FIX: only save custom fields if they actually change

app/jobs/regular/pull_hotlinked_images.rb

@@ -49,6 +49,12 @@ module Jobs
       start_raw = raw.dup
       downloaded_urls = {}
       large_images = post.custom_fields[LARGE_IMAGES].presence || []
+
+      # recover from bad custom field silently
+      unless Array === large_images
+        large_images = []
+      end
+
       broken_images, new_large_images = [], []
 
       extract_images_from(post.cooked).each do |image|
@@ -108,8 +114,11 @@ module Jobs
 
       end
 
-      post.custom_fields[LARGE_IMAGES] = large_images
-      post.save!
+      if new_large_images.length > 0
+        post.custom_fields[LARGE_IMAGES] = large_images
+        post.save_custom_fields
+      end
+
       post.reload
 
       if start_raw == post.raw && raw != post.raw

spec/jobs/pull_hotlinked_images_spec.rb

@@ -20,6 +20,17 @@ describe Jobs::PullHotlinkedImages do
     SiteSetting.download_remote_images_threshold = 0
   end
 
+  describe "#nochange" do
+    it 'does saves nothing if there are no large images to pull' do
+      post = Fabricate(:post, raw: 'bob bob')
+      orig = post.updated_at
+
+      freeze_time 1.week.from_now
+      Jobs::PullHotlinkedImages.new.execute(post_id: post.id)
+      expect(orig).to be_within(1.second).of(post.reload.updated_at)
+    end
+  end
+
   describe '#execute' do
     before do
       FastImage.expects(:size).returns([100, 100]).at_least_once