active-storage-proxy

01_readme.md

ActiveStorageProxy

Adds support for proxying Active Storage blobs (to serve them via CDN).

Based on rails/rails#34477.

Usage

To serve a blob via proxy use generate the URL using the following url helper

rails_proxy_blob_url(signed_id: attachment.signed_id, filename: attachment.filename)

# and for variants
variant = attachment.variant(:medium)
rails_proxy_blob_url(signed_id: attachment.signed_id, variation_key: variant.variation.key, filename: variant.filename)

Configuration

You can configure the cache headers:

# config/environments/production.rb

# Default values are
config.active_storage_proxy.proxy_urls_expire_in = 1.year
config.active_storage_proxy.proxy_urls_public = true

02_engine.rb

# frozen_string_literal: true

require "rails/engine"
require "active_storage/engine"

require_relative "./variant_download"

module ActiveStorageProxy
  class Engine < ::Rails::Engine
    isolate_namespace ActiveStorageProxy
    engine_name "active_storage_proxy"

    config.proxy_urls_expire_in = 1.year
    config.proxy_urls_public = true

    initializer "active_storage_proxy.routes" do |_app|
      config.after_initialize do |app|
        app.routes.prepend do
          scope ActiveStorage.routes_prefix do
            get "/proxy/:signed_id(/:variation_key)/*filename" => "active_storage/proxy#show", :as => :rails_proxy_blob
          end
        end
      end
    end
  end
end

03_proxy_controller.rb

# frozen_string_literal: true

# Takes a blob using a signed reference and proxies the contents of the blob
# Based on https://github.com/rails/rails/pull/34477/files
class ActiveStorage::ProxyController < ActiveStorage::BaseController
  include ActiveStorage::SetBlob

  def show
    expires_in(
      ActiveStorageProxy::Engine.config.proxy_urls_expire_in,
      public: ActiveStorageProxy::Engine.config.proxy_urls_public
    )

    @blob = @blob.representation(params[:variation_key]).processed if params[:variation_key]

    response.headers["Content-Type"] = @blob.content_type
    response.headers["Content-Disposition"] = ActionDispatch::Http::ContentDisposition.format(
      disposition: params[:disposition] || "inline",
      filename: @blob.filename.sanitized
    )

    @blob.download do |chunk|
      response.stream.write(chunk)
    end
  ensure
    response.stream.close
  end
end

04_variant_download.rb

# frozen_string_literal: true

module ActiveStorageProxy
  # Adds `download` for variants
  module VariantDownload
    def download(&block)
      service.download key, &block
    end
  end
end

ActiveSupport.on_load :active_storage_blob do
  ActiveStorage::Variant.prepend(ActiveStorageProxy::VariantDownload)
end

05_blob_url_helper.rb

# frozen_string_literal: true

module ActiveStorage
  # Provides methods to generate `asset_host`-aware blob urls.
  #
  # When `asset_host` is present then generates a proxy URL.
  # Otherwise uses a default URL (redirect).
  #
  # Also takes care of GIFs: skip variants generation and return originals.
  #
  # Example:
  #   # you can use it directly
  #   ActiveStorage::BlobUrlHelper.blob_url(user.avatar)
  #
  #   # or include into controller and add a helper
  #   include ActiveStorage::BlobUrlHelper
  #   helper_method :blob_path
  #
  #   # pass a variant as an arg to handle GIFs (skip transformation)
  #   ActiveStorage::BlobUrlHelper.blob_url(user.avatar, variant: :medium)
  module BlobUrlHelper
    module_function

    def blob_url(attachment, variant: nil, **options)
      attachment = attachment.variant(variant) if attachment.variable? && variant && attachment.content_type !~ /gif/
      if Rails.application.config.action_controller.asset_host
        Rails.application.routes.url_helpers.rails_proxy_blob_url(
          signed_id: attachment.is_a?(::ActiveStorage::Variant) ? attachment.blob.signed_id : attachment.signed_id,
          variation_key: attachment.is_a?(::ActiveStorage::Variant) ? attachment.variation.key : nil,
          filename: attachment.filename,
          **blob_url_options.merge(options)
        )
      else
        Rails.application.routes.url_helpers.polymorphic_url(
          attachment,
          blob_url_options.merge(options)
        )
      end
    end

    # Returns a path to blob if no asset host provided.
    # Otherwise returns an URL.
    def blob_path(attachment, **options)
      if Rails.application.config.action_controller.asset_host
        blob_url(attachment, **options)
      else
        blob_url(attachment, **options, only_path: true)
      end
    end

    def blob_url_options
      {}.tap do |opts|
        opts[:protocol] = Rails.application.config.force_ssl ? :https : :http
        opts[:host] = Rails.application.config.action_controller.asset_host
      end.compact
    end
  end
end

Hi! This seems what I'm looking for until Rails has something built in to allow for usa with CDNs. Question: which syntax should I use to generate a variant with e.g. resize_to_limit and similar? Thanks

Another question: how do I specify the host? For example the app is at app.domain.com but I want to serve the assets from cdn.domain.com. Thanks

@vitobotta Added BlobUrlHelper which used to generate URLs for blobs and variants with a CDN host if any.
We used the same CDN for assets and uploads, so we relied on the presence of the Rails.application.config.action_controller.asset_host parameter.

@vitobotta Added BlobUrlHelper which used to generate URLs for blobs and variants with a CDN host if any.
We used the same CDN for assets and uploads, so we relied on the presence of the Rails.application.config.action_controller.asset_host parameter.

Hi, thanks for adding this. What about the variants and specifying the size etc? Thanks!

With this helper you can call: blob_url(attachment, variant: {resize_to_limit: [w, h]})

Perfect, thanks a lot!