Truncate long URLs while providing alt text for inline images

app/lib/sanitize_config.rb

@@ -27,7 +27,15 @@ class Sanitize
       node.name = 'a'
 
       node['href'] = node['src']
-      node.content = "[🖼 #{node['alt'] || node['href']}]"
+      if node['alt'].present?
+        node.content = "[🖼  #{node['alt']}]"
+      else
+        url = node['href']
+        prefix = url.match(/\Ahttps?:\/\/(www\.)?/).to_s
+        text   = url[prefix.length, 30]
+        text   = text + "…" if url[prefix.length..-1].length > 30
+        node.content = "[🖼  #{text}]"
+      end
     end
 
     MASTODON_STRICT ||= freeze_config(