gh-111089: Add PyUnicode_AsUTF8() to the limited C API (#111121)

Add PyUnicode_AsUTF8() function to the limited C API.

multiprocessing posixshmem now uses PyUnicode_AsUTF8() instead of
PyUnicode_AsUTF8AndSize(): the extension is built with the limited C
API. The function now raises an exception if the filename contains an
embedded null character instead of truncating silently the filename.

Author: vstinner

Doc/data/stable_abi.dat

@@ -1069,6 +1069,9 @@ New Features
   limited C API.
   (Contributed by Victor Stinner in :gh:`85283`.)
 
+* Add :c:func:`PyUnicode_AsUTF8` function to the limited C API.
+  (Contributed by Victor Stinner in :gh:`111089`.)
+
 
 Porting to Python 3.13
 ----------------------

Doc/whatsnew/3.13.rst

@@ -440,19 +440,6 @@ PyAPI_FUNC(PyObject*) PyUnicode_FromKindAndData(
     const void *buffer,
     Py_ssize_t size);
 
-/* --- Manage the default encoding ---------------------------------------- */
-
-// Returns a pointer to the default encoding (UTF-8) of the
-// Unicode object unicode.
-//
-// Raise an exception if the string contains embedded null characters.
-// Use PyUnicode_AsUTF8AndSize() to accept embedded null characters.
-//
-// This function caches the UTF-8 encoded string in the Unicode object
-// and subsequent calls will return the same string. The memory is released
-// when the Unicode object is deallocated.
-PyAPI_FUNC(const char *) PyUnicode_AsUTF8(PyObject *unicode);
-
 
 /* === Characters Type APIs =============================================== */
 

Include/cpython/unicodeobject.h

@@ -443,7 +443,17 @@ PyAPI_FUNC(PyObject*) PyUnicode_AsUTF8String(
     PyObject *unicode           /* Unicode object */
     );
 
-// Returns a pointer to the default encoding (UTF-8) of the
+// Returns a pointer to the UTF-8 encoding of the Unicode object unicode.
+//
+// Raise an exception if the string contains embedded null characters.
+// Use PyUnicode_AsUTF8AndSize() to accept embedded null characters.
+//
+// This function caches the UTF-8 encoded string in the Unicode object
+// and subsequent calls will return the same string. The memory is released
+// when the Unicode object is deallocated.
+PyAPI_FUNC(const char *) PyUnicode_AsUTF8(PyObject *unicode);
+
+// Returns a pointer to the UTF-8 encoding of the
 // Unicode object unicode and the size of the encoded representation
 // in bytes stored in `*size` (if size is not NULL).
 //

Include/unicodeobject.h

@@ -0,0 +1,2 @@
+Add :c:func:`PyUnicode_AsUTF8` function to the limited C API. Patch by
+Victor Stinner.

Lib/test/test_stable_abi_ctypes.py

@@ -2478,3 +2478,5 @@
     added = '3.13'
 [function.PySys_AuditTuple]
     added = '3.13'
+[function.PyUnicode_AsUTF8]
+    added = '3.13'

Misc/NEWS.d/next/C API/2023-10-20-18-07-24.gh-issue-111089.RxkyrQ.rst

@@ -44,7 +44,7 @@ _posixshmem_shm_open_impl(PyObject *module, PyObject *path, int flags,
 {
     int fd;
     int async_err = 0;
-    const char *name = PyUnicode_AsUTF8AndSize(path, NULL);
+    const char *name = PyUnicode_AsUTF8(path);
     if (name == NULL) {
         return -1;
     }
@@ -83,7 +83,7 @@ _posixshmem_shm_unlink_impl(PyObject *module, PyObject *path)
 {
     int rv;
     int async_err = 0;
-    const char *name = PyUnicode_AsUTF8AndSize(path, NULL);
+    const char *name = PyUnicode_AsUTF8(path);
     if (name == NULL) {
         return NULL;
     }