bpo-29615: SimpleXMLRPCDispatcher no longer chains KeyError (#260)

(or any other exception) to exception(s) raised in the dispatched methods.
Patch by Petr Motejlek.

Lib/test/test_xmlrpc.py

@@ -343,6 +343,94 @@ class XMLRPCTestCase(unittest.TestCase):
             self.assertEqual(p.method(), 5)
             self.assertEqual(p.method(), 5)
 
+
+class SimpleXMLRPCDispatcherTestCase(unittest.TestCase):
+    class DispatchExc(Exception):
+        """Raised inside the dispatched functions when checking for
+        chained exceptions"""
+
+    def test_call_registered_func(self):
+        """Calls explicitly registered function"""
+        # Makes sure any exception raised inside the function has no other
+        # exception chained to it
+
+        exp_params = 1, 2, 3
+
+        def dispatched_func(*params):
+            raise self.DispatchExc(params)
+
+        dispatcher = xmlrpc.server.SimpleXMLRPCDispatcher()
+        dispatcher.register_function(dispatched_func)
+        with self.assertRaises(self.DispatchExc) as exc_ctx:
+            dispatcher._dispatch('dispatched_func', exp_params)
+        self.assertEqual(exc_ctx.exception.args, (exp_params,))
+        self.assertIsNone(exc_ctx.exception.__cause__)
+        self.assertIsNone(exc_ctx.exception.__context__)
+
+    def test_call_instance_func(self):
+        """Calls a registered instance attribute as a function"""
+        # Makes sure any exception raised inside the function has no other
+        # exception chained to it
+
+        exp_params = 1, 2, 3
+
+        class DispatchedClass:
+            def dispatched_func(self, *params):
+                raise SimpleXMLRPCDispatcherTestCase.DispatchExc(params)
+
+        dispatcher = xmlrpc.server.SimpleXMLRPCDispatcher()
+        dispatcher.register_instance(DispatchedClass())
+        with self.assertRaises(self.DispatchExc) as exc_ctx:
+            dispatcher._dispatch('dispatched_func', exp_params)
+        self.assertEqual(exc_ctx.exception.args, (exp_params,))
+        self.assertIsNone(exc_ctx.exception.__cause__)
+        self.assertIsNone(exc_ctx.exception.__context__)
+
+    def test_call_dispatch_func(self):
+        """Calls the registered instance's `_dispatch` function"""
+        # Makes sure any exception raised inside the function has no other
+        # exception chained to it
+
+        exp_method = 'method'
+        exp_params = 1, 2, 3
+
+        class TestInstance:
+            def _dispatch(self, method, params):
+                raise SimpleXMLRPCDispatcherTestCase.DispatchExc(
+                    method, params)
+
+        dispatcher = xmlrpc.server.SimpleXMLRPCDispatcher()
+        dispatcher.register_instance(TestInstance())
+        with self.assertRaises(self.DispatchExc) as exc_ctx:
+            dispatcher._dispatch(exp_method, exp_params)
+        self.assertEqual(exc_ctx.exception.args, (exp_method, exp_params))
+        self.assertIsNone(exc_ctx.exception.__cause__)
+        self.assertIsNone(exc_ctx.exception.__context__)
+
+    def test_registered_func_is_none(self):
+        """Calls explicitly registered function which is None"""
+
+        dispatcher = xmlrpc.server.SimpleXMLRPCDispatcher()
+        dispatcher.register_function(None, name='method')
+        with self.assertRaises(Exception, expected_regex='method'):
+            dispatcher._dispatch('method', ('param',))
+
+    def test_instance_has_no_func(self):
+        """Attempts to call nonexistent function on a registered instance"""
+
+        dispatcher = xmlrpc.server.SimpleXMLRPCDispatcher()
+        dispatcher.register_instance(object())
+        with self.assertRaises(Exception, expected_regex='method'):
+            dispatcher._dispatch('method', ('param',))
+
+    def test_cannot_locate_func(self):
+        """Calls a function that the dispatcher cannot locate"""
+
+        dispatcher = xmlrpc.server.SimpleXMLRPCDispatcher()
+        with self.assertRaises(Exception, expected_regex='method'):
+            dispatcher._dispatch('method', ('param',))
+
+
 class HelperTestCase(unittest.TestCase):
     def test_escape(self):
         self.assertEqual(xmlrpclib.escape("a&b"), "a&b")
@@ -1313,7 +1401,7 @@ def test_main():
             KeepaliveServerTestCase1, KeepaliveServerTestCase2,
             GzipServerTestCase, GzipUtilTestCase,
             MultiPathServerTestCase, ServerProxyTestCase, FailingServerTestCase,
-            CGIHandlerTestCase)
+            CGIHandlerTestCase, SimpleXMLRPCDispatcherTestCase)
 
 
 if __name__ == "__main__":

Lib/xmlrpc/server.py

@@ -392,17 +392,22 @@ class SimpleXMLRPCDispatcher:
         not be called.
         """
 
-        func = None
         try:
-            # check to see if a matching function has been registered
+            # call the matching registered function
             func = self.funcs[method]
         except KeyError:
-            if self.instance is not None:
-                # check for a _dispatch method
-                if hasattr(self.instance, '_dispatch'):
-                    return self.instance._dispatch(method, params)
+            pass
         else:
-                    # call instance method directly
+            if func is not None:
+                return func(*params)
+            raise Exception('method "%s" is not supported' % method)
+
+        if self.instance is not None:
+            if hasattr(self.instance, '_dispatch'):
+                # call the `_dispatch` method on the instance
+                return self.instance._dispatch(method, params)
+
+            # call the instance's method directly
             try:
                 func = resolve_dotted_attribute(
                     self.instance,
@@ -411,10 +416,10 @@ class SimpleXMLRPCDispatcher:
                 )
             except AttributeError:
                 pass
-
+            else:
                 if func is not None:
                     return func(*params)
-        else:
+
         raise Exception('method "%s" is not supported' % method)
 
 class SimpleXMLRPCRequestHandler(BaseHTTPRequestHandler):

Misc/NEWS

@@ -253,6 +253,10 @@ Extension Modules
 Library
 -------
 
+- bpo-29615: SimpleXMLRPCDispatcher no longer chains KeyError (or any other
+  exception) to exception(s) raised in the dispatched methods.
+  Patch by Petr Motejlek.
+
 - bpo-7769: Method register_function() of xmlrpc.server.SimpleXMLRPCDispatcher
   and its subclasses can now be used as a decorator.