pf tests: Add option to send fragmented packets

[vegeta_tuxpowered.net]

Summary

Add option to send fragmented packets and to properly sniff them by reassembling them by the sniffer itself.

Sponsored by: InnoGames GmbH

tests/sys/netpfil/common/sniffer.py

 # SUCH DAMAGE.
 #
 
 import threading
 import scapy.all as sp
 import sys
 
 class Sniffer(threading.Thread):
-        def __init__(self, args, check_function, recvif, timeout=3):
+        def __init__(self, args, check_function, recvif, timeout=3, defrag=False):
                 threading.Thread.__init__(self)
 
                 self._sem = threading.Semaphore(0)
                 self._args = args
                 self._timeout = timeout
                 self._recvif = recvif
                 self._check_function = check_function
+                self._defrag = defrag
                 self.correctPackets = 0
 
                 self.start()
                 if not self._sem.acquire(timeout=30):
                         raise Exception("Failed to start sniffer")
 
         def _checkPacket(self, packet):
                 ret = self._check_function(self._args, packet)
                 if ret:
                         self.correctPackets += 1
                 return ret
 
         def _startedCb(self):
                 self._sem.release()
 
         def run(self):
                 self.packets = []
+                if self._defrag:
+                        # With fragment reassembly we can't stop the sniffer after catching
+                        # the good packets, as those have not been reassembled. We must
+                        #  wait for sniffer to finish and check returned packets instead.
+                        self.packets = sp.sniff(session=sp.IPSession, iface=self._recvif,
+                                timeout=self._timeout, started_callback=self._startedCb)
+                        for p in self.packets:
+                                self._checkPacket(p)
+                else:
                         self.packets = sp.sniff(iface=self._recvif,
                                 stop_filter=self._checkPacket, timeout=self._timeout,
                                 started_callback=self._startedCb)