Adding udp_listen

Author: freol35241

README.md

@@ -28,6 +28,8 @@ The following "special" binaries are included in the toolbox:
   Prepend a RFC3339 timestamp of nanosecond resolution to each line on stdin
 * **to_csv**
   Processes a crowsnest log file into a set of "topic-specific" csv files
+* **udp_listen**
+  Eavesdrop onto UDP traffic and output to stdout, currently only supports multicast.
 
 
 ## Recipes
@@ -36,7 +38,7 @@ The following are "recipes" for "run" commands that can be used with this image.
 
 * Injecting data from "any" source into a mqtt broker using the standard brefv format (examplified by a multicast stream). Every UDP packet gets base64-encoded and packaged into a brefv envelope and then published to the broker:
   ```
-  socat -u UDP4-RECVFROM:60002,reuseaddr,ip-add-membership=239.192.0.2:enp2s0,fork SYSTEM:echo $$(base64 --wrap=0) \
+  udp_listen --encode multicast 239.192.0.2 60002 --interface=172.16.6.1 \
   | raw_to_brefv \
   | mosquitto_pub -l -t '<topic>'
   ```

bin/udp_listen

@@ -0,0 +1,77 @@
+#!/usr/bin/env python3.9
+
+"""
+Command line utility tool for listening to udp traffic and
+outputting to stdout.
+"""
+
+import sys
+import socket
+import struct
+import argparse
+from base64 import b64encode
+
+
+def process_multicast(args: argparse.Namespace):
+    """Listen in on multicast traffic and output to stdout
+
+    Args:
+        args (argparse.Namespace): Command-line arguments
+    """
+
+    sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, socket.IPPROTO_UDP)
+    sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
+    sock.setsockopt(socket.IPPROTO_IP, socket.IP_MULTICAST_TTL, args.TTL)
+    sock.setsockopt(socket.IPPROTO_IP, socket.IP_MULTICAST_LOOP, int(args.loopback))
+    sock.setsockopt(
+        socket.IPPROTO_IP, socket.IP_MULTICAST_IF, socket.inet_aton(args.interface)
+    )
+    sock.setsockopt(
+        socket.IPPROTO_IP,
+        socket.IP_ADD_MEMBERSHIP,
+        socket.inet_aton(args.group) + socket.inet_aton(args.interface),
+    )
+    sock.bind((args.group, args.port))
+    sock.setblocking(True)
+
+    try:
+        while True:
+            data = sock.recvmsg(65535)[0]
+            sys.stdout.write(
+                (b64encode(data).decode() + "\n") if args.encode else data.decode()
+            )
+            sys.stdout.flush()
+    finally:
+        sock.setsockopt(
+            socket.IPPROTO_IP,
+            socket.IP_DROP_MEMBERSHIP,
+            socket.inet_aton(args.group) + socket.inet_aton(args.interface),
+        )
+        sock.close()
+
+
+if __name__ == "__main__":
+    parser = argparse.ArgumentParser(description="UDP listener")
+    parser.add_argument(
+        "--encode",
+        action="store_true",
+        default=False,
+        help="base64 encode each packet content",
+    )
+
+    sub_commands = parser.add_subparsers()
+
+    multicast_parser = sub_commands.add_parser("multicast")
+    multicast_parser.add_argument("group", type=str)
+    multicast_parser.add_argument("port", type=int)
+    multicast_parser.add_argument("--interface", type=str, default="0.0.0.0")
+    multicast_parser.add_argument("--loopback", type=bool, default=False)
+    multicast_parser.add_argument(
+        "--TTL",
+        type=int,
+        default=1,
+    )
+    multicast_parser.set_defaults(func=process_multicast)
+
+    args = parser.parse_args()
+    args.func(args)