FIX: automatically bust cache for share ai assets

SamSaffron · SamSaffron · commit fda08e225a1f · 2024-11-22T08:10:35.000+11:00
CDNs can be configured to strip query params in Discourse
hosting. This is generally safe, but in this case we had
no way of busting the cache using the path.

New design properly caches and properly breaks busts the
cache if asset changes so we don't need to worry about versions
diff --git a/app/controllers/discourse_ai/ai_bot/shared_ai_conversations_controller.rb b/app/controllers/discourse_ai/ai_bot/shared_ai_conversations_controller.rb
@@ -7,7 +7,8 @@ class SharedAiConversationsController < ::ApplicationController
       requires_login only: %i[create update destroy]
       before_action :require_site_settings!
 
-      skip_before_action :preload_json, :check_xhr, only: %i[show]
+      skip_before_action :preload_json, :check_xhr, only: %i[show asset]
+      skip_before_action :verify_authenticity_token, only: ["asset"]
 
       def create
         ensure_allowed_create!
@@ -50,6 +51,30 @@ def show
         end
       end
 
+      def asset
+        no_cookies
+
+        name = params[:name]
+        path, content_type =
+          if name == "share"
+            %w[share.css text/css]
+          elsif name == "highlight"
+            %w[highlight.min.js application/javascript]
+          else
+            raise Discourse::NotFound
+          end
+
+        content = File.read(DiscourseAi.public_asset_path("ai-share/#{path}"))
+
+        # note, path contains a ":version" which automatically busts the cache
+        # based on file content, so this is safe
+        response.headers["Last-Modified"] = 10.years.ago.httpdate
+        response.headers["Content-Length"] = content.bytesize.to_s
+        immutable_for 1.year
+
+        render plain: content, disposition: :nil, content_type: content_type
+      end
+
       def preview
         ensure_allowed_preview!
         data = SharedAiConversation.build_conversation_data(@topic, include_usernames: true)
diff --git a/app/helpers/discourse_ai/ai_bot/shared_ai_conversations_helper.rb b/app/helpers/discourse_ai/ai_bot/shared_ai_conversations_helper.rb
@@ -2,13 +2,29 @@
 module DiscourseAi
   module AiBot
     module SharedAiConversationsHelper
-      # bump up version when assets change
-      # long term we may want to change this cause it is hard to remember
-      # to bump versions, but for now this does the job
-      VERSION = "1"
+      # keeping it here for caching
+      def self.share_asset_url(asset_name)
+        if !%w[share.css highlight.js].include?(asset_name)
+          raise StandardError, "unknown asset type #{asset_name}"
+        end
 
-      def share_asset_url(short_path)
-        ::UrlHelper.absolute("/plugins/discourse-ai/ai-share/#{short_path}?#{VERSION}")
+        @urls ||= {}
+        url = @urls[asset_name]
+        return url if url
+
+        path = asset_name
+        path = "highlight.min.js" if asset_name == "highlight.js"
+
+        content = File.read(DiscourseAi.public_asset_path("ai-share/#{path}"))
+        sha1 = Digest::SHA1.hexdigest(content)
+
+        url = "/discourse-ai/ai-bot/shared-ai-conversations/asset/#{sha1}/#{asset_name}"
+
+        @urls[asset_name] = GlobalPath.cdn_path(url)
+      end
+
+      def share_asset_url(asset_name)
+        DiscourseAi::AiBot::SharedAiConversationsHelper.share_asset_url(asset_name)
       end
     end
   end
diff --git a/app/views/discourse_ai/ai_bot/shared_ai_conversations/show.html.erb b/app/views/discourse_ai/ai_bot/shared_ai_conversations/show.html.erb
@@ -10,7 +10,7 @@
     <meta name="twitter:title" content="<%= I18n.t("discourse_ai.share_ai.title", title: @shared_conversation.title, site_name: SiteSetting.title) %>">
     <meta name="twitter:description" content="<%= @shared_conversation.formatted_excerpt %>">
     <meta name="viewport" content="width=device-width">
-    <link rel="stylesheet" href="<%= ::UrlHelper.absolute("/plugins/discourse-ai/ai-share/share.css?v=1") %>">
+    <link rel="stylesheet" href="<%= share_asset_url("share.css")  %>">
   </head>
   <body>
     <header class="site-header">
@@ -54,7 +54,7 @@
         </article>
       <% end %>
     </section>
-    <script src="<%= share_asset_url("highlight.min.js") %>" nonce="<%= csp_nonce_placeholder %>" ></script>
+    <script src="<%= share_asset_url("highlight.js") %>" nonce="<%= csp_nonce_placeholder %>" ></script>
     <script nonce="<%= csp_nonce_placeholder %>">
       document.querySelectorAll('pre code').forEach((el) => {
         hljs.highlightElement(el);
diff --git a/config/routes.rb b/config/routes.rb
@@ -30,6 +30,7 @@
     post "/" => "shared_ai_conversations#create"
     delete "/:share_key" => "shared_ai_conversations#destroy"
     get "/:share_key" => "shared_ai_conversations#show"
+    get "/asset/:version/:name" => "shared_ai_conversations#asset"
     get "/preview/:topic_id" => "shared_ai_conversations#preview"
   end
 
diff --git a/plugin.rb b/plugin.rb
@@ -43,6 +43,10 @@
 
 module ::DiscourseAi
   PLUGIN_NAME = "discourse-ai"
+
+  def self.public_asset_path(name)
+    File.expand_path(File.join(__dir__, "public", name))
+  end
 end
 
 Rails.autoloaders.main.push_dir(File.join(__dir__, "lib"), namespace: ::DiscourseAi)
diff --git a/spec/requests/ai_bot/shared_ai_conversations_controller_spec.rb b/spec/requests/ai_bot/shared_ai_conversations_controller_spec.rb
@@ -294,6 +294,35 @@ def share_error(key)
     end
   end
 
+  describe "GET asset" do
+
+    let(:helper) do
+      Class.new do
+        extend DiscourseAi::AiBot::SharedAiConversationsHelper
+      end
+    end
+
+    it "renders highlight js correctly" do
+      get helper.share_asset_url("highlight.js")
+
+      expect(response).to be_successful
+      expect(response.headers["Content-Type"]).to eq("application/javascript; charset=utf-8")
+
+      js = File.read(DiscourseAi.public_asset_path("ai-share/highlight.min.js"))
+      expect(response.body).to eq(js)
+    end
+
+    it "renders css correctly" do
+      get helper.share_asset_url("share.css")
+
+      expect(response).to be_successful
+      expect(response.headers["Content-Type"]).to eq("text/css; charset=utf-8")
+
+      css = File.read(DiscourseAi.public_asset_path("ai-share/share.css"))
+      expect(response.body).to eq(css)
+    end
+  end
+
   describe "GET preview" do
     it "denies preview from logged out users" do
       get "#{path}/preview/#{user_pm_share.id}.json"
