media assets: track corrupted files in media metadata.

If a media asset is corrupt, include the error message from libvips or
ffmpeg in the "Vips:Error" or "FFmpeg:Error" fields in the media
metadata table.

Corrupt files can't be uploaded nowadays, but they could be in the past,
so we have some old corrupted files that we can't generate thumbnails
for. This lets us mark these files in the metadata so they're findable
with the tag search `exif:Vips:Error`.

Known bug: Vips has a single global error buffer that is shared between
threads and that isn't cleared between operations. So we can't reliably
get the actual error message because it may pick up errors from other
threads, or from previous operations in the same thread.

app/logical/ffmpeg.rb

@@ -41,8 +41,8 @@ class FFmpeg
     output = shell!("ffprobe -v quiet -print_format json -show_format -show_streams #{file.path.shellescape}")
     json = JSON.parse(output)
     json.with_indifferent_access
-  rescue Error
-    {}
+  rescue Error => e
+    { error: e.message.strip }.with_indifferent_access
   end
 
   def width
@@ -107,6 +107,16 @@ class FFmpeg
     audio_streams.present?
   end
 
+  # @return [Boolean] True if the video is unplayable.
+  def is_corrupt?
+    error.present?
+  end
+
+  # @return [String, nil] The error message if the video is unplayable, or nil if no error.
+  def error
+    metadata[:error] || playback_info[:error]
+  end
+
   # Decode the full video and return a hash containing the frame count, fps, and runtime.
   def playback_info
     output = shell!("ffmpeg -i #{file.path.shellescape} -f null /dev/null")
@@ -117,7 +127,7 @@ class FFmpeg
     info = status_line.scan(/\S+=\s*\S+/).map { |pair| pair.split(/=\s*/) }.to_h
     info.with_indifferent_access
   rescue Error => e
-    {}
+    { error: e.message.strip }.with_indifferent_access
   end
 
   def shell!(command)
@@ -127,5 +137,5 @@ class FFmpeg
     output
   end
 
-  memoize :metadata, :playback_info, :frame_count, :duration
+  memoize :metadata, :playback_info, :frame_count, :duration, :error
 end

app/logical/media_file.rb

@@ -10,7 +10,7 @@ class MediaFile
   extend Memoist
   include ActiveModel::Serializers::JSON
 
-  attr_accessor :file, :strict
+  attr_accessor :file
 
   # delegate all File methods to `file`.
   delegate *(File.instance_methods - MediaFile.instance_methods), to: :file
@@ -122,11 +122,8 @@ class MediaFile
   # Initialize a MediaFile from a regular File.
   #
   # @param file [File] The image file.
-  # @param strict [Boolean] If true, raise errors if the file is corrupt. If false,
-  #   try to process corrupt files without raising any errors.
-  def initialize(file, strict: true, **options)
+  def initialize(file, **options)
     @file = file
-    @strict = strict
   end
 
   # @return [Array<(Integer, Integer)>] the width and height of the file
@@ -164,7 +161,15 @@ class MediaFile
     file.size
   end
 
+  # @return [ExifTool::Metadata] The metadata for the file. Subclasses may override this to add
+  #   extra non-ExifTool metadata, such as error messages, Ugoira frame delays, or ffprobe metadata.
+  #   This metadata may be slower to calculate than the raw `exif_metadata`.
   def metadata
+    exif_metadata
+  end
+
+  # @return [ExifTool::Metadata] The metadata for the file, as returned by ExifTool.
+  def exif_metadata
     ExifTool.new(file).metadata
   end
 
@@ -207,9 +212,14 @@ class MediaFile
     file_ext == :swf
   end
 
-  # @return [Boolean] true if the file is corrupted in some way
+  # @return [Boolean] True if the file is too corrupted to read or generate thumbnails without error.
   def is_corrupt?
-    false
+    error.present?
+  end
+
+  # @return [String, nil] The error message when reading the file, or nil if there are no errors.
+  def error
+    nil
   end
 
   # @return [Boolean] true if the file is animated. Note that GIFs and PNGs may be animated.
@@ -278,7 +288,7 @@ class MediaFile
       height: height,
       file_size: file_size,
       file_ext: file_ext,
-      mime_type: mime_type,
+      mime_type: mime_type.to_s,
       md5: md5,
       is_corrupt?: is_corrupt?,
       is_supported?: is_supported?,
@@ -302,5 +312,5 @@ class MediaFile
     end
   end
 
-  memoize :file_ext, :file_size, :md5, :metadata, :mime_type
+  memoize :file_ext, :file_size, :md5, :mime_type, :exif_metadata
 end

app/logical/media_file/image.rb

@@ -28,10 +28,22 @@ class MediaFile::Image < MediaFile
   end
 
   def is_corrupt?
+    error.present?
+  end
+
+  def error
+    image = Vips::Image.new_from_file(file.path, fail: true)
     image.stats
-    false
-  rescue Vips::Error
-    true
+    nil
+  rescue Vips::Error => e
+    # XXX Vips has a single global error buffer that is shared between threads and that isn't cleared between operations.
+    # We can't reliably use `e.message` here because it may pick up errors from other threads, or from previous
+    # operations in the same thread.
+    "libvips error"
+  end
+
+  def metadata
+    super.merge({ "Vips:Error" => error }.compact_blank)
   end
 
   def duration
@@ -44,7 +56,7 @@ class MediaFile::Image < MediaFile
     when :gif, :webp
       n_pages
     when :png
-      metadata.fetch("PNG:AnimationFrames", 1)
+      exif_metadata.fetch("PNG:AnimationFrames", 1)
     when :avif
       video.frame_count
     else
@@ -156,12 +168,12 @@ class MediaFile::Image < MediaFile
 
   # @return [Vips::Image] the Vips image object for the file
   def image
-    Vips::Image.new_from_file(file.path, fail: strict).autorot
+    Vips::Image.new_from_file(file.path, fail: false).autorot
   end
 
   def video
     FFmpeg.new(file)
   end
 
-  memoize :image, :video, :dimensions, :is_corrupt?, :is_animated_gif?, :is_animated_png?
+  memoize :image, :video, :preview_frame, :dimensions, :error, :metadata, :is_corrupt?, :is_animated_gif?, :is_animated_png?
 end

app/logical/media_file/ugoira.rb

@@ -108,5 +108,5 @@ class MediaFile::Ugoira < MediaFile
     FFmpeg.new(convert).smart_video_preview
   end
 
-  memoize :zipfile, :preview_frame, :dimensions, :convert
+  memoize :zipfile, :preview_frame, :dimensions, :convert, :metadata
 end

app/logical/media_file/video.rb

@@ -5,7 +5,7 @@
 #
 # @see https://github.com/streamio/streamio-ffmpeg
 class MediaFile::Video < MediaFile
-  delegate :duration, :frame_count, :frame_rate, :has_audio?, :pix_fmt, :video_codec, :video_stream, :video_streams, :audio_streams, to: :video
+  delegate :duration, :frame_count, :frame_rate, :has_audio?, :is_corrupt?, :pix_fmt, :video_codec, :video_stream, :video_streams, :audio_streams, :error, to: :video
 
   def dimensions
     [video.width, video.height]
@@ -15,10 +15,14 @@ class MediaFile::Video < MediaFile
     preview_frame.preview!(max_width, max_height, **options)
   end
 
+  def metadata
+    super.merge({ "FFmpeg:Error" => error }.compact_blank)
+  end
+
   def is_supported?
     return false if video_streams.size != 1
     return false if audio_streams.size > 1
-    return false if is_webm? && metadata["Matroska:DocType"] != "webm"
+    return false if is_webm? && exif_metadata["Matroska:DocType"] != "webm"
     return false if is_mp4? && !video_codec.in?(["h264", "vp9"])
 
     # Only allow pixel formats supported by most browsers. Don't allow 10-bit video or 4:4:4 subsampling (neither are supported by Firefox).
@@ -35,11 +39,6 @@ class MediaFile::Video < MediaFile
     true
   end
 
-  # True if decoding the video fails.
-  def is_corrupt?
-    video.playback_info.blank?
-  end
-
   private
 
   def video
@@ -50,5 +49,5 @@ class MediaFile::Video < MediaFile
     video.smart_video_preview
   end
 
-  memoize :video, :preview_frame, :dimensions, :duration, :has_audio?
+  memoize :video, :preview_frame, :dimensions, :metadata, :duration, :has_audio?
 end

app/models/media_asset.rb

@@ -89,7 +89,7 @@ class MediaAsset < ApplicationRecord
     def open_file!(&block)
       file = storage_service.open(file_path)
       frame_delays = media_asset.frame_delays if media_asset.is_ugoira?
-      MediaFile.open(file, frame_delays: frame_delays, strict: false, &block)
+      MediaFile.open(file, frame_delays: frame_delays, &block)
     end
 
     def convert_file(media_file)

test/unit/media_file_test.rb

@@ -467,10 +467,11 @@ class MediaFileTest < ActiveSupport::TestCase
       @metadata = @file.metadata
 
       assert_equal(true, @file.is_corrupt?)
+      assert_equal("libvips error", @file.error)
       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)
+      assert_equal(10, @metadata.count)
     end
 
     should "not raise an exception when reading the frame count" do
@@ -478,11 +479,12 @@ class MediaFileTest < ActiveSupport::TestCase
       @metadata = @file.metadata
 
       assert_equal(true, @file.is_corrupt?)
+      assert_equal("libvips error", @file.error)
       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)
+      assert_equal(10, @metadata.count)
       assert_nothing_raised { @file.attributes }
     end
   end
@@ -493,8 +495,9 @@ class MediaFileTest < ActiveSupport::TestCase
       @metadata = @file.metadata
 
       assert_equal(true, @file.is_corrupt?)
+      assert_equal("libvips error", @file.error)
       assert_equal("Grayscale", @metadata["PNG:ColorType"])
-      assert_equal(9, @metadata.count)
+      assert_equal(10, @metadata.count)
     end
   end
 
@@ -504,8 +507,9 @@ class MediaFileTest < ActiveSupport::TestCase
       @metadata = @file.metadata
 
       assert_equal(true, @file.is_corrupt?)
+      assert_equal("libvips error", @file.error)
       assert_equal(1, @metadata["File:ColorComponents"])
-      assert_equal(10, @metadata.count)
+      assert_equal(11, @metadata.count)
     end
   end