From 45a7c3677c52c9d8166184d5263f1083d32e8899 Mon Sep 17 00:00:00 2001
From: Sergei Ozeranskii <1898297+ozeranskii@users.noreply.github.com>
Date: Sun, 18 Oct 2026 20:46:48 +0200
Subject: [PATCH 1/2] Avoid removed Py_FileSystemDefaultEncoding in
 load_library

CPython 3.16 removed Py_FileSystemDefaultEncoding from the headers, so
_cffi_backend.c no longer compiled. Convert the file name with
PyUnicode_FSConverter instead, which uses the filesystem encoding,
rejects embedded null characters and is available on all supported
versions. The encoded name is kept in *p_temp, which the callers
already release.
---
 src/c/_cffi_backend.c | 10 ++++------
 src/c/test_c.py       |  7 +++++++
 2 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/src/c/_cffi_backend.c b/src/c/_cffi_backend.c
index a9bc9c5a..48c872df 100644
--- a/src/c/_cffi_backend.c
+++ b/src/c/_cffi_backend.c
@@ -4537,14 +4537,13 @@ static void *b_do_dlopen(PyObject *args, const char **p_printable_filename,
         }
         PyErr_Clear();
 #endif
-        if (!PyArg_ParseTuple(args, "et|i:load_library",
-                     Py_FileSystemDefaultEncoding, &filename_or_null, &flags))
+        if (!PyArg_ParseTuple(args, "O&|i:load_library",
+                     PyUnicode_FSConverter, p_temp, &flags))
             return NULL;
         *p_printable_filename = PyUnicode_AsUTF8(s);
-        if (*p_printable_filename == NULL) {
-            PyMem_Free(filename_or_null);
+        if (*p_printable_filename == NULL)
             return NULL;
-        }
+        filename_or_null = PyBytes_AS_STRING(*p_temp);
     }
     if ((flags & (RTLD_NOW | RTLD_LAZY)) == 0)
         flags |= RTLD_NOW;
@@ -4557,7 +4556,6 @@ static void *b_do_dlopen(PyObject *args, const char **p_printable_filename,
 #endif
 
     handle = dlopen(filename_or_null, flags);
-    PyMem_Free(filename_or_null);
 
 #ifdef MS_WIN32
   got_handle:
diff --git a/src/c/test_c.py b/src/c/test_c.py
index 8ddea1fb..9dc9041e 100644
--- a/src/c/test_c.py
+++ b/src/c/test_c.py
@@ -134,6 +134,13 @@ def test_load_library():
     x = find_and_load_library('c', RTLD_LAZY)
     assert repr(x).startswith("<clibrary '")
 
+def test_load_library_invalid_filename():
+    pytest.raises(TypeError, load_library, b"foo")
+    pytest.raises(TypeError, load_library, "foo", "not-an-int")
+    if sys.platform != 'win32':
+        # the Windows code path does not reject embedded null characters
+        pytest.raises(ValueError, load_library, "foo\x00bar")
+
 def test_all_rtld_symbols():
     import sys
     FFI_DEFAULT_ABI        # these symbols must be defined

From 38dd2f699cff97e41d75bdaf6a570b789fb8a515 Mon Sep 17 00:00:00 2001
From: Sergei Ozeranskii <1898297+ozeranskii@users.noreply.github.com>
Date: Sun, 18 Oct 2026 20:46:48 +0200
Subject: [PATCH 2/2] Add whatsnew entry for #287

---
 doc/source/whatsnew.rst | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/doc/source/whatsnew.rst b/doc/source/whatsnew.rst
index 8ef0a42a..0b48dc0d 100644
--- a/doc/source/whatsnew.rst
+++ b/doc/source/whatsnew.rst
@@ -17,8 +17,14 @@ v2.2.0.dev0
   ``FILE`` type. This could happen with an already-preprocessed system
   header, which spells out the real struct. (`#281`_).
 
+* Fixed building on CPython 3.16, which removed
+  ``Py_FileSystemDefaultEncoding``. A file name with an embedded null
+  character passed to ``ffi.dlopen()`` now raises ``ValueError`` instead of
+  ``TypeError``. (`#287`_).
+
 .. _`#265`: https://github.com/python-cffi/cffi/pull/265
 .. _`#281`: https://github.com/python-cffi/cffi/pull/281
+.. _`#287`: https://github.com/python-cffi/cffi/pull/287
 
 v2.1.0
 ======