posts: fix incorrect exif rotation for PNGs.

Fix a bug where where PNG images could be incorrectly detected as
exif-rotated. This would happen when a PNG contained the
IFD0:Orientation flag. It's technically possible for a PNG to contain
this flag, but it's ignored by libvips and by browsers.

post #3762340 (nsfw) is an example of a PNG like this.

The fix is to use `autorot` to let libvips apply the rotation instead of
trying to interpret the exif data ourselves. Note that libvips-8.9 has a
bug where it doesn't strip the orientation flag after applying
`autorot`, which leads to the image being incorrectly rotated a second
time when generating the thumbnail. Use libvips-8.11 instead.

app/logical/media_file/image.rb

@@ -11,23 +11,11 @@ class MediaFile::Image < MediaFile
   CROP_OPTIONS = { crop: :attention, linear: false }
 
   def dimensions
-    [width, height]
+    image.size
   rescue Vips::Error
     [0, 0]
   end
 
-  def width
-    is_rotated? ? image.height : image.width
-  rescue Vips::Error
-    0
-  end
-
-  def height
-    is_rotated? ? image.width : image.height
-  rescue Vips::Error
-    0
-  end
-
   def is_corrupt?
     image.stats
     false
@@ -81,14 +69,9 @@ class MediaFile::Image < MediaFile
     file_ext == :png && metadata.fetch("PNG:AnimationFrames", 1) > 1
   end
 
-  # https://exiftool.org/TagNames/EXIF.html
-  def is_rotated?
-    metadata["IFD0:Orientation"].in?(["Rotate 90 CW", "Rotate 270 CW"])
-  end
-
   # @return [Vips::Image] the Vips image object for the file
   def image
-    Vips::Image.new_from_file(file.path, fail: true)
+    Vips::Image.new_from_file(file.path, fail: true).autorot
   end
 
   memoize :image, :dimensions, :is_corrupt?, :is_animated_gif?, :is_animated_png?

app/models/media_asset.rb

@@ -49,7 +49,7 @@ class MediaAsset < ApplicationRecord
 
   # https://exiftool.org/TagNames/EXIF.html
   def is_rotated?
-    metadata["IFD0:Orientation"].in?(["Rotate 90 CW", "Rotate 270 CW", "Rotate 180"])
+    file_ext == "jpg" && metadata["IFD0:Orientation"].in?(["Rotate 90 CW", "Rotate 270 CW", "Rotate 180"])
   end
 
   # Some animations technically have a finite loop count, but loop for hundreds

test/unit/media_file_test.rb

@@ -359,4 +359,16 @@ class MediaFileTest < ActiveSupport::TestCase
       assert_equal([33, 50], @file.preview(50, 50).dimensions)
     end
   end
+
+  context "a PNG with an exif orientation flag" do
+    should "not generate rotated dimensions" do
+      @file = MediaFile.open("test/files/test-rotation-90cw.png")
+      assert_equal([128, 96], @file.dimensions)
+    end
+
+    should "not generate a rotated thumbnail" do
+      @file = MediaFile.open("test/files/test-rotation-90cw.png")
+      assert_equal([64, 48], @file.preview(64, 64).dimensions)
+    end
+  end
 end

test/unit/post_test.rb

@@ -1336,6 +1336,15 @@ class PostTest < ActiveSupport::TestCase
         end
       end
 
+      context "a PNG with the exif orientation flag" do
+        should "not add the exif_rotation tag" do
+          @media_asset = MediaAsset.create!(file: "test/files/test-rotation-90cw.png")
+          @post.update!(md5: @media_asset.md5)
+          @post.reload.update!(tag_string: "tagme")
+          assert_equal("tagme", @post.tag_string)
+        end
+      end
+
       context "a non-repeating GIF missing the non-repeating_animation tag" do
         should "automatically add the non-repeating_animation tag" do
           @media_asset = MediaAsset.create!(file: "test/files/test-animated-86x52-loop-1.gif")