igmp: fix IGMPv3()/IGMPv3mr() compatibility

scapy/layers/igmp.py

@@ -159,6 +159,10 @@ def dispatch_hook(cls, _pkt=None, *args, **kargs):
             elif typ == 0x32:
                 return IGMPv3_MRT
 
+        # IGMPv3() has no raw bytes yet. Keep that class; falling through to
+        # IGMP_MQ made the pre-2.8 stack IGMPv3()/IGMPv3mr() a v1/v2 query.
+        if issubclass(cls, IGMPv3):
+            return cls
         return IGMP_MQ
 
     def answers(self, other):
@@ -252,6 +256,41 @@ def mysummary(self):
         else:
             return self.sprintf(f"IGMPv3 %{t}.type%")
 
+    def _stacked_full_message(self, payload):
+        """True when payload is already a complete IGMPv3 message.
+
+        contrib.igmpv3 aliases IGMPv3mr to IGMPv3_MR. Code written for 2.7
+        still does IGMPv3()/IGMPv3mr(), which used to be one report. IGMPv3_MR
+        already includes the header, so keep that message and drop this one.
+        """
+        return (
+            type(self) is IGMPv3
+            and isinstance(payload, IGMPv3)
+            and type(payload) is not IGMPv3
+        )
+
+    def add_payload(self, payload):
+        # IP()/IGMPv3()/IGMPv3_MR() lands here: IP.add_payload delegates to us.
+        if self._stacked_full_message(payload) and self.underlayer is not None:
+            under = self.underlayer
+            under.remove_payload()
+            under.add_payload(payload)
+            return
+        super(IGMPv3, self).add_payload(payload)
+
+    def __div__(self, other):
+        if isinstance(other, Packet) and self._stacked_full_message(other):
+            other = other.copy()
+            if self.underlayer is not None:
+                under = self.underlayer.copy()
+                under.remove_payload()
+                under.add_payload(other)
+                return under
+            return other
+        return super(IGMPv3, self).__div__(other)
+
+    __truediv__ = __div__
+
 
 class IGMPv3_MQ(IGMPv3):
     """

test/scapy/layers/igmp.uts

@@ -121,3 +121,17 @@ assert isinstance(IGMP(raw(IGMPv3_MQ())), IGMPv3)
 
 pkt = IGMPv3_MR(records=[IGMPv3_MR_Group(maddr="127.0.0.1")])
 assert pkt.summary() == 'IGMPv3 Version 3 - Membership Report'
+
+= IGMPv3 - legacy contrib stack is one report
+
+load_contrib("igmpv3")
+from scapy.contrib.igmpv3 import IGMPv3mr, IGMPv3gr
+group = "232.1.1.12"
+sources = ["10.0.0.1", "10.0.0.2"]
+legacy = IGMPv3()/IGMPv3mr(records=[IGMPv3gr(rtype=1, maddr=group, srcaddrs=sources)])
+current = IGMPv3_MR(records=[IGMPv3_MR_Group(rtype=1, maddr=group, srcaddrs=sources)])
+assert bytes(legacy) == bytes(current)
+assert bytes(legacy)[0] == 0x22
+legacy_ip = IP(src="192.168.10.2", dst="224.0.0.22")/IGMPv3()/IGMPv3mr(records=[IGMPv3gr(rtype=1, maddr=group, srcaddrs=sources)])
+assert bytes(legacy_ip[IGMPv3]) == bytes(current)
+assert IGMPv3_MR in legacy_ip