Add validation of base exception type(s) in failure type

All python exceptions should originate from either base
exception or exception, so in the failure validation logic
check and verify that these are the root exception type names
that have been captured and raise and invalid format error
if anything else is found.

Change-Id: I8ba1b68799703d6a857c51867d9e6cb0f884397c

taskflow/tests/unit/test_failure.py

@@ -168,6 +168,19 @@ class FailureObjectTestCase(test.TestCase):
         f2 = failure.Failure.from_dict(d_f)
         self.assertTrue(f.matches(f2))
 
+    def test_bad_root_exception(self):
+        f = _captured_failure('Woot!')
+        d_f = f.to_dict()
+        d_f['exc_type_names'] = ['Junk']
+        self.assertRaises(exceptions.InvalidFormat,
+                          failure.Failure.validate, d_f)
+
+    def test_valid_from_dict_to_dict_2(self):
+        f = _captured_failure('Woot!')
+        d_f = f.to_dict()
+        d_f['exc_type_names'] = ['RuntimeError', 'Exception', 'BaseException']
+        failure.Failure.validate(d_f)
+
     def test_dont_catch_base_exception(self):
         try:
             raise SystemExit()

taskflow/types/failure.py

@@ -14,6 +14,7 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+import collections
 import copy
 import os
 import sys
@@ -28,6 +29,7 @@ from taskflow.utils import iter_utils
 from taskflow.utils import mixins
 from taskflow.utils import schema_utils as su
 
+
 _exception_message = encodeutils.exception_to_unicode
 
 
@@ -121,6 +123,13 @@ class Failure(mixins.StrMixin):
     """
     DICT_VERSION = 1
 
+    BASE_EXCEPTIONS = ('BaseException', 'Exception')
+    """
+    Root exceptions of all other python exceptions.
+
+    See: https://docs.python.org/2/library/exceptions.html
+    """
+
     #: Expected failure schema (in json schema format).
     SCHEMA = {
         "$ref": "#/definitions/cause",
@@ -206,11 +215,29 @@ class Failure(mixins.StrMixin):
 
     @classmethod
     def validate(cls, data):
+        """Validate input data matches expected failure ``dict`` format."""
         try:
             su.schema_validate(data, cls.SCHEMA)
         except su.ValidationError as e:
             raise exc.InvalidFormat("Failure data not of the"
                                     " expected format: %s" % (e.message), e)
+        else:
+            # Ensure that all 'exc_type_names' originate from one of
+            # BASE_EXCEPTIONS, because those are the root exceptions that
+            # python mandates/provides and anything else is invalid...
+            causes = collections.deque([data])
+            while causes:
+                cause = causes.popleft()
+                root_exc_type = cause['exc_type_names'][-1]
+                if root_exc_type not in cls.BASE_EXCEPTIONS:
+                    raise exc.InvalidFormat(
+                        "Failure data 'exc_type_names' must"
+                        " have an initial exception type that is one"
+                        " of %s types: '%s' is not one of those"
+                        " types" % (cls.BASE_EXCEPTIONS, root_exc_type))
+                sub_causes = cause.get('causes')
+                if sub_causes:
+                    causes.extend(sub_causes)
 
     def _matches(self, other):
         if self is other: