resolves asciidoctor#443 escape double quotes in alt text

CHANGELOG.adoc

@@ -10,6 +10,7 @@ For a detailed view of what has changed, refer to the {uri-repo}/commits/master[
 * add XML declarations to XHTML files (#424 by @abbrev)
 * bump the oldest supported Ruby to 2.6
 * bump the oldest supported Asciidoctor to 2.0
+* escape double quotes in alt text
 
 == 1.5.1 (2021-04-29) - @slonopotamus
 

lib/asciidoctor-epub3/converter.rb

@@ -1057,9 +1057,14 @@ def register_media_file(node, target, media_type)
         @media_files[target] ||= { path: fs_path, media_type: media_type }
       end
 
+      # @param node [Asciidoctor::Block]
+      # @return [Array<String>]
       def resolve_image_attrs(node)
         img_attrs = []
-        img_attrs << %(alt="#{node.attr 'alt'}") if node.attr? 'alt'
+
+        unless (alt = encode_attribute_value(node.alt)).empty?
+          img_attrs << %(alt="#{alt}")
+        end
 
         # Unlike browsers, Calibre/Kindle *do* scale image if only height is specified
         # So, in order to match browser behavior, we just always omit height
@@ -1145,6 +1150,8 @@ def convert_video(node)
 </figure>)
       end
 
+      # @param node [Asciidoctor::Block]
+      # @return [String]
       def convert_image(node)
         target = node.image_uri node.attr 'target'
         register_media_file node, target, 'image'
@@ -1333,6 +1340,10 @@ def output_content(node)
         node.content_model == :simple ? %(<p>#{node.content}</p>) : node.content
       end
 
+      def encode_attribute_value(val)
+        val.gsub '"', '&quot;'
+      end
+
       # FIXME: merge into with xml_sanitize helper
       def xml_sanitize(value, target = :attribute)
         sanitized = value.include?('<') ? value.gsub(XML_ELEMENT_RX, '').strip.tr_s(' ', ' ') : value

spec/fixtures/image-dimensions/chapter.adoc

@@ -4,4 +4,4 @@ image::square.png[100x100,100,100]
 image::square.png[50x50,50,50]
 image::square.png[50x?,50]
 image::square.png[25%x?,25%]
-image::square.png[invalid,25em]
+image::square.png[invalid",25em]

spec/image_spec.rb

@@ -78,7 +78,7 @@
     expect(chapter.content).to include '<img src="square.png" alt="50x50" width="50" />'
     expect(chapter.content).to include '<img src="square.png" alt="50x?" width="50" />'
     expect(chapter.content).to include '<img src="square.png" alt="25%x?" style="width: 25%" />'
-    expect(chapter.content).to include '<img src="square.png" alt="invalid" width="25em" />'
+    expect(chapter.content).to include '<img src="square.png" alt="invalid&quot;" width="25em" />'
   end
 
   # If this test fails for you, make sure you're using gepub >= 1.0.11