From 28c7e1452ea9a9321a3430f3d9c16333d1e64182 Mon Sep 17 00:00:00 2001
From: Hanaasagi <ambiguous404@gmail.com>
Date: Wed, 21 Jul 2021 16:28:29 +0000
Subject: [PATCH] Fix: fix the code about handling `getaddrinfo` when disable
 ipv6 in CPython and enable ipv6 in system. Related to #5901; `getaddrinfo`
 will return an `(int, bytes)` tuple, if CPython could not handle the address
 family. It will cause a index out of range error in aiohttp.

---
 CHANGES/5901.bugfix | 4 ++++
 aiohttp/resolver.py | 6 +++++-
 2 files changed, 9 insertions(+), 1 deletion(-)
 create mode 100644 CHANGES/5901.bugfix

diff --git a/CHANGES/5901.bugfix b/CHANGES/5901.bugfix
new file mode 100644
index 00000000000..5c5940fde1b
--- /dev/null
+++ b/CHANGES/5901.bugfix
@@ -0,0 +1,4 @@
+Fix the error in handling the return value of `getaddrinfo`.
+`getaddrinfo` will return an `(int, bytes)` tuple, if CPython could not handle the address family.
+It will cause a index out of range error in aiohttp. For example, if user compile CPython with
+`--disable-ipv6` option but his system enable the ipv6.
diff --git a/aiohttp/resolver.py b/aiohttp/resolver.py
index e62e7f377b6..d82aee6acf3 100644
--- a/aiohttp/resolver.py
+++ b/aiohttp/resolver.py
@@ -37,7 +37,11 @@ async def resolve(
 
         hosts = []
         for family, _, proto, _, address in infos:
-            if family == socket.AF_INET6 and address[3]:  # type: ignore[misc]
+            if (
+                socket.has_ipv6
+                and family == socket.AF_INET6
+                and address[3]  # type: ignore[misc]
+            ):
                 # This is essential for link-local IPv6 addresses.
                 # LL IPv6 is a VERY rare case. Strictly speaking, we should use
                 # getnameinfo() unconditionally, but performance makes sense.