BUGFIX: mobile ui was being cached for anon views

app/helpers/application_helper.rb

@@ -4,6 +4,7 @@ require_dependency 'guardian'
 require_dependency 'unread'
 require_dependency 'age_words'
 require_dependency 'configurable_urls'
+require_dependency 'mobile_detection'
 
 module ApplicationHelper
   include CurrentUser
@@ -109,21 +110,16 @@ module ApplicationHelper
   end
 
   def mobile_view?
-    return false unless SiteSetting.enable_mobile_theme
-    if session[:mobile_view]
-      session[:mobile_view] == '1'
-    else
-      mobile_device?
-    end
+    MobileDetection.resolve_mobile_view!(request.user_agent,params,session)
   end
 
   def mobile_device?
-    # TODO: this is dumb. user agent matching is a doomed approach. a better solution is coming.
-    request.user_agent =~ /Mobile|webOS|Nexus 7/ and !(request.user_agent =~ /iPad/)
+    MobileDetection.mobile_device?(request.user_agent)
   end
 
   def customization_disabled?
     controller.class.name.split("::").first == "Admin" || session[:disable_customization]
   end
 
+
 end

config/initializers/99-anon-cache.rb

@@ -7,6 +7,7 @@ enabled = if Rails.configuration.respond_to?(:enable_anon_caching)
           end
 
 if !ENV['DISCOURSE_DISABLE_ANON_CACHE'] && enabled
-  Rails.configuration.middleware.insert 0, Middleware::AnonymousCache
+  # in an ideal world this is position 0, but mobile detection uses ... session and request and params
+  Rails.configuration.middleware.insert_after ActionDispatch::ParamsParser, Middleware::AnonymousCache
 end
 

lib/middleware/anonymous_cache.rb

@@ -1,3 +1,5 @@
+require_dependency "mobile_detection"
+
 module Middleware
   class AnonymousCache
 
@@ -10,8 +12,19 @@ module Middleware
         @env = env
       end
 
+      def is_mobile?
+        @is_mobile ||=
+          begin
+            session = @env["rack.session"]
+            params = ActionDispatch::Request.new(@env).params
+            user_agent  = @env["HTTP_USER_AGENT"]
+
+            MobileDetection.resolve_mobile_view!(user_agent,params,session) ? :true : :false
+          end == :true
+      end
+
       def cache_key
-        @cache_key ||= "ANON_CACHE_#{@env["HTTP_HOST"]}#{@env["REQUEST_URI"]}"
+        @cache_key ||= "ANON_CACHE_#{@env["HTTP_HOST"]}#{@env["REQUEST_URI"]}|m=#{is_mobile?}"
       end
 
       def cache_key_body

lib/mobile_detection.rb

@@ -0,0 +1,19 @@
+module MobileDetection
+  def self.mobile_device?(user_agent)
+    # TODO: this is dumb. user agent matching is a doomed approach. a better solution is coming.
+    user_agent =~ /Mobile|webOS|Nexus 7/ && !(user_agent =~ /iPad/)
+  end
+
+  # we need this as a reusable chunk that is called from the cache
+  def self.resolve_mobile_view!(user_agent, params, session)
+    return false unless SiteSetting.enable_mobile_theme
+
+    session[:mobile_view] = params[:mobile_view] if params.has_key?(:mobile_view)
+
+    if session[:mobile_view]
+      session[:mobile_view] == '1'
+    else
+      mobile_device?(user_agent)
+    end
+  end
+end