Custom emoji (#4988)

* Custom emoji

- In OStatus: `<link rel="emoji" name="coolcat" href="http://..." />`
- In ActivityPub: `{ type: "Emoji", name: ":coolcat:", href: "http://..." }`
- In REST API: Status object includes `emojis` array (`shortcode`, `url`)
- Domain blocks with reject media stop emojis
- Emoji file up to 50KB
- Web UI handles custom emojis
- Static pages render custom emojis as `<img />` tags

Side effects:

- Undo #4500 optimization, as I needed to modify it to restore
  shortcode handling in emojify()
- Formatter#plaintext should now make sure stripped out line-breaks
  and paragraphs are replaced with newlines

* Fix emoji at the start not being converted

app/lib/ostatus/activity/creation.rb

@@ -42,6 +42,7 @@ class OStatus::Activity::Creation < OStatus::Activity::Base
       save_mentions(status)
       save_hashtags(status)
       save_media(status)
+      save_emojis(status)
     end
 
     if thread? && status.thread.nil?
@@ -150,6 +151,25 @@ class OStatus::Activity::Creation < OStatus::Activity::Base
     end
   end
 
+  def save_emojis(parent)
+    do_not_download = DomainBlock.find_by(domain: parent.account.domain)&.reject_media?
+
+    return if do_not_download
+
+    @xml.xpath('./xmlns:link[@rel="emoji"]', xmlns: TagManager::XMLNS).each do |link|
+      next unless link['href'] && link['name']
+
+      shortcode = link['name'].delete(':')
+      emoji     = CustomEmoji.find_by(shortcode: shortcode, domain: parent.account.domain)
+
+      next unless emoji.nil?
+
+      emoji = CustomEmoji.new(shortcode: shortcode, domain: parent.account.domain)
+      emoji.image_remote_url = link['href']
+      emoji.save
+    end
+  end
+
   def account_from_href(href)
     url = Addressable::URI.parse(href).normalize
 

app/lib/ostatus/atom_serializer.rb

@@ -368,5 +368,9 @@ class OStatus::AtomSerializer
     end
 
     append_element(entry, 'mastodon:scope', status.visibility)
+
+    status.emojis.each do |emoji|
+      append_element(entry, 'link', nil, rel: :emoji, href: full_asset_url(emoji.image.url), name: emoji.shortcode)
+    end
   end
 end