make socket listen on IPv4 and IPv6

hbd/server.py

@@ -1,7 +1,7 @@
 """Server runtime: starts UDP listener, HTTP server and websocket stubs."""
 import asyncio
 import logging
-import atexit
+import socket
 import time
 import signal
 import sys
@@ -85,8 +85,20 @@ async def _run_async(config):
     email = notify_mod.email
     pushmsg = notify_mod.pushmsg_from_config
 
+    sock = socket.socket(socket.AF_INET6, socket.SOCK_DGRAM)
+    # Disable IPV6_V6ONLY option to enable dual-stack (listen on IPv4 as well)
+    # This option is system-dependent; on many systems, setting it to False enables
+    # the socket to handle both IPv4 and IPv6 traffic.
+    try:
+        sock.setsockopt(socket.IPPROTO_IPV6, socket.IPV6_V6ONLY, False)
+    except OSError as e:
+        logger.error(f"Warning: Could not set IPV6_V6ONLY to False. System may not support dual-stack or option is unavailable. Error: {e}")
+
+    # 3. Bind to all interfaces (::) on a specific port
+
     # UDP server endpoint (handler wired to handle_datagram with context)
-    bind_addr = ("0.0.0.0", config.get("hb_port", 50003))
+    bind_addr = ("::", config.get("hb_port", 50003))
+    sock.bind(bind_addr)
     logger.info("Starting UDP server on %s:%s", *bind_addr)
 
     def udp_handler(msg, addr, transport):
@@ -104,7 +116,7 @@ async def _run_async(config):
 
     transport, protocol = await loop.create_datagram_endpoint(
         lambda: udp.EchoServerProtocol(config=config, handler=udp_handler),
-        local_addr=bind_addr,
+        sock=sock,
     )
 
     # HTTP server (asyncio-based via aiohttp)