Listen on dual stack

f2b-responder.py

@@ -1,11 +1,12 @@
 #!/usr/bin/env python
 
+from contextlib import suppress
 from http import HTTPStatus
 from http.server import SimpleHTTPRequestHandler, ThreadingHTTPServer
 from pathlib import Path
 from random import choices
 from signal import SIGTERM, signal
-from socket import socket
+from socket import AF_INET6, IPPROTO_IPV6, IPV6_V6ONLY, socket
 from sqlite3 import connect
 from string import ascii_lowercase
 from tempfile import gettempdir
@@ -111,7 +112,17 @@ class F2bRemoteRequestHandler(SimpleHTTPRequestHandler):
     do_HEAD = do_POST = __send_403
 
 
-server = ThreadingHTTPServer(
+class DualStackThreadingHttpServer(ThreadingHTTPServer):
+    address_family = AF_INET6
+
+    def server_bind(self):
+        # suppress exception when protocol is IPv4-only
+        with suppress(OSError):
+            self.socket.setsockopt(IPPROTO_IPV6, IPV6_V6ONLY, 0)
+        return super().server_bind()
+
+
+server = DualStackThreadingHttpServer(
     server_address=('', 8000), RequestHandlerClass=F2bRemoteRequestHandler,
     bind_and_activate=True)