Bug: Earlier Check for Session in Forgery Protection

The session is used by the form_authenticity_token method before it is
tested to be valid.  This patch moves a few lines around so that the
session is validated first.

Without this patch, if you try to use forgery protection with sessions
turned off, you get this exception message:

  undefined method `session_id' for {}:Hash

The patch includes a test that can be used to see this behavior before
the request_forgery_protection.rb file is patched to fix it.

actionpack/lib/action_controller/request_forgery_protection.rb

@@ -105,12 +105,12 @@ def verifiable_request_format?
       # Sets the token value for the current session.  Pass a <tt>:secret</tt> option
       # in +protect_from_forgery+ to add a custom salt to the hash.
       def form_authenticity_token
-        @form_authenticity_token ||= if request_forgery_protection_options[:secret]
+        @form_authenticity_token ||= if !session.respond_to?(:session_id)
+          raise InvalidAuthenticityToken, "Request Forgery Protection requires a valid session.  Use #allow_forgery_protection to disable it, or use a valid session."
+        elsif request_forgery_protection_options[:secret]
           authenticity_token_from_session_id
         elsif session.respond_to?(:dbman) && session.dbman.respond_to?(:generate_digest)
           authenticity_token_from_cookie_session
-        elsif session.nil?
-          raise InvalidAuthenticityToken, "Request Forgery Protection requires a valid session.  Use #allow_forgery_protection to disable it, or use a valid session."
         else
           raise InvalidAuthenticityToken, "No :secret given to the #protect_from_forgery call.  Set that or use a session store capable of generating its own keys (Cookie Session Store)."
         end

actionpack/test/controller/request_forgery_protection_test.rb

@@ -50,6 +50,14 @@ class CsrfCookieMonsterController < ActionController::Base
   protect_from_forgery :only => :index
 end
 
+# sessions are turned off
+class SessionOffController < ActionController::Base
+  protect_from_forgery :secret => 'foobar'
+  session :off
+  def rescue_action(e) raise e end
+  include RequestForgeryProtectionActions
+end
+
 class FreeCookieController < CsrfCookieMonsterController
   self.allow_forgery_protection = false
   
@@ -224,3 +232,19 @@ def test_should_allow_all_methods_without_token
     end
   end
 end
+
+class SessionOffControllerTest < Test::Unit::TestCase
+  def setup
+    @controller = SessionOffController.new
+    @request    = ActionController::TestRequest.new
+    @response   = ActionController::TestResponse.new
+    @token      = OpenSSL::HMAC.hexdigest(OpenSSL::Digest::Digest.new('SHA1'), 'abc', '123')
+  end
+
+  def test_should_raise_correct_exception
+    @request.session = {} # session(:off) doesn't appear to work with controller tests
+    assert_raises(ActionController::InvalidAuthenticityToken) do
+      post :index, :authenticity_token => @token
+    end
+  end
+end