Track to_primitive() depth after iteritems().

Change jsonutils.to_primitive() to increase the recursion depth counter
when calling to_primitive() on the result of iteritems() from the
current element.  Previously, the only time the counter was increased
was when converting the __dict__ from an object.  The iteritems() case
risks cycles, as well.

I hit a problem with this when trying to call to_primitive on an
instance of nova.db.sqlalchemy.models.Instance.  An Instance includes a
reference to InstanceInfoCache, which has a reference back to the
Instance.  Without this change, to_primitive() would raise an exception
for an Instance due to excessive recursion.

Related to nova blueprint no-db-messaging.

Change-Id: Ifb878368d97e92ab6c361a4dd5f5ab2e68fc16e2

openstack/common/jsonutils.py

@@ -107,7 +107,7 @@ def to_primitive(value, convert_instances=False, level=0):
         elif hasattr(value, 'iteritems'):
             return to_primitive(dict(value.iteritems()),
                                 convert_instances=convert_instances,
-                                level=level)
+                                level=level + 1)
         elif hasattr(value, '__iter__'):
             return to_primitive(list(value), level)
         elif convert_instances and hasattr(value, '__dict__'):

tests/unit/test_jsonutils.py

@@ -95,6 +95,24 @@ class ToPrimitiveTestCase(unittest.TestCase):
         p = jsonutils.to_primitive(x)
         self.assertEquals(p, {'a': 1, 'b': 2, 'c': 3})
 
+    def test_iteritems_with_cycle(self):
+        class IterItemsClass(object):
+            def __init__(self):
+                self.data = dict(a=1, b=2, c=3)
+                self.index = 0
+
+            def iteritems(self):
+                return self.data.items()
+
+        x = IterItemsClass()
+        x2 = IterItemsClass()
+        x.data['other'] = x2
+        x2.data['other'] = x
+
+        # If the cycle isn't caught, to_primitive() will eventually result in
+        # an exception due to excessive recursion depth.
+        p = jsonutils.to_primitive(x)
+
     def test_instance(self):
         class MysteryClass(object):
             a = 10