gh-59060: Support IPv6 in logging.handlers.DatagramHandler

It always created an IPv4 socket, so sending to an IPv6 address failed and
the log record was silently lost.  Create a socket of the family of the
resolved address if the host has no IPv4 address.

Also add a timeout to the waits in DatagramHandlerTest.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: serhiy-storchaka

Doc/library/logging.handlers.rst

@@ -594,6 +594,9 @@ over UDP sockets.
       If ``port`` is specified as ``None``, a Unix domain socket is created
       using the value in ``host`` - otherwise, a UDP socket is created.
 
+   .. versionchanged:: next
+      Added support for IPv6.
+
    .. method:: emit()
 
       Pickles the record's attribute dictionary and writes it to the socket in

Doc/whatsnew/3.16.rst

@@ -349,6 +349,11 @@ logging
   before the rotation interval expires.
   (Contributed by Iván Márton and Serhiy Storchaka in :gh:`84649`.)
 
+* :class:`~logging.handlers.DatagramHandler` now supports IPv6.
+  Previously it always created an IPv4 socket, so sending to an IPv6 address
+  failed and the log record was silently lost.
+  (Contributed by Serhiy Storchaka in :gh:`59060`.)
+
 
 lzma
 ----

Lib/logging/handlers.py

@@ -758,6 +758,16 @@ def makeSocket(self):
             family = socket.AF_UNIX
         else:
             family = socket.AF_INET
+            # The host can have no IPv4 address, for example if it is an
+            # IPv6 address.  Leave resolution errors to sendto().
+            try:
+                infos = socket.getaddrinfo(self.host, self.port,
+                                           type=socket.SOCK_DGRAM)
+            except OSError:
+                pass
+            else:
+                if not any(info[0] == family for info in infos):
+                    family = infos[0][0]
         s = socket.socket(family, socket.SOCK_DGRAM)
         return s
 

Lib/test/test_logging.py

@@ -1982,7 +1982,7 @@ def setUp(self):
         server.ready.wait()
         hcls = logging.handlers.DatagramHandler
         if isinstance(server.server_address, tuple):
-            self.sock_hdlr = hcls('localhost', server.port)
+            self.sock_hdlr = hcls(self.address[0], server.port)
         else:
             self.sock_hdlr = hcls(server.server_address, None)
         self.log_output = ''
@@ -2015,12 +2015,29 @@ def test_output(self):
             self.skipTest(self.server_exception)
         logger = logging.getLogger("udp")
         logger.error("spam")
-        self.handled.wait()
+        self.handled.wait(support.LONG_TIMEOUT)
         self.handled.clear()
         logger.error("eggs")
-        self.handled.wait()
+        self.handled.wait(support.LONG_TIMEOUT)
         self.assertEqual(self.log_output, "spam\neggs\n")
 
+@unittest.skipUnless(socket_helper.IPV6_ENABLED,
+                     'IPv6 support required for this test.')
+class IPv6DatagramHandlerTest(DatagramHandlerTest):
+
+    """Test for DatagramHandler with IPv6 host."""
+
+    server_class = TestUDPServer
+    address = ('::1', 0)
+
+    def setUp(self):
+        self.server_class.address_family = socket.AF_INET6
+        super().setUp()
+
+    def tearDown(self):
+        self.server_class.address_family = socket.AF_INET
+        super().tearDown()
+
 @unittest.skipUnless(hasattr(socket, "AF_UNIX"), "Unix sockets required")
 class UnixDatagramHandlerTest(DatagramHandlerTest):
 

Misc/NEWS.d/next/Library/2026-07-22-16-20-17.gh-issue-59060.1nZ8hJ.rst

@@ -0,0 +1,4 @@
+:class:`logging.handlers.DatagramHandler` now supports IPv6:
+it creates an IPv6 socket if the host has no IPv4 address.
+Previously it always created an IPv4 socket,
+so the log records were silently lost.