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Process your uploads in the background by uploading directly to S3


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CarrierWave is a great way to upload files from Ruby applications, but since processing and saving is done in-process, it doesn't scale well. A better way is to upload your files directly then handle the processing and saving in a background process.

CarrierWaveDirect works on top of CarrierWave and provides a simple way to achieve this.

Example Application

For a concrete example on how to use CarrierWaveDirect in a Rails application check out the Example Application.


Right now, CarrierWaveDirect works with Amazon S3. Adding support for Google Storage for Developers should be fairly straight forward since the direct upload form is essentially the same. Please see the contributing section if you would like support for Google Storage for Developers or any other service that provides direct upload capabilities.

Please be aware that this gem (and S3 in general) only support single file uploads. If you want to upload multiple files simultaneously you'll have to use a javascript or flash uploader.


Install the latest release:

gem install carrierwave_direct

In Rails, add it to your Gemfile:

gem 'carrierwave_direct'

Note that CarrierWaveDirect is not compatible with Rails 2.

Getting Started

Please read the CarrierWave readme first

CarrierWaveDirect works with fog so make sure you have CarrierWave set up and initialized with your fog credentials, for example:

CarrierWave.configure do |config|
  config.fog_credentials = {
    :provider               => 'AWS',       # required
    :aws_access_key_id      => 'xxx',       # required
    :aws_secret_access_key  => 'yyy',       # required
    :region                 => 'eu-west-1'  # optional, defaults to 'us-east-1'
  config.fog_directory  = 'name_of_your_aws_bucket' # required
  # see https://github.com/jnicklas/carrierwave#using-amazon-s3
  # for more optional configuration

If you haven't already done so generate an uploader

rails generate uploader Avatar

this should give you a file in:


Check out this file for some hints on how you can customize your uploader. It should look something like this:

class AvatarUploader < CarrierWave::Uploader::Base
  storage :file

Remove the line storage :file and replace it with include CarrierWaveDirect::Uploader so it should look something like:

class AvatarUploader < CarrierWave::Uploader::Base
  include CarrierWaveDirect::Uploader

This adds the extra functionality for direct uploading.

Optional: Remove the store_dir method in order to default CarrierWaveDirect to its own storage directory.


If you're not using Rails you can generate a direct upload form to S3 similar to this example by making use of the CarrierWaveDirect helper methods.


Here is an example using Sinatra and Haml

# uploader_test.rb

CarrierWave.configure do |config|
  config.fog_credentials = {
    :provider               => 'AWS',
    :aws_access_key_id      => ENV['AWS_ACCESS_KEY_ID'],
    :aws_secret_access_key  => ENV['AWS_SECRET_ACCESS_KEY']
  config.fog_directory  = ENV['AWS_FOG_DIRECTORY'] # bucket name

class ImageUploader < CarrierWave::Uploader::Base
  include CarrierWaveDirect::Uploader

class UploaderTest < Sinatra::Base
  get "/" do
    @uploader = ImageUploader.new
    @uploader.success_action_redirect = request.url
    haml :index
# index.haml
# Now using AWS POST authentication V4
# See http://docs.aws.amazon.com/AmazonS3/latest/API/sigv4-authentication-HTTPPOST.html for more information

%form{:action => @uploader.direct_fog_url, :method => "post", :enctype => "multipart/form-data"}
  - @uploader.direct_fog_hash.each do |key, value|
    - if key != :uri
      %input{:type => "hidden", :name => key, :value => value}
  %input{:type => "hidden", :name => "success_action_redirect", :value => @uploader.success_action_redirect}
  %input{:name => "file", :type => "file"}
  %input{:type => "submit", :value => "Upload to S3"}


If you are using Rails and you've mounted your uploader like this:

class User < ActiveRecord::Base
  mount_uploader :avatar, AvatarUploader

things just got a whole lot easier. You can generate a direct upload form like this:

class AvatarController < ApplicationController
  def new
    @uploader = User.new.avatar
    @uploader.success_action_redirect = new_user_url
<%= direct_upload_form_for @uploader do |f| %>
  <%= f.file_field :avatar %>
  <%= f.submit %>
<% end %>

After uploading to S3, You'll need to update the uploader object with the returned key in the controller action that corresponds to new_user_url:

@uploader.update_attribute :avatar_key, params[:key]

You can also pass html options like this:

<%= direct_upload_form_for @uploader, :html => { :target => "_blank_iframe" } do |f| %>
  <%= f.file_field :avatar %>
  <%= f.submit %>
<% end %>

Note if User is not an ActiveRecord object e.g.

class User
  extend CarrierWave::Mount
  extend CarrierWaveDirect::Mount

  mount_uploader :avatar, AvatarUploader

you can still use the form helper by including the ActiveModel modules your uploader:

class AvatarUploader < CarrierWave::Uploader::Base
  include CarrierWaveDirect::Uploader

  include ActiveModel::Conversion
  extend ActiveModel::Naming

Note if you're using Rails 3.0.x you'll also need to disable forgery protection

# config/application.rb
config.action_controller.allow_forgery_protection = false

Once you've uploaded your file directly to the cloud you'll probably need a way to reference it with an ORM and process it.

Content-Type / Mime

The default amazon content-type is "binary/octet-stream" and for many cases this will work just fine. But if you are trying to stream video or audio you will need to set the mime type manually as Amazon will not calculate it for you. All mime types are supported: http://en.wikipedia.org/wiki/Internet_media_type.

First, tell CarrierWaveDirect what your default content type should be:

CarrierWave.configure do |config|
  # ... fog configuration and other options ...
  config.will_include_content_type = true

  config.default_content_type = 'video/mpeg'
  config.allowed_content_types = %w(video/mpeg video/mp4 video/ogg)


class VideoUploader < CarrierWave::Uploader::Base
  include CarrierWaveDirect::Uploader

  def will_include_content_type

  default_content_type  'video/mpeg'
  allowed_content_types %w(video/mpeg video/mp4 video/ogg)

Note: If will_include_content_type is true and default_content_type is nil, the content type will default to 'binary/octet-stream'.

For the forms, no change is required to use the default_content_type.

<%= direct_upload_form_for @uploader do |f| %>
  <%= f.file_field :avatar %> # Content-Type will automatically be set to the default
  <%= f.submit %>
<% end %>

You could use a manual select as well.

<%= direct_upload_form_for @uploader do |f| %>
  <%= select_tag 'Content-Type', options_for_select([
  ], 'video/mpeg') %><br>
  <%= f.file_field :avatar, exclude_content_type: true %> # Must tell the file_field helper not to include content type
  <%= f.submit %>
<% end %>

Or you can use the helper which shows all possible content types as a select, with the default content type selected.

<%= direct_upload_form_for @uploader do |f| %>
  <%= f.content_type_label %><br>
  <%= f.content_type_select %><br><br>

  <%= f.file_field :avatar, exclude_content_type: true %><br> # Must tell the file_field helper not to include its own content type
  <%= f.submit %>
<% end %>

Processing and referencing files in a background process

Processing and saving file uploads are typically long running tasks and should be done in a background process. CarrierWaveDirect gives you a few methods to help you do this with your favorite background processor such as DelayedJob or Resque.

If your upload was successful then you will be redirected to the success_action_redirect url you specified in your uploader. S3 replies with a redirect like this: http://example.com?bucket=your_fog_directory&key=uploads%2Fguid%2Ffile.ext&etag=%22d41d8cd98f00b204e9800998ecf8427%22

The key is the most important piece of information as we can use it for validating the file extension, downloading the file from S3, processing it and re-uploading it.

If you're using ActiveRecord, CarrierWaveDirect will by default validate the file extension based off your extension_allowlist in your uploader. See the CarrierWave readme for more info. You can then use the helper filename_valid? to check if the filename is valid. e.g.

class UsersController < ApplicationController
  def new
    @user = User.new(params)
    unless @user.filename_valid?
      flash[:error] = @user.errors.full_messages.to_sentence
      redirect_to new_avatar_path

CarrierWaveDirect automatically gives you an accessible key attribute in your mounted model when using ActiveRecord. You can use this to put a hidden field for the key into your model's form.

<%= form_for @user do |f| %>
  <%= f.hidden_field :key %>
  <%= f.label :email %>
  <%= f.text_field :email %>
  <%= f.submit %>
<% end %>

then in your controller you can do something like this:

def create
  @user = User.new(params[:user])
  if @user.save_and_process_avatar
    flash[:notice] = "User being created"
    redirect_to :action => :index
    render :new

Background processing

Now that the basic building blocks are in place you can process and save your avatar in the background. This example uses Resque but the same logic could be applied to DelayedJob or any other background processor.

class User < ActiveRecord::Base
  def save_and_process_avatar(options = {})
    if options[:now]
      self.remote_avatar_url = avatar.url
      Resque.enqueue(AvatarProcessor, attributes)

class AvatarProcessor
  @queue = :avatar_processor_queue

  def self.perform(attributes)
    user = User.new(attributes)
    user.save_and_process_avatar(:now => true)

The method self.remote_avatar_url= from CarrierWave downloads the avatar from S3 and processes it. save then re-uploads the processed avatar to S3

Uploading from a remote location

Your users may find it convenient to upload a file from a location on the Internet via a URL. CarrierWaveDirect gives you another accessor to achieve this.

<%= form_for @user do |f| %>
  <%= f.hidden_field :key %>
  <% unless @user.has_avatar_upload? %>
    <%= f.label :remote_avatar_net_url %>
    <%= f.text_field :remote_avatar_net_url %>
  <%= f.submit %>
<% end %>
class User < ActiveRecord::Base
  def save_and_process_avatar(options = {})
    if options[:now]
      self.remote_avatar_url = has_remote_avatar_net_url? ? remote_avatar_net_url : avatar.url
      Resque.enqueue(AvatarProcessor, attributes)

The methods has_avatar_upload?, remote_avatar_net_url and has_remote_avatar_net_url? are automatically added to your mounted model


Along with validating the extension of the filename, CarrierWaveDirect also gives you some other validations:

validates :avatar :is_uploaded => true

Validates that your mounted model has an avatar uploaded from file or specified by remote url. It does not check that an your mounted model actually has a valid avatar after the download has taken place. Turned off by default

validates :avatar, :is_attached => true

Validates that your mounted model has an avatar attached. This checks whether there is an actual avatar attached to the mounted model after downloading. Turned off by default

validates :avatar, :filename_uniqueness => true

Validates that the filename in the database is unique. Turned on by default

validates :avatar, :filename_format => true

Validates that the uploaded filename is valid. As well as validating the extension against the extension_allowlist it also validates that the upload_dir is correct. Turned on by default

validates :avatar, :remote_net_url_format => true

Validates that the remote net url is valid. As well as validating the extension against the extension_allowlist it also validates that url is valid and has only the schemes specified in the url_scheme_whitelist. Turned on by default


As well as the built in validations CarrierWaveDirect provides, some validations, such as max file size and upload expiration can be performed on the S3 side.

CarrierWave.configure do |config|
  config.validate_is_attached = true             # defaults to false
  config.validate_is_uploaded = true             # defaults to false
  config.validate_unique_filename = false        # defaults to true
  config.validate_filename_format = false        # defaults to true
  config.validate_remote_net_url_format = false  # defaults to true

  config.min_file_size             = 5.kilobytes  # defaults to 1.byte
  config.max_file_size             = 10.megabytes # defaults to 5.megabytes
  config.upload_expiration         = 1.hour       # defaults to 10.hours
  config.will_include_content_type = 'video/mp4'  # defaults to false; if true, content-type will be set
                                                  # on s3, but you must include an input field named
                                                  # Content-Type on every direct upload form

  config.use_action_status = true                 # defaults to false; if true, you must set
                                                  # success_action_status in your uploader:
                                                  #   uploader.success_action_status = "201"
                                                  # and add use_action_status to the file field:
                                                  #   f.file_field :avatar, use_action_status: true'

Bucket CORS configuration and usage with CloudFront

If you are using a javascript uploader (e.g. Dropzone, jQuery Upload, Uploadify, etc.) you will need to add CORS configuration to your bucket, otherwise default bucket configuration will deny CORS requests. To do that open your bucket in Amazon console, click on its properties and add a CORS configuration similar to this

        <!--  Optionally change this with your domain, it should not be an issue since your bucket accepts only signed writes -->

When you use this gem in conjunction with CloudFront you'll need an additional step otherwise it won't work as expected. This is strictly necessary if you configured CarrierWave asset_host to use a CloudFront in front of your bucket because your forms will be posted to that url.

To solve this issue you must enable POST requests in your CloudFront distribution settings. Here is a step by step walkthrough that explain this setup. It also explain CORS configuration.

Testing with CarrierWaveDirect

CarrierWaveDirect provides a couple of helpers to help with integration and unit testing. You don't want to contact the Internet during your tests as this is slow, expensive and unreliable. You should first put fog into mock mode by doing something like this.


def fog_directory

connection = ::Fog::Storage.new(
  :aws_access_key_id      => ENV['AWS_ACCESS_KEY_ID'],
  :aws_secret_access_key  => ENV['AWS_SECRET_ACCESS_KEY'],
  :provider               => 'AWS'

connection.directories.create(:key => fog_directory)

Using Capybara

If you're using Capybara with Cucumber or RSpec, CarrierWaveDirect gives you a few useful helpers. To get the Capybara helpers, include the module into your test file or helper

describe AvatarUploadSpec
  include CarrierWaveDirect::Test::CapybaraHelpers

To attach a file to the direct upload form you can use


To simulate a successful upload and redirect to S3 you can use

upload_directly(AvatarUploader.new, "Upload to S3")

This will click the Upload to S3 button on the form and redirect you to the success_action_redirect url (in the form) with a sample response from S3

To simulate an unsuccessful upload you can pass :success => false and you'll remain on the upload page e.g.

upload_directly(AvatarUploader.new, "Upload to S3", :success => false)

You can also use find_key and find_upload_path to get the key and upload path from the form

Unit tests

If your mounted model validates a file is uploaded you might want to make use of the sample_key method

include CarrierWaveDirect::Test::Helpers

Factory.define :user |f|
  f.email "some1@example.com"
  f.key { sample_key(AvatarUploader.new) }

This will return a valid key based off your upload_dir and your extension_allowlist

Faking a background download

If you wanted to fake a download in the background you could do something like this

uploader = AvatarUploader.new

upload_path = find_upload_path
redirect_key = sample_key(:base => find_key, :filename => File.basename(upload_path))

uploader.key = redirect_key
download_url = uploader.url

# Register the download url and return the uploaded file in the body
FakeWeb.register_uri(:get, download_url, :body => File.open(upload_path))


The Active Record validations use the Rails i18n framework. Add these keys to your translations file:

      carrierwave_direct_filename_taken: filename was already taken
      carrierwave_direct_upload_missing: upload is missing
      carrierwave_direct_attachment_missing: attachment is missing
      carrierwave_direct_filename_invalid: "is invalid. "
      carrierwave_direct_allowed_extensions: Allowed file types are %{extensions}
      carrierwave_direct_allowed_schemes: Allowed schemes are %{schemes}


If you're Rails app was newly generated after version 3.2.3 and your testing this in development you may run into an issue where an ActiveModel::MassAssignmentSecurity::Error is raised when being redirected from S3. You can fix this by setting config.active_record.mass_assignment_sanitizer = :logger in your config/environments/development.rb file.

Contributing to CarrierWaveDirect

Pull requests are very welcome. Before submitting a pull request, please make sure that your changes are well tested. Pull requests without tests will not be accepted.

gem install bundler
bundle install

You should now be able to run the tests

bundle exec rake

Using the Sample Application

After you have fixed a bug or added a feature please also use the CarrierWaveDirect Sample Application to ensure that the gem still works correctly.


Thank you to everybody who has contributed to CarrierWaveDirect. A special thanks to nddeluca (Nicholas DeLuca) who does a great job maintaining this gem. If you'd like to help him out see #83