The Traffic Machine - a demonstration of background File Upload with Progress Bar
JavaScript Ruby
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Developer Challenge

Design and implement a system that will accept a multipart form upload (say, containing an audio file) while displaying a percentage progress.


The basic HTML design should look like:

  • Display form with file input field
  • Display a title text field
  • Display a status text paragraph "select file"
  • Optionally display a submit button


  • When the user picks a file from their computer and optionally presses the submit button, the upload begins.
  • While uploading, the status text paragraph should be updating with the current percentage complete at least once every 2 seconds.
  • While uploading, the user should be able to enter text into the title text field.
  • When the upload completes, the status text should display the path on the server to the saved file.


  • The upload should honor proxy settings on the browser
  • The system must function behind a firewall that blocks all but port 80
  • The server must support at least 2 concurrent uploads
  • Any technology that can be web deployed to IE, Firefox, Safari, Chrome on any platform is supported


I came up with a small & simple rails app called The Traffic Machine - a demonstration of background File Upload with Progress Bar.

According to the specs, two major issues had to be solved: 1. upload the file in background, while user enters additional title/comment/text to the file 2. get the upload progress and show it to the user

Usually, Flash solutions address those problems, but bring other disadvantages as well (wrong version/not installed/disabled). So I was looking for a solution without Flash. The latest specs of HTML5 give some further possibilities as well, but are not supported by majority of current web browsers (greetings to IE - ahhrgg!!!). See sources at the bottom for further info

Luckily, I didn't had to reinvent the wheel, as there are already good solutions for both problems out there. For the background upload, Ajaxupload looked just fine for me. It's a jQuery implementation of uploading a file to a hidden iFrame which happens in background and doesn't block the user from adding additional infromation.

To track the upload progress, I used the Apache-upload-progress Module, which adds an access point to Apache, so you can easily retrieve the total and uploaded file size in JSON format.

Basic Infrastrukture

The Magic


Passenger File

ServerName nups.loc DocumentRoot "/Users/ted/Sites/rails/fup/public" RailsEnv development RailsAllowModRewrite off

#Porter On #PorterSharedSecret fup

Order allow,deny Allow from all

# needed for tracking upload progess # enable tracking uploads in / TrackUploads On

# enable upload progress reports in /progress ReportUploads On

Future Improvements

A quick step by step Howto:

  • get apachemodule, compile with: sudo apxs -c -i -a -Wc,-arch -Wc,ppc7400 -Wl,-arch -Wl,ppc7400 -Wc,-arch -Wc,x86_64 -Wl,-arch -Wl,x86_64 -Wc,-arch -Wc,i386 -Wl,-arch -Wl,i386 mod_upload_progress.c

  • update apache conf and create vhost

  • create rails app
  • add plugins

    • paperclip: config.gem 'paperclip', :source => ''
    • default value: script/plugin install git://
    • jQuery + jRails: script/plugin install git://
  • add blueprint css files

  • add basic html layout
  • add asset controller
  • add asset model, add uuid
  • add tests
  • add ajaxupload for background upload
  • add jQuery Ajax call to check upload progress
  • finish it up and make it nice
  • deploy with capistrano and git+passenger

Further reading and other resources: