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multiparty

Parse http requests with content-type multipart/form-data, also known as file uploads.

See also busboy - a faster alternative which may be worth looking into.

Why the fork?

  • This module uses the Node.js v0.10 streams properly, even in Node.js v0.8
  • It will not create a temp file for you unless you want it to.
  • Counts bytes and does math to help you figure out the Content-Length of each part.
  • You can easily stream uploads to s3 with knox, for example.
  • Less bugs. This code is simpler, has all deprecated functionality removed, has cleaner tests, and does not try to do anything beyond multipart stream parsing.

Installation

npm install multiparty

Usage

Parse an incoming multipart/form-data request.

var multiparty = require('multiparty')
  , http = require('http')
  , util = require('util')

http.createServer(function(req, res) {
  if (req.url === '/upload' && req.method === 'POST') {
    // parse a file upload
    var form = new multiparty.Form();

    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

multiparty.Form

var form = new multiparty.Form(options)

Creates a new form. Options:

  • encoding - sets encoding for the incoming form fields. Defaults to utf8.
  • maxFieldSize - Limits the amount of memory a field (not a file) can allocate in bytes. If this value is exceeded, an error event is emitted. The default size is 2MB.
  • maxFields - Limits the number of fields that will be parsed before emitting an error event. A file counts as a field in this case. Defaults to 1000.
  • autoFields - Enables field events. This is automatically set to true if you add a field listener.
  • autoFiles - Enables file events. This is automatically set to true if you add a file listener.
  • uploadDir - Only relevant when autoFiles is true. The directory for placing file uploads in. You can move them later using fs.rename(). Defaults to os.tmpDir().
  • hash - Only relevant when autoFiles is true. If you want checksums calculated for incoming files, set this to either sha1 or md5. Defaults to off.

form.parse(request, [cb])

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

form.parse(req, function(err, fieldsObject, filesObject, fieldsList, filesList) {
  // ...
});

It is often convenient to access a field or file by name. In this situation, use fieldsObject or filesObject. However sometimes, as in the case of a <input type="file" multiple="multiple"> the multipart stream will contain multiple files of the same input name, and you are interested in all of them. In this case, use filesList.

Another example is when you do not care what the field name of a file is; you are merely interested in a single upload. In this case, set maxFields to 1 (assuming no other fields expected besides the file) and use filesList[0].

form.bytesReceived

The amount of bytes received for this form so far.

form.bytesExpected

The expected number of bytes in this form.

Events

'error' (err)

You definitely want to handle this event. If not your server will crash when users submit bogus multipart requests!

'part' (part)

Emitted when a part is encountered in the request. part is a ReadableStream. It also has the following properties:

  • headers - the headers for this part. For example, you may be interested in content-type.
  • name - the field name for this part
  • filename - only if the part is an incoming file
  • byteOffset - the byte offset of this part in the request body
  • byteCount - assuming that this is the last part in the request, this is the size of this part in bytes. You could use this, for example, to set the Content-Length header if uploading to S3. If the part had a Content-Length header then that value is used here instead.

'aborted'

Emitted when the request is aborted. This event will be followed shortly by an error event. In practice you do not need to handle this event.

'progress' (bytesReceived, bytesExpected)

'close'

Emitted after all parts have been parsed and emitted. Not emitted if an error event is emitted. This is typically when you would send your response.

'file' (name, file)

By default multiparty will not touch your hard drive. But if you add this listener, multiparty automatically sets form.autoFiles to true and will stream uploads to disk for you.

  • name - the field name for this file
  • file - an object with these properties:
    • fieldName - same as name - the field name for this file
    • originalFilename - the filename that the user reports for the file
    • path - the absolute path of the uploaded file on disk
    • headers - the HTTP headers that were sent along with this file
    • size - size of the file in bytes

If you set the form.hash option, then file will also contain a hash property which is the checksum of the file.

'field' (name, value)

  • name - field name
  • value - string field value
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