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gh-82535: Ignore address resolution failure in SysLogHandler constructor #154504

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gh-82535: Ignore address resolution failure in SysLogHandler constructor #154504

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6 changes: 5 additions & 1 deletion Lib/logging/handlers.py
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Original file line number Diff line number Diff line change
Expand Up @@ -901,7 +901,11 @@ def __init__(self, address=('localhost', SYSLOG_UDP_PORT),
self.socktype = socktype
self.timeout = timeout
self.socket = None
self.createSocket()
# The address is resolved again when emitting an event.
try:
self.createSocket()
except socket.gaierror:
pass

def _connect_unixsocket(self, address):
use_socktype = self.socktype
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18 changes: 18 additions & 0 deletions Lib/test/test_logging.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2155,6 +2155,24 @@ def tearDown(self):
self.server_class.address_family = socket.AF_INET
super(IPv6SysLogHandlerTest, self).tearDown()

@support.requires_working_socket()
class UnresolvableSysLogAddressTest(BaseTest):

"""Test for SysLogHandler with a temporarily unresolvable address."""

@patch('socket.getaddrinfo')
def test_unresolvable_address(self, mock_getaddrinfo):
# The address can be unresolvable when the handler is created.
mock_getaddrinfo.side_effect = socket.gaierror
hdlr = logging.handlers.SysLogHandler(('localhost', 514))
self.addCleanup(hdlr.close)
self.assertIsNone(hdlr.socket)
# It is resolved again when a record is emitted.
calls = mock_getaddrinfo.call_count
with support.captured_stderr():
hdlr.emit(logging.makeLogRecord({'msg': 'sp\xe4m'}))
self.assertGreater(mock_getaddrinfo.call_count, calls)

@support.requires_working_socket()
@threading_helper.requires_working_threading()
class HTTPHandlerTest(BaseTest):
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3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Library/2026-07-22-19-21-20.gh-issue-82535.METFqd.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
:class:`logging.handlers.SysLogHandler` no longer fails
if the address cannot be resolved when the handler is created.
The address is resolved again when a record is emitted.
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