Disable the Accept header by default

The accept header is poorly implemented by browsers and causes strange errors when used on public sites where crawlers make requests too.  You should use formatted urls (e.g. /people/1.xml) to support API clients. Alternatively to re-enable it you need to set:

config.action_controller.use_accept_header = true

A special case remains for ajax requests which will have a javascript format for the base resource (/people/1) if the X-Requested-With header is present.  This lets ajax pages still use format.js despite there being no params[:format]

actionpack/CHANGELOG

 *Edge*
 
+* Disable the Accept header by default [Michael Koziarski]
+
+    The accept header is poorly implemented by browsers and causes strange
+	errors when used on public sites where crawlers make requests too.  You
+	should use formatted urls (e.g. /people/1.xml) to support API clients.
+
+	Alternatively to re-enable it you need to set:
+
+	config.action_controller.use_accept_header = true
+
 * Do not stat template files in production mode before rendering. You will no longer be able to modify templates in production mode without restarting the server [Josh Peek]
 
 * Deprecated TemplateHandler line offset [Josh Peek]

actionpack/lib/action_controller/base.rb

@@ -340,6 +340,16 @@ class Base
     cattr_accessor :optimise_named_routes
     self.optimise_named_routes = true
 
+    # Indicates whether the response format should be determined by examining the Accept HTTP header,
+    # or by using the simpler params + ajax rules.
+    #
+    # If this is set to +true+ then +respond_to+ and +Request#format+ will take the Accept header into
+    # account.  If it is set to false (the default) then the request format will be determined solely
+    # by examining params[:format].  If params format is missing, the format will be either HTML or
+    # Javascript depending on whether the request is an AJAX request.
+    cattr_accessor :use_accept_header
+    self.use_accept_header = false
+
     # Controls whether request forgergy protection is turned on or not. Turned off by default only in test mode.
     class_inheritable_accessor :allow_forgery_protection
     self.allow_forgery_protection = true

actionpack/lib/action_controller/caching/actions.rb

@@ -166,10 +166,7 @@ def extract_extension(request)
 
             # If there's no extension in the path, check request.format
             if extension.nil?
-              extension = request.format.to_sym.to_s
-              if extension=='all'
-                extension = nil
-              end
+              extension = request.cache_format
             end
             extension
           end

actionpack/lib/action_controller/mime_responds.rb

@@ -114,7 +114,11 @@ def initialize(controller)
         @request    = controller.request
         @response   = controller.response
 
-        @mime_type_priority = Array(Mime::Type.lookup_by_extension(@request.parameters[:format]) || @request.accepts)
+        if ActionController::Base.use_accept_header
+          @mime_type_priority = Array(Mime::Type.lookup_by_extension(@request.parameters[:format]) || @request.accepts)
+        else
+          @mime_type_priority = [@request.format]
+        end
 
         @order     = []
         @responses = {}

actionpack/lib/action_controller/request.rb

@@ -89,14 +89,23 @@ def accepts
         end
     end
 
-    # Returns the Mime type for the format used in the request. If there is no format available, the first of the 
-    # accept types will be used. Examples:
+    # Returns the Mime type for the format used in the request.
     #
     #   GET /posts/5.xml   | request.format => Mime::XML
     #   GET /posts/5.xhtml | request.format => Mime::HTML
-    #   GET /posts/5       | request.format => request.accepts.first (usually Mime::HTML for browsers)
+    #   GET /posts/5       | request.format => Mime::HTML or MIME::JS, or request.accepts.first depending on the value of <tt>ActionController::Base.use_accept_header</tt>
     def format
-      @format ||= parameters[:format] ? Mime::Type.lookup_by_extension(parameters[:format]) : accepts.first
+      @format ||= begin
+        if parameters[:format]
+          Mime::Type.lookup_by_extension(parameters[:format])
+        elsif ActionController::Base.use_accept_header
+          accepts.first
+        elsif xhr?
+          Mime::Type.lookup_by_extension("js")
+        else
+          Mime::Type.lookup_by_extension("html")
+        end
+      end
     end
     
     
@@ -116,19 +125,26 @@ def format=(extension)
       @format = Mime::Type.lookup_by_extension(parameters[:format])
     end
 
+    # Returns a symbolized version of the <tt>:format</tt> parameter of the request.
+    # If no format is given it returns <tt>:js</tt>for AJAX requests and <tt>:html</tt>
+    # otherwise.
     def template_format
       parameter_format = parameters[:format]
 
-      case
-      when parameter_format.blank? && !xhr?
-        :html
-      when parameter_format.blank? && xhr?
+      if parameter_format
+        parameter_format.to_sym
+      elsif xhr?
         :js
       else
-        parameter_format.to_sym
+        :html
       end
     end
 
+    def cache_format
+      parameter_format = parameters[:format]
+      parameter_format && parameter_format.to_sym
+    end
+
     # Returns true if the request's "X-Requested-With" header contains
     # "XMLHttpRequest". (The Prototype Javascript library sends this header with
     # every Ajax request.)

actionpack/lib/action_view/base.rb

@@ -256,13 +256,9 @@ def file_public?(template_path)#:nodoc:
       template_path.split('/').last[0,1] != '_'
     end
 
-    # Returns a symbolized version of the <tt>:format</tt> parameter of the request,
-    # or <tt>:html</tt> by default.
-    #
-    # EXCEPTION: If the <tt>:format</tt> parameter is not set, the Accept header will be examined for
-    # whether it contains the JavaScript mime type as its first priority. If that's the case,
-    # it will be used. This ensures that Ajax applications can use the same URL to support both
-    # JavaScript and non-JavaScript users.
+    # The format to be used when choosing between multiple templates with
+    # the same name but differing formats.  See +Request#template_format+
+    # for more details.
     def template_format
       return @template_format if @template_format
 

actionpack/test/controller/caching_test.rb

@@ -131,8 +131,7 @@ def test_should_cache_ok_at_custom_path
   end
 
   def test_page_caching_conditional_options
-    @request.env['HTTP_ACCEPT'] = 'application/json'
-    get :ok
+    get :ok, :format=>'json'
     assert_page_not_cached :ok
   end
 
@@ -219,6 +218,7 @@ def request
     Object.new.instance_eval(<<-EVAL)
       def path; '#{@mock_path}' end
       def format; 'all' end
+      def cache_format; nil end
       self
     EVAL
   end
@@ -414,12 +414,6 @@ def test_xml_version_of_resource_is_treated_as_different_cache
       assert_equal 'application/xml', @response.content_type
       reset!
 
-      @request.env['HTTP_ACCEPT'] = "application/xml"
-      get :index
-      assert_equal cached_time, @response.body
-      assert_equal 'application/xml', @response.content_type
-      reset!
-
       get :expire_xml
       reset!
 

actionpack/test/controller/content_type_test.rb

@@ -114,6 +114,20 @@ def test_change_for_rxml
     assert_equal Mime::HTML, @response.content_type
     assert_equal "utf-8", @response.charset
   end
+end
+
+class AcceptBasedContentTypeTest < ActionController::TestCase
+
+  tests ContentTypeController
+
+  def setup
+    ActionController::Base.use_accept_header = true
+  end
+
+  def tear_down
+    ActionController::Base.use_accept_header = false
+  end
+
 
   def test_render_default_content_types_for_respond_to
     @request.env["HTTP_ACCEPT"] = Mime::HTML.to_s

actionpack/test/controller/mime_responds_test.rb

@@ -166,6 +166,7 @@ def set_layout
 
 class MimeControllerTest < Test::Unit::TestCase
   def setup
+    ActionController::Base.use_accept_header = true
     @request    = ActionController::TestRequest.new
     @response   = ActionController::TestResponse.new
 
@@ -173,6 +174,10 @@ def setup
     @request.host = "www.example.com"
   end
 
+  def teardown
+    ActionController::Base.use_accept_header = false
+  end
+
   def test_html
     @request.env["HTTP_ACCEPT"] = "text/html"
     get :js_or_html

actionpack/test/controller/request_test.rb

@@ -386,7 +386,7 @@ def test_txt_format
 
   def test_nil_format
     @request.instance_eval { @parameters = { :format => nil } }
-    @request.env["HTTP_ACCEPT"] = "text/javascript"
+    @request.env["HTTP_X_REQUESTED_WITH"] = "XMLHttpRequest"
     assert_equal Mime::JS, @request.format
   end