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This module is a variant of formidable with tweaks to enable use in serverless environments (AWS Lambda, Firebase/Google Cloud Functions, etc.) and environments where the request has already been processed (e.g. by bodyparser).

The functionality and usage/API are identical to formidable (documentation cloned below).


Sponsored and maintained by the folks at

How it works

The preprocessing by bodyparsers built-in to serverless environments breaks formidable's parse handlers and causes "Request Aborted" errors. This module imports formidable as a dependency and modifies the handlers to support preprocessed request bodies.

This module can also be used in non-serverless environments (usage and API are identical), but it may be a version or two behind. This package is focused on serverless - if you have issues with formidable itself, please open them in the formidable repo.


A Node.js module for parsing form data, especially file uploads.

Formidable was developed for Transloadit, a service focused on uploading and encoding images and videos. It has been battle-tested against hundreds of GB of file uploads from a large variety of clients and is considered production-ready.


  • Fast (~500mb/sec), non-buffering multipart parser
  • Automatically writing file uploads to disk
  • Low memory footprint
  • Graceful error handling
  • Very high test coverage


npm install --save formidable-serverless

This is a low-level package, and if you're using a high-level framework it may already be included. However, Express v4 does not include any multipart handling, nor does body-parser.


Parse an incoming file upload.

const formidable = require('formidable-serverless');
const http = require('http');
const util = require('util');

http.createServer(function(req, res) {
  if (req.url == '/upload' && req.method.toLowerCase() == 'post') {
    // parse a file upload
    const form = new formidable.IncomingForm();

    form.parse(req, function(err, fields, files) {
      res.writeHead(200, {'content-type': 'text/plain'});
      res.write('received upload:\n\n');
      res.end(util.inspect({fields: fields, files: files}));


  // show a file upload form
  res.writeHead(200, {'content-type': 'text/html'});
    '<form action="/upload" enctype="multipart/form-data" method="post">'+
    '<input type="text" name="title"><br>'+
    '<input type="file" name="upload" multiple="multiple"><br>'+
    '<input type="submit" value="Upload">'+



var form = new formidable.IncomingForm()

Creates a new incoming form.

form.encoding = 'utf-8';

Sets encoding for incoming form fields.

form.uploadDir = "/my/dir";

Sets the directory for placing file uploads in. You can move them later on using fs.rename(). The default is os.tmpdir().

form.keepExtensions = false;

If you want the files written to form.uploadDir to include the extensions of the original files, set this property to true.


Either 'multipart' or 'urlencoded' depending on the incoming request.

form.maxFieldsSize = 20 * 1024 * 1024;

Limits the amount of memory all fields together (except files) can allocate in bytes. If this value is exceeded, an 'error' event is emitted. The default size is 20MB.

form.maxFileSize = 200 * 1024 * 1024;

Limits the size of uploaded file. If this value is exceeded, an 'error' event is emitted. The default size is 200MB.

form.maxFields = 1000;

Limits the number of fields that the querystring parser will decode. Defaults to 1000 (0 for unlimited).

form.hash = false;

If you want checksums calculated for incoming files, set this to either 'sha1' or 'md5'.

form.multiples = false;

If this option is enabled, when you call form.parse, the files argument will contain arrays of files for inputs which submit multiple files using the HTML5 multiple attribute.


The amount of bytes received for this form so far.


The expected number of bytes in this form.

form.parse(request, [cb]);

Parses an incoming node.js request containing form data. If cb is provided, all fields and files are collected and passed to the callback:

form.parse(req, function(err, fields, files) {
  // ...


You may overwrite this method if you are interested in directly accessing the multipart stream. Doing so will disable any 'field' / 'file' events processing which would occur otherwise, making you fully responsible for handling the processing.

form.onPart = function(part) {
  part.addListener('data', function() {
    // ...

If you want to use formidable to only handle certain parts for you, you can do so:

form.onPart = function(part) {
  if (!part.filename) {
    // let formidable handle all non-file parts

Check the code in this method for further inspiration.


file.size = 0

The size of the uploaded file in bytes. If the file is still being uploaded (see 'fileBegin' event), this property says how many bytes of the file have been written to disk yet.

file.path = null

The path this file is being written to. You can modify this in the 'fileBegin' event in case you are unhappy with the way formidable generates a temporary path for your files. = null

The name this file had according to the uploading client.

file.type = null

The mime type of this file, according to the uploading client.

file.lastModifiedDate = null

A date object (or null) containing the time this file was last written to. Mostly here for compatibility with the W3C File API Draft.

file.hash = null

If hash calculation was set, you can read the hex digest out of this var.


This method returns a JSON-representation of the file, allowing you to JSON.stringify() the file which is useful for logging and responding to requests.



Emitted after each incoming chunk of data that has been parsed. Can be used to roll your own progress bar.

form.on('progress', function(bytesReceived, bytesExpected) {


Emitted whenever a field / value pair has been received.

form.on('field', function(name, value) {


Emitted whenever a new file is detected in the upload stream. Use this event if you want to stream the file to somewhere else while buffering the upload on the file system.

form.on('fileBegin', function(name, file) {


Emitted whenever a field / file pair has been received. file is an instance of File.

form.on('file', function(name, file) {


Emitted when there is an error processing the incoming form. A request that experiences an error is automatically paused, you will have to manually call request.resume() if you want the request to continue firing 'data' events.

form.on('error', function(err) {


Emitted when the request was aborted by the user. Right now this can be due to a 'timeout' or 'close' event on the socket. After this event is emitted, an error event will follow. In the future there will be a separate 'timeout' event (needs a change in the node core).

form.on('aborted', function() {
form.on('end', function() {

Emitted when the entire request has been received, and all contained files have finished flushing to disk. This is a great place for you to send your response.


Formidable and formidable-serverless are licensed under the MIT license.

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