From: Miss Islington (bot) <31488909+miss-islington@users.noreply.github.com>
Date: Sun, 25 Jan 2026 17:11:45 +0000 (+0100)
Subject: [3.14] gh-143237: Fix support of named pipes in the rotating logging handlers (GH... 
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=c9548f3dfc3c56bff355caf1416326c0da2f67f5;p=thirdparty%2FPython%2Fcpython.git

[3.14] gh-143237: Fix support of named pipes in the rotating logging handlers (GH-143259) (#143297)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
---

diff --git a/Lib/logging/handlers.py b/Lib/logging/handlers.py
index 2748b5941ead..4a07258f8d6d 100644
--- a/Lib/logging/handlers.py
+++ b/Lib/logging/handlers.py
@@ -196,7 +196,11 @@ class RotatingFileHandler(BaseRotatingHandler):
         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 99869fdd9e70..c1dc06e02d96 100644
--- a/Lib/test/test_logging.py
+++ b/Lib/test/test_logging.py
@@ -25,6 +25,7 @@ import logging.config
 
 import codecs
 import configparser
+import contextlib
 import copy
 import datetime
 import pathlib
@@ -6343,6 +6344,32 @@ class RotatingFileHandlerTest(BaseFileTest):
         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)
+
+        data = 'not read'
+        def other_side():
+            nonlocal data
+            with open(filename, 'rb') as f:
+                data = f.read()
+
+        thread = threading.Thread(target=other_side)
+        with threading_helper.start_threads([thread]):
+            rh = logging.handlers.RotatingFileHandler(
+                    filename, encoding="utf-8", maxBytes=1)
+            with contextlib.closing(rh):
+                m = self.next_rec()
+                self.assertFalse(rh.shouldRollover(m))
+                rh.emit(m)
+        self.assertEqual(data.decode(), m.msg + os.linesep)
+
     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 000000000000..131bebcd984a
--- /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.