PYTHON-5013 Add NULL checks in InvalidDocument bson handling

bson/_cbsonmodule.c

@@ -1644,6 +1644,56 @@ static int write_raw_doc(buffer_t buffer, PyObject* raw, PyObject* _raw_str) {
     return bytes_written;
 }
 
+
+/* Update Invalid Document error message to include doc.
+ */
+void handle_invalid_doc_error(PyObject* dict) {
+    PyObject *etype = NULL, *evalue = NULL, *etrace = NULL;
+    PyObject *msg = NULL, *dict_str = NULL, *new_msg = NULL;
+    PyErr_Fetch(&etype, &evalue, &etrace);
+    PyObject *InvalidDocument = _error("InvalidDocument");
+    if (InvalidDocument == NULL) {
+        goto cleanup;
+    }
+
+    if (evalue && PyErr_GivenExceptionMatches(etype, InvalidDocument)) {
+        PyObject *msg = PyObject_Str(evalue);
+        if (msg) {
+            // Prepend doc to the existing message
+            PyObject *dict_str = PyObject_Str(dict);
+            if (dict_str == NULL) {
+                goto cleanup;
+            }
+            const char * dict_str_utf8 = PyUnicode_AsUTF8(dict_str);
+            if (dict_str_utf8 == NULL) {
+                goto cleanup;
+            }
+            const char * msg_utf8 = PyUnicode_AsUTF8(msg);
+            if (msg_utf8 == NULL) {
+                goto cleanup;
+            }
+            PyObject *new_msg = PyUnicode_FromFormat("Invalid document %s | %s", dict_str_utf8, msg_utf8);
+            Py_DECREF(evalue);
+            Py_DECREF(etype);
+            etype = InvalidDocument;
+            InvalidDocument = NULL;
+            if (new_msg) {
+                evalue = new_msg;
+            } else {
+                evalue = msg;
+            }
+        }
+        PyErr_NormalizeException(&etype, &evalue, &etrace);
+    }
+cleanup:
+    PyErr_Restore(etype, evalue, etrace);
+    Py_XDECREF(msg);
+    Py_XDECREF(InvalidDocument);
+    Py_XDECREF(dict_str);
+    Py_XDECREF(new_msg);
+}
+
+
 /* returns the number of bytes written or 0 on failure */
 int write_dict(PyObject* self, buffer_t buffer,
                PyObject* dict, unsigned char check_keys,
@@ -1743,40 +1793,8 @@ int write_dict(PyObject* self, buffer_t buffer,
         while (PyDict_Next(dict, &pos, &key, &value)) {
             if (!decode_and_write_pair(self, buffer, key, value,
                                     check_keys, options, top_level)) {
-                if (PyErr_Occurred()) {
-                    PyObject *etype = NULL, *evalue = NULL, *etrace = NULL;
-                    PyErr_Fetch(&etype, &evalue, &etrace);
-                    PyObject *InvalidDocument = _error("InvalidDocument");
-
-                    if (top_level && InvalidDocument && PyErr_GivenExceptionMatches(etype, InvalidDocument)) {
-
-                        Py_DECREF(etype);
-                        etype = InvalidDocument;
-
-                        if (evalue) {
-                            PyObject *msg = PyObject_Str(evalue);
-                            Py_DECREF(evalue);
-
-                            if (msg) {
-                                // Prepend doc to the existing message
-                                PyObject *dict_str = PyObject_Str(dict);
-                                PyObject *new_msg = PyUnicode_FromFormat("Invalid document %s | %s", PyUnicode_AsUTF8(dict_str), PyUnicode_AsUTF8(msg));
-                                Py_DECREF(dict_str);
-
-                                if (new_msg) {
-                                    evalue = new_msg;
-                                }
-                                else {
-                                evalue = msg;
-                                }
-                            }
-                        }
-                        PyErr_NormalizeException(&etype, &evalue, &etrace);
-                    }
-                    else {
-                        Py_DECREF(InvalidDocument);
-                    }
-                    PyErr_Restore(etype, evalue, etrace);
+                if (PyErr_Occurred() && top_level) {
+                    handle_invalid_doc_error(dict);
                 }
                 return 0;
             }
@@ -1796,6 +1814,9 @@ int write_dict(PyObject* self, buffer_t buffer,
             }
             if (!decode_and_write_pair(self, buffer, key, value,
                                     check_keys, options, top_level)) {
+                if (PyErr_Occurred() && top_level) {
+                    handle_invalid_doc_error(dict);
+                }
                 Py_DECREF(key);
                 Py_DECREF(value);
                 Py_DECREF(iter);

test/test_bson.py

@@ -1112,6 +1112,34 @@ def __repr__(self):
         with self.assertRaisesRegex(InvalidDocument, f"Invalid document {doc}"):
             encode(doc)
 
+    def test_doc_in_invalid_document_error_message_mapping(self):
+        class MyMapping(abc.Mapping):
+            def keys():
+                return ["t"]
+
+            def __getitem__(self, name):
+                if name == "_id":
+                    return None
+                return Wrapper(name)
+
+            def __len__(self):
+                return 1
+
+            def __iter__(self):
+                return iter(["t"])
+
+        class Wrapper:
+            def __init__(self, val):
+                self.val = val
+
+            def __repr__(self):
+                return repr(self.val)
+
+        self.assertEqual("1", repr(Wrapper(1)))
+        doc = MyMapping()
+        with self.assertRaisesRegex(InvalidDocument, f"Invalid document {doc}"):
+            encode(doc)
+
 
 class TestCodecOptions(unittest.TestCase):
     def test_document_class(self):