[master] [2013] make sure datasrc error is converted to SERVFAIL.

also update the ddns handle_request() doc clarfiying exception considerations.

src/bin/ddns/ddns.py.in

@@ -315,6 +315,13 @@ class DDNSServer:
         SocketSessionReceiver, i.e. tuple
         (socket, local_address, remote_address, data).
 
+        In general, this method doesn't propagate exceptions outside the
+        method.  Most of protocol or system errors will result in an error
+        response to the update client or dropping the update request.
+        The update session class should also ensure this.  Critical exceptions
+        such as memory allocation failure will be propagated, however, and
+        will subsequently terminate the server process.
+
         """
         # give tuple elements intuitive names
         (sock, local_addr, remote_addr, req_data) = req_session
@@ -336,9 +343,6 @@ class DDNSServer:
             logger.error(DDNS_REQUEST_PARSE_FAIL, ex)
             return False
 
-        # TODO: Don't propagate most of the exceptions (like datasrc errors),
-        # just drop the packet.
-
         # Let an update session object handle the request.  Note: things around
         # ZoneConfig will soon be substantially revised.  For now we don't
         # bother to generalize it.

src/lib/python/isc/ddns/libddns_messages.mes

@@ -15,6 +15,17 @@
 # No namespace declaration - these constants go in the global namespace
 # of the libddns_messages python module.
 
+% LIBDDNS_DATASRC_ERROR update client %1 failed due to data source error: %2
+An update attempt failed due to some error in the corresponding data
+source.  This is generally an unexpected event, but can still happen
+for various reasons such as DB lock contention or a failure of the
+backend DB server.  The cause of the error is also logged.  It's
+advisable to check the message, and, if necessary, take an appropriate
+action (e.g., restarting the DB server if it dies).  If this message
+is logged the data source isn't modified due to the
+corresponding update request.  When used by the b10-ddns, the server
+will return a response with an RCODE of SERVFAIL.
+
 % LIBDDNS_PREREQ_FORMERR update client %1 for zone %2: Format error in prerequisite (%3). Non-zero TTL.
 The prerequisite with the given name, class and type is not well-formed.
 The specific prerequisite is shown. In this case, it has a non-zero TTL value.

src/lib/python/isc/ddns/session.py

@@ -145,6 +145,11 @@ class UpdateSession:
                 return UPDATE_ERROR, None, None
             self.__message = None
             return UPDATE_DROP, None, None
+        except isc.datasrc.Error as e:
+            logger.error(LIBDDNS_DATASRC_ERROR,
+                         ClientFormatter(self.__client_addr, self.__tsig), e)
+            self.__make_response(Rcode.SERVFAIL())
+            return UPDATE_ERROR, None, None
 
     def __get_update_zone(self):
         '''Parse the zone section and find the zone to be updated.

src/lib/python/isc/ddns/tests/session_tests.py

@@ -160,6 +160,21 @@ class SessionTest(SesseionTestBase):
         # zone class doesn't match
         self.check_notauth(Name('example.org'), RRClass.CH())
 
+    def test_update_datasrc_error(self):
+        # if the data source client raises an exception, it should result in
+        # a SERVFAIL.
+        class BadDataSourceClient:
+            def find_zone(self, name):
+                raise isc.datasrc.Error('faked exception')
+        msg = create_update_msg(zones=[Question(TEST_ZONE_NAME, TEST_RRCLASS,
+                                                RRType.SOA())])
+        session = UpdateSession(msg, TEST_CLIENT4,
+                                ZoneConfig([(TEST_ZONE_NAME, TEST_RRCLASS)],
+                                           TEST_RRCLASS,
+                                           BadDataSourceClient()))
+        self.assertEqual(UPDATE_ERROR, session.handle()[0])
+        self.check_response(session.get_message(), Rcode.SERVFAIL())
+
     def __prereq_helper(self, method, expected, rrset):
         '''Calls the given method with self._datasrc_client
            and the given rrset, and compares the return value.