URL-escape resource filenames in stacks urls

lib/embed/stacks_image.rb

@@ -18,7 +18,7 @@ def stacks_image_url(druid, file_name)
     private
 
     def normalized_stacks_image_file_name(file_name)
-      file_name.gsub(/\.\w+$/, '')
+      ERB::Util.url_encode(file_name.gsub(/\.\w+$/, ''))
     end
   end
 end

spec/lib/embed/stacks_image_spec.rb

@@ -37,11 +37,19 @@
     it 'accpets an optional size parameter' do
       expect(subject.stacks_square_url('abc123', 'filename.jpg', size: 50)).to match(%r{square/50,50/})
     end
+
+    it 'escapes special characters in the image file name' do
+      expect(subject.stacks_square_url('abc123', 'file name.jpg')).to match(/file%20name/)
+    end
   end
 
   describe '#stacks_thumb_url' do
     it 'requests an image that is 400px on the long edge' do
       expect(subject.stacks_thumb_url('abc123', 'filename.jpg')).to match(%r{/full/\!400,400/})
     end
+
+    it 'escapes special characters in the image file name' do
+      expect(subject.stacks_thumb_url('abc123', 'file name.jpg')).to match(/file%20name/)
+    end
   end
 end