PYTHON-698 - Try encoding types with broken __getattr__ methods

Author: behackett

bson/_cbsonmodule.c

@@ -554,33 +554,40 @@ static int _write_element_to_buffer(PyObject* self, buffer_t buffer,
  unsigned char check_keys,
  unsigned char uuid_subtype) {
  struct module_state *state = GETSTATE(self);
+ PyObject* type_marker = NULL;
 
  /*
  * Don't use PyObject_IsInstance for our custom types. It causes
  * problems with python sub interpreters. Our custom types should
  * have a _type_marker attribute, which we can switch on instead.
  */
  if (PyObject_HasAttrString(value, "_type_marker")) {
- long type;
- PyObject* type_marker = PyObject_GetAttrString(value, "_type_marker");
- if (type_marker == NULL)
+ type_marker = PyObject_GetAttrString(value, "_type_marker");
+ if (type_marker == NULL) {
  return 0;
+ }
+ }
+ /*
+ * Python objects with broken __getattr__ implementations could return
+ * arbitrary types for a call to PyObject_GetAttrString. For example
+ * pymongo.database.Database returns a new Collection instance for
+ * __getattr__ calls with names that don't match an existing attribute
+ * or method. In some cases "value" could be a subtype of something
+ * we know how to serialize. Make a best effort to encode these types.
+ */
 #if PY_MAJOR_VERSION >= 3
- type = PyLong_AsLong(type_marker);
+ if (type_marker && PyLong_CheckExact(type_marker)) {
+ long type = PyLong_AsLong(type_marker);
 #else
- type = PyInt_AsLong(type_marker);
+ if (type_marker && PyInt_CheckExact(type_marker)) {
+ long type = PyInt_AsLong(type_marker);
 #endif
  Py_DECREF(type_marker);
  /* 
  * Py(Long|Int)_AsLong returns -1 for error but -1 is a valid value
  * so we call PyErr_Occurred to differentiate.
- *
- * One potential reason for an error is the user passing an invalid
- * type that overrides __getattr__ (e.g. pymongo.collection.Collection)
  */
  if (type == -1 && PyErr_Occurred()) {
- PyErr_Clear();
- _set_cannot_encode(value);
  return 0;
  }
  switch (type) {
@@ -792,6 +799,8 @@ static int _write_element_to_buffer(PyObject* self, buffer_t buffer,
  return 1;
  }
  }
+ } else {
+ Py_XDECREF(type_marker);
  }
 
  /* No _type_marker attibute or not one of our types. */

test/test_collection.py

@@ -2085,8 +2085,17 @@ def test_drop_indexes_non_existant(self):
  # (Shame on me)
  def test_bad_encode(self):
  c = self.db.test
+ c.drop()
  self.assertRaises(InvalidDocument, c.save, {"x": c})
 
+ class BadGetAttr(dict):
+ def __getattr__(self, name):
+ pass
+
+ bad = BadGetAttr([('foo', 'bar')])
+ c.insert({'bad': bad})
+ self.assertEqual('bar', c.find_one()['bad']['foo'])
+
  def test_bad_dbref(self):
  c = self.db.test
  c.drop()