formidable

What is formidable?

The formidable npm package is a Node.js module for parsing form data, especially file uploads. It can handle multipart/form-data, which is used for uploading files through forms.

What are formidable's main functionalities?

File Upload

This code creates an HTTP server that listens for POST requests on the '/upload' path. It uses formidable to parse the incoming form data and handle file uploads.

const formidable = require('formidable');
const http = require('http');

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

    form.parse(req, (err, fields, files) => {
      if (err) {
        res.writeHead(500, { 'content-type': 'text/plain' });
        res.end('Error parsing the files');
        return;
      }
      res.writeHead(200, { 'content-type': 'text/plain' });
      res.write('Files uploaded successfully:\n');
      res.end(JSON.stringify(files, null, 2));
    });
  }
}).listen(8080);

Form Field Parsing

This code snippet demonstrates how to use formidable to parse regular form fields (text inputs, selects, etc.) in addition to file uploads.

const formidable = require('formidable');
const http = require('http');

http.createServer((req, res) => {
  if (req.url === '/submit' && req.method.toLowerCase() === 'post') {
    const form = new formidable.IncomingForm();

    form.parse(req, (err, fields, files) => {
      if (err) {
        res.writeHead(500, { 'content-type': 'text/plain' });
        res.end('Error parsing the form fields');
        return;
      }
      res.writeHead(200, { 'content-type': 'text/plain' });
      res.write('Form fields submitted:\n');
      res.end(JSON.stringify(fields, null, 2));
    });
  }
}).listen(8080);

File Upload Progress

This example shows how to track the progress of a file upload using formidable's 'progress' event, which provides the bytes received and the total bytes expected.

const formidable = require('formidable');
const http = require('http');

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

    form.on('progress', (bytesReceived, bytesExpected) => {
      console.log(`Progress: ${bytesReceived}/${bytesExpected}`);
    });

    form.parse(req, (err, fields, files) => {
      // Handle file upload and response
    });
  }
}).listen(8080);

Other packages similar to formidable

multer

Multer is another popular Node.js middleware for handling multipart/form-data, which is primarily used for uploading files. It is built on top of busboy for maximum efficiency. Unlike formidable, multer is specifically designed for use with Express applications and includes more options for file storage and manipulation.

busboy

Busboy is a low-level Node.js module for parsing multipart/form-data request bodies. Formidable is actually built on top of busboy. Busboy is faster and more efficient but requires more setup and manual handling compared to formidable, which provides a higher-level API.

multiparty

Multiparty is a Node.js module for parsing multipart/form-data requests. It is similar to formidable in terms of functionality but has a different API and is known for being more memory efficient, as it streams files to disk instead of buffering them in memory.

README

formidable

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

Important Notes

For more info, check the CHANGELOG on the master branch.

v1 is deprecated

All v1 versions are deprecated in NPM for over 2 years. You can find it at formidable@v1 or formidable@legacy on NPM, and on v1-legacy branch on GitHub.
We highly recommend to use v2 or v3. Both are already in use by many, especially v2 which was on formidable@canary for 2 years.

• Status: Not Maintained!
• We won't provide support or accept reports on that version.
• No Backporting: bugfixes, security fixes, or new features WILL NOT happen!
• Please move to at least v2!
• Try with installing formidable@v2 and if still have the problem - report!

---

v2 is the new latest

The v2 will be simultaneously on two places for some time - formidable@latest and formidable@v2. The source code be available only on v2 branch. If you want to use v2, it's recommended to use the v2 dist-tag formidable@v2.

Main Differences from v1:

• Better organization and modernized code, requiring newer Node.js versions (>= v10).
• A lot of bugfixes, closed issues, merged or closed PRs.
• Backward compatible to v1! Should not have problems, the major version bump is just for ensurance.
• Better docs, new features (plugins, parsers, options) and optimizations.

---

v3 - ESModules, Promises, Monorepo structure

We recommend to use formidable@v3, as it uses more modern Node.js Streams, has support for Promises and more stuff. You can see more info and track some ideas on issue#635.

• The source code can be found on the master branch on GitHub.
• It will be published on formidable@latest after some time.
• Dropping older Node.js versions, requiring higher than v12-v14.
• Dropping v1 compatibility.
• Rewritten to ESModules, more optimizations.
• Moving to monorepo structure, more plugins & helper utils.

---

If you have any how-to kind of questions, please read the Contributing Guide and Code of Conduct documents.
For bugs reports and feature requests, please create an issue or ping @tunnckoCore at Twitter.

This project is semantically versioned and available as part of the Tidelift Subscription for professional grade assurances, enhanced support and security. Learn more.

The maintainers of formidable and thousands of other packages are working with Tidelift to deliver commercial support and maintenance for the Open Source dependencies you use to build your applications. Save time, reduce risk, and improve code health, while paying the maintainers of the exact dependencies you use.

v1 status: not maintained!

Project Status: Maintained

This module was initially developed by @felixge for Transloadit, a service focused on uploading and encoding images and videos. It has been battle-tested against hundreds of GBs of file uploads from a large variety of clients and is considered production-ready and is used in production for years.

Currently, we are few maintainers trying to deal with it. :) More contributors are always welcome! :heart: Jump on issue #412 which is closed, but if you are interested we can discuss it and add you after strict rules, like enabling Two-Factor Auth in your npm and GitHub accounts.

Features

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

Installation

npm install formidable@v1
npm install formidable@v2
npm install formidable@v3

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.

Note: Formidable requires gently to run the unit tests, but you won't need it for just using the library.

Example

Parse an incoming file upload.

var formidable = require('formidable'),
    http = require('http'),
    util = require('util');

http.createServer(function(req, res) {
  if (req.url == '/upload' && req.method.toLowerCase() == 'post') {
    // parse a file upload
    var 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}));
    });

    return;
  }

  // show a file upload form
  res.writeHead(200, {'content-type': 'text/html'});
  res.end(
    '<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">'+
    '</form>'
  );
}).listen(8080);

API

Formidable.IncomingForm

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.

form.type

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.

form.bytesReceived

The amount of bytes received for this form so far.

form.bytesExpected

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) {
  // ...
});

form.onPart(part);

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
    form.handlePart(part);
  }
}

Check the code in this method for further inspiration.

Formidable.File

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.

file.name = 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.

Formidable.File#toJSON()

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.

Events

'progress'

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) {
});

'field'

Emitted whenever a field / value pair has been received.

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

'fileBegin'

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) {
});

'file'

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

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

'error'

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) {
});

'aborted'

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() {
});

'end'

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.

Changelog

./CHANGELOG.md

Credits

• multipart-parser: a C++ parser based on formidable
• Ryan Dahl for his work on http-parser which heavily inspired the initial multipart_parser.js.

From Felix blog post:

• Sven Lito for fixing bugs and merging patches
• egirshov for contributing many improvements to the node-formidable multipart parser
• Andrew Kelley for also helping with fixing bugs and making improvements
• Mike Frey for contributing JSON support

Contributing

If the documentation is unclear or has a typo, please click on the page's Edit button (pencil icon) and suggest a correction. If you would like to help us fix a bug or add a new feature, please check our Contributing Guide. Pull requests are welcome!

License

Formidable is licensed under the MIT License.