tests: Add multicast tester library for topotests

Signed-off-by: Martin Winter <mwinter@opensourcerouting.org>

diff --git a/tests/topotests/lib/mcast-tester.py b/tests/topotests/lib/mcast-tester.py
new file mode 100755 (executable)
index 0000000..07e4ab8
--- /dev/null
+++ b/tests/topotests/lib/mcast-tester.py
@@ -0,0 +1,129 @@
+#!/usr/bin/env python3
+#
+# Copyright (C) 2021 by
+# Network Device Education Foundation, Inc. ("NetDEF")
+#
+# Permission to use, copy, modify, and/or distribute this software for any
+# purpose with or without fee is hereby granted, provided that the above
+# copyright notice and this permission notice appear in all copies.
+#
+# THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+# REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+# AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+# INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+# LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+# OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+# PERFORMANCE OF THIS SOFTWARE.
+
+"""
+Subscribe to a multicast group so that the kernel sends an IGMP JOIN
+for the multicast group we subscribed to.
+"""
+
+import argparse
+import os
+import json
+import socket
+import subprocess
+import struct
+import sys
+import time
+
+#
+# Functions
+#
+def interface_name_to_index(name):
+    "Gets the interface index using its name. Returns None on failure."
+    interfaces = json.loads(
+        subprocess.check_output('ip -j link show', shell=True))
+
+    for interface in interfaces:
+        if interface['ifname'] == name:
+            return interface['ifindex']
+
+    return None
+
+
+def multicast_join(sock, ifindex, group, port):
+    "Joins a multicast group."
+    mreq = struct.pack(
+        "=4sLL", socket.inet_aton(args.group), socket.INADDR_ANY, ifindex
+    )
+
+    sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
+    sock.bind((group, port))
+    sock.setsockopt(socket.IPPROTO_IP, socket.IP_ADD_MEMBERSHIP, mreq)
+
+
+#
+# Main code.
+#
+parser = argparse.ArgumentParser(description="Multicast RX utility")
+parser.add_argument('socket', help='Point to topotest UNIX socket')
+parser.add_argument('group', help='Multicast IP')
+parser.add_argument('interface', help='Interface name')
+parser.add_argument(
+    '--send',
+    help='Transmit instead of join with interval (defaults to 0.7 sec)',
+    type=float, default=0)
+args = parser.parse_args()
+
+ttl = 16
+port = 1000
+
+# Get interface index/validate.
+ifindex = interface_name_to_index(args.interface)
+if ifindex is None:
+    sys.stderr.write('Interface {} does not exists\n'.format(args.interface))
+    sys.exit(1)
+
+# We need root privileges to set up multicast.
+if os.geteuid() != 0:
+    sys.stderr.write("ERROR: You must have root privileges\n")
+    sys.exit(1)
+
+# Wait for topotest to synchronize with us.
+toposock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM, 0)
+while True:
+    try:
+        toposock.connect(args.socket)
+        break
+    except ConnectionRefusedError:
+        time.sleep(1)
+        continue
+
+msock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
+if args.send > 0:
+    # Prepare multicast bit in that interface.
+    msock.setsockopt(
+        socket.SOL_SOCKET, 25,
+        struct.pack("%ds" % len(args.interface),
+                    args.interface.encode('utf-8')))
+    # Set packets TTL.
+    msock.setsockopt(
+        socket.IPPROTO_IP, socket.IP_MULTICAST_TTL, struct.pack("b", ttl))
+    # Block to ensure packet send.
+    msock.setblocking(True)
+    # Set topotest socket non blocking so we can multiplex the main loop.
+    toposock.setblocking(False)
+else:
+    multicast_join(msock, ifindex, args.group, port)
+
+counter = 0
+while True:
+    if args.send > 0:
+        msock.sendto(b"test %d" % counter, (args.group, port))
+        counter += 1
+        time.sleep(args.send)
+
+    try:
+        data = toposock.recv(1)
+        if data == b'':
+            print(' -> Connection closed')
+            break
+    except BlockingIOError:
+        continue
+
+msock.close()
+
+sys.exit(0)