[tests] fix key_id_mode handling and add exception handle (#4927)

This commit fixes key_id_mode handling and added exception handling
when key_id_mode is 0.

According to IEEE Std 802.15.4-2015, when Key Id Mode is 0x00:

    Key is determined implicitly from the originator and recipient(s)
    of the frame, as indicated in the frame header.

Our test scripts cannot handle such packets. If we leave key_id_mode =
0 case unhandled, we would get some exceptions that may cause
developers to think that something is wrong. However dropping packets
in this case is a normal behavior.

tests/scripts/thread-cert/mac802154.py

@@ -42,6 +42,15 @@ from net_crypto import (
 )
 
 
+class KeyIdMode0Exception(Exception):
+    """
+    Raised when key id mode of packet is 0.
+    Such packet wouldn't be handled in test scripts,
+    but it's not abnormal behavior.
+    """
+    pass
+
+
 class DeviceDescriptors:
     """Class representing 802.15.4 Device Descriptors."""
 
@@ -377,11 +386,13 @@ class MacFrame:
         key_id_mode = (security_control & 0x18) >> 3
 
         if key_id_mode == 0:
-            key_id = data.read(9)
+            raise KeyIdMode0Exception
         elif key_id_mode == 1:
             key_id = data.read(1)
         elif key_id_mode == 2:
             key_id = data.read(5)
+        elif key_id_mode == 3:
+            key_id = data.read(9)
         else:
             pass
 

tests/scripts/thread-cert/message.py

@@ -41,6 +41,10 @@ import mle
 from enum import IntEnum
 
 
+class DropPacketException(Exception):
+    pass
+
+
 class MessageType(IntEnum):
     MLE = 0
     COAP = 1
@@ -598,30 +602,38 @@ class MessageFactory:
         self._lowpan_parser.set_lowpan_context(cid, prefix)
 
     def create(self, data):
-        message = Message()
-        message.channel = struct.unpack(">B", data.read(1))
+        try:
+            message = Message()
+            message.channel = struct.unpack(">B", data.read(1))
 
-        # Parse MAC header
-        mac_frame = self._parse_mac_frame(data)
-        message.mac_header = mac_frame.header
+            # Parse MAC header
+            mac_frame = self._parse_mac_frame(data)
+            message.mac_header = mac_frame.header
 
-        if message.mac_header.frame_type != mac802154.MacHeader.FrameType.DATA:
-            return [message]
+            if message.mac_header.frame_type != mac802154.MacHeader.FrameType.DATA:
+                return [message]
 
-        message_info = common.MessageInfo()
-        message_info.source_mac_address = message.mac_header.src_address
-        message_info.destination_mac_address = message.mac_header.dest_address
+            message_info = common.MessageInfo()
+            message_info.source_mac_address = message.mac_header.src_address
+            message_info.destination_mac_address = message.mac_header.dest_address
 
-        # Create stream with 6LoWPAN datagram
-        lowpan_payload = io.BytesIO(mac_frame.payload.data)
+            # Create stream with 6LoWPAN datagram
+            lowpan_payload = io.BytesIO(mac_frame.payload.data)
 
-        ipv6_packet = self._lowpan_parser.parse(lowpan_payload, message_info)
-        if ipv6_packet is None:
-            return [message]
+            ipv6_packet = self._lowpan_parser.parse(lowpan_payload,
+                                                    message_info)
+            if ipv6_packet is None:
+                return [message]
 
-        message.ipv6_packet = ipv6_packet
+            message.ipv6_packet = ipv6_packet
 
-        if message.type == MessageType.MLE:
-            self._add_device_descriptors(message)
+            if message.type == MessageType.MLE:
+                self._add_device_descriptors(message)
 
-        return message.try_extract_dtls_messages()
+            return message.try_extract_dtls_messages()
+
+        except mac802154.KeyIdMode0Exception:
+            print(
+                'Received packet with key_id_mode = 0, cannot be handled in test scripts'
+            )
+            raise DropPacketException

tests/scripts/thread-cert/simulator.py

@@ -175,14 +175,18 @@ class VirtualTime(BaseSimulator):
         self.sock.close()
         self.sock = None
 
-    def _add_message(self, nodeid, message):
+    def _add_message(self, nodeid, message_obj):
         addr = ('127.0.0.1', self.port + nodeid)
 
         # Ignore any exceptions
         try:
-            messages = self._message_factory.create(io.BytesIO(message))
+            messages = self._message_factory.create(io.BytesIO(message_obj))
             self.devices[addr]['msgs'] += messages
 
+        except message.DropPacketException:
+            print(
+                'Drop current packet because it cannot be handled in test scripts'
+            )
         except Exception as e:
             # Just print the exception to the console
             print("EXCEPTION: %s" % e)