From 7cdc31a14c824000cbe8b487900c9826a33f6940 Mon Sep 17 00:00:00 2001
From: "Jason R. Coombs" <jaraco@jaraco.com>
Date: Mon, 6 Jan 2020 07:59:36 -0500
Subject: bpo-38907: Suppress any exception when attempting to set V6ONLY.
 (GH-17864)

Fixes error attempting to bind to IPv4 address.
---
 Lib/http/server.py | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/Lib/http/server.py b/Lib/http/server.py
index b9a2717..c6e5ed6 100644
--- a/Lib/http/server.py
+++ b/Lib/http/server.py
@@ -103,6 +103,7 @@ import socketserver
 import sys
 import time
 import urllib.parse
+import contextlib
 from functools import partial
 
 from http import HTTPStatus
@@ -1286,7 +1287,10 @@ if __name__ == '__main__':
     # ensure dual-stack is not disabled; ref #38907
     class DualStackServer(ThreadingHTTPServer):
         def server_bind(self):
-            self.socket.setsockopt(socket.IPPROTO_IPV6, socket.IPV6_V6ONLY, 0)
+            # suppress exception when protocol is IPv4
+            with contextlib.suppress(Exception):
+                self.socket.setsockopt(
+                    socket.IPPROTO_IPV6, socket.IPV6_V6ONLY, 0)
             return super().server_bind()
 
     test(
-- 
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