Add MediaMetadata model.

Add a model for storing image and video metadata for uploaded files.

Metadata is extracted using ExifTool. You will need to install ExifTool
after this commit. ExifTool 12.22 is the minimum required version
because we use the `--binary` option, which was added in this release.

The MediaMetadata model is separate from the MediaAsset model because
some files contain tons of metadata, and most of it is non-essential.
The MediaAsset model represents an uploaded file and contains essential
metadata, like the file's size and type, while the MediaMetadata model
represents all the other non-essential metadata associated with a file.

Metadata is stored as a JSON column in the database.

ExifTool returns all the file's metadata, not just the EXIF metadata.
EXIF is one of several types of image metadata, hence why we call
it MediaMetadata instead of EXIFMetadata.

app/controllers/media_metadata_controller.rb

@@ -0,0 +1,8 @@
+class MediaMetadataController < ApplicationController
+  respond_to :json, :xml
+
+  def index
+    @media_metadata = authorize MediaMetadata.visible(CurrentUser.user).paginated_search(params, count_pages: true)
+    respond_with(@media_metadata)
+  end
+end

app/logical/exif_tool.rb

@@ -0,0 +1,42 @@
+require "shellwords"
+
+# A wrapper for the exiftool command.
+class ExifTool
+  extend Memoist
+
+  class Error < StandardError; end
+
+  # @see https://exiftool.org/exiftool_pod.html#OPTIONS
+  DEFAULT_OPTIONS = %q(
+    -G1 -duplicates -unknown -struct --binary
+    -x 'System:*' -x ExifToolVersion -x FileType -x FileTypeExtension
+    -x MIMEType -x ImageWidth -x ImageHeight -x ImageSize -x MegaPixels
+  ).squish
+
+  attr_reader :file
+
+  # Open a file with ExifTool.
+  # @param file [File, String] an image or video file
+  def initialize(file)
+    @file = file.is_a?(String) ? File.open(file) : file
+  end
+
+  # Get the file's metadata.
+  # @see https://exiftool.org/TagNames/index.html
+  # @param options [String] the options to pass to exiftool
+  # @return [Hash] the file's metadata
+  def metadata(options: DEFAULT_OPTIONS)
+    output = shell!("exiftool #{options} -json #{file.path.shellescape}")
+    json = JSON.parse(output).first
+    json = json.except("SourceFile")
+    json.with_indifferent_access
+  end
+
+  def shell!(command)
+    output, status = Open3.capture2e(command)
+    raise Error, "#{command}` failed: #{output}" if !status.success?
+    output
+  end
+
+  memoize :metadata
+end

app/logical/media_file.rb

@@ -102,6 +102,10 @@ class MediaFile
     file.size
   end
 
+  def metadata
+    ExifTool.new(file).metadata
+  end
+
   # @return [Boolean] true if the file is an image
   def is_image?
     file_ext.in?([:jpg, :png, :gif])
@@ -164,5 +168,5 @@ class MediaFile
     nil
   end
 
-  memoize :file_ext, :file_size, :md5
+  memoize :file_ext, :file_size, :md5, :metadata
 end

app/logical/upload_service.rb

@@ -104,13 +104,6 @@ class UploadService
       p.uploader_id = upload.uploader_id
       p.uploader_ip_addr = upload.uploader_ip_addr
       p.parent_id = upload.parent_id
-      p.media_asset = MediaAsset.new(
-        md5: upload.md5,
-        file_ext: upload.file_ext,
-        file_size: upload.file_size,
-        image_width: upload.image_width,
-        image_height: upload.image_height,
-      )
 
       if !upload.uploader.can_upload_free? || upload.upload_as_pending?
         p.is_pending = true

app/logical/upload_service/utils.rb

@@ -62,6 +62,8 @@ class UploadService
       upload.tag_string = "#{upload.tag_string} #{Utils.automatic_tags(media_file)}"
 
       process_resizes(upload, file, original_post_id)
+
+      MediaAsset.create_from_media_file!(media_file)
     end
 
     def automatic_tags(media_file)

app/models/media_asset.rb

@@ -1,4 +1,17 @@
 class MediaAsset < ApplicationRecord
+  has_one :media_metadata, dependent: :destroy
+
+  def self.create_from_media_file!(media_file)
+    create!(
+      md5: media_file.md5,
+      file_ext: media_file.file_ext,
+      file_size: media_file.file_size,
+      image_width: media_file.width,
+      image_height: media_file.height,
+      media_metadata: MediaMetadata.new(metadata: media_file.metadata),
+    )
+  end
+
   def self.search(params)
     q = search_attributes(params, :id, :created_at, :updated_at, :md5, :file_ext, :file_size, :image_width, :image_height)
     q = q.apply_default_order(params)

app/models/media_metadata.rb

@@ -0,0 +1,22 @@
+# MediaMetadata represents the EXIF and other metadata associated with a
+# MediaAsset (an uploaded image or video file). The `metadata` field contains a
+# JSON hash of the file's metadata as returned by ExifTool.
+#
+# @see ExifTool
+# @see https://exiftool.org/TagNames/index.html
+class MediaMetadata < ApplicationRecord
+  self.table_name = "media_metadata"
+
+  attribute :id
+  attribute :created_at
+  attribute :updated_at
+  attribute :media_asset_id
+  attribute :metadata
+  belongs_to :media_asset
+
+  def self.search(params)
+    q = search_attributes(params, :id, :created_at, :updated_at, :media_asset_id)
+    q = q.apply_default_order(params)
+    q
+  end
+end

app/models/upload.rb

@@ -65,6 +65,7 @@ class Upload < ApplicationRecord
 
   belongs_to :uploader, :class_name => "User"
   belongs_to :post, optional: true
+  has_one :media_asset, foreign_key: :md5, primary_key: :md5
 
   before_validation :initialize_attributes, on: :create
   before_validation :assign_rating_from_tags
@@ -114,6 +115,7 @@ class Upload < ApplicationRecord
         return
       end
 
+      media_asset.destroy!
       DanbooruLogger.info("Uploads: Deleting files for upload md5=#{md5}")
       Danbooru.config.storage_manager.delete_file(nil, md5, file_ext, :original)
       Danbooru.config.storage_manager.delete_file(nil, md5, file_ext, :large)

app/policies/media_metadata_policy.rb

@@ -0,0 +1,5 @@
+class MediaMetadataPolicy < ApplicationPolicy
+  def index?
+    true
+  end
+end