add an example

examples/ipcounter.py

+"""example program to count IPv4 and IPv6 packets"""
+
+from asyncio import get_event_loop, sleep
+from ebpfcat.hashmap import HashMap
+from ebpfcat.xdp import PacketVar, XDP, XDPExitCode, XDPFlags
+
+class IPCount(XDP):
+    license = "GPL"
+
+    minimumPacketSize = 14
+
+    userspace = HashMap()
+    ipv4count = userspace.globalVar()
+    ipv6count = userspace.globalVar()
+    ethertype = PacketVar(12, "!H")
+
+    def program(self):
+        with self.ethertype == 0x800 as Else:
+            self.ipv4count += 1
+        with Else, self.ethertype == 0x86dd: 
+            self.ipv6count += 1
+        self.exit(XDPExitCode.PASS)
+
+
+async def main():
+    c = IPCount()
+
+    async with c.run("eth0", XDPFlags.DRV_MODE):
+        for i in range(10):
+            await sleep(0.1)
+            print(f"packets arrived: IPv4 {c.ipv4count} IPv6 {c.ipv6count}")
+
+
+if __name__ == "__main__":
+    get_event_loop().run_until_complete(main())