media assets: add file_key, is_public columns.

`file_key` is a random 9-character base-62 string that will be used as
the image filename in the future.

`is_public` is whether the image can be viewed without authentication or not.

Users running downstream boorus must run `bin/rails db:migrate` and
`script/fixes/109_generate_media_asset_file_keys.rb` after this commit.

app/models/media_asset.rb

@@ -3,6 +3,7 @@
 class MediaAsset < ApplicationRecord
   class Error < StandardError; end
 
+  FILE_KEY_LENGTH = 9
   VARIANTS = %i[preview 180x180 360x360 720x720 sample original]
   MAX_VIDEO_DURATION = Danbooru.config.max_video_duration.to_i
   MAX_IMAGE_RESOLUTION = Danbooru.config.max_image_resolution
@@ -22,6 +23,9 @@ class MediaAsset < ApplicationRecord
   delegate :metadata, to: :media_metadata
   delegate :is_non_repeating_animation?, :is_greyscale?, :is_rotated?, to: :metadata
 
+  scope :public_only, -> { where(is_public: true) }
+  scope :private_only, -> { where(is_public: false) }
+
   # Processing: The asset's files are currently being resized and distributed to the backend servers.
   # Active: The asset has been successfully uploaded and is ready to use.
   # Deleted: The asset's files have been deleted by moving them to a trash folder. They can be undeleted by moving them out of the trash folder.
@@ -39,9 +43,12 @@ class MediaAsset < ApplicationRecord
   validates :md5, uniqueness: { conditions: -> { where(status: [:processing, :active]) } }
   validates :file_ext, inclusion: { in: %w[jpg png gif mp4 webm swf zip], message: "File is not an image or video" }
   validates :file_size, numericality: { less_than_or_equal_to: Danbooru.config.max_file_size, message: ->(asset, _) { "too large (size: #{asset.file_size.to_formatted_s(:human_size)}; max size: #{Danbooru.config.max_file_size.to_formatted_s(:human_size)})" } }
+  validates :file_key, length: { is: FILE_KEY_LENGTH }, uniqueness: true, if: :file_key_changed?
   validates :duration, numericality: { less_than_or_equal_to: MAX_VIDEO_DURATION, message: "must be less than #{MAX_VIDEO_DURATION} seconds", allow_nil: true }, on: :create # XXX should allow admins to bypass
   validate :validate_resolution, on: :create
 
+  before_create :initialize_file_key
+
   class Variant
     extend Memoist
 
@@ -186,7 +193,7 @@ class MediaAsset < ApplicationRecord
   concerning :SearchMethods do
     class_methods do
       def search(params)
-        q = search_attributes(params, :id, :created_at, :updated_at, :md5, :file_ext, :file_size, :image_width, :image_height)
+        q = search_attributes(params, :id, :created_at, :updated_at, :md5, :file_ext, :file_size, :image_width, :image_height, :file_key, :is_public)
 
         if params[:metadata].present?
           q = q.joins(:media_metadata).merge(MediaMetadata.search(metadata: params[:metadata]))
@@ -368,4 +375,15 @@ class MediaAsset < ApplicationRecord
       end
     end
   end
+
+  def self.generate_file_key
+    loop do
+      key = SecureRandom.send(:choose, [*"0".."9", *"A".."Z", *"a".."z"], FILE_KEY_LENGTH) # base62
+      return key unless MediaAsset.exists?(file_key: key)
+    end
+  end
+
+  def initialize_file_key
+    self.file_key = MediaAsset.generate_file_key
+  end
 end

app/policies/media_asset_policy.rb

@@ -13,7 +13,7 @@ class MediaAssetPolicy < ApplicationPolicy
     if can_see_image?
       super
     else
-      super.excluding(:md5)
+      super.excluding(:md5, :file_key)
     end
   end
 end

db/migrate/20220504235329_add_file_key_to_media_assets.rb

@@ -0,0 +1,9 @@
+class AddFileKeyToMediaAssets < ActiveRecord::Migration[7.0]
+  def change
+    add_column :media_assets, :file_key, :string, null: true
+    add_column :media_assets, :is_public, :boolean, default: true, null: false
+
+    add_index :media_assets, :file_key, unique: true
+    add_index :media_assets, :is_public, where: "is_public = FALSE"
+  end
+end

db/structure.sql

@@ -1102,7 +1102,9 @@ CREATE TABLE public.media_assets (
     image_width integer NOT NULL,
     image_height integer NOT NULL,
     duration double precision,
-    status integer DEFAULT 200 NOT NULL
+    status integer DEFAULT 200 NOT NULL,
+    file_key character varying,
+    is_public boolean DEFAULT true NOT NULL
 );
 
 
@@ -3805,6 +3807,13 @@ CREATE INDEX index_media_assets_on_duration ON public.media_assets USING btree (
 CREATE INDEX index_media_assets_on_file_ext ON public.media_assets USING btree (file_ext);
 
 
+--
+-- Name: index_media_assets_on_file_key; Type: INDEX; Schema: public; Owner: -
+--
+
+CREATE UNIQUE INDEX index_media_assets_on_file_key ON public.media_assets USING btree (file_key);
+
+
 --
 -- Name: index_media_assets_on_file_size; Type: INDEX; Schema: public; Owner: -
 --
@@ -3826,6 +3835,13 @@ CREATE INDEX index_media_assets_on_image_height ON public.media_assets USING btr
 CREATE INDEX index_media_assets_on_image_width ON public.media_assets USING btree (image_width);
 
 
+--
+-- Name: index_media_assets_on_is_public; Type: INDEX; Schema: public; Owner: -
+--
+
+CREATE INDEX index_media_assets_on_is_public ON public.media_assets USING btree (is_public) WHERE (is_public = false);
+
+
 --
 -- Name: index_media_assets_on_md5; Type: INDEX; Schema: public; Owner: -
 --
@@ -5806,6 +5822,7 @@ INSERT INTO "schema_migrations" (version) VALUES
 ('20220403042706'),
 ('20220403220558'),
 ('20220407203236'),
-('20220410050628');
+('20220410050628'),
+('20220504235329');
 
 

script/fixes/109_generate_media_asset_file_keys.rb

@@ -0,0 +1,8 @@
+#!/usr/bin/env ruby
+
+require_relative "base"
+
+MediaAsset.where(file_key: nil).parallel_each do |asset|
+  asset.update_columns(file_key: MediaAsset.generate_file_key)
+  puts "id=#{asset.id} file_key=#{asset.file_key}"
+end