dont download original artstation images if they dont exist

app/logical/downloads/rewrite_strategies/art_station.rb

@@ -4,7 +4,10 @@ module Downloads
       def rewrite(url, headers, data = {})
         # example: https://cdnb3.artstation.com/p/assets/images/images/003/716/071/large/aoi-ogata-hate-city.jpg?1476754974
         if url =~ %r!^https?://cdn\w*\.artstation\.com/p/assets/images/images/\d+/\d+/\d+/(?:medium|small|large)/!
-          url, headers = rewrite_large_url(url, headers)
+          original_url, headers = rewrite_large_url(url, headers)
+          if test_original(original_url)
+            url = original_url
+          end
         elsif url =~ %r!https?://\w+\.artstation\.com/artwork/!
           url, headers = rewrite_html_url(url, headers)
         end
@@ -13,6 +16,11 @@ module Downloads
       end
 
     protected
+      def test_original(url)
+        res = http_head_request(url, {})
+        res.is_a?(Net::HTTPSuccess)
+      end
+
       def rewrite_html_url(url, headers)
         source = Sources::Site.new(url)
         source.get

test/unit/downloads/art_station_test.rb

@@ -14,5 +14,18 @@ module Downloads
         assert_equal("https://cdnb3.artstation.com/p/assets/images/images/003/716/071/original/aoi-ogata-hate-city.jpg?1476754974", @download.source)
       end
     end
+
+    context "for an image where an original does not exist" do
+      setup do
+        @source = "https://cdna.artstation.com/p/assets/images/images/004/730/278/large/mendel-oh-dragonll.jpg"
+        @tempfile = Tempfile.new("danbooru-test")
+        @download = Downloads::File.new(@source, @tempfile.path)
+        @download.download!
+      end
+
+      should "not try to download the original" do
+        assert_equal("https://cdna.artstation.com/p/assets/images/images/004/730/278/large/mendel-oh-dragonll.jpg", @download.source)
+      end
+    end
   end
 end