media assets: fix dimensions of corrupt GIFs.

Fix certain corrupt GIFs returning dimensions of 0x0. This happened
when the GIF was too corrupt for libvips to read. Fixed by using
ExifTool to read the dimensions instead.

Also add validations to ensure that it's not possible to have media
assets with a width or height of 0.

app/logical/exif_tool.rb

@@ -120,6 +120,14 @@ class ExifTool
         metadata.has_key?("PNG:Dream")
     end
 
+    def width
+      metadata.find { |name, value| name.match?(/\A(File|PNG|GIF|RIFF|Flash|Track\d+):ImageWidth\z/) }&.second
+    end
+
+    def height
+      metadata.find { |name, value| name.match?(/\A(File|PNG|GIF|RIFF|Flash|Track\d+):ImageHeight\z/) }&.second
+    end
+
     # @see http://www.vurdalakov.net/misc/gif/netscape-looping-application-extension
     # @see https://wiki.mozilla.org/APNG_Specification#.60acTL.60:_The_Animation_Control_Chunk
     # @see https://danbooru.donmai.us/posts?tags=-exif:GIF:AnimationIterations=Infinite+animated_gif

app/logical/media_file/image.rb

@@ -10,6 +10,8 @@ class MediaFile::Image < MediaFile
   def dimensions
     image.size
   rescue Vips::Error
+    [metadata.width, metadata.height]
+  rescue
     [0, 0]
   end
 

app/models/media_asset.rb

@@ -45,6 +45,9 @@ class MediaAsset < ApplicationRecord
   validates :md5, uniqueness: { conditions: -> { where(status: [:processing, :active]) } }, if: :md5_changed?
   validates :file_ext, inclusion: { in: FILE_TYPES, message: "File is not an image or video" }
   validates :file_key, length: { is: FILE_KEY_LENGTH }, uniqueness: true, if: :file_key_changed?
+  validates :file_size, comparison: { greater_than: 0 }, if: :file_size_changed?
+  validates :image_width, comparison: { greater_than: 0 }, if: :image_width_changed?
+  validates :image_height, comparison: { greater_than: 0 }, if: :image_height_changed?
 
   before_create :initialize_file_key
 

test/unit/media_file_test.rb

@@ -467,6 +467,7 @@ class MediaFileTest < ActiveSupport::TestCase
       @metadata = @file.metadata
 
       assert_equal(true, @file.is_corrupt?)
+      assert_equal([475, 600], @file.dimensions)
       assert_equal("File format error", @metadata["ExifTool:Error"])
       assert_equal("89a", @metadata["GIF:GIFVersion"])
       assert_equal(9, @metadata.count)
@@ -478,6 +479,7 @@ class MediaFileTest < ActiveSupport::TestCase
 
       assert_equal(true, @file.is_corrupt?)
       assert_equal(nil, @file.frame_count)
+      assert_equal([575, 800], @file.dimensions)
       assert_equal("File format error", @metadata["ExifTool:Error"])
       assert_equal("89a", @metadata["GIF:GIFVersion"])
       assert_equal(9, @metadata.count)