err,file,data);
       });
   },
   function modify(file, text, callback) {
      var adjdata=text.replace(/somecompany\.com/g,'burningbird.net');
      callback(null, file, adjdata);
   },
   function writeData(file, text, callback) {
       fs.writeFile(_dir + file, text, function(err) {
          callback(err,file);
       });
   },

   function logChange(file, callback) {
       writeStream.write('changed ' + file + '\n', 'utf8',
                       function(err) {
          callback(err);
      });
   }
], function (err) {
         if (err) {
            console.log(err.message);
         } else {
            console.log('modified files');
         }
});

What did you expect to happen?

That I wouldn’t get an error

What was the actual result?

I’m getting

/home/examples/public_html/learnnode2-examples/chap3/node_modules/async/dist/async.js:837 if (fn === null) throw new Error(“Callback was already called.”); ^

Error: Callback was already called.

The callback function in the following section of the code

function loopFiles(files, callback) { files.forEach(function (name) { callback (null, name); }); },

Is lost on the second run.

I’ve run this code successfully through several versions of Node. I believe I did test this when Node 6 was first released.

In the second iteration, the function isn’t null, but something is happening in the Async code resulting in this error.

[megawac]

I just ran slightly modified code in Ubuntu 16.04 in node 6.0.0 and 6.2.2. In both cases I got the same output:

• data1.txt, callback for the first item (data1.txt)
• Error: callback was already called

Modified script:

var fs = require('fs'),
    async = require('async'),
    _dir = './data/';

async.waterfall([
   function readDir(callback) {
      fs.readdir(_dir, callback);
   },
   function loopFiles(files, callback) {
      files.forEach(function (name) {
         callback (null, name);
      });
   },
   console.log.bind(console)
], console.error)

$ ls data
> data1.txt  data2.txt

[ex1st]

Because you called callback many times in here:

function loopFiles(files, callback) {
    files.forEach(function(name) {
        callback(null, name);
    });
},

Please use async.forEach for this case.