Active Storage Overview

1 What is Active Storage?

Active Storage facilitates uploading files to a cloud storage service like Amazon S3, Google Cloud Storage, or Microsoft Azure Storage and attaching those files to Active Record objects. It comes with a local disk-based service for development and testing and supports mirroring files to subordinate services for backups and migrations.

Using Active Storage, an application can transform image uploads or generate image representations of non-image uploads like PDFs and videos, and extract metadata from arbitrary files.

1.1 Requirements

Various features of Active Storage depend on third-party software which Rails will not install, and must be installed separately:

• libvips v8.6+ or ImageMagick for image analysis and transformations
• ffmpeg v3.4+ for video previews and ffprobe for video/audio analysis
• poppler or muPDF for PDF previews

Image analysis and transformations also require the image_processing gem. Uncomment it in your Gemfile, or add it if necessary:

gem "image_processing", ">= 1.2"

2 Setup

$ bin/rails active_storage:install
$ bin/rails db:migrate

This sets up configuration, and creates the three tables Active Storage uses: active_storage_blobs, active_storage_attachments, and active_storage_variant_records.

Declare Active Storage services in config/storage.yml. For each service your application uses, provide a name and the requisite configuration. The example below declares three services named local, test, and amazon:

local:
  service: Disk
  root: <%= Rails.root.join("storage") %>

test:
  service: Disk
  root: <%= Rails.root.join("tmp/storage") %>

amazon:
  service: S3
  access_key_id: ""
  secret_access_key: ""
  bucket: ""
  region: "" # e.g. 'us-east-1'

Tell Active Storage which service to use by setting Rails.application.config.active_storage.service. Because each environment will likely use a different service, it is recommended to do this on a per-environment basis. To use the disk service from the previous example in the development environment, you would add the following to config/environments/development.rb:

# Store files locally.
config.active_storage.service = :local

To use the S3 service in production, you add the following to config/environments/production.rb:

# Store files on Amazon S3.
config.active_storage.service = :amazon

To use the test service when testing, you add the following to config/environments/test.rb:

# Store uploaded files on the local file system in a temporary directory.
config.active_storage.service = :test

It is recommended to use Rails.env in the bucket names to further reduce the risk of accidentally destroying production data.

amazon:
  service: S3
  # ...
  bucket: your_own_bucket-<%= Rails.env %>

google:
  service: GCS
  # ...
  bucket: your_own_bucket-<%= Rails.env %>

azure:
  service: AzureStorage
  # ...
  container: your_container_name-<%= Rails.env %>

Continue reading for more information on the built-in service adapters (e.g. Disk and S3) and the configuration they require.

2.1 Disk Service

Declare a Disk service in config/storage.yml:

local:
  service: Disk
  root: <%= Rails.root.join("storage") %>

2.2 S3 Service (Amazon S3 and S3-compatible APIs)

To connect to Amazon S3, declare an S3 service in config/storage.yml:

amazon:
  service: S3
  access_key_id: ""
  secret_access_key: ""
  region: ""
  bucket: ""

Optionally provide client and upload options:

amazon:
  service: S3
  access_key_id: ""
  secret_access_key: ""
  region: ""
  bucket: ""
  http_open_timeout: 0
  http_read_timeout: 0
  retry_limit: 0
  upload:
    server_side_encryption: "" # 'aws:kms' or 'AES256'
    cache_control: "private, max-age=<%= 1.day.to_i %>"

Add the aws-sdk-s3 gem to your Gemfile:

gem "aws-sdk-s3", require: false

To connect to an S3-compatible object storage API such as DigitalOcean Spaces, provide the endpoint:

digitalocean:
  service: S3
  endpoint: https://nyc3.digitaloceanspaces.com
  access_key_id: ...
  secret_access_key: ...
  # ...and other options

There are many other options available. You can check them in AWS S3 Client documentation.

2.3 Microsoft Azure Storage Service

Declare an Azure Storage service in config/storage.yml:

azure:
  service: AzureStorage
  storage_account_name: ""
  storage_access_key: ""
  container: ""

Add the azure-storage-blob gem to your Gemfile:

gem "azure-storage-blob", "~> 2.0", require: false

2.4 Google Cloud Storage Service

Declare a Google Cloud Storage service in config/storage.yml:

google:
  service: GCS
  credentials: <%= Rails.root.join("path/to/keyfile.json") %>
  project: ""
  bucket: ""

Optionally provide a Hash of credentials instead of a keyfile path:

google:
  service: GCS
  credentials:
    type: "service_account"
    project_id: ""
    private_key_id: <%= Rails.application.credentials.dig(:gcs, :private_key_id) %>
    private_key: <%= Rails.application.credentials.dig(:gcs, :private_key).dump %>
    client_email: ""
    client_id: ""
    auth_uri: "https://accounts.google.com/o/oauth2/auth"
    token_uri: "https://accounts.google.com/o/oauth2/token"
    auth_provider_x509_cert_url: "https://www.googleapis.com/oauth2/v1/certs"
    client_x509_cert_url: ""
  project: ""
  bucket: ""

Optionally provide a Cache-Control metadata to set on uploaded assets:

google:
  service: GCS
  ...
  cache_control: "public, max-age=3600"

Optionally use IAM instead of the credentials when signing URLs. This is useful if you are authenticating your GKE applications with Workload Identity, see this Google Cloud blog post for more information.

google:
  service: GCS
  ...
  iam: true

Optionally use a specific GSA when signing URLs. When using IAM, the metadata server will be contacted to get the GSA email, but this metadata server is not always present (e.g. local tests) and you may wish to use a non-default GSA.

google:
  service: GCS
  ...
  iam: true
  gsa_email: "foobar@baz.iam.gserviceaccount.com"

Add the google-cloud-storage gem to your Gemfile:

gem "google-cloud-storage", "~> 1.11", require: false

2.5 Mirror Service

You can keep multiple services in sync by defining a mirror service. A mirror service replicates uploads and deletes across two or more subordinate services.

A mirror service is intended to be used temporarily during a migration between services in production. You can start mirroring to a new service, copy pre-existing files from the old service to the new, then go all-in on the new service.

Define each of the services you'd like to mirror as described above. Reference them by name when defining a mirror service:

s3_west_coast:
  service: S3
  access_key_id: ""
  secret_access_key: ""
  region: ""
  bucket: ""

s3_east_coast:
  service: S3
  access_key_id: ""
  secret_access_key: ""
  region: ""
  bucket: ""

production:
  service: Mirror
  primary: s3_east_coast
  mirrors:
    - s3_west_coast

Although all secondary services receive uploads, downloads are always handled by the primary service.

Mirror services are compatible with direct uploads. New files are directly uploaded to the primary service. When a directly-uploaded file is attached to a record, a background job is enqueued to copy it to the secondary services.

2.6 Public access

By default, Active Storage assumes private access to services. This means generating signed, single-use URLs for blobs. If you'd rather make blobs publicly accessible, specify public: true in your app's config/storage.yml:

gcs: &gcs
  service: GCS
  project: ""

private_gcs:
  <<: *gcs
  credentials: <%= Rails.root.join("path/to/private_key.json") %>
  bucket: ""

public_gcs:
  <<: *gcs
  credentials: <%= Rails.root.join("path/to/public_key.json") %>
  bucket: ""
  public: true

Make sure your buckets are properly configured for public access. See docs on how to enable public read permissions for Amazon S3, Google Cloud Storage, and Microsoft Azure storage services. Amazon S3 additionally requires that you have the s3:PutObjectAcl permission.

When converting an existing application to use public: true, make sure to update every individual file in the bucket to be publicly-readable before switching over.

3 Attaching Files to Records

3.1 has_one_attached

The has_one_attached macro sets up a one-to-one mapping between records and files. Each record can have one file attached to it.

For example, suppose your application has a User model. If you want each user to have an avatar, define the User model as follows:

class User < ApplicationRecord
  has_one_attached :avatar
end

or if you are using Rails 6.0+, you can run a model generator command like this:

$ bin/rails generate model User avatar:attachment

You can create a user with an avatar:

<%= form.file_field :avatar %>

class SignupController < ApplicationController
  def create
    user = User.create!(user_params)
    session[:user_id] = user.id
    redirect_to root_path
  end

  private
    def user_params
      params.require(:user).permit(:email_address, :password, :avatar)
    end
end

Call avatar.attach to attach an avatar to an existing user:

user.avatar.attach(params[:avatar])

Call avatar.attached? to determine whether a particular user has an avatar:

user.avatar.attached?

In some cases you might want to override a default service for a specific attachment. You can configure specific services per attachment using the service option with the name of your service:

class User < ApplicationRecord
  has_one_attached :avatar, service: :google
end

You can configure specific variants per attachment by calling the variant method on yielded attachable object:

class User < ApplicationRecord
  has_one_attached :avatar do |attachable|
    attachable.variant :thumb, resize_to_limit: [100, 100]
  end
end

Call avatar.variant(:thumb) to get a thumb variant of an avatar:

<%= image_tag user.avatar.variant(:thumb) %>

You can use specific variants for previews as well:

class User < ApplicationRecord
  has_one_attached :video do |attachable|
    attachable.variant :thumb, resize_to_limit: [100, 100]
  end
end

<%= image_tag user.video.preview(:thumb) %>

If you know in advance that your variants will be accessed, you can specify that Rails should generate them ahead of time:

class User < ApplicationRecord
  has_one_attached :video do |attachable|
    attachable.variant :thumb, resize_to_limit: [100, 100], preprocessed: true
  end
end

Rails will enqueue a job to generate the variant after the attachment is attached to the record.

3.2 has_many_attached

The has_many_attached macro sets up a one-to-many relationship between records and files. Each record can have many files attached to it.

For example, suppose your application has a Message model. If you want each message to have many images, define the Message model as follows:

class Message < ApplicationRecord
  has_many_attached :images
end

or if you are using Rails 6.0+, you can run a model generator command like this:

$ bin/rails generate model Message images:attachments

You can create a message with images:

class MessagesController < ApplicationController
  def create
    message = Message.create!(message_params)
    redirect_to message
  end

  private
    def message_params
      params.require(:message).permit(:title, :content, images: [])
    end
end

Call images.attach to add new images to an existing message:

@message.images.attach(params[:images])

Call images.attached? to determine whether a particular message has any images:

@message.images.attached?

Overriding the default service is done the same way as has_one_attached, by using the service option:

class Message < ApplicationRecord
  has_many_attached :images, service: :s3
end

Configuring specific variants is done the same way as has_one_attached, by calling the variant method on the yielded attachable object:

class Message < ApplicationRecord
  has_many_attached :images do |attachable|
    attachable.variant :thumb, resize_to_limit: [100, 100]
  end
end

3.3 Attaching File/IO Objects

Sometimes you need to attach a file that doesn’t arrive via an HTTP request. For example, you may want to attach a file you generated on disk or downloaded from a user-submitted URL. You may also want to attach a fixture file in a model test. To do that, provide a Hash containing at least an open IO object and a filename:

@message.images.attach(io: File.open('/path/to/file'), filename: 'file.pdf')

When possible, provide a content type as well. Active Storage attempts to determine a file’s content type from its data. It falls back to the content type you provide if it can’t do that.

@message.images.attach(io: File.open('/path/to/file'), filename: 'file.pdf', content_type: 'application/pdf')

You can bypass the content type inference from the data by passing in identify: false along with the content_type.

@message.images.attach(
  io: File.open('/path/to/file'),
  filename: 'file.pdf',
  content_type: 'application/pdf',
  identify: false
)

If you don’t provide a content type and Active Storage can’t determine the file’s content type automatically, it defaults to application/octet-stream.

There is an additional parameter key that can be used to specify folders/sub-folders in your S3 Bucket. AWS S3 otherwise uses a random key to name your files. This approach is helpful if you want to organize your S3 Bucket files better.

@message.images.attach(
  io: File.open('/path/to/file'),
  filename: 'file.pdf',
  content_type: 'application/pdf',
  key: "#{Rails.env}/blog_content/intuitive_filename.pdf",
  identify: false
)

This way the file will get saved in the folder [S3_BUCKET]/development/blog_content/ when you test this from your development environment. Note that if you use the key parameter, you have to ensure the key to be unique for the upload to go through. It is recommended to append the filename with a unique random key, something like:

def s3_file_key
  "#{Rails.env}/blog_content/intuitive_filename-#{SecureRandom.uuid}.pdf"
end

@message.images.attach(
  io: File.open('/path/to/file'),
  filename: 'file.pdf',
  content_type: 'application/pdf',
  key: s3_file_key,
  identify: false
)

3.4 Replacing vs Adding Attachments

By default in Rails, attaching files to a has_many_attached association will replace any existing attachments.

To keep existing attachments, you can use hidden form fields with the signed_id of each attached file:

<% @message.images.each do |image| %>
  <%= form.hidden_field :images, multiple: true, value: image.signed_id %>
<% end %>

<%= form.file_field :images, multiple: true %>

This has the advantage of making it possible to remove existing attachments selectively, e.g. by using JavaScript to remove individual hidden fields.

3.5 Form Validation

Attachments aren't sent to the storage service until a successful save on the associated record. This means that if a form submission fails validation, any new attachment(s) will be lost and must be uploaded again. Since direct uploads are stored before the form is submitted, they can be used to retain uploads when validation fails:

<%= form.hidden_field :avatar, value: @user.avatar.signed_id if @user.avatar.attached? %>
<%= form.file_field :avatar, direct_upload: true %>

4 Removing Files

To remove an attachment from a model, call purge on the attachment. If your application is set up to use Active Job, removal can be done in the background instead by calling purge_later. Purging deletes the blob and the file from the storage service.

# Synchronously destroy the avatar and actual resource files.
user.avatar.purge

# Destroy the associated models and actual resource files async, via Active Job.
user.avatar.purge_later

5 Serving Files

Active Storage supports two ways to serve files: redirecting and proxying.

5.1 Redirect Mode

To generate a permanent URL for a blob, you can pass the blob to the url_for view helper. This generates a URL with the blob's signed_id that is routed to the blob's RedirectController

url_for(user.avatar)
# => https://www.example.com/rails/active_storage/blobs/redirect/:signed_id/my-avatar.png

The RedirectController redirects to the actual service endpoint. This indirection decouples the service URL from the actual one, and allows, for example, mirroring attachments in different services for high-availability. The redirection has an HTTP expiration of 5 minutes.

To create a download link, use the rails_blob_{path|url} helper. Using this helper allows you to set the disposition.

rails_blob_path(user.avatar, disposition: "attachment")

If you need to create a link from outside of controller/view context (Background jobs, Cronjobs, etc.), you can access the rails_blob_path like this:

Rails.application.routes.url_helpers.rails_blob_path(user.avatar, only_path: true)

5.2 Proxy Mode

Optionally, files can be proxied instead. This means that your application servers will download file data from the storage service in response to requests. This can be useful for serving files from a CDN.

You can configure Active Storage to use proxying by default:

# config/initializers/active_storage.rb
Rails.application.config.active_storage.resolve_model_to_route = :rails_storage_proxy

Or if you want to explicitly proxy specific attachments there are URL helpers you can use in the form of rails_storage_proxy_path and rails_storage_proxy_url.

<%= image_tag rails_storage_proxy_path(@user.avatar) %>

5.2.1 Putting a CDN in Front of Active Storage

Additionally, in order to use a CDN for Active Storage attachments, you will need to generate URLs with proxy mode so that they are served by your app and the CDN will cache the attachment without any extra configuration. This works out of the box because the default Active Storage proxy controller sets an HTTP header indicating to the CDN to cache the response.

You should also make sure that the generated URLs use the CDN host instead of your app host. There are multiple ways to achieve this, but in general it involves tweaking your config/routes.rb file so that you can generate the proper URLs for the attachments and their variations. As an example, you could add this:

# config/routes.rb
direct :cdn_image do |model, options|
  expires_in = options.delete(:expires_in) { ActiveStorage.urls_expire_in }

  if model.respond_to?(:signed_id)
    route_for(
      :rails_service_blob_proxy,
      model.signed_id(expires_in: expires_in),
      model.filename,
      options.merge(host: ENV['CDN_HOST'])
    )
  else
    signed_blob_id = model.blob.signed_id(expires_in: expires_in)
    variation_key  = model.variation.key
    filename       = model.blob.filename

    route_for(
      :rails_blob_representation_proxy,
      signed_blob_id,
      variation_key,
      filename,
      options.merge(host: ENV['CDN_HOST'])
    )
  end
end

and then generate routes like this:

<%= cdn_image_url(user.avatar.variant(resize_to_limit: [128, 128])) %>

5.3 Authenticated Controllers

All Active Storage controllers are publicly accessible by default. The generated URLs use a plain signed_id, making them hard to guess but permanent. Anyone that knows the blob URL will be able to access it, even if a before_action in your ApplicationController would otherwise require a login. If your files require a higher level of protection, you can implement your own authenticated controllers, based on the ActiveStorage::Blobs::RedirectController, ActiveStorage::Blobs::ProxyController, ActiveStorage::Representations::RedirectController and ActiveStorage::Representations::ProxyController

To only allow an account to access their own logo you could do the following:

# config/routes.rb
resource :account do
  resource :logo
end

# app/controllers/logos_controller.rb
class LogosController < ApplicationController
  # Through ApplicationController:
  # include Authenticate, SetCurrentAccount

  def show
    redirect_to Current.account.logo.url
  end
end

<%= image_tag account_logo_path %>

And then you should disable the Active Storage default routes with:

config.active_storage.draw_routes = false

to prevent files being accessed with the publicly accessible URLs.

6 Downloading Files

Sometimes you need to process a blob after it’s uploaded—for example, to convert it to a different format. Use the attachment's download method to read a blob’s binary data into memory:

binary = user.avatar.download

You might want to download a blob to a file on disk so an external program (e.g. a virus scanner or media transcoder) can operate on it. Use the attachment's open method to download a blob to a tempfile on disk:

message.video.open do |file|
  system '/path/to/virus/scanner', file.path
  # ...
end

It's important to know that the file is not yet available in the after_create callback but in the after_create_commit only.

7 Analyzing Files

Active Storage analyzes files once they've been uploaded by queuing a job in Active Job. Analyzed files will store additional information in the metadata hash, including analyzed: true. You can check whether a blob has been analyzed by calling analyzed? on it.

Image analysis provides width and height attributes. Video analysis provides these, as well as duration, angle, display_aspect_ratio, and video and audio booleans to indicate the presence of those channels. Audio analysis provides duration and bit_rate attributes.

8 Displaying Images, Videos, and PDFs

Active Storage supports representing a variety of files. You can call representation on an attachment to display an image variant, or a preview of a video or PDF. Before calling representation, check if the attachment can be represented by calling representable?. Some file formats can't be previewed by Active Storage out of the box (e.g. Word documents); if representable? returns false you may want to link to the file instead.

<ul>
  <% @message.files.each do |file| %>
    <li>
      <% if file.representable? %>
        <%= image_tag file.representation(resize_to_limit: [100, 100]) %>
      <% else %>
        <%= link_to rails_blob_path(file, disposition: "attachment") do %>
          <%= image_tag "placeholder.png", alt: "Download file" %>
        <% end %>
      <% end %>
    </li>
  <% end %>
</ul>

Internally, representation calls variant for images, and preview for previewable files. You can also call these methods directly.

8.1 Lazy vs Immediate Loading

By default, Active Storage will process representations lazily. This code:

image_tag file.representation(resize_to_limit: [100, 100])

Will generate an <img> tag with the src pointing to the ActiveStorage::Representations::RedirectController. The browser will make a request to that controller, which will perform the following:

1. Process file and upload the processed file if necessary.
2. Return a 302 redirect to the file either to
   • the remote service (e.g., S3).
   • or ActiveStorage::Blobs::ProxyController which will return the file contents if proxy mode is enabled.

Loading the file lazily allows features like single use URLs to work without slowing down your initial page loads.

This works fine for most cases.

If you want to generate URLs for images immediately, you can call .processed.url:

image_tag file.representation(resize_to_limit: [100, 100]).processed.url

The Active Storage variant tracker improves performance of this, by storing a record in the database if the requested representation has been processed before. Thus, the above code will only make an API call to the remote service (e.g. S3) once, and once a variant is stored, will use that. The variant tracker runs automatically, but can be disabled through config.active_storage.track_variants.

If you're rendering lots of images on a page, the above example could result in N+1 queries loading all the variant records. To avoid these N+1 queries, use the named scopes on ActiveStorage::Attachment.

message.images.with_all_variant_records.each do |file|
  image_tag file.representation(resize_to_limit: [100, 100]).processed.url
end

8.2 Transforming Images

Transforming images allows you to display the image at your choice of dimensions. To create a variation of an image, call variant on the attachment. You can pass any transformation supported by the variant processor to the method. When the browser hits the variant URL, Active Storage will lazily transform the original blob into the specified format and redirect to its new service location.

<%= image_tag user.avatar.variant(resize_to_limit: [100, 100]) %>

If a variant is requested, Active Storage will automatically apply transformations depending on the image's format:

1. Content types that are variable (as dictated by config.active_storage.variable_content_types) and not considered web images (as dictated by config.active_storage.web_image_content_types), will be converted to PNG.

2. If quality is not specified, the variant processor's default quality for the format will be used.

Active Storage can use either Vips or MiniMagick as the variant processor. The default depends on your config.load_defaults target version, and the processor can be changed by setting config.active_storage.variant_processor.

The parameters available are defined by the image_processing gem and depend on the variant processor that you are using, but both support the following parameters:

image_processing has all parameters available in it's own documentation for both the Vips and MiniMagick processors.

Some parameters, including those listed above, accept additional processor specific options which can be passed as key: value pairs inside a hash:

<!-- Vips supports configuring `crop` for many of its transformations -->
<%= image_tag user.avatar.variant(resize_to_fill: [100, 100, { crop: :centre }]) %>

If migrating an existing application between MiniMagick and Vips, processor specific options will need to be updated:

<!-- MiniMagick -->
<%= image_tag user.avatar.variant(resize_to_limit: [100, 100], format: :jpeg, sampling_factor: "4:2:0", strip: true, interlace: "JPEG", colorspace: "sRGB", quality: 80) %>

<!-- Vips -->
<%= image_tag user.avatar.variant(resize_to_limit: [100, 100], format: :jpeg, saver: { subsample_mode: "on", strip: true, interlace: true, quality: 80 }) %>

8.3 Previewing Files

Some non-image files can be previewed: that is, they can be presented as images. For example, a video file can be previewed by extracting its first frame. Out of the box, Active Storage supports previewing videos and PDF documents. To create a link to a lazily-generated preview, use the attachment's preview method:

<%= image_tag message.video.preview(resize_to_limit: [100, 100]) %>

To add support for another format, add your own previewer. See the ActiveStorage::Preview documentation for more information.

9 Direct Uploads

Active Storage, with its included JavaScript library, supports uploading directly from the client to the cloud.

9.1 Usage

1. Include activestorage.js in your application's JavaScript bundle.

   Using the asset pipeline:

   //= require activestorage
   

   Copy

   Using the npm package:

   import * as ActiveStorage from "@rails/activestorage"
   ActiveStorage.start()
   

   Copy

2. Add direct_upload: true to your file field:

   <%= form.file_field :attachments, multiple: true, direct_upload: true %>
   

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   Or, if you aren't using a FormBuilder, add the data attribute directly:

   <input type="file" data-direct-upload-url="<%= rails_direct_uploads_url %>" />
   

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3. Configure CORS on third-party storage services to allow direct upload requests.

4. That's it! Uploads begin upon form submission.

9.2 Cross-Origin Resource Sharing (CORS) Configuration

To make direct uploads to a third-party service work, you’ll need to configure the service to allow cross-origin requests from your app. Consult the CORS documentation for your service:

• S3
• Google Cloud Storage
• Azure Storage

Take care to allow:

• All origins from which your app is accessed
• The PUT request method
• The following headers:
  • Content-Type
  • Content-MD5
  • Content-Disposition (except for Azure Storage)
  • x-ms-blob-content-disposition (for Azure Storage only)
  • x-ms-blob-type (for Azure Storage only)
  • Cache-Control (for GCS, only if cache_control is set)

No CORS configuration is required for the Disk service since it shares your app’s origin.

9.2.1 Example: S3 CORS Configuration

[
  {
    "AllowedHeaders": [
      "Content-Type",
      "Content-MD5",
      "Content-Disposition"
    ],
    "AllowedMethods": [
      "PUT"
    ],
    "AllowedOrigins": [
      "https://www.example.com"
    ],
    "MaxAgeSeconds": 3600
  }
]

9.2.2 Example: Google Cloud Storage CORS Configuration

[
  {
    "origin": ["https://www.example.com"],
    "method": ["PUT"],
    "responseHeader": ["Content-Type", "Content-MD5", "Content-Disposition"],
    "maxAgeSeconds": 3600
  }
]

9.2.3 Example: Azure Storage CORS Configuration

<Cors>
  <CorsRule>
    <AllowedOrigins>https://www.example.com</AllowedOrigins>
    <AllowedMethods>PUT</AllowedMethods>
    <AllowedHeaders>Content-Type, Content-MD5, x-ms-blob-content-disposition, x-ms-blob-type</AllowedHeaders>
    <MaxAgeInSeconds>3600</MaxAgeInSeconds>
  </CorsRule>
</Cors>

9.3 Direct Upload JavaScript Events

9.4 Example

You can use these events to show the progress of an upload.

To show the uploaded files in a form:

// direct_uploads.js

addEventListener("direct-upload:initialize", event => {
  const { target, detail } = event
  const { id, file } = detail
  target.insertAdjacentHTML("beforebegin", `
    <div id="direct-upload-${id}" class="direct-upload direct-upload--pending">
      <div id="direct-upload-progress-${id}" class="direct-upload__progress" style="width: 0%"></div>
      <span class="direct-upload__filename"></span>
    </div>
  `)
  target.previousElementSibling.querySelector(`.direct-upload__filename`).textContent = file.name
})

addEventListener("direct-upload:start", event => {
  const { id } = event.detail
  const element = document.getElementById(`direct-upload-${id}`)
  element.classList.remove("direct-upload--pending")
})

addEventListener("direct-upload:progress", event => {
  const { id, progress } = event.detail
  const progressElement = document.getElementById(`direct-upload-progress-${id}`)
  progressElement.style.width = `${progress}%`
})

addEventListener("direct-upload:error", event => {
  event.preventDefault()
  const { id, error } = event.detail
  const element = document.getElementById(`direct-upload-${id}`)
  element.classList.add("direct-upload--error")
  element.setAttribute("title", error)
})

addEventListener("direct-upload:end", event => {
  const { id } = event.detail
  const element = document.getElementById(`direct-upload-${id}`)
  element.classList.add("direct-upload--complete")
})

Add styles:

/* direct_uploads.css */

.direct-upload {
  display: inline-block;
  position: relative;
  padding: 2px 4px;
  margin: 0 3px 3px 0;
  border: 1px solid rgba(0, 0, 0, 0.3);
  border-radius: 3px;
  font-size: 11px;
  line-height: 13px;
}

.direct-upload--pending {
  opacity: 0.6;
}

.direct-upload__progress {
  position: absolute;
  top: 0;
  left: 0;
  bottom: 0;
  opacity: 0.2;
  background: #0076ff;
  transition: width 120ms ease-out, opacity 60ms 60ms ease-in;
  transform: translate3d(0, 0, 0);
}

.direct-upload--complete .direct-upload__progress {
  opacity: 0.4;
}

.direct-upload--error {
  border-color: red;
}

input[type=file][data-direct-upload-url][disabled] {
  display: none;
}

9.5 Custom drag and drop solutions

You can use the DirectUpload class for this purpose. Upon receiving a file from your library of choice, instantiate a DirectUpload and call its create method. Create takes a callback to invoke when the upload completes.

import { DirectUpload } from "@rails/activestorage"

const input = document.querySelector('input[type=file]')

// Bind to file drop - use the ondrop on a parent element or use a
//  library like Dropzone
const onDrop = (event) => {
  event.preventDefault()
  const files = event.dataTransfer.files;
  Array.from(files).forEach(file => uploadFile(file))
}

// Bind to normal file selection
input.addEventListener('change', (event) => {
  Array.from(input.files).forEach(file => uploadFile(file))
  // you might clear the selected files from the input
  input.value = null
})

const uploadFile = (file) => {
  // your form needs the file_field direct_upload: true, which
  //  provides data-direct-upload-url
  const url = input.dataset.directUploadUrl
  const upload = new DirectUpload(file, url)

  upload.create((error, blob) => {
    if (error) {
      // Handle the error
    } else {
      // Add an appropriately-named hidden input to the form with a
      //  value of blob.signed_id so that the blob ids will be
      //  transmitted in the normal upload flow
      const hiddenField = document.createElement('input')
      hiddenField.setAttribute("type", "hidden");
      hiddenField.setAttribute("value", blob.signed_id);
      hiddenField.name = input.name
      document.querySelector('form').appendChild(hiddenField)
    }
  })
}

9.6 Track the progress of the file upload

When using the DirectUpload constructor, it is possible to include a third parameter. This will allow the DirectUpload object to invoke the directUploadWillStoreFileWithXHR method during the upload process. You can then attach your own progress handler to the XHR to suit your needs.

import { DirectUpload } from "@rails/activestorage"

class Uploader {
  constructor(file, url) {
    this.upload = new DirectUpload(file, url, this)
  }

  uploadFile(file) {
    this.upload.create((error, blob) => {
      if (error) {
        // Handle the error
      } else {
        // Add an appropriately-named hidden input to the form
        // with a value of blob.signed_id
      }
    })
  }

  directUploadWillStoreFileWithXHR(request) {
    request.upload.addEventListener("progress",
      event => this.directUploadDidProgress(event))
  }

  directUploadDidProgress(event) {
    // Use event.loaded and event.total to update the progress bar
  }
}

9.7 Integrating with Libraries or Frameworks

Once you receive a file from the library you have selected, you need to create a DirectUpload instance and use its "create" method to initiate the upload process, adding any required additional headers as necessary. The "create" method also requires a callback function to be provided that will be triggered once the upload has finished.

import { DirectUpload } from "@rails/activestorage"

class Uploader {
  constructor(file, url, token) {
    const headers = { 'Authentication': `Bearer ${token}` }
    // INFO: Sending headers is an optional parameter. If you choose not to send headers,
    //       authentication will be performed using cookies or session data.
    this.upload = new DirectUpload(file, url, this, headers)
  }

  uploadFile(file) {
    this.upload.create((error, blob) => {
      if (error) {
        // Handle the error
      } else {
        // Use the with blob.signed_id as a file reference in next request
      }
    })
  }

  directUploadWillStoreFileWithXHR(request) {
    request.upload.addEventListener("progress",
      event => this.directUploadDidProgress(event))
  }

  directUploadDidProgress(event) {
    // Use event.loaded and event.total to update the progress bar
  }
}

To implement customized authentication, a new controller must be created on the Rails application, similar to the following:

class DirectUploadsController < ActiveStorage::DirectUploadsController
  skip_forgery_protection
  before_action :authenticate!

  def authenticate!
    @token = request.headers['Authorization']&.split&.last

    head :unauthorized unless valid_token?(@token)
  end
end

10 Testing

Use file_fixture_upload to test uploading a file in an integration or controller test. Rails handles files like any other parameter.

class SignupController < ActionDispatch::IntegrationTest
  test "can sign up" do
    post signup_path, params: {
      name: "David",
      avatar: file_fixture_upload("david.png", "image/png")
    }

    user = User.order(:created_at).last
    assert user.avatar.attached?
  end
end

10.1 Discarding Files Created During Tests

10.1.1 System Tests

System tests clean up test data by rolling back a transaction. Because destroy is never called on an object, the attached files are never cleaned up. If you want to clear the files, you can do it in an after_teardown callback. Doing it here ensures that all connections created during the test are complete and you won't receive an error from Active Storage saying it can't find a file.

class ApplicationSystemTestCase < ActionDispatch::SystemTestCase
  # ...
  def after_teardown
    super
    FileUtils.rm_rf(ActiveStorage::Blob.service.root)
  end
  # ...
end

If you're using parallel tests and the DiskService, you should configure each process to use its own folder for Active Storage. This way, the teardown callback will only delete files from the relevant process' tests.

class ApplicationSystemTestCase < ActionDispatch::SystemTestCase
  # ...
  parallelize_setup do |i|
    ActiveStorage::Blob.service.root = "#{ActiveStorage::Blob.service.root}-#{i}"
  end
  # ...
end

If your system tests verify the deletion of a model with attachments and you're using Active Job, set your test environment to use the inline queue adapter so the purge job is executed immediately rather at an unknown time in the future.

# Use inline job processing to make things happen immediately
config.active_job.queue_adapter = :inline

10.1.2 Integration Tests

Similarly to System Tests, files uploaded during Integration Tests will not be automatically cleaned up. If you want to clear the files, you can do it in an teardown callback.

class ActionDispatch::IntegrationTest
  def after_teardown
    super
    FileUtils.rm_rf(ActiveStorage::Blob.service.root)
  end
end

If you're using parallel tests and the Disk service, you should configure each process to use its own folder for Active Storage. This way, the teardown callback will only delete files from the relevant process' tests.

class ActionDispatch::IntegrationTest
  parallelize_setup do |i|
    ActiveStorage::Blob.service.root = "#{ActiveStorage::Blob.service.root}-#{i}"
  end
end

10.2 Adding Attachments to Fixtures

You can add attachments to your existing fixtures. First, you'll want to create a separate storage service:

# config/storage.yml

test_fixtures:
  service: Disk
  root: <%= Rails.root.join("tmp/storage_fixtures") %>

This tells Active Storage where to "upload" fixture files to, so it should be a temporary directory. By making it a different directory to your regular test service, you can separate fixture files from files uploaded during a test.

Next, create fixture files for the Active Storage classes:

# active_storage/attachments.yml
david_avatar:
  name: avatar
  record: david (User)
  blob: david_avatar_blob

# active_storage/blobs.yml
david_avatar_blob: <%= ActiveStorage::FixtureSet.blob filename: "david.png", service_name: "test_fixtures" %>

Then put a file in your fixtures directory (the default path is test/fixtures/files) with the corresponding filename. See the ActiveStorage::FixtureSet docs for more information.

Once everything is set up, you'll be able to access attachments in your tests:

class UserTest < ActiveSupport::TestCase
  def test_avatar
    avatar = users(:david).avatar

    assert avatar.attached?
    assert_not_nil avatar.download
    assert_equal 1000, avatar.byte_size
  end
end

10.2.1 Cleaning up Fixtures

While files uploaded in tests are cleaned up at the end of each test, you only need to clean up fixture files once: when all your tests complete.

If you're using parallel tests, call parallelize_teardown:

class ActiveSupport::TestCase
  # ...
  parallelize_teardown do |i|
    FileUtils.rm_rf(ActiveStorage::Blob.services.fetch(:test_fixtures).root)
  end
  # ...
end

If you're not running parallel tests, use Minitest.after_run or the equivalent for your test framework (e.g. after(:suite) for RSpec):

# test_helper.rb

Minitest.after_run do
  FileUtils.rm_rf(ActiveStorage::Blob.services.fetch(:test_fixtures).root)
end

10.3 Configuring services

You can add config/storage/test.yml to configure services to be used in test environment This is useful when the service option is used.

class User < ApplicationRecord
  has_one_attached :avatar, service: :s3
end

Without config/storage/test.yml, the s3 service configured in config/storage.yml is used - even when running tests.

The default configuration would be used and files would be uploaded to the service provider configured in config/storage.yml.

In this case, you can add config/storage/test.yml and use Disk service for s3 service to prevent sending requests.

test:
  service: Disk
  root: <%= Rails.root.join("tmp/storage") %>

s3:
  service: Disk
  root: <%= Rails.root.join("tmp/storage") %>

11 Implementing Support for Other Cloud Services

If you need to support a cloud service other than these, you will need to implement the Service. Each service extends ActiveStorage::Service by implementing the methods necessary to upload and download files to the cloud.

12 Purging Unattached Uploads

There are cases where a file is uploaded but never attached to a record. This can happen when using Direct Uploads. You can query for unattached records using the unattached scope. Below is an example using a custom rake task.

namespace :active_storage do
  desc "Purges unattached Active Storage blobs. Run regularly."
  task purge_unattached: :environment do
    ActiveStorage::Blob.unattached.where(created_at: ..2.days.ago).find_each(&:purge_later)
  end
end

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