Add null terminator for char* based json string unescape, and precond…

…ition on input length (Azure#2303)

* Add null terminator for char* based json string unescape, and precondition on input length

* Add remark comment about precondition and null terimination

* Update doc comment typo

* Remove the test cases about insufficient space.

* Fix clang formatting.

* Add null terminator tests.

* Test that the null terminator is there at the end.

* Fix build errors.

sdk/src/azure/core/az_json_private.h

@@ -120,6 +120,24 @@ AZ_NODISCARD AZ_INLINE _az_json_stack_item _az_json_stack_peek(_az_json_bit_stac
                                                          : _az_JSON_STACK_ARRAY;
 }
 
+AZ_NODISCARD AZ_INLINE bool _az_is_valid_escaped_character(uint8_t byte)
+{
+  switch (byte)
+  {
+    case '\\':
+    case '"':
+    case '/':
+    case 'b':
+    case 'f':
+    case 'n':
+    case 'r':
+    case 't':
+      return true;
+    default:
+      return false;
+  }
+}
+
 #include <azure/core/_az_cfg_suffix.h>
 
 #endif // _az_SPAN_PRIVATE_H

sdk/src/azure/core/az_json_reader.c

@@ -237,24 +237,6 @@ AZ_NODISCARD static az_result _az_json_reader_process_container_start(
   return AZ_OK;
 }
 
-AZ_NODISCARD static bool _az_is_valid_escaped_character(uint8_t byte)
-{
-  switch (byte)
-  {
-    case '\\':
-    case '"':
-    case '/':
-    case 'b':
-    case 'f':
-    case 'n':
-    case 'r':
-    case 't':
-      return true;
-    default:
-      return false;
-  }
-}
-
 AZ_NODISCARD static az_result _az_json_reader_process_string(az_json_reader* ref_json_reader)
 {
   // Move past the first '"' character

sdk/tests/core/test_az_json.c

@@ -1,5 +1,8 @@
 // Copyright (c) Microsoft Corporation. All rights reserved.
 // SPDX-License-Identifier: MIT
+#if defined(_WIN32) || defined(__WIN32__) || defined(WIN32)
+#define strdup _strdup
+#endif
 
 #include "az_test_definitions.h"
 #include <azure/core/az_json.h>
@@ -13,7 +16,7 @@
 #include <cmocka.h>
 
 #include <azure/core/_az_cfg.h>
-
+#include <stdlib.h>
 #define TEST_EXPECT_SUCCESS(exp) assert_true(az_result_succeeded(exp))
 
 az_result test_allocator(
@@ -3373,6 +3376,8 @@ int test_az_json()
           cmocka_unit_test(test_az_json_token_number_too_large),
           cmocka_unit_test(test_az_json_token_literal),
           cmocka_unit_test(test_az_json_token_copy),
-          cmocka_unit_test(test_az_json_reader_chunked) };
+          cmocka_unit_test(test_az_json_reader_chunked),
+          cmocka_unit_test(test_az_json_string_unescape),
+          cmocka_unit_test(test_az_json_string_unescape_same_buffer) };
   return cmocka_run_group_tests_name("az_core_json", tests, NULL, NULL);
 }