bpo-46063: Improve algorithm for computing which rolled-over log file… (GH-30093)

Doc/library/logging.handlers.rst

@@ -234,6 +234,19 @@ need to override.
          return the same output every time for a given input, otherwise the
          rollover behaviour may not work as expected.
 
+         It's also worth noting that care should be taken when using a namer to
+         preserve certain attributes in the filename which are used during rotation.
+         For example, :class:`RotatingFileHandler` expects to have a set of log files
+         whose names contain successive integers, so that rotation works as expected,
+         and :class:`TimedRotatingFileHandler` deletes old log files (based on the
+         ``backupCount`` parameter passed to the handler's initializer) by determining
+         the oldest files to delete. For this to happen, the filenames should be
+         sortable using the date/time portion of the filename, and a namer needs to
+         respect this. (If a namer is wanted that doesn't respect this scheme, it will
+         need to be used in a subclass of :class:`TimedRotatingFileHandler` which
+         overrides the :meth:`~TimedRotatingFileHandler.getFilesToDelete` method to
+         fit in with the custom naming scheme.)
+
       .. versionadded:: 3.3
 
 
@@ -443,6 +456,10 @@ timed intervals.
 
       Outputs the record to the file, catering for rollover as described above.
 
+   .. method:: getFilesToDelete()
+
+      Returns a list of filenames which should be deleted as part of rollover. These
+      are the absolute paths of the oldest backup log files written by the handler.
 
 .. _socket-handler:
 

Lib/logging/handlers.py

@@ -1,4 +1,4 @@
-# Copyright 2001-2016 by Vinay Sajip. All Rights Reserved.
+# Copyright 2001-2021 by Vinay Sajip. All Rights Reserved.
 #
 # Permission to use, copy, modify, and distribute this software and its
 # documentation for any purpose and without fee is hereby granted,
@@ -18,7 +18,7 @@
 Additional handlers for the logging package for Python. The core package is
 based on PEP 282 and comments thereto in comp.lang.python.
 
-Copyright (C) 2001-2016 Vinay Sajip. All Rights Reserved.
+Copyright (C) 2001-2021 Vinay Sajip. All Rights Reserved.
 
 To use, simply 'import logging.handlers' and log away!
 """
@@ -366,9 +366,22 @@ class TimedRotatingFileHandler(BaseRotatingHandler):
         fileNames = os.listdir(dirName)
         result = []
         # See bpo-44753: Don't use the extension when computing the prefix.
-        prefix = os.path.splitext(baseName)[0] + "."
+        n, e = os.path.splitext(baseName)
+        prefix = n + '.'
         plen = len(prefix)
         for fileName in fileNames:
+            if self.namer is None:
+                # Our files will always start with baseName
+                if not fileName.startswith(baseName):
+                    continue
+            else:
+                # Our files could be just about anything after custom naming, but
+                # likely candidates are of the form
+                # foo.log.DATETIME_SUFFIX or foo.DATETIME_SUFFIX.log
+                if (not fileName.startswith(baseName) and fileName.endswith(e) and
+                    len(fileName) > (plen + 1) and not fileName[plen+1].isdigit()):
+                    continue
+
             if fileName[:plen] == prefix:
                 suffix = fileName[plen:]
                 # See bpo-45628: The date/time suffix could be anywhere in the

Lib/test/test_logging.py

@@ -1,4 +1,4 @@
-# Copyright 2001-2019 by Vinay Sajip. All Rights Reserved.
+# Copyright 2001-2021 by Vinay Sajip. All Rights Reserved.
 #
 # Permission to use, copy, modify, and distribute this software and its
 # documentation for any purpose and without fee is hereby granted,
@@ -16,7 +16,7 @@
 
 """Test harness for the logging module. Run all tests.
 
-Copyright (C) 2001-2019 Vinay Sajip. All Rights Reserved.
+Copyright (C) 2001-2021 Vinay Sajip. All Rights Reserved.
 """
 
 import logging
@@ -36,6 +36,7 @@ import os
 import queue
 import random
 import re
+import shutil
 import socket
 import struct
 import sys
@@ -5434,6 +5435,53 @@ class TimedRotatingFileHandlerTest(BaseFileTest):
             finally:
                 rh.close()
 
+    def test_compute_files_to_delete(self):
+        # See bpo-46063 for background
+        wd = tempfile.mkdtemp(prefix='test_logging_')
+        self.addCleanup(shutil.rmtree, wd)
+        times = []
+        dt = datetime.datetime.now()
+        for i in range(10):
+            times.append(dt.strftime('%Y-%m-%d_%H-%M-%S'))
+            dt += datetime.timedelta(seconds=5)
+        prefixes = ('a.b', 'a.b.c', 'd.e', 'd.e.f')
+        files = []
+        rotators = []
+        for prefix in prefixes:
+            p = os.path.join(wd, '%s.log' % prefix)
+            rotator = logging.handlers.TimedRotatingFileHandler(p, when='s',
+                                                                interval=5,
+                                                                backupCount=7)
+            rotators.append(rotator)
+            if prefix.startswith('a.b'):
+                for t in times:
+                    files.append('%s.log.%s' % (prefix, t))
+            else:
+                rotator.namer = lambda name: name.replace('.log', '') + '.log'
+                for t in times:
+                    files.append('%s.%s.log' % (prefix, t))
+        # Create empty files
+        for fn in files:
+            p = os.path.join(wd, fn)
+            with open(p, 'wb') as f:
+                pass
+        # Now the checks that only the correct files are offered up for deletion
+        for i, prefix in enumerate(prefixes):
+            rotator = rotators[i]
+            candidates = rotator.getFilesToDelete()
+            self.assertEqual(len(candidates), 3)
+            if prefix.startswith('a.b'):
+                p = '%s.log.' % prefix
+                for c in candidates:
+                    d, fn = os.path.split(c)
+                    self.assertTrue(fn.startswith(p))
+            else:
+                for c in candidates:
+                    d, fn = os.path.split(c)
+                    self.assertTrue(fn.endswith('.log'))
+                    self.assertTrue(fn.startswith(prefix + '.') and
+                                    fn[len(prefix) + 2].isdigit())
+
 
 def secs(**kw):
     return datetime.timedelta(**kw) // datetime.timedelta(seconds=1)