Ruby file uploads, take 3
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Latest commit d7a42dc Jun 10, 2016 @jnicklas jnicklas committed on GitHub Merge pull request #480 from sobrinho/master
Make attachment_cache_field public


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Refile is a modern file upload library for Ruby applications. It is simple, yet powerful.



  • Configurable backends, file system, S3, etc...
  • Convenient integration with ORMs
  • On the fly manipulation of images and other files
  • Streaming IO for fast and memory friendly uploads
  • Works across form redisplays, i.e. when validations fail, even on S3
  • Effortless direct uploads, even to S3
  • Support for multiple file uploads

Sponsored by:


Quick start, Rails

Add the gem:

gem "refile", require: "refile/rails"
gem "refile-mini_magick"

We're requiring both Refile's Rails integration and image processing via the MiniMagick gem, which requires ImageMagick (or GraphicsMagick) to be installed. To install it simply run:

brew install imagemagick # OS X
sudo apt-get install imagemagick # Ubuntu

Use the attachment method to use Refile in a model:

class User < ActiveRecord::Base
  attachment :profile_image

Generate a migration:

rails generate migration add_profile_image_to_users profile_image_id:string
rake db:migrate

Add an attachment field to your form:

<%= form_for @user do |form| %>
  <%= form.attachment_field :profile_image %>
<% end %>

Set up strong parameters:

def user_params

And start uploading! Finally show the file in your view:

<%= image_tag attachment_url(@user, :profile_image, :fill, 300, 300, format: "jpg") %>

How it works

Refile consists of several parts:

  1. Backends: cache and persist files
  2. Model attachments: map files to model columns
  3. A Rack application: streams files and accepts uploads
  4. Rails helpers: conveniently generate markup in your views
  5. A JavaScript library: facilitates direct uploads

Let's look at each of these in more detail!

1. Backend

Files are uploaded to a backend. The backend assigns an ID to this file, which will be unique for this file within the backend.

Let's look at a simple example of using the backend:

backend ="tmp")

file = backend.upload("hello")) # => "b205bc..." # => "hello"

backend.get( # => "hello"

As you may notice, backends are "flat". Files do not have directories, nor do they have names or permissions, they are only identified by their ID.

Refile has a global registry of backends, accessed through Refile.backends.

There are two "special" backends, which are only really special in that they are the default backends for attachments. They are cache and store.

The cache is intended to be transient. Files are added here before they are meant to be permanently stored. Usually files are then moved to the store for permanent storage, but this isn't always the case.

Suppose for example that a user uploads a file in a form and receives a validation error. In that case the file has been temporarily stored in the cache. The user might decide to fix the error and resubmit, at which point the file will be promoted to the store. On the other hand, the user might simply give up and leave, now the file is left in the cache for later cleanup.

Refile has convenient accessors for setting the cache and store, so for example if you add the refile-s3 gem to your Gemfile:

gem "refile-s3"

Now you can upload files to S3 easily by using these accessors:

# config/initializers/refile.rb
require "refile/s3"

aws = {
  access_key_id: "xyz",
  secret_access_key: "abc",
  region: "sa-east-1",
  bucket: "my-bucket",
Refile.cache = "cache", **aws) = "store", **aws)

Try this in the quick start example above and your files are now uploaded to S3.

Backends also provide the option of restricting the size of files they accept. For example:

Refile.cache = 10.megabytes, ...)

The Refile gem only ships with a FileSystem backend. Additional backends are provided by other gems.


The upload method on backends can be called with a variety of objects. It requires that the object passed to it behaves similarly to Ruby IO objects, in particular it must implement the methods size, read(length = nil, buffer = nil), eof?, rewind, and close. All of File, Tempfile, ActionDispath::UploadedFile and StringIO implement this interface, however String does not. If you want to upload a file from a String you must wrap it in a StringIO first.

2. Attachments

You've already seen the attachment method:

class User < ActiveRecord::Base
  attachment :profile_image

Calling attachment generates a getter and setter with the given name. When you assign a file to the setter, it is uploaded to the cache:

# with a ActionDispatch::UploadedFile
user.profile_image = params[:file]

# with a regular File object"/some/path", "rb") do |file|
  user.profile_image = file

# or a StringIO
user.profile_image ="hello world") # => "fec421..." # => "hello world"

When you call save on the record, the uploaded file is transferred from the cache to the store. Where possible, Refile does this move efficiently. For example if both cache and store are on the same S3 account, instead of downloading the file and uploading it again, Refile will simply issue a copy command to S3.

Other ORMs

Refile comes with ActiveRecord integration built-in, but is built to integrate with any ORM, so building your own should not be too difficult. Some integrations are already available via gems:

Pure Ruby classes

You can also use attachments in pure Ruby classes like this:

class User
  extend Refile::Attachment

  attr_accessor :profile_image_id

  attachment :profile_image

Keeping uploaded files

By default Refile will delete a stored file when its model is destroyed. You can change this behaviour by passing in the destroy option.

class User < ActiveRecord::Base
  attachment :profile_image, destroy: false

Now Refile will not delete the profile_image file from the store if the user is destroyed.

3. Rack Application

Refile includes a Rack application (an endpoint, not a middleware), written in Sinatra. This application streams files from backends and can even accept file uploads and upload them to backends.

Important: Unlike other file upload solutions, Refile always streams your files through your application. It cannot generate URLs to your files. This means that you should always put a CDN or other HTTP cache in front of your application. Serving files through your app takes a lot of resources and you want it to happen rarely.

Setting this up is actually quite simple, you can use the same CDN you would use for your application's static assets. This blog post explains how to set this up (bonus: faster static assets!). Once you've set this up, simply configure Refile to use your CDN:

Refile.cdn_host = ""

Using the HTTPS protocol for Refile.cdn_host is recommended. There aren't any performance concerns, and it is always safe to request HTTPS assets.


If you are using Rails and have required refile/rails.rb, then the Rack application is mounted for you at /attachments. You should be able to see this when you run rake routes.

You could also run the application on its own, it doesn't need to be mounted to work.

Retrieving files

Files can be retrieved from the application by calling:

GET /attachments/:token/:backend_name/:id/:filename

The :filename serves no other purpose than generating a nice name when the user downloads the file, it does not in any way affect the downloaded file. For caching purposes you should always use the same filename for the same file. The Rails helpers default this to the name of the column.

The :token is a generated digest of the request path when the Refile.secret_key is configured; otherwise, the application will raise an error. The digest feature provides a security measure against unverified requests.


Refile provides on the fly processing of files. You can trigger it by calling a URL like this:

GET /attachments/:token/:backend_name/:processor_name/*args/:id/:filename

Suppose we have uploaded a file:

Refile.cache.upload("hello")).id # => "a4e8ce"

And we've defined a processor like this:

Refile.processor :reverse do |file|

Then you could do the following.


Refile calls call on the processor and passes in the retrieved file, as well as all additional arguments sent through the URL.

4. Rails helpers

Refile provides the attachment_field form helper which generates a file field as well as a hidden field. This field keeps track of the file in case it is not yet permanently stored, for example if validations fail. It is also used for direct and presigned uploads. For this reason it is highly recommended to use attachment_field instead of file_field.

<%= form_for @user do |form| %>
  <%= form.attachment_field :profile_image %>
<% end %>

Will generate something like:

<form action="/users" enctype="multipart/form-data" method="post">
  <input name="user[profile_image]" type="hidden">
  <input name="user[profile_image]" type="file">

The attachment_url helper can then be used for generating URLs for the uploaded files:

<%= link_to "Image", attachment_url(@user, :profile_image) %>

Any additional arguments to it are included in the URL as processor arguments:

<%= link_to "Image", attachment_url(@user, :profile_image, :fill, 300, 300) %>

There's also a helper for generating image tags:

<%= attachment_image_tag(@user, :profile_image, :fill, 300, 300) %>

With this helper you can specify an image/asset which is used as a fallback in case no file has been uploaded:

<%= attachment_url(@user, :profile_image, :fill, 300, 300, fallback: "default.png") %>
<%= attachment_image_tag(@user, :profile_image, :fill, 300, 300, fallback: "default.png") %>

5. JavaScript library

Refile's JavaScript library is small but powerful.

Uploading files is slow, so anything we can do to speed up the process is going to lead to happier users. One way to cheat is to start uploading files directly after the user has chosen a file, instead of waiting until they hit the submit button. This provides a significantly better user experience. Implementing this is usually tricky, but thankfully Refile makes it very easy.

First, load the JavaScript file. If you're using the asset pipeline, you can simply include it like this:

//= require refile

Otherwise you can grab a copy here. Be sure to always update your copy of this file when you upgrade to the latest Refile version.

Now mark the field for direct upload:

<%= form.attachment_field :profile_image, direct: true %>

There is no step 3 ;)

The file is now uploaded to the cache immediately after the user chooses a file. If you try this in the browser, you'll notice that an AJAX request is fired as soon as you choose a file. Then when you submit to the server, the file is no longer submitted, only its id.

If you want to improve the experience of this, the JavaScript library fires a couple of custom DOM events. These events bubble, so you can also listen for them on the form for example:

form.addEventListener("upload:start", function() {
  // ...

form.addEventListener("upload:success", function() {
  // ...

input.addEventListener("upload:progress", function() {
  // ...

You can also listen for them with jQuery, even with event delegation:

$(document).on("upload:start", "form", function(e) {
  // ...

This way you could for example disable the submit button until all files have uploaded:

$(document).on("upload:start", "form", function(e) {
  $(this).find("input[type=submit]").attr("disabled", true)

$(document).on("upload:complete", "form", function(e) {
  if(!$(this).find("input.uploading").length) {

Presigned uploads

Amazon S3 supports uploads directly from the browser to S3 buckets. With this feature you can bypass your application entirely; uploads never hit your application at all. Unfortunately the default configuration of S3 buckets does not allow cross site AJAX requests from posting to buckets. Fixing this is easy though.

  • Open the AWS S3 console and locate your bucket
  • Right click on it and choose "Properties"
  • Open the "Permission" section
  • Click "Add CORS Configuration"

The default configuration only allows "GET", you'll want to allow "POST" as well. You'll also want to permit the "Content-Type" and "Origin" headers.

It could look something like this:


If you're paranoid you can restrict the allowed origin to only your domain, but since your bucket is only writable with authentication anyway, this shouldn't be necessary. Note that you do not need to, and in fact you shouldn't, make your bucket world writable.

Once you've put in the new configuration, click "Save". After that it may take some time for the CORS setup to kick in (because of DNS propagation).

Now you can enable presigned uploads:

<%= form.attachment_field :profile_image, presigned: true %>

You can also enable both direct and presigned uploads, and it'll fall back to direct uploads if presigned uploads aren't available. This is useful if you're using the FileSystem backend in development or test mode and the S3 backend in production mode.

<%= form.attachment_field :profile_image, direct: true, presigned: true %>

Browser compatibility

Refile's JavaScript library requires HTML5 features which are unavailable on IE9 and earlier versions. All other major browsers are supported.


URLs generated by Refile are cryptographically signed. This ensures that a file cannot be downloaded unless you hand someone the URL to that file. This is essentially equivalent to token base authentication.

Unfortunately a similar system is not in place for file uploads, meaning that direct file uploads are open to anyone. By default only the cache backend can be uploaded to, and you are encouraged to purge unused files from this backend periodically. This might seem insecure, but consider the fact that anyone who can access file uploads in your application will be able to upload files into it anyway.

Nevertheless, you can disable direct file uploads by setting:

Refile.allow_uploads_to = []

You also have the option of explicitly authenticating anyone who tries to access the Refile application. Since the Refile application is a Sinatra application, you can use Sinatra's before hooks to set up authentication like this:

Refile::App.before do
  halt 403 unless User.find_by(id: session[:user_id])

Additional metadata

In the quick start example above, we chose to only store the file id, but often it is useful to store the file's filename, size and content type as well. Refile makes it easy to extract this data and store it alongside the id. All you need to do is add columns for these:

class StoreMetadata < ActiveRecord::Migration
  def change
    add_column :users, :profile_image_filename, :string
    add_column :users, :profile_image_size, :integer
    add_column :users, :profile_image_content_type, :string

These columns will now be filled automatically.

File type validations

Refile can check that attached files have a given content type or extension. This allows you to warn users if they try to upload an invalid file.

Important: You should regard this as a convenience feature for your users, not a security feature. Both file extension and content type can easily be spoofed.

In order to limit attachments to an extension or content type, you can provide them like this:

attachment :cv, extension: "pdf"
attachment :profile_image, content_type: "image/jpeg"

You can also provide a list of content types or extensions:

attachment :cv, extension: ["pdf", "doc"]
attachment :profile_image, content_type: ["image/jpeg", "image/png", "image/gif"]

Since the combination of JPEG, PNG and GIF is so common, you can also specify this more succinctly like this:

attachment :profile_image, type: :image

When a user uploads a file with an invalid extension or content type and submits the form, they'll be presented with a validation error.

If you use a particular content type or set of content types frequently you can define your own types like this:

Refile.types[:document] =,
  content_type: %w[text/plain application/pdf]

Now you can use them like this:

attachment :profile_image, type: :document

Multiple file uploads

File input fields support the multiple attribute which allows users to attach multiple files at once. Refile supports this attribute. You can add the attribute to your attachment fields like this:

<%= form.attachment_field :images_files, multiple: true %>

Multiple file uploads also work nicely with direct and presigned uploads:

<%= form.attachment_field :images_files, multiple: true, direct: true, presigned: true %>

Note that you will get separate events for each uploaded file. So when you attach two files, the upload:start event and other events will be triggered twice, once for each file.

When you upload multiple files, your application will receive an array of files, instead of a single file. To map these files to model object, Refile's ActiveRecord integration ships with a nice macro that makes this trivial. Suppose you have an image model like this:

class Image < ActiveRecord::Base
  belongs_to :post
  attachment :file

Note it must be possible to persist images given only the associated post and a file. There must not be any other validations or constraints which prevent images from being saved.

From the post model, you can use the accepts_attachments_for macro:

class Post < ActiveRecord::Base
  has_many :images, dependent: :destroy
  accepts_attachments_for :images, attachment: :file

The attachment option defaults to :file, so we could have left it out in this case.

class Post < ActiveRecord::Base
  has_many :images, dependent: :destroy
  accepts_attachments_for :images

You can add the attachment field to your post form:

<%= form_for @post do |form| %>
  <%= form.label :images_files %>
  <%= form.attachment_field :images_files, multiple: true %>
<% end %>

Now you only need to permit the generated accessor in your controller. Since images_files is an array, you need to tell Rails to allow array values for it:

def post_params
  params.require(:post).permit(images_files: [])

When editing a record with accepts_attachments_for, the default behaviour is to replace the entire list of attachments when new attachments are uploaded. It is also possible to append the new attachments to the list of attachments instead so that older attachments are kept. To enable this, set the append option to true.

class Post < ActiveRecord::Base
  has_many :images, dependent: :destroy
  accepts_attachments_for :images, append: true

Removing attached files

File input fields unfortunately do not have the option of removing an already uploaded file. This is problematic when editing a model which has a file attached and the user wants to remove this file. To work around this, Refile automatically adds an attribute to your model when you use the attachment method, which is designed to be used with a checkbox in a form.

<%= form_for @user do |form| %>
  <%= form.label :profile_image %>
  <%= form.attachment_field :profile_image %>

  <%= form.check_box :remove_profile_image %>
  <%= form.label :remove_profile_image %>
<% end %>

Don't forget to permit this attribute in your controller:

def user_params
  params.require(:user).permit(:profile_image, :remove_profile_image)

Now when you check this checkbox and submit the form, the previously attached file will be removed.

Fetching remote files by URL

You might want to give you users the option of uploading a file by its URL. This could be either just via a textfield or through some other interface. Refile makes it easy to fetch this file and upload it. Just add a field like this:

<%= form_for @user do |form| %>
  <%= form.label :profile_image, "Attach image" %>
  <%= form.attachment_field :profile_image %>

  <%= form.label :remote_profile_image_url, "Or specify URL" %>
  <%= form.text_field :remote_profile_image_url %>
<% end %>

Then permit this field in your controller:

def user_params
  params.require(:user).permit(:profile_image, :remote_profile_image_url)

Refile will now fetch the file from the given URL, following redirects if needed.

Cache expiry

Files will accumulate in your cache, and you'll probably want to remove them after some time.

The FileSystem backend does not currently provide any method of doing this. PRs welcome ;)

On S3 this can be conveniently handled through lifecycle rules. Exactly how depends a bit on your setup. If you are using the suggested setup of having one bucket with cache and store being directories in that bucket (or prefixes in S3 parlance), then follow the following steps, otherwise adapt them to your needs:

  • Open the AWS S3 console and locate your bucket
  • Right click on it and choose "Properties"
  • Open the "Lifecycle" section
  • Click "Add rule"
  • Choose "Apply the rule to: A prefix"
  • Enter "cache/" as the prefix (trailing slash!)
  • Click "Configure rule"
  • For "Action on Objects" you'll probably want to choose "Permanently Delete Only"
  • Choose whatever number of days you're comfortable with, I chose "1"
  • Click "Review" and finally "Create and activate Rule"


When testing your own classes that use Refile, you can use Refile::FileDouble objects instead of real files.

# app/models/post.rb
class Post < ActiveRecord::Base
  attachment :image, type: :image

# spec/models/post_spec.rb
require "rails_helper"
require "refile/file_double"

RSpec.describe Post, type: :model do
  it "allows attaching an image" do
    post =

    post.image ="dummy", "logo.png", content_type: "image/png")

    expect(post.image_id).not_to be_nil

  it "doesn't allow attaching other files" do
    post =

    post.image ="dummy", "file.txt", content_type: "text/plain")

    expect(post.image_id).to be_nil


simple_form gem is also supported:

# in initializer or Gemfile
require 'refile/simple_form'

# in forms
<%= f.input :cover_image, as: :attachment, direct: true, presigned: true %>