From 6fe3609ae7d137a84226aed19440960c3f79340f Mon Sep 17 00:00:00 2001
From: Stan Ulbrych <89152624+StanFromIreland@users.noreply.github.com>
Date: Tue, 17 Mar 2026 14:02:59 +0000
Subject: [PATCH] gh-146054: Limit the growth of `encodings.search_function`
 cache (GH-146055) (cherry picked from commit
 9d7621b75bc4935e14d4f12dffb3cb1d89ea1bc6)

Co-authored-by: Stan Ulbrych <89152624+StanFromIreland@users.noreply.github.com>
---
 Lib/encodings/__init__.py                             |  5 +++++
 Lib/test/test_codecs.py                               | 11 +++++++++++
 .../2026-03-17-11-46-20.gh-issue-146054.udYcqn.rst    |  2 ++
 3 files changed, 18 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Library/2026-03-17-11-46-20.gh-issue-146054.udYcqn.rst

diff --git a/Lib/encodings/__init__.py b/Lib/encodings/__init__.py
index 298177eb8003a7..8548bbe04ad37c 100644
--- a/Lib/encodings/__init__.py
+++ b/Lib/encodings/__init__.py
@@ -33,6 +33,7 @@
 from . import aliases
 
 _cache = {}
+_MAXCACHE = 500
 _unknown = '--unknown--'
 _import_tail = ['*']
 _aliases = aliases.aliases
@@ -115,6 +116,8 @@ def search_function(encoding):
 
     if mod is None:
         # Cache misses
+        if len(_cache) >= _MAXCACHE:
+            _cache.clear()
         _cache[encoding] = None
         return None
 
@@ -136,6 +139,8 @@ def search_function(encoding):
         entry = codecs.CodecInfo(*entry)
 
     # Cache the codec registry entry
+    if len(_cache) >= _MAXCACHE:
+        _cache.clear()
     _cache[encoding] = entry
 
     # Register its aliases (without overwriting previously registered
diff --git a/Lib/test/test_codecs.py b/Lib/test/test_codecs.py
index fd7769e8c275d3..1533fdcc9d3483 100644
--- a/Lib/test/test_codecs.py
+++ b/Lib/test/test_codecs.py
@@ -3907,5 +3907,16 @@ def test_encodings_normalize_encoding(self):
         self.assertEqual(normalize('utf...8'), 'utf...8')
 
 
+class CodecCacheTest(unittest.TestCase):
+    def test_cache_bounded(self):
+        for i in range(encodings._MAXCACHE + 1000):
+            try:
+                b'x'.decode(f'nonexist_{i}')
+            except LookupError:
+                pass
+
+        self.assertLessEqual(len(encodings._cache), encodings._MAXCACHE)
+
+
 if __name__ == "__main__":
     unittest.main()
diff --git a/Misc/NEWS.d/next/Library/2026-03-17-11-46-20.gh-issue-146054.udYcqn.rst b/Misc/NEWS.d/next/Library/2026-03-17-11-46-20.gh-issue-146054.udYcqn.rst
new file mode 100644
index 00000000000000..8692c7f171d0fb
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-03-17-11-46-20.gh-issue-146054.udYcqn.rst
@@ -0,0 +1,2 @@
+Limit the size of :func:`encodings.search_function` cache.
+Found by OSS Fuzz in :oss-fuzz:`493449985`.