fix stylesheet cache to recover if file is on disk

app/controllers/stylesheets_controller.rb

@@ -4,43 +4,53 @@ class StylesheetsController < ApplicationController
   def show
 
     target,digest = params[:name].split("_")
-    digest_orig = digest
-    digest = "_" + digest if digest
 
     cache_time = request.env["HTTP_IF_MODIFIED_SINCE"]
     cache_time = Time.rfc2822(cache_time) rescue nil if cache_time
 
     query = StylesheetCache.where(target: target)
     if digest
-      query = query.where(digest: digest_orig)
+      query = query.where(digest: digest)
     else
       query = query.order('id desc')
     end
 
+    # Security note, safe due to route constraint
+    underscore_digest = digest ? "_" + digest : ""
+    location = "#{Rails.root}/#{DiscourseStylesheets::CACHE_PATH}/#{target}#{underscore_digest}.css"
+
     stylesheet_time = query.pluck(:created_at).first
+
     if !stylesheet_time
-      return render nothing: true, status: 404
+      handle_missing_cache(location, target, digest)
     end
 
     if cache_time && stylesheet_time && stylesheet_time <= cache_time
       return render nothing: true, status: 304
     end
 
-    # Security note, safe due to route constraint
-    location = "#{Rails.root}/#{DiscourseStylesheets::CACHE_PATH}/#{target}#{digest}.css"
 
     unless File.exist?(location)
       if current = query.first
         File.write(location, current.content)
       else
-        return render nothing: true, status: 404
+        raise Discourse::NotFound
       end
     end
 
-    response.headers['Last-Modified'] = stylesheet_time.httpdate
+    response.headers['Last-Modified'] = stylesheet_time.httpdate if stylesheet_time
     expires_in 1.year, public: true unless Rails.env == "development"
     send_file(location, disposition: :inline)
-
   end
+
+  protected
+
+  def handle_missing_cache(location, name, digest)
+    existing = File.read(location) rescue nil
+    if existing && digest
+      StylesheetCache.add(name, digest, existing)
+    end
+  end
+
 end
 

app/models/stylesheet_cache.rb

@@ -1,7 +1,7 @@
 class StylesheetCache < ActiveRecord::Base
   self.table_name = 'stylesheet_cache'
 
-  MAX_TO_KEEP = 10
+  MAX_TO_KEEP = 50
 
   def self.add(target,digest,content)
 

lib/sass/discourse_stylesheets.rb

@@ -118,10 +118,14 @@ class DiscourseStylesheets
     end
   end
 
-  def cache_fullpath
+  def self.cache_fullpath
     "#{Rails.root}/#{CACHE_PATH}"
   end
 
+  def cache_fullpath
+    self.class.cache_fullpath
+  end
+
   def stylesheet_fullpath
     "#{cache_fullpath}/#{stylesheet_filename}"
   end

spec/controllers/stylesheets_controller_spec.rb

@@ -0,0 +1,25 @@
+require 'spec_helper'
+
+describe StylesheetsController do
+
+  it 'can survive cache miss' do
+    DiscourseStylesheets.cache.clear
+    DiscourseStylesheets.stylesheet_link_tag('desktop_rtl')
+
+    StylesheetCache.destroy_all
+
+    # digestless
+    get :show, name: 'desktop_rtl'
+    expect(response).to be_success
+
+    # tmp folder destruction and cached
+    `rm #{DiscourseStylesheets.cache_fullpath}/*`
+
+    get :show, name: 'desktop_rtl'
+    expect(response).to be_success
+
+    # there is an edge case which is ... disk and db cache is nuked, very unlikely to happen
+
+  end
+
+end