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.

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 if you are interested.

Note: Master is a "development" branch - try it with npm i formidable@canary. Do not expect (for now) things from it to be inside thelatest"dist-tag" in the Npm. Theformidable@latestis thev1.2.1 version and probably it will be the lastv1 release!

Note: v2 is coming soon!

Highlights

• Fast (~900-2500 mb/sec), streaming multipart parser
• Automatically writing file uploads to disk
• Low memory footprint
• Graceful error handling
• Very high test coverage

Install

npm install formidable
# or the development version
npm install formidable@canary

or with Yarn v1/v2

yarn add formidable
# or the development version
yarn add formidable@canary

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.

For koa there is koa-better-body which can handle ANY type of body / form-data - JSON, urlencoded, multpart and so on. A new major release is coming there too.

Example

Parse an incoming file upload.

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

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

      form.parse(req, (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, () => {
    console.log('Server listening on http://localhost:8080/ ...');
  });

Benchmarks

The benchmark is quite old, from the old codebase. But maybe quite true though. Previously the numbers was around ~500 mb/sec. Currently with moving to the new Node.js Streams API it's faster. You can clearly see the differences between the Node versions.

Note: a lot better benchmarking could and should be done in future.

Benchmarked on 8GB RAM, Xeon X3440 (2.53 GHz, 4 cores, 8 threads)

~/github/node-formidable master
❯ nve --parallel 8 10 12 13 node benchmark/bench-multipart-parser.js

 ⬢  Node 8

1261.08 mb/sec

 ⬢  Node 10

1113.04 mb/sec

 ⬢  Node 12

2107.00 mb/sec

 ⬢  Node 13

2566.42 mb/sec

API

Formidable / IncomingForm

All shown are equivalent.

Please pass options to the function/constructor, not by passing assigning them to the instance form

const formidable = require('formidable');
const form = formidable(options);

// or
const { formidable } = require('formidable');
const form = formidable(options);

// or
const { IncomingForm } = require('formidable');
const form = new IncomingForm(options);

// or
const { Formidable } = require('formidable');
const form = new Formidable(options);

Options

See it's defaults in src/Formidable.js (the DEFAULT_OPTIONS constant).

• options.encoding {string} - default 'utf-8'; sets encoding for incoming form fields,
• options.uploadDir {string} - default os.tmpdir(); the directory for placing file uploads in. You can move them later by using fs.rename()
• options.keepExtensions {boolean} - default false; to include the extensions of the original files or not
• options.maxFieldsSize {number} - default 20 * 1024 * 1024 (20mb); limit the amount of memory all fields together (except files) can allocate in bytes.
• options.maxFieldsSize {number} - default 200 * 1024 * 1024 (200mb); limit the size of uploaded file.
• options.maxFields {number} - default 1000; limit the number of fields that the Querystring parser will decode, set 0 for unlimited
• options.hash {boolean} - default false; include checksums calculated for incoming files, set this to some hash algorithm, see crypto.createHash for available algorithms
• options.multiples {boolean} - default false; when you call the .parse method, the files argument (of the callback) will contain arrays of files for inputs which submit multiple files using the HTML5 multiple attribute. Also, the fields argument will contain arrays of values for fields that have names ending with '[]'.

Note: If this value is exceeded, an 'error' event is emitted.

// The amount of bytes received for this form so far.
form.bytesReceived;

// The expected number of bytes in this form.
form.bytesExpected;

.parse(request, callback)

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

const formidable = require('formidable');

const form = formidable({ multiples: true, uploadDir: __dirname });

form.parse(req, (err, fields, files) => {
  console.log('fields:', fields);
  console.log('files:', 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.

In the example below, we listen on couple of events and direct them to the data listener, so you can do whatever you choose there, based on whether its before the file been emitted, the header value, the header name, on field, on file and etc.

Or the other way could be to just override the form.onPart as it's shown a bit later.

form.once('error', console.error);

form.on('fileBegin', (filename, file) => {
  form.emit('data', { name: 'fileBegin', filename, value: file });
});

form.on('file', (filename, file) => {
  form.emit('data', { name: 'file', key: filename, value: file });
});

form.on('field', (fieldName, fieldValue) => {
  form.emit('data', { name: 'field', key: fieldName, value: fieldValue });
});

form.once('end', () => {
  console.log('Done!');
});

// If you want to customize whatever you want...
form.on('data', ({ name, key, value, buffer, start, end, ...more }) => {
  if (name === 'partBegin') {
  }
  if (name === 'partData') {
  }
  if (name === 'headerField') {
  }
  if (name === 'headerValue') {
  }
  if (name === 'headerEnd') {
  }
  if (name === 'headersEnd') {
  }
  if (name === 'field') {
    console.log('field name:', key);
    console.log('field value:', value);
  }
  if (name === 'file') {
    console.log('file:', key, value);
  }
  if (name === 'fileBegin') {
    console.log('fileBegin:', key, value);
  }
});

form.onPart

If you want to use Formidable to only handle certain parts for you, you can do something similar. Or see #387 for inspiration, you can for example validate the mime-type.

const form = formidable();

form.onPart = (part) => {
  part.on('data', (buffer) {
    // do whatever you want here
  });
};

For example, force Formidable to be used only on non-file "parts" (i.e., html fields)

const form = formidable();

form.onPart = function(part) {
  // let formidable handle only non-file parts
  if (part.filename === '' || !part.mime) {
    // used internally, please do not override!
    form.handlePart(part);
  }
};

File

export interface File {
  // 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.size: number;

  // 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.path: string;

  // The name this file had according to the uploading client.
  file.name: string | null;

  // The mime type of this file, according to the uploading client.
  file.type: string | 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](http://dev.w3.org/2006/webapi/FileAPI/).
  file.lastModifiedDate: Date | null;

  // If `options.hash` calculation was set, you can read the hex digest out of this var.
  file.hash: string | 'sha1' | 'md5' | 'sha256' | null;
}

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', (bytesReceived, bytesExpected) => {});

'field'

Emitted whenever a field / value pair has been received.

form.on('field', (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', (name, file) => {});

'file'

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

form.on('file', (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', (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', () => {});

'end'

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.

form.on('end', () => {});

License

Formidable is licensed under the MIT License.

Ports

• multipart-parser: a C++ parser based on formidable

Credits

• Ryan Dahl for his work on http-parser which heavily inspired multipart_parser.js