Reject a NUL in complexstr()

A NUL cell ends a batch write and a cell array read (add_wchnstr(3X)), so
addstr() would write only the cells before it and in_wchstr() would read
only those, on both a wide and a narrow build.  addstr() already rejects an
embedded NUL in a str.

Author: serhiy-storchaka

Lib/test/test_curses.py

@@ -1044,9 +1044,9 @@ def test_cell_null_char(self):
         win = curses.newwin(3, 8, 0, 0)
         win.insch(0, 0, '\0')
         self.assertEqual(win.in_wch(0, 0), cell)
-        # complexstr() splits a NUL into a cell of its own.
-        self.assertEqual(len(curses.complexstr('a\0b')), 3)
-        self.assertEqual(curses.complexstr('\0')[0], cell)
+        # A string of cells cannot hold a NUL: it would end a batch write.
+        self.assertRaises(ValueError, curses.complexstr, 'a\0b')
+        self.assertRaises(ValueError, curses.complexstr, '\0')
 
     def test_add_string_behavior(self):
         # addstr() advances the cursor past the written text; addnstr()

Modules/_cursesmodule.c

@@ -1324,6 +1324,16 @@ static PyObject *
 complexstr_from_string(cursesmodule_state *state, PyObject *str,
                        attr_t attr, int pair)
 {
+    /* A NUL cell ends a batch write and a cell array read (add_wchnstr(3X)),
+       so a string of cells cannot hold one, as addstr() cannot either. */
+    Py_ssize_t nul = PyUnicode_FindChar(str, 0, 0, PyUnicode_GET_LENGTH(str), 1);
+    if (nul < -1) {
+        return NULL;
+    }
+    if (nul >= 0) {
+        PyErr_SetString(PyExc_ValueError, "embedded null character");
+        return NULL;
+    }
 #ifdef HAVE_NCURSESW
     Py_ssize_t n;
     wchar_t *wbuf = PyUnicode_AsWideCharString(str, &n);
@@ -1340,9 +1350,7 @@ complexstr_from_string(cursesmodule_state *state, PyObject *str,
         wchar_t cell[CCHARW_MAX + 1];
         Py_ssize_t k = 0;
         cell[k++] = wbuf[i++];
-        while (i < n && k < CCHARW_MAX && wbuf[i] != L'\0' &&
-               wcwidth(wbuf[i]) == 0)
-        {
+        while (i < n && k < CCHARW_MAX && wcwidth(wbuf[i]) == 0) {
             cell[k++] = wbuf[i++];
         }
         cell[k] = L'\0';
@@ -1351,7 +1359,7 @@ complexstr_from_string(cursesmodule_state *state, PyObject *str,
            control character (wcwidth < 0) may stand alone but cannot carry
            combining marks. */
         int width = wcwidth(cell[0]);
-        if ((width == 0 && cell[0] != L'\0') || (k > 1 && width < 0)) {
+        if (width == 0 || (k > 1 && width < 0)) {
             PyErr_Format(PyExc_ValueError,
                          "a character cell must be a single spacing character "
                          "optionally followed by up to %d combining characters",