gh-146054: Limit the growth of `encodings.search_function` cache (GH-146055)

Lib/encodings/__init__.py

diff --git a/Lib/encodings/__init__.py b/Lib/encodings/__init__.py
index e205ec3..169c483 100644
--- a/Lib/encodings/__init__.py
+++ b/Lib/encodings/__init__.py
@@ -34,6 +34,7 @@
 from . import aliases
 
 _cache = {}
+_MAXCACHE = 500
 _unknown = '--unknown--'
 _import_tail = ['*']
 _aliases = aliases.aliases
@@ -111,6 +112,8 @@ def search_function(encoding):
 
     if mod is None:
         # Cache misses
+        if len(_cache) >= _MAXCACHE:
+            _cache.clear()
         _cache[encoding] = None
         return None
 
@@ -132,6 +135,8 @@ 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

Lib/test/test_codecs.py

diff --git a/Lib/test/test_codecs.py b/Lib/test/test_codecs.py
index c31faec..79c8a7e 100644
--- a/Lib/test/test_codecs.py
+++ b/Lib/test/test_codecs.py
@@ -3908,5 +3908,16 @@ def test_encodings_normalize_encoding(self):
             self.assertEqual(normalize('utf\xE9\u20AC\U0010ffff-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()

Misc/NEWS.d/next/Library/2026-03-17-11-46-20.gh-issue-146054.udYcqn.rst

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 0000000..8692c7f
--- /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`.