1 files changed, 28 insertions, 0 deletions
diff --git a/activesupport/lib/active_support/json.rb b/activesupport/lib/active_support/json.rb
new file mode 100644
index 0000000000..77c7225c66
--- /dev/null
+++ b/activesupport/lib/active_support/json.rb
@@ -0,0 +1,28 @@
+require 'active_support/json/encoders'
+
+module ActiveSupport
+  module JSON #:nodoc:
+    class CircularReferenceError < StandardError; end
+      
+    class << self
+      REFERENCE_STACK_VARIABLE = :json_reference_stack
+      
+      def encode(value)
+        raise_on_circular_reference(value) do
+          Encoders[value.class].call(value)
+        end
+      end
+      
+      protected
+        def raise_on_circular_reference(value)
+          stack = Thread.current[REFERENCE_STACK_VARIABLE] ||= []
+          raise CircularReferenceError, 'object references itself' if
+            stack.include? value
+          stack << value
+          yield
+        ensure
+          stack.pop
+        end
+    end
+  end
+end