Direct Upload to Amazon S3 With CORS
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Easily generate a form that allows you to upload directly to Amazon S3. Multi file uploading supported by jquery-fileupload.

Code extracted from Ryan Bates' gallery-jquery-fileupload.


Add this line to your application's Gemfile:

gem 's3_direct_upload'

Then add a new initalizer with your AWS credentials:


S3DirectUpload.config do |c|
  c.access_key_id = ""       # your access key id
  c.secret_access_key = ""   # your secret access key
  c.bucket = ""              # your bucket name

Make sure your AWS S3 CORS settings for your bucket look something like this:


In production the AllowedOrigin key should be your domain.

Add the following js and css to your asset pipeline:

#= require s3_direct_upload


//= require s3_direct_upload_progress_bars


Create a new view that uses the form helper s3_uploader_form:

<%= s3_uploader_form post: model_url, as: "model[image_url]", id: "myS3Uploader" do %>
  <%= file_field_tag :file, multiple: true %>
<% end %>

Then in your, call the S3Uploader jQuery plugin on the element you created above:

jQuery ->

Optionally, you can also place this template in the same view for the progress bars:

<script id="template-upload" type="text/x-tmpl">
<div class="upload">
  <div class="progress"><div class="bar" style="width: 0%"></div></div>

Options for form helper

  • post: url in which is POST'd to after file is uploaded to S3. If you don't specify this option, no callback to the server will be made after the file has uploaded to S3.
  • as: parameter value for the POST in which the key will be the URL of the file on S3. If for example this is set to "model[image_url]" then the data posted would be model[image_url] :
  • key: key on s3. defaults to "uploads/#{SecureRandom.hex}/${filename}". needs to be at least "${filename}".
  • acl: acl for files uploaded to s3, defaults to "public-read"
  • max_file_size: maximum file size, defaults to 500.megabytes
  • id: html id for the form, its recommended that you give the form an id so you can reference with the jQuery plugin.
  • class: optional html class for the form.
  • data: Optional html data

Persisting the S3 url

It is recommended that you persist the image_url that is sent back from the POST request (to the url given to the post option and as the key given in the as option). So to access your files later.

One way to do this is to make sure you have resources model in your routes file, and add the image_url (or whatever you would like to name it) attribute to your model, and then make sure you have the create action in your controller for that model.

You could then have your create action render a javascript file like this: create.js.erb

<% if @model.new_record? %>
  alert("Failed to upload model: <%= j @model.errors.full_messages.join(', ').html_safe %>");
<% else %>
  $("#container").append("<%= j render(@model) %>");
<% end %>

So that javascript code would be executed after the model instance is created, without a page refresh. See @rbates's gallery-jquery-fileupload) for an example of that method.

Note: the POST request to the rails app also includes the following parameters filesize, filetype, filename and filepath.

Advanced Customizations

Feel free to override the styling for the progress bars in s3_direct_upload_progress_bars.css, look at the source for inspiration.

Also feel free to write your own js to interface with jquery-file-upload. You might want to do this to do custom validations on the files before it is sent to S3 for example. To do this remove s3_direct_upload from your application.js and include the necessary jquery-file-upload scripts in your asset pipeline (they are included in this gem automatically):

#= require jquery-fileupload/basic
#= require jquery-fileupload/vendor/tmpl

Use the javascript in s3_direct_upload as a guide.

Options for S3Upload jQuery Plugin

  • path: manual path for the files on your s3 bucket. Example: path/to/my/files/on/s3
    Note: the file path in your s3 bucket will effectively be path + key.
  • additional_data: You can send additional data to your rails app in the persistence POST request. This would be accessable in your params hash as params[:key][:value]
    Example: {key: value}
  • remove_completed_progress_bar: By default, the progress bar will be removed once the file has been successfully uploaded. You can set this to false if you want to keep the progress bar.
  • before_add: Callback function that executes before a file is added to the queue. It is passed file object and expects true or false to be returned. This could be useful if you would like to validate the filenames of files to be uploaded for example. If true is returned file will be uploaded as normal, false will cancel the upload.

Example with all options.

jQuery ->
    path: 'path/to/my/files/on/s3'
    additional_data: {key: 'value'}
    remove_completed_progress_bar: false
    before_add: myCallBackFunction() # must return true or false if set

Public methods

You can change the settings on your form later on by accessing the jQuery instance:

jQuery ->
  v = $("#myS3Uploader").S3Uploader()

Javascript Events Hooks

Successfull upload

When a file has been successfully to S3, the s3_upload_complete is triggered on the form. A content object is passed along with the following attributes :

  • url The full URL to the uploaded file on S3.
  • filename The original name of the uploaded file.
  • filepath The path to the file (without the filename or domain)
  • filesize The size of the uploaded file.
  • filetype The type of the uploaded file.

This hook could be used for example to fill a form hidden field with the returned S3 url :

$('#myS3Uploader').bind "s3_upload_complete", (e, content) ->

Failed upload

When an error occured during the transferm the s3_upload_failed is triggered on the form with the same content object is passed for the successful upload with the addition of the error_thrown attribute. The most basic way to handle this error would be to display an alert message to the user in case the upload fails :

$('#myS3Uploader').bind "s3_upload_failed", (e, content) ->
  alert("#{content.filename} failed to upload : #{content.error_thrown}")

All uploads completed

When all uploads finish in a batch an s3_uploads_complete event will be triggered on document, so you could do something like:

$(document).bind 's3_uploads_complete', ->
    alert("All Uploads completed")

Contributing / TODO

This is just a simple gem that only really provides some javascript and a form helper. This gem could go all sorts of ways based on what people want and how people contribute. Ideas:

  • More specs!
  • More options to control file types, ability to batch upload.
  • More convention over configuration on rails side
  • Create generators.
  • Model methods.
  • Model method to delete files from s3


This gem is basically a small wrapper around code that Ryan Bates wrote for Railscast#383. Most of the code in this gem was extracted from gallery-jquery-fileupload.

Thank you Ryan Bates!

This code also uses the excellecnt jQuery-File-Upload, which is included in this gem by its rails counterpart jquery-fileupload-rails