A simple, Busboy-powered streaming file upload interface.

Uploader.js

var util    = require('util')
,   path    = require('path')
,   Busboy  = require('busboy')
,   Emitter = require('events').EventEmitter
,   Uploader;

Uploader = function () {
  Emitter.call(this);
};

util.inherits(Uploader, Emitter);

Uploader.prototype.onField = function (field, value, fTrunc, vTrunc) {
  this.emit('field', field, value, fTrunc, vTrunc);
};

Uploader.prototype.onFile = function (field, stream, name, enc, mime) {
  this.emit('file', field, stream, name, enc, mime);
};

Uploader.prototype.onError = function (err) {
  this.emit('error', err);
};

Uploader.prototype.onFinish = function (body, files) {
  this.emit('finish', body, files);
};

Uploader.prototype.parse = function (headers) {
  var self  = this
  ,   body  = {}
  ,   files = {};

  self.parser = self.parser || new Busboy({ headers: headers });

  self.parser.on('error', function (err) {
    self.onError(err);
  });

  self.parser.on('field', function (field, value, fTrunc, vTrunc) {
    body[field] = value;
    self.onField(field, value, fTrunc, vTrunc);
  });

  self.parser.on('file', function (field, stream, name, enc, mime) {
    if (!name) return stream.resume();

    if (!self.fields) return self.onFile(field, stream, name, enc, mime);

    if (self.fields && self.fields[field]) {
      var ext = path.extname(name).replace('.', '');

      if (self.fields[field].length &&
          self.fields[field].indexOf(ext) !== -1) {
        files[field] = name;
        self.onFile(field, stream, name, enc, mime);
      } else {
        self.onError(new Error('Validation of ' + field + ' failed.'));
        stream.resume();
      }
    }
  });

  self.parser.on('finish', function () {
    self.onFinish(body, files);
  });

  return self;
};

module.exports = Uploader;