FEATURE: fallback asset path for multi host setups

app/controllers/static_controller.rb

@@ -127,64 +127,62 @@ class StaticController < ApplicationController
   end
 
   def brotli_asset
-    path = File.expand_path(Rails.root + "public/assets/" + params[:path])
+    serve_asset(".br") do
-    path += ".br"
+      response.headers["Content-Encoding"] = 'br'
-
-    # SECURITY what if path has /../
-    raise Discourse::NotFound unless path.start_with?(Rails.root.to_s + "/public/assets")
-
-    opts = { disposition: nil }
-    opts[:type] = "application/javascript" if path =~ /\.js.br$/
-
-    begin
-      response.headers["Last-Modified"] = File.ctime(path).httpdate
-      response.headers["Content-Length"] = File.size(path).to_s
-    rescue Errno::ENOENT
-      response.headers["Expires"] = 5.seconds.from_now.httpdate
-      response.headers["Cache-Control"] = 'max-age=5, public'
-      expires_in 5.seconds, public: true, must_revalidate: false
-
-      render text: "missing brotli asset", status: 404
-      return
     end
-
-    response.headers["Content-Encoding"] = 'br'
-
-    # disable NGINX mucking with transfer
-    request.env['sendfile.type'] = ''
-    immutable_for 1.year
-    send_file(path, opts)
   end
 
 
   def cdn_asset
-    path = File.expand_path(Rails.root + "public/assets/" + params[:path])
+    serve_asset
+  end
+
+  protected
+
+  def serve_asset(suffix=nil)
+
+    path = File.expand_path(Rails.root + "public/assets/#{params[:path]}#{suffix}")
 
     # SECURITY what if path has /../
     raise Discourse::NotFound unless path.start_with?(Rails.root.to_s + "/public/assets")
 
-    immutable_for 1.year
 
     response.headers["Expires"] = 1.year.from_now.httpdate
     response.headers["Access-Control-Allow-Origin"] = params[:origin] if params[:origin]
 
     begin
       response.headers["Last-Modified"] = File.ctime(path).httpdate
-      response.headers["Content-Length"] = File.size(path).to_s
     rescue Errno::ENOENT
-      raise Discourse::NotFound
+      begin
+        if GlobalSetting.fallback_assets_path.present?
+          path = File.expand_path("#{GlobalSetting.fallback_assets_path}/#{params[:path]}#{suffix}")
+          response.headers["Last-Modified"] = File.ctime(path).httpdate
+        else
+          raise
+        end
+      rescue Errno::ENOENT
+        response.headers["Expires"] = 5.seconds.from_now.httpdate
+        response.headers["Cache-Control"] = 'max-age=5, public'
+        expires_in 1.second, public: true, must_revalidate: false
+
+        render text: "can not find #{params[:path]}", status: 404
+        return
+      end
     end
 
+    response.headers["Content-Length"] = File.size(path).to_s
+
+    yield if block_given?
+
+    immutable_for 1.year
+
+    # disable NGINX mucking with transfer
+    request.env['sendfile.type'] = ''
+
     opts = { disposition: nil }
     opts[:type] = "application/javascript" if path =~ /\.js$/
-
-    immutable_for(1.year)
-
-    # we must disable acceleration otherwise NGINX strips
-    # access control headers
-    request.env['sendfile.type'] = ''
-    # TODO send_file chunks which kills caching, need to render text here
     send_file(path, opts)
+
   end
 
 end

config/discourse_defaults.conf

@@ -150,3 +150,9 @@ message_bus_max_backlog_size = 100
 
 # must be a 64 byte hex string, anything else will be ignored with a warning
 secret_key_base =
+
+# fallback path for all assets which are served via the application
+# used by static_controller
+# in multi host setups this allows you to have old unicorn instances serve
+# newly compiled assets
+fallback_assets_path =

lib/tasks/assets.rake

@@ -175,11 +175,11 @@ task 'assets:precompile' => 'assets:precompile:before' do
     # protected
     manifest.send :save
 
-    if backup_path=ENV["BACKUP_ASSET_PATH"]
+    if GlobalSetting.fallback_assets_path.present?
       begin
-        FileUtils.cp_r("#{Rails.root}/public/assets/.", backup_path)
+        FileUtils.cp_r("#{Rails.root}/public/assets/.", GlobalSetting.fallback_assets_path)
       rescue => e
-        STDERR.puts "Failed to backup assets to #{backup_path}"
+        STDERR.puts "Failed to backup assets to #{GlobalSetting.fallback_assets_path}"
         STDERR.puts e
         STDERR.puts e.backtrace
       end

spec/controllers/static_controller_spec.rb

@@ -3,13 +3,33 @@ require 'rails_helper'
 describe StaticController do
 
   context 'brotli_asset' do
-    it 'returns a brotli encoded 404 if asset is missing' do
+    it 'returns a non brotli encoded 404 if asset is missing' do
 
         get :brotli_asset, path: 'missing.js'
 
         expect(response.status).to eq(404)
         expect(response.headers['Content-Encoding']).not_to eq('br')
-        expect(response.headers["Cache-Control"]).to match(/max-age=5/)
+        expect(response.headers["Cache-Control"]).to match(/max-age=1/)
+    end
+
+    it 'can handle fallback brotli assets' do
+      begin
+        assets_path = Rails.root.join("tmp/backup_assets")
+
+        GlobalSetting.stubs(:fallback_assets_path).returns(assets_path.to_s)
+
+        FileUtils.mkdir_p(assets_path)
+
+        file_path = assets_path.join("test.js.br")
+        File.write(file_path, 'fake brotli file')
+
+        get :brotli_asset, path: 'test.js'
+
+        expect(response.status).to eq(200)
+        expect(response.headers["Cache-Control"]).to match(/public/)
+      ensure
+        File.delete(file_path)
+      end
     end
 
     it 'has correct headers for brotli assets' do