FIX: add short_path to upload_serializer (PR #9417)

What problem I am trying to solve?

When an encrypted message is crafted and the image is added - discourse needs a hard refresh to display that image.

What is happening?

Everything starts here - when the upload is finished we add serialized object to the cache https://github.com/discourse/discourse/blob/master/app/assets/javascripts/discourse/components/composer-editor.js#L748:L757

Then, discourse-encrypt is trying to get an image from the cache and use short_path property https://github.com/discourse/discourse-encrypt/blob/master/assets/javascripts/discourse/initializers/hook-decrypt-post.js.es6#L142:L143

Why is it working after a hard refresh?

After refresh, we populate cache once again using that function: https://github.com/discourse/discourse/blob/master/app/assets/javascripts/pretty-text/upload-short-url.js#L11:L17

And lookup_urls method from backend is returning short_path https://github.com/discourse/discourse/blob/master/app/controllers/uploads_controller.rb#L55:L64

TL;DR We should expose short path in upload serializer. I ensured that this serializer is used only when attachments are uploaded so it should not affect performance.

GitHub

Nice detective work :mag: