2.0.2 • Public • Published

Formaline v2.x

Formaline extends PoorForm to create a very developer-friendly form parser, and still easy to get at the guts.

If you don't think Formaline is light-weight enough for you, you're crazy. Also, you'd probably really like PoorForm.

The Formaline v0.x documentation is available on the v0.x branch.


Formaline.create(request, options)

Returns an instance of PoorForm with a few extra events tacked on as described above.

Like PoorForm, it returns null if either it's not a multi-part form or the form has already been parsed.


    tmpDir: null || pathString || os.tmpDir()
  , hashes: ["md5", "sha1", ...] || []
  , arrayFields: [fieldNameString] || null

Set tmpDir to null if you plan to manage the file streams from the file event on your own (i.e. you want to store them in S3 or whatever and never let them hit the fs). Also, in almost all cases tmpDir should be on the same partition as the final destination, so change it if the system's default tmp is a different partition than your destination.


An array of hashes that should be performed on each file (fields are excluded). The hash will be attached to the file before the end event.


When end fires it hands back a map for both fields and files, all of which are assumed to be arrays by default (as per the HTTP spec).

However, if arrayFields is an array of field names (or an empty array), two special things happen:

  1. All of the fields listed will always return an array, even if it's empty
I.E. The user created an album, but uploaded 0 photos.
  1. All fields and files not listed in arrayFields will be treated as single values (if the field is encountered multiple times, only the first value is kept)
I.E. If `username` is given twice, only the first value is kept.


(function () {
  "use strict";
  var Formaline = require('formaline').Formaline
  // Using Connect, for example
  app.use(function (req, res, next) {
    var form = Formaline.create(req, {
            tmpDir: '/mnt/my-app-data/tmp'
          , hashes: ['md5']
          , arrayFields: ['photos']
      , fieldsMap
      , filesMap
    if (!form) {
      console.log("Either this was already parsed or it isn't a multi-part form");
    // form.on('field', ...)
    // ...

Formaline#on('progress', function () {})

Fires after Formaline#loaded is updated so you can compare that against Formaline#total.

form.on('progress', function () {
  var ratio = poorForm.loaded /
    , percent = Math.round(ratio * 100)
  console.log(percent + '% complete (' + poorForm.loaded + ' bytes)');
  // might be 0 because is Infinity when Content-Length is undefined
  // I.E. Transfer-Encoding: chunked

Formaline#on('field', function (name, decodedValue) {})

Provides the form name and decoded string abstracted from PoorForm's fieldstart, fielddata, and fieldend events (remember than a field's data is occasionally chunked across two fielddata events).

form.on('field', function (key, value) {
  // both key and value have been run through `str = decodeURIComponent(str)`
  fieldsMap[key] = value;
  console.log(key, value);

Formaline#on('file', function (name, formFileStream, headers) {})

Provides the form name (not filename) as well as a FormFile stream (described below, has the filename), and all associated headers (generally not needed).

Remember: If you specify options.tmpDir = null, you are entirely responsible for writing the file to disk, GridStore, S3, the toilet, or wherever.

form.on('file', function (key, formFile) {
  // for example, we want to save to amazon s3 using knox
  var s3 = require('knox').createClient({ key: '<api-key>', secret: '<secret>', bucket: '<foo>'})
    , s3req
    , metadata
  // and let's say we have a field called `metadata` containing a hash with metadata
  // such as `lastModifiedDate` and `size` for every file to be uploaded
  if (!fieldMaps.metadata) {
    console.error('sad day, no metadata');
  } else {
    metadata = JSON.parse(fieldMaps.metadata[]);
  s3req = s3.put('/test/file.bin', {
      'Content-Length': metadata.size
    , 'Content-Type': 'application/octet-stream'
  formFile.on('end', function () {
    // formFile is an instance of EventEmitter, but it `JSON.stringify()`s as you would expect.
    // Also note that some of the properties are added just before the `end` event fires.
    formFile.lastModifiedDate = metadata.lastModifiedDate;
    if (!formFile.sha1 === metadata.sha1) {
      console.error("Oh No! The sha1 sums don't match!");
    console.log(key, JSON.stringify(formFile));
  s3.on('response', function(res){
    if (200 == res.statusCode) {
      console.log('saved to %s', req.url);
    } else {
      console.error("fell on hard times, didn't save %s", req.url);


A simple EventEmitter FileStream (pausable, resumable, etc) abstracted from PoorForm's fieldstart, fielddata, and fieldend events.

  • name is taken from the filename in the Content-Disposition
  • fieldname is the actual name of the field
  • size is the current byte size of the file, which changes until the end event is called
  • type is the contentType
  • lastModifiedDate is updated each time a chunk is written to the file
  • path is the current file path (either in /tmp or a path you specified)
  • headers is the array of MIME headers associated with the form
  • md5, sha1, sha256, sha512, etc are attached as per the options.hashes array

Formaline#on('end', function (fields, files) {})

Congratulations. You've reached the end of the form.

  • fields is a map of arrays of Strings { "anyFieldName": ["decodedStringValue"] }
  • files is a map of arrays of FormFiles { "anyFileName": [aFormFile, anOtherFormFile] }
  • options.arrayFields changes the behavior such that only the listed fields are arrays and all others are singular
form.on('end', function (fields, files) {
  // Normally the values for each key of fields and files would be arrays
  // However, I specified `arrayFields`, which means that those names not listed are not arrays
  // this is an array because it would be by default if I ha (formFile) {
    // JSON.stringify ignores the non-enumerable properties of the underlying EventEmitter
  console.log('uploads complete');

NOTE: I put a lot of thought (too much, in fact) into how to represent fields and files in a way which is both consistent and easy to use.

It makes sense to separate fields from files. Treating all fields as files would have unneccesary overhead in parsing. What you're likely to do with a field (store it in a database as metadata) is different from what you'll do with a file (store it in a file system).

The hybrid approach of mapping pure arrays makes it simple to ignore (and or error check) duplicate fields that should have been singular without the confusion of other common methodologies (see below).

Using maps where username and categories are sometimes treated as single-value fields (i.e. if only one category is selected in the browser UI) but sometimes treated as arrays (i.e. a developer accidentally sends two username form parts) is inconsistent and likely to cause wierd breakage in your app.

Using pure arrays where you have to .forEach and handle the fields in a switch is ugly / cumbersome.

Another workaround is to require php-style field naming conventions such as categories[] and username, but PHP is <insert-profanity-here> and self-respecting individuals have a hard time taking anything that started with PHP seriously, even though it's atually not a terribly profane solution. The downside to this solution is that it requires parsing field names.

Future Enhancements (TODO)

The following are abbreviated security concerns for a form handler with generous and reasonable defaults

  • error - abstract req.on('error') and poorForm.on('error', fn) as to handle malformed requests
  • maxHeaderSize - default 256 Bytes - prevent memory attacks
  • maxUniqueFieldNames - default 1000 - prevent hash collision attacks
  • maxFieldSize - default 4KB - prevent memory attacks
  • maxFieldTotalSize - default 1MB - prevent memory attacks
  • maxFileSize - default 4 GiB - prevent storage attacks
  • maxUploadSize - default 16 GiB - prevent memory / storage attacks
  • removeIncomplete - default true - ignore unless creating a resumable upload service


  • Apache 2
  • MIT

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