add new example scripts

backend/example_scripts/packet_loss.py

@@ -0,0 +1,67 @@
+#!/usr/bin/env python3
+"""Minimal NFQUEUE example: randomly drop packets by percentage."""
+
+import random
+import signal
+import sys
+
+from netfilterqueue import NetfilterQueue
+
+DEFAULT_LOSS_PERCENT = 10.0
+
+nfq = NetfilterQueue()
+loss_percent = DEFAULT_LOSS_PERCENT
+
+
+def _handle_packet(packet) -> None:
+    if random.random() < (loss_percent / 100.0):
+        packet.drop()
+        return
+
+    packet.accept()
+
+
+def _stop(_sig, _frame) -> None:
+    raise SystemExit(0)
+
+
+def main() -> int:
+    global loss_percent
+
+    if len(sys.argv) not in (2, 3):
+        print("Usage: packet_loss.py <qnum> [loss_percent]", file=sys.stderr)
+        return 1
+
+    try:
+        qnum = int(sys.argv[1])
+    except ValueError:
+        print("qnum must be an integer", file=sys.stderr)
+        return 1
+
+    if len(sys.argv) == 3:
+        try:
+            loss_percent = float(sys.argv[2])
+        except ValueError:
+            print("loss_percent must be a number between 0 and 100", file=sys.stderr)
+            return 1
+
+    if not 0.0 <= loss_percent <= 100.0:
+        print("loss_percent must be between 0 and 100", file=sys.stderr)
+        return 1
+
+    signal.signal(signal.SIGINT, _stop)
+    signal.signal(signal.SIGTERM, _stop)
+
+    nfq.bind(qnum, _handle_packet)
+    try:
+        nfq.run()
+    except KeyboardInterrupt:
+        pass
+    finally:
+        nfq.unbind()
+
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())