Workaround issue with dnspython >= 2.3.0

The dnspython module >= 2.3.0 now validates the opcodes used when building DNS messages. This breaks Designate because designate is using an "unassigned"[1] opcode 14 for command/control messages inside the backend agents framework.

This patch adds a workaround to override the dnspython opcode enum to include
opcode 14. This will give us time to either remove the agent framework via deprecation or to change the agent framework protocol to not rely on unassigned opcode values.

[1] https://www.iana.org/assignments/dns-parameters/dns-parameters.xhtml#dns-parameters-5

Partial-Bug: #2002950

Change-Id: If10443b2e361aa1b467fb64124ad3c82540bcddd

designate/agent/handler.py

@@ -56,6 +56,10 @@ class RequestHandler(object):
         backend_driver = cfg.CONF['service:agent'].backend_driver
         self.backend = agent_backend.get_backend(backend_driver, self)
 
+        # TODO(johnsom) Remove this after the agents framework is removed or
+        # the protocol has been updated to not use an unassigned opcode(14).
+        dns.opcode.Opcode = pcodes.OpcodeWith14
+
     def __call__(self, request):
         """
         :param request: DNS Request Message

designate/backend/agent.py

@@ -59,6 +59,10 @@ class AgentPoolBackend(base.Backend):
         self.max_retries = CONF['service:worker'].poll_max_retries
         # FIXME: the agent retries creating zones without any interval
 
+        # TODO(johnsom) Remove this after the agents framework is removed or
+        # the protocol has been updated to not use an unassigned opcode(14).
+        dns.opcode.Opcode = private_codes.OpcodeWith14
+
     def create_zone(self, context, zone):
         LOG.debug('Create Zone')
         response = self._make_and_send_dns_message(

designate/backend/private_codes.py

@@ -13,7 +13,7 @@
 # WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 # License for the specific language governing permissions and limitations
 # under the License.
-
+import dns
 
 """
     backend.private_codes
@@ -33,3 +33,55 @@ SUCCESS = 65280
 FAILURE = 65281
 CREATE = 65282
 DELETE = 65283
+
+# TODO(johnsom) Remove this after the agents framework is removed or the
+#               protocol has been updated to not use an unassigned opcode(14).
+#
+# This is an Opcode Enum class that includes the unassigned[1][2]
+# opcode 14 used in the Designate agent framework until the agent framework
+# can be removed or fixed.
+# [1] https://www.rfc-editor.org/rfc/rfc6895.html#section-2.2
+# [2] https://www.iana.org/assignments/dns-parameters/ \
+#     dns-parameters.xhtml#dns-parameters-5
+#
+# Based on dns.opcode.Opcode:
+#
+# Copyright (C) Dnspython Contributors, see LICENSE for text of ISC license
+# Copyright (C) 2001-2017 Nominum, Inc.
+#
+# Permission to use, copy, modify, and distribute this software and its
+# documentation for any purpose with or without fee is hereby granted,
+# provided that the above copyright notice and this permission notice
+# appear in all copies.
+#
+# THE SOFTWARE IS PROVIDED "AS IS" AND NOMINUM DISCLAIMS ALL WARRANTIES
+# WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+# MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL NOMINUM BE LIABLE FOR
+# ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+# WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+# ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
+# OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+
+
+class OpcodeWith14(dns.enum.IntEnum):
+    #: Query
+    QUERY = 0
+    #: Inverse Query (historical)
+    IQUERY = 1
+    #: Server Status (unspecified and unimplemented anywhere)
+    STATUS = 2
+    #: Notify
+    NOTIFY = 4
+    #: Dynamic Update
+    UPDATE = 5
+
+    # Unassigned, but used by Designate for command/control in the agents
+    UNASSIGNED14 = 14
+
+    @classmethod
+    def _maximum(cls):
+        return 15
+
+    @classmethod
+    def _unknown_exception_class(cls):
+        return dns.opcode.UnknownOpcode

designate/tests/unit/agent/test_handler.py

@@ -21,6 +21,7 @@ import dns.resolver
 
 import designate
 from designate.agent import handler
+from designate.backend import private_codes
 import designate.tests
 
 
@@ -35,6 +36,10 @@ class AgentRequestHandlerTest(designate.tests.TestCase):
         self.handler = handler.RequestHandler()
         self.addr = ['0.0.0.0', 5558]
 
+        # TODO(johnsom) Remove this after the agents framework is removed or
+        # the protocol has been updated to not use an unassigned opcode(14).
+        dns.opcode.Opcode = private_codes.OpcodeWith14
+
     def test_init(self):
         self.CONF.set_override('masters', ['192.168.0.1', '192.168.0.2'],
                                'service:agent')

releasenotes/notes/Workaround-unassigned-opcode-14-d5e1c759db58bb10.yaml

@@ -0,0 +1,7 @@
+---
+fixes:
+  - |
+    Workaround the use of an unassigned opcode(14) by Designate that fails
+    validation when used with dnspython >= 2.3.0.
+
+    `LP#2002950 <https://launchpad.net/bugs/2002950>`__