refactor: Use functions from limited API

Replace unsafe macros and direct struct access with functions from
the subset of limited API functions.

* `PySequence_Fast_GET_ITEM` -> `PySequence_GetItem`
* `PyTuple_SET_ITEM` -> `PyTuple_SetItem`
* `PyList_SET_ITEM` -> `PyList_SetItem`
* `PyUnicode_AsUTF8AndSize` -> `PyUnicode_AsUTF8String` +
  `PyBytes_AsStringAndSize`. The function `PyUnicode_AsUTF8AndSize` is
  not in limited API before Python 3.10.
* `const char *tp_name` -> `Py_TYPE()` string representation

See: python-ldap#540
Signed-off-by: Christian Heimes <cheimes@redhat.com>

Modules/LDAPObject.c

@@ -280,9 +280,9 @@ attrs_from_List(PyObject *attrlist, char ***attrsp)
     }
     else {
         PyObject *item = NULL;
+        PyObject *bstr;
         Py_ssize_t i, len, strlen;
-
-        const char *str;
+        char *str;
 
         seq = PySequence_Fast(attrlist, "expected list of strings or None");
         if (seq == NULL)
@@ -297,24 +297,35 @@ attrs_from_List(PyObject *attrlist, char ***attrsp)
 
         for (i = 0; i < len; i++) {
             attrs[i] = NULL;
-            item = PySequence_Fast_GET_ITEM(seq, i);
+            item = PySequence_GetItem(seq, i);
             if (item == NULL)
                 goto error;
             if (!PyUnicode_Check(item)) {
                 LDAPerror_TypeError
                     ("attrs_from_List(): expected string in list", item);
+                Py_DECREF(item);
+                goto error;
+            }
+            // PyUnicode_AsUTF8AndSize is not in limited API < 3.10.
+            bstr = PyUnicode_AsUTF8String(item);
+            Py_DECREF(item);
+            if (bstr == NULL) {
+                goto error;
+            }
+            if (PyBytes_AsStringAndSize(bstr, &str, &strlen) < 0) {
+                Py_DECREF(bstr);
                 goto error;
             }
-            str = PyUnicode_AsUTF8AndSize(item, &strlen);
             /* Make a copy. PyBytes_AsString* / PyUnicode_AsUTF8* return
-             * internal values that must be treated like const char. Python
-             * 3.7 actually returns a const char.
+             * internal values that must be treated like const char.
              */
             attrs[i] = (char *)PyMem_NEW(char, strlen + 1);
-
-            if (attrs[i] == NULL)
+            if (attrs[i] == NULL) {
+                Py_DECREF(bstr);
                 goto nomem;
+            }
             memcpy(attrs[i], str, strlen + 1);
+            Py_DECREF(bstr);
         }
         attrs[len] = NULL;
         Py_DECREF(seq);

Modules/ldapcontrol.c

@@ -186,7 +186,7 @@ LDAPControls_to_List(LDAPControl **ldcs)
             Py_DECREF(res);
             return NULL;
         }
-        PyList_SET_ITEM(res, i, pyctrl);
+        PyList_SetItem(res, i, pyctrl);
     }
     return res;
 }

Modules/options.c

@@ -183,8 +183,8 @@ LDAP_set_option(LDAPObject *self, int option, PyObject *value)
                     /* TypeError: mention either float or None is expected */
                     PyErr_Clear();
                     PyErr_Format(PyExc_TypeError,
-                                 "A float or None is expected for timeout, got %.100s",
-                                 Py_TYPE(value)->tp_name);
+                                 "A float or None is expected for timeout, got %S",
+                                 Py_TYPE(value));
                 }
                 return 0;
             }
@@ -302,9 +302,9 @@ LDAP_get_option(LDAPObject *self, int option)
             num_extensions++;
         extensions = PyTuple_New(num_extensions);
         for (i = 0; i < num_extensions; i++)
-            PyTuple_SET_ITEM(extensions, i,
-                             PyUnicode_FromString(apiinfo.ldapai_extensions
-                                                  [i]));
+            PyTuple_SetItem(extensions, i,
+                            PyUnicode_FromString(apiinfo.ldapai_extensions
+                                                 [i]));
 
         /* return api info as a dictionary */
         v = Py_BuildValue("{s:i, s:i, s:i, s:s, s:i, s:O}",