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 "canary" 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!

You can try the
Plugins API
(#545), which is
available through formidable@dev.

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 canary version
npm install formidable@canary

or with Yarn v1/v2

yarn add formidable
# or the canary 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.maxFileSize {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.maxFieldsSize {number} - default 20 * 1024 * 1024 (20mb);
  limit the amount of memory all fields together (except files) can allocate in
  bytes.
• 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', () => {});

Ports & 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.

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!

Thanks goes to these wonderful people
(emoji key):

License

Formidable is licensed under the MIT License.