ctypes: remove use of legacy unicode API (GH-12340)

PyUnicode_AsUnicodeAndSize() -> PyUnicode_AsWideChar()

Modules/_ctypes/_ctypes.c

@@ -1304,8 +1304,6 @@ static int
 WCharArray_set_value(CDataObject *self, PyObject *value, void *Py_UNUSED(ignored))
 {
     Py_ssize_t result = 0;
-    Py_UNICODE *wstr;
-    Py_ssize_t len;
 
     if (value == NULL) {
         PyErr_SetString(PyExc_TypeError,
@@ -1320,12 +1318,14 @@ WCharArray_set_value(CDataObject *self, PyObject *value, void *Py_UNUSED(ignored
     } else
         Py_INCREF(value);
 
-    wstr = PyUnicode_AsUnicodeAndSize(value, &len);
-    if (wstr == NULL)
+    Py_ssize_t len = PyUnicode_AsWideChar(value, NULL, 0);
+    if (len < 0) {
         return -1;
-    if ((size_t)len > self->b_size/sizeof(wchar_t)) {
-        PyErr_SetString(PyExc_ValueError,
-                        "string too long");
+    }
+    // PyUnicode_AsWideChar() returns number of wchars including trailing null byte,
+    // when it is called with NULL.
+    if (((size_t)len-1) > self->b_size/sizeof(wchar_t)) {
+        PyErr_SetString(PyExc_ValueError, "string too long");
         result = -1;
         goto done;
     }

Modules/_ctypes/cfield.c

@@ -1229,9 +1229,6 @@ U_get(void *ptr, Py_ssize_t size)
 static PyObject *
 U_set(void *ptr, PyObject *value, Py_ssize_t length)
 {
-    Py_UNICODE *wstr;
-    Py_ssize_t size;
-
     /* It's easier to calculate in characters than in bytes */
     length /= sizeof(wchar_t);
 
@@ -1242,9 +1239,14 @@ U_set(void *ptr, PyObject *value, Py_ssize_t length)
         return NULL;
     }
 
-    wstr = PyUnicode_AsUnicodeAndSize(value, &size);
-    if (wstr == NULL)
+    Py_ssize_t size = PyUnicode_AsWideChar(value, NULL, 0);
+    if (size < 0) {
         return NULL;
+    }
+    // PyUnicode_AsWideChar() returns number of wchars including trailing null byte,
+    // when it is called with NULL.
+    size--;
+    assert(size >= 0);
     if (size > length) {
         PyErr_Format(PyExc_ValueError,
                      "string too long (%zd, maximum length %zd)",
@@ -1421,16 +1423,18 @@ BSTR_set(void *ptr, PyObject *value, Py_ssize_t size)
 
     /* create a BSTR from value */
     if (value) {
-        wchar_t* wvalue;
         Py_ssize_t wsize;
-        wvalue = PyUnicode_AsUnicodeAndSize(value, &wsize);
-        if (wvalue == NULL)
+        wchar_t *wvalue = PyUnicode_AsWideCharString(value, &wsize);
+        if (wvalue == NULL) {
             return NULL;
+        }
         if ((unsigned) wsize != wsize) {
             PyErr_SetString(PyExc_ValueError, "String too long for BSTR");
+            PyMem_Free(wvalue);
             return NULL;
         }
         bstr = SysAllocStringLen(wvalue, (unsigned)wsize);
+        PyMem_Free(wvalue);
     } else
         bstr = NULL;