express-Formidable "Can't set headers after they are sent."

Question

i use the module express formidable

when i load a page 2 time i have that on console

GET /users 304 6.948 ms - -
GET /users 304 213.344 ms - -
Error: Can't set headers after they are sent.
at validateHeader (_http_outgoing.js:489:11)
at ServerResponse.setHeader (_http_outgoing.js:496:3)
at ServerResponse.header (/home/neolinux/Encoding-Service/encode-service/node_modules/express/lib/response.js:730:10)
at ServerResponse.contentType (/home/neolinux/Encoding-Service/encode-service/node_modules/express/lib/response.js:558:15)
at ServerResponse.send (/home/neolinux/Encoding-Service/encode-service/node_modules/express/lib/response.js:145:14)
at done (/home/neolinux/Encoding-Service/encode-service/node_modules/express/lib/response.js:967:10)
at Object.exports.renderFile (/home/neolinux/Encoding-Service/encode-service/node_modules/pug/lib/index.js:422:12)
at View.exports.__express [as engine] (/home/neolinux/Encoding-Service/encode-service/node_modules/pug/lib/index.js:465:11)
at View.render (/home/neolinux/Encoding-Service/encode-service/node_modules/express/lib/view.js:127:8)
at tryRender (/home/neolinux/Encoding-Service/encode-service/node_modules/express/lib/application.js:640:10)

this is my app.js

var express = require('express');
var path = require('path');
var favicon = require('serve-favicon');
var logger = require('morgan');
var cookieParser = require('cookie-parser');


var index = require('./routes/index');
var users = require('./routes/users');

const util=require("util");
var app = express();

const formidable = require('express-formidable');

// view engine setup
app.set('views', path.join(__dirname, 'views'));
app.set('view engine', 'pug');

// uncomment after placing your favicon in /public
//app.use(favicon(path.join(__dirname, 'public', 'favicon.ico')));
app.use(logger('dev'));

app.use(cookieParser());
app.use(express.static(path.join(__dirname, 'public')));

app.use(formidable({
    uploadDir:  path.join(__dirname, '/Upload'),
}));

app.use('/', index);
app.use('/users', users);

// catch 404 and forward to error handler
app.use(function(req, res, next) {
  var err = new Error('Not Found');
  err.status = 404;
  next(err);
});

// error handler
app.use(function(err, req, res, next) {
  // set locals, only providing error in development
  res.locals.message = err.message;
  res.locals.error = req.app.get('env') === 'development' ? err : {};

  // render the error page
  res.status(err.status || 500);
  res.render('error');
});

module.exports = app;

you must now, if i remove formidable i don't have the error . Any idea ?

express v 4.5 node v8

don't read the next text, this is just for remove the stackoverflow error !!! i don't know how to add more information for this problem.

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Answer 1

There is a solution, express-formidable have probleme in middleware version,

there are two of each event handler which means each event is handled twice, leading to two next() calls and hence an exception about headers being set too late.

the solution is in app.js:

const formidable = require('formidable');
app.use(function (req, res, next) {
    var form = new formidable.IncomingForm({
        encoding: 'utf-8',
        uploadDir:  path.join(__dirname, '/Upload'),
        multiples: true,
        keepExtensions: true
    })
    form.once('error', console.log)
    form.parse(req, function (err, fields, files) {
        Object.assign(req, {fields, files});
        next();
    })
})
app.use('/', index);