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.

Doc/data/stable_abi.dat

@@ -726,6 +726,7 @@ function,PyUnicode_AsUCS4,3.7,,
 function,PyUnicode_AsUCS4Copy,3.7,,
 function,PyUnicode_AsUTF16String,3.2,,
 function,PyUnicode_AsUTF32String,3.2,,
+function,PyUnicode_AsUTF8,3.13,,
 function,PyUnicode_AsUTF8AndSize,3.10,,
 function,PyUnicode_AsUTF8String,3.2,,
 function,PyUnicode_AsUnicodeEscapeString,3.2,,

Doc/whatsnew/3.13.rst

@@ -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
 ----------------------

Include/cpython/unicodeobject.h

@@ -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/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).
 //

Lib/test/test_stable_abi_ctypes.py

@@ -745,6 +745,7 @@ SYMBOL_NAMES = (
     "PyUnicode_AsUCS4Copy",
     "PyUnicode_AsUTF16String",
     "PyUnicode_AsUTF32String",
+    "PyUnicode_AsUTF8",
     "PyUnicode_AsUTF8AndSize",
     "PyUnicode_AsUTF8String",
     "PyUnicode_AsUnicodeEscapeString",

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

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

Misc/stable_abi.toml

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

Modules/_multiprocessing/posixshmem.c

@@ -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;
     }

PC/python3dll.c

@@ -661,6 +661,7 @@ EXPORT_FUNC(PyUnicode_AsUCS4Copy)
 EXPORT_FUNC(PyUnicode_AsUnicodeEscapeString)
 EXPORT_FUNC(PyUnicode_AsUTF16String)
 EXPORT_FUNC(PyUnicode_AsUTF32String)
+EXPORT_FUNC(PyUnicode_AsUTF8)
 EXPORT_FUNC(PyUnicode_AsUTF8AndSize)
 EXPORT_FUNC(PyUnicode_AsUTF8String)
 EXPORT_FUNC(PyUnicode_AsWideChar)