Fix VideoLinkFilter for uppercase file extensions

Also fixed to handle images with blank src
attributes gracefully

changelogs/unreleased/29284-video-preview-not-working.yml

+---
+title: Fix inline rendering of videos for uploads with uppercase file extensions
+merge_request: 17924
+author:
+type: fixed

lib/banzai/filter/video_link_filter.rb

@@ -8,8 +8,8 @@ module Banzai
     # a "Download" link in the case the video cannot be played.
     class VideoLinkFilter < HTML::Pipeline::Filter
       def call
-        doc.xpath(query).each do |el|
-          el.replace(video_node(doc, el))
+        doc.xpath('descendant-or-self::img[not(ancestor::a)]').each do |el|
+          el.replace(video_node(doc, el)) if has_video_extension?(el)
         end
 
         doc
@@ -17,22 +17,13 @@ module Banzai
 
       private
 
-      def query
-        @query ||= begin
-          src_query = UploaderHelper::SAFE_VIDEO_EXT.map do |ext|
-            "'.#{ext}' = substring(@src, string-length(@src) - #{ext.size})"
-          end
+      def has_video_extension?(element)
+        src = element.attr('data-canonical-src').presence || element.attr('src')
 
-          if context[:asset_proxy_enabled].present?
-            src_query.concat(
-              UploaderHelper::SAFE_VIDEO_EXT.map do |ext|
-                "'.#{ext}' = substring(@data-canonical-src, string-length(@data-canonical-src) - #{ext.size})"
-              end
-            )
-          end
+        return unless src.present?
 
-          "descendant-or-self::img[not(ancestor::a) and (#{src_query.join(' or ')})]"
-        end
+        src_ext = File.extname(src).sub('.', '').downcase
+        Gitlab::FileTypeDetection::SAFE_VIDEO_EXT.include?(src_ext)
       end
 
       def video_node(doc, element)

spec/lib/banzai/filter/video_link_filter_spec.rb

@@ -12,15 +12,18 @@ describe Banzai::Filter::VideoLinkFilter do
   end
 
   def link_to_image(path)
-    %(<img src="#{path}" />)
+    return '<img/>' if path.nil?
+
+    %(<img src="#{path}"/>)
   end
 
   let(:project) { create(:project, :repository) }
 
-  context 'when the element src has a video extension' do
-    UploaderHelper::SAFE_VIDEO_EXT.each do |ext|
-      it "replaces the image tag 'path/video.#{ext}' with a video tag" do
-        container = filter(link_to_image("/path/video.#{ext}")).children.first
+  shared_examples 'a video element' do
+    let(:image) { link_to_image(src) }
+
+    it 'replaces the image tag with a video tag' do
+      container = filter(image).children.first
 
       expect(container.name).to eq 'div'
       expect(container['class']).to eq 'video-container'
@@ -28,36 +31,79 @@ describe Banzai::Filter::VideoLinkFilter do
       video, paragraph = container.children
 
       expect(video.name).to eq 'video'
-        expect(video['src']).to eq "/path/video.#{ext}"
+      expect(video['src']).to eq src
 
       expect(paragraph.name).to eq 'p'
 
       link = paragraph.children.first
 
       expect(link.name).to eq 'a'
-        expect(link['href']).to eq "/path/video.#{ext}"
+      expect(link['href']).to eq src
       expect(link['target']).to eq '_blank'
     end
   end
-  end
 
-  context 'when the element src is an image' do
+  shared_examples 'an unchanged element' do |ext|
     it 'leaves the document unchanged' do
-      element = filter(link_to_image('/path/my_image.jpg')).children.first
+      element = filter(link_to_image(src)).children.first
 
       expect(element.name).to eq 'img'
-      expect(element['src']).to eq '/path/my_image.jpg'
+      expect(element['src']).to eq src
     end
   end
 
-  context 'when asset proxy is enabled' do
-    it 'uses the correct src' do
-      stub_asset_proxy_setting(enabled: true)
+  context 'when the element src has a video extension' do
+    Gitlab::FileTypeDetection::SAFE_VIDEO_EXT.each do |ext|
+      it_behaves_like 'a video element' do
+        let(:src) { "/path/video.#{ext}" }
+      end
 
+      it_behaves_like 'a video element' do
+        let(:src) { "/path/video.#{ext.upcase}" }
+      end
+    end
+  end
+
+  context 'when the element has no src attribute' do
+    let(:src) { nil }
+
+    it_behaves_like 'an unchanged element'
+  end
+
+  context 'when the element src is an image' do
+    let(:src) { '/path/my_image.jpg' }
+
+    it_behaves_like 'an unchanged element'
+  end
+
+  context 'when the element src has an invalid file extension' do
+    let(:src) { '/path/my_video.somemp4' }
+
+    it_behaves_like 'an unchanged element'
+  end
+
+  context 'when data-canonical-src is empty' do
+    let(:image) { %(<img src="#{src}" data-canonical-src=""/>) }
+
+    context 'and src is a video' do
+      let(:src) { '/path/video.mp4' }
+
+      it_behaves_like 'a video element'
+    end
+
+    context 'and src is an image' do
+      let(:src) { '/path/my_image.jpg' }
+
+      it_behaves_like 'an unchanged element'
+    end
+  end
+
+  context 'when data-canonical-src is set' do
+    it 'uses the correct src' do
       proxy_src = 'https://assets.example.com/6d8b63'
       canonical_src = 'http://example.com/test.mp4'
-      image = %(<img src="#{proxy_src}" data-canonical-src="#{canonical_src}" />)
-      container = filter(image, asset_proxy_enabled: true).children.first
+      image = %(<img src="#{proxy_src}" data-canonical-src="#{canonical_src}"/>)
+      container = filter(image).children.first
 
       expect(container['class']).to eq 'video-container'