From c0264c8013615cb725f9fd2d69bea60ea4a13324 Mon Sep 17 00:00:00 2001
From: Matt Jankowski <matt@jankowski.online>
Date: Wed, 8 Jan 2025 03:48:45 -0500
Subject: [PATCH] Extend custom CSS cache time with digest paths (#33207)

---
 app/controllers/custom_css_controller.rb |  2 +-
 app/helpers/theme_helper.rb              | 23 +++++++++++++++
 app/models/form/admin_settings.rb        | 18 ++++++++++++
 app/views/layouts/application.html.haml  |  2 +-
 config/initializers/settings_digests.rb  | 18 ++++++++++++
 config/routes.rb                         |  3 +-
 spec/helpers/theme_helper_spec.rb        | 20 +++++++++++++
 spec/models/form/admin_settings_spec.rb  | 36 ++++++++++++++++++++++++
 spec/requests/cache_spec.rb              |  1 +
 spec/requests/custom_css_spec.rb         |  6 ++--
 spec/routing/custom_css_routing_spec.rb  | 19 +++++++++++++
 11 files changed, 142 insertions(+), 6 deletions(-)
 create mode 100644 config/initializers/settings_digests.rb
 create mode 100644 spec/routing/custom_css_routing_spec.rb

diff --git a/app/controllers/custom_css_controller.rb b/app/controllers/custom_css_controller.rb
index 9f33870bd2..5b98914114 100644
--- a/app/controllers/custom_css_controller.rb
+++ b/app/controllers/custom_css_controller.rb
@@ -2,7 +2,7 @@
 
 class CustomCssController < ActionController::Base # rubocop:disable Rails/ApplicationController
   def show
-    expires_in 3.minutes, public: true
+    expires_in 1.month, public: true
     render content_type: 'text/css'
   end
 
diff --git a/app/helpers/theme_helper.rb b/app/helpers/theme_helper.rb
index fab899a533..5dfb4a5184 100644
--- a/app/helpers/theme_helper.rb
+++ b/app/helpers/theme_helper.rb
@@ -23,8 +23,31 @@ module ThemeHelper
     end
   end
 
+  def custom_stylesheet
+    if active_custom_stylesheet.present?
+      stylesheet_link_tag(
+        custom_css_path(active_custom_stylesheet),
+        host: root_url,
+        media: :all,
+        skip_pipeline: true
+      )
+    end
+  end
+
   private
 
+  def active_custom_stylesheet
+    if cached_custom_css_digest.present?
+      [:custom, cached_custom_css_digest.to_s.first(8)]
+        .compact_blank
+        .join('-')
+    end
+  end
+
+  def cached_custom_css_digest
+    Rails.cache.read(:setting_digest_custom_css)
+  end
+
   def theme_color_for(theme)
     theme == 'mastodon-light' ? Themes::THEME_COLORS[:light] : Themes::THEME_COLORS[:dark]
   end
diff --git a/app/models/form/admin_settings.rb b/app/models/form/admin_settings.rb
index 515909d5cf..ffd2d4049c 100644
--- a/app/models/form/admin_settings.rb
+++ b/app/models/form/admin_settings.rb
@@ -69,6 +69,10 @@ class Form::AdminSettings
     favicon
   ).freeze
 
+  DIGEST_KEYS = %i(
+    custom_css
+  ).freeze
+
   OVERRIDEN_SETTINGS = {
     authorized_fetch: :authorized_fetch_mode?,
   }.freeze
@@ -122,6 +126,8 @@ class Form::AdminSettings
     KEYS.each do |key|
       next unless instance_variable_defined?(:"@#{key}")
 
+      cache_digest_value(key) if DIGEST_KEYS.include?(key)
+
       if UPLOAD_KEYS.include?(key)
         public_send(key).save
       else
@@ -133,6 +139,18 @@ class Form::AdminSettings
 
   private
 
+  def cache_digest_value(key)
+    Rails.cache.delete(:"setting_digest_#{key}")
+
+    key_value = instance_variable_get(:"@#{key}")
+    if key_value.present?
+      Rails.cache.write(
+        :"setting_digest_#{key}",
+        Digest::SHA256.hexdigest(key_value)
+      )
+    end
+  end
+
   def typecast_value(key, value)
     if BOOLEAN_KEYS.include?(key)
       value == '1'
diff --git a/app/views/layouts/application.html.haml b/app/views/layouts/application.html.haml
index 99e89d45ce..6f016c6cf5 100755
--- a/app/views/layouts/application.html.haml
+++ b/app/views/layouts/application.html.haml
@@ -34,7 +34,7 @@
     = csrf_meta_tags unless skip_csrf_meta_tags?
     %meta{ name: 'style-nonce', content: request.content_security_policy_nonce }
 
-    = stylesheet_link_tag custom_css_path, skip_pipeline: true, host: root_url, media: 'all'
+    = custom_stylesheet
 
     = yield :header_tags
 
diff --git a/config/initializers/settings_digests.rb b/config/initializers/settings_digests.rb
new file mode 100644
index 0000000000..2a5d925c70
--- /dev/null
+++ b/config/initializers/settings_digests.rb
@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+
+Rails.application.config.to_prepare do
+  custom_css = begin
+    Setting.custom_css
+  rescue ActiveRecord::AdapterError # Running without a database, not migrated, no connection, etc
+    nil
+  end
+
+  if custom_css.present?
+    Rails
+      .cache
+      .write(
+        :setting_digest_custom_css,
+        Digest::SHA256.hexdigest(custom_css)
+      )
+  end
+end
diff --git a/config/routes.rb b/config/routes.rb
index 3909dd1b77..5adec04c7d 100644
--- a/config/routes.rb
+++ b/config/routes.rb
@@ -55,7 +55,8 @@ Rails.application.routes.draw do
 
   get 'manifest', to: 'manifests#show', defaults: { format: 'json' }
   get 'intent', to: 'intents#show'
-  get 'custom.css', to: 'custom_css#show', as: :custom_css
+  get 'custom.css', to: 'custom_css#show'
+  resources :custom_css, only: :show, path: :css
 
   get 'remote_interaction_helper', to: 'remote_interaction_helper#index'
 
diff --git a/spec/helpers/theme_helper_spec.rb b/spec/helpers/theme_helper_spec.rb
index 7663e59436..c811b7c981 100644
--- a/spec/helpers/theme_helper_spec.rb
+++ b/spec/helpers/theme_helper_spec.rb
@@ -79,6 +79,26 @@ RSpec.describe ThemeHelper do
     end
   end
 
+  describe '#custom_stylesheet' do
+    context 'when custom css setting value digest is present' do
+      before { Rails.cache.write(:setting_digest_custom_css, '1a2s3d4f1a2s3d4f') }
+
+      it 'returns value from settings' do
+        expect(custom_stylesheet)
+          .to match('/css/custom-1a2s3d4f.css')
+      end
+    end
+
+    context 'when custom css setting value digest is not present' do
+      before { Rails.cache.delete(:setting_digest_custom_css) }
+
+      it 'returns default value' do
+        expect(custom_stylesheet)
+          .to be_blank
+      end
+    end
+  end
+
   private
 
   def html_links
diff --git a/spec/models/form/admin_settings_spec.rb b/spec/models/form/admin_settings_spec.rb
index 73106f2b69..899d56703a 100644
--- a/spec/models/form/admin_settings_spec.rb
+++ b/spec/models/form/admin_settings_spec.rb
@@ -17,4 +17,40 @@ RSpec.describe Form::AdminSettings do
       end
     end
   end
+
+  describe '#save' do
+    describe 'updating digest values' do
+      context 'when updating custom css to real value' do
+        subject { described_class.new(custom_css: css) }
+
+        let(:css) { 'body { color: red; }' }
+        let(:digested) { Digest::SHA256.hexdigest(css) }
+
+        it 'changes relevant digest value' do
+          expect { subject.save }
+            .to(change { Rails.cache.read(:setting_digest_custom_css) }.to(digested))
+        end
+      end
+
+      context 'when updating custom css to empty value' do
+        subject { described_class.new(custom_css: '') }
+
+        before { Rails.cache.write(:setting_digest_custom_css, 'previous-value') }
+
+        it 'changes relevant digest value' do
+          expect { subject.save }
+            .to(change { Rails.cache.read(:setting_digest_custom_css) }.to(be_blank))
+        end
+      end
+
+      context 'when updating other fields' do
+        subject { described_class.new(site_contact_email: 'test@example.host') }
+
+        it 'does not update digests' do
+          expect { subject.save }
+            .to(not_change { Rails.cache.read(:setting_digest_custom_css) })
+        end
+      end
+    end
+  end
 end
diff --git a/spec/requests/cache_spec.rb b/spec/requests/cache_spec.rb
index 2a52e4dea9..8ca2817263 100644
--- a/spec/requests/cache_spec.rb
+++ b/spec/requests/cache_spec.rb
@@ -10,6 +10,7 @@ module TestEndpoints
     /.well-known/nodeinfo
     /nodeinfo/2.0
     /manifest
+    /css/custom-1a2s3d4f.css
     /custom.css
     /actor
     /api/v1/instance/extended_description
diff --git a/spec/requests/custom_css_spec.rb b/spec/requests/custom_css_spec.rb
index 380c32908a..66ff5c4b13 100644
--- a/spec/requests/custom_css_spec.rb
+++ b/spec/requests/custom_css_spec.rb
@@ -5,10 +5,10 @@ require 'rails_helper'
 RSpec.describe 'Custom CSS' do
   include RoutingHelper
 
-  describe 'GET /custom.css' do
+  describe 'GET /css/:id.css' do
     context 'without any CSS or User Roles' do
       it 'returns empty stylesheet' do
-        get '/custom.css'
+        get '/css/custom-123.css'
 
         expect(response)
           .to have_http_status(200)
@@ -27,7 +27,7 @@ RSpec.describe 'Custom CSS' do
       end
 
       it 'returns stylesheet from settings' do
-        get '/custom.css'
+        get '/css/custom-456.css'
 
         expect(response)
           .to have_http_status(200)
diff --git a/spec/routing/custom_css_routing_spec.rb b/spec/routing/custom_css_routing_spec.rb
new file mode 100644
index 0000000000..26139b4744
--- /dev/null
+++ b/spec/routing/custom_css_routing_spec.rb
@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+RSpec.describe 'Custom CSS routes' do
+  describe 'the legacy route' do
+    it 'routes to correct place' do
+      expect(get('/custom.css'))
+        .to route_to('custom_css#show')
+    end
+  end
+
+  describe 'the custom digest route' do
+    it 'routes to correct place' do
+      expect(get('/css/custom-1a2s3d4f.css'))
+        .to route_to('custom_css#show', id: 'custom-1a2s3d4f', format: 'css')
+    end
+  end
+end