When accessing uncached media attachment, redownload it (#4955)

* When accessing uncached media attachment, redownload it

* Prevent re-download of rejected media

3 files changed, 58 insertions, 4 deletions

diff --git a/app/controllers/media_proxy_controller.rb b/app/controllers/media_proxy_controller.rb
new file mode 100644
index 000000000..6a83cf9dc
--- /dev/null
+++ b/app/controllers/media_proxy_controller.rb
@@ -0,0 +1,40 @@
+# frozen_string_literal: true
+
+class MediaProxyController < ApplicationController
+  include RoutingHelper
+
+  def show
+    RedisLock.acquire(lock_options) do |lock|
+      if lock.acquired?
+        @media_attachment = MediaAttachment.remote.find(params[:id])
+        redownload! if @media_attachment.needs_redownload? && !reject_media?
+      end
+    end
+
+    redirect_to full_asset_url(@media_attachment.file.url(version))
+  end
+
+  private
+
+  def redownload!
+    @media_attachment.file_remote_url = @media_attachment.remote_url
+    @media_attachment.touch(:created_at)
+    @media_attachment.save!
+  end
+
+  def version
+    if request.path.ends_with?('/small')
+      :small
+    else
+      :original
+    end
+  end
+
+  def lock_options
+    { redis: Redis.current, key: "media_download:#{params[:id]}" }
+  end
+
+  def reject_media?
+    DomainBlock.find_by(domain: @media_attachment.account.domain)&.reject_media?
+  end
+end
diff --git a/app/models/media_attachment.rb b/app/models/media_attachment.rb
index d83ca44f1..d913e7372 100644
--- a/app/models/media_attachment.rb
+++ b/app/models/media_attachment.rb
@@ -56,15 +56,21 @@ class MediaAttachment < ApplicationRecord
 
   validates :account, presence: true
 
-  scope :attached, -> { where.not(status_id: nil) }
+  scope :attached,   -> { where.not(status_id: nil) }
   scope :unattached, -> { where(status_id: nil) }
-  scope :local, -> { where(remote_url: '') }
+  scope :local,      -> { where(remote_url: '') }
+  scope :remote,     -> { where.not(remote_url: '') }
+
   default_scope { order(id: :asc) }
 
   def local?
     remote_url.blank?
   end
 
+  def needs_redownload?
+    file.blank? && remote_url.present?
+  end
+
   def to_param
     shortcode
   end
diff --git a/app/serializers/rest/media_attachment_serializer.rb b/app/serializers/rest/media_attachment_serializer.rb
index 9055b8db4..31189406a 100644
--- a/app/serializers/rest/media_attachment_serializer.rb
+++ b/app/serializers/rest/media_attachment_serializer.rb
@@ -7,11 +7,19 @@ class REST::MediaAttachmentSerializer < ActiveModel::Serializer
              :remote_url, :text_url, :meta
 
   def url
-    full_asset_url(object.file.url(:original))
+    if object.needs_redownload?
+      media_proxy_url(object.id, :original)
+    else
+      full_asset_url(object.file.url(:original))
+    end
   end
 
   def preview_url
-    full_asset_url(object.file.url(:small))
+    if object.needs_redownload?
+      media_proxy_url(object.id, :small)
+    else
+      full_asset_url(object.file.url(:small))
+    end
   end
 
   def text_url