From cc46702ef7b6a3ff339e253f3f1246095a139fbe Mon Sep 17 00:00:00 2001
From: Serhiy Storchaka <storchaka@gmail.com>
Date: Sun, 28 Dec 2025 20:28:17 +0200
Subject: [PATCH] gh-143237: Fix support of named pipes in the rotating logging
 handlers

This fixes regression introduced in GH-105887.
---
 Lib/logging/handlers.py                       |  6 ++++-
 Lib/test/test_logging.py                      | 23 +++++++++++++++++++
 ...-12-28-20-28-05.gh-issue-143237.q1ymuA.rst |  1 +
 3 files changed, 29 insertions(+), 1 deletion(-)
 create mode 100644 Misc/NEWS.d/next/Library/2025-12-28-20-28-05.gh-issue-143237.q1ymuA.rst

diff --git a/Lib/logging/handlers.py b/Lib/logging/handlers.py
index 2748b5941eade2..4a07258f8d6d07 100644
--- a/Lib/logging/handlers.py
+++ b/Lib/logging/handlers.py
@@ -196,7 +196,11 @@ def shouldRollover(self, record):
         if self.stream is None:                 # delay was set...
             self.stream = self._open()
         if self.maxBytes > 0:                   # are we rolling over?
-            pos = self.stream.tell()
+            try:
+                pos = self.stream.tell()
+            except io.UnsupportedOperation:
+                # gh-143237: Never rollover a named pipe.
+                return False
             if not pos:
                 # gh-116263: Never rollover an empty file
                 return False
diff --git a/Lib/test/test_logging.py b/Lib/test/test_logging.py
index 8815426fc99c39..cf712ef4aa1a53 100644
--- a/Lib/test/test_logging.py
+++ b/Lib/test/test_logging.py
@@ -6369,6 +6369,29 @@ def test_should_not_rollover_non_file(self):
         self.assertFalse(rh.shouldRollover(self.next_rec()))
         rh.close()
 
+    @unittest.skipUnless(hasattr(os, "mkfifo"), 'requires os.mkfifo()')
+    def test_should_not_rollover_named_pipe(self):
+        # gh-143237 - test with non-seekable special file (named pipe)
+        filename = os_helper.TESTFN
+        self.addCleanup(os_helper.unlink, filename)
+        try:
+            os.mkfifo(filename)
+        except PermissionError as e:
+            self.skipTest('os.mkfifo(): %s' % e)
+
+        def other_side():
+            with open(filename, 'rb') as f:
+                f.read(1)
+
+        thread = threading.Thread(target=other_side)
+        with threading_helper.start_threads([thread]):
+            rh = logging.handlers.RotatingFileHandler(
+                    filename, encoding="utf-8", maxBytes=1)
+            try:
+                self.assertFalse(rh.shouldRollover(self.next_rec()))
+            finally:
+                rh.close()
+
     def test_should_rollover(self):
         with open(self.fn, 'wb') as f:
             f.write(b'\n')
diff --git a/Misc/NEWS.d/next/Library/2025-12-28-20-28-05.gh-issue-143237.q1ymuA.rst b/Misc/NEWS.d/next/Library/2025-12-28-20-28-05.gh-issue-143237.q1ymuA.rst
new file mode 100644
index 00000000000000..131bebcd984ac2
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2025-12-28-20-28-05.gh-issue-143237.q1ymuA.rst
@@ -0,0 +1 @@
+Fix support of named pipes in the rotating :mod:`logging` handlers.