update cJSON_SetValuestring and testcase

README.md

@@ -212,7 +212,7 @@ For every value type there is a `cJSON_Create...` function that can be used to c
 All of these will allocate a `cJSON` struct that can later be deleted with `cJSON_Delete`.
 Note that you have to delete them at some point, otherwise you will get a memory leak.  
 **Important**: If you have added an item to an array or an object already, you **mustn't** delete it with `cJSON_Delete`. Adding it to an array or object transfers its ownership so that when that array or object is deleted, 
-it gets deleted as well. You also could use `cJSON_SetValuestringToObject` to change a `cJSON_Object`'s `valuestring`, and you needn't to free the previous `valuestring` manually.
+it gets deleted as well. You also could use `cJSON_SetValuestring` to change a `cJSON_String`'s `valuestring`, and you needn't to free the previous `valuestring` manually.
 
 #### Basic types
 

cJSON.c

@@ -368,23 +368,25 @@ CJSON_PUBLIC(double) cJSON_SetNumberHelper(cJSON *object, double number)
     return object->valuedouble = number;
 }
 
-CJSON_PUBLIC(char*) cJSON_SetValuestringToObject(cJSON *object, const char *valuestring)
+CJSON_PUBLIC(char*) cJSON_SetValuestring(cJSON *object, const char *valuestring)
 {
-    size_t length = 0;
     char *copy = NULL;
-    /* if object->valuestring is NULL, it should not set valuestring */
-    if (object->valuestring == NULL)
+    /* if object's type is not cJSON_String or is cJSON_IsReference, it should not set valuestring */
+    if (!(object->type & cJSON_String) || (object->type & cJSON_IsReference))
     {
         return NULL;
     }
-    length = strlen(valuestring) + sizeof("");
-    copy = (char*) cJSON_malloc(length);
+    if (strlen(valuestring) <= strlen(object->valuestring))
+    {
+        strcpy(object->valuestring, valuestring);
+        return object->valuestring;
+    }
+    copy = (char*) cJSON_strdup((const unsigned char*)valuestring, &global_hooks);
     if (copy == NULL)
     {
         return NULL;
     }
-    memcpy(copy, valuestring, length);
-    if (!(object->type & cJSON_IsReference) && (object->valuestring != NULL))
+    if (object->valuestring != NULL)
     {
         cJSON_free(object->valuestring);
     }

cJSON.h

@@ -278,8 +278,8 @@ CJSON_PUBLIC(cJSON*) cJSON_AddArrayToObject(cJSON * const object, const char * c
 /* helper for the cJSON_SetNumberValue macro */
 CJSON_PUBLIC(double) cJSON_SetNumberHelper(cJSON *object, double number);
 #define cJSON_SetNumberValue(object, number) ((object != NULL) ? cJSON_SetNumberHelper(object, (double)number) : (number))
-/* Only takes effect when type of object is JSON_Object */
-CJSON_PUBLIC(char*) cJSON_SetValuestringToObject(cJSON *object, const char *valuestring);
+/* Change the valuestring of a cJSON_String object, only takes effect when type of object is cJSON_String */
+CJSON_PUBLIC(char*) cJSON_SetValuestring(cJSON *object, const char *valuestring);
 
 /* Macro for iterating over an array or object */
 #define cJSON_ArrayForEach(element, array) for(element = (array != NULL) ? (array)->child : NULL; element != NULL; element = element->next)

tests/misc_tests.c

@@ -587,24 +587,34 @@ static void cjson_delete_item_from_array_should_not_broken_list_structure(void)
 static void cjson_set_valuestring_to_object_should_not_leak_memory(void)
 {
     cJSON *root = cJSON_Parse("{}");
-    cJSON *item1 = cJSON_CreateString("valuestring could be changed safely");
-    cJSON *item2 = cJSON_CreateStringReference("reference item should be freed by yourself");
-    const char *newValuestring = "new valuestring which much longer than previous";
-    char *returnValue = NULL;
+    const char *stringvalue = "valuestring could be changed safely";
+    const char *reference_valuestring = "reference item should be freed by yourself";
+    const char *short_valuestring = "shorter valuestring";
+    const char *long_valuestring = "new valuestring which much longer than previous should be changed safely";
+    cJSON *item1 = cJSON_CreateString(stringvalue);
+    cJSON *item2 = cJSON_CreateStringReference(reference_valuestring);
+    char *ptr1 = NULL;
+    char *return_value = NULL;
     
     cJSON_AddItemToObject(root, "one", item1);
     cJSON_AddItemToObject(root, "two", item2);
 
+    ptr1 = item1->valuestring;
+    return_value = cJSON_SetValuestring(cJSON_GetObjectItem(root, "one"), short_valuestring);
+    TEST_ASSERT_NOT_NULL(return_value);
+    TEST_ASSERT_EQUAL_PTR_MESSAGE(ptr1, return_value, "new valuestring shorter than old should not reallocate memory");
+    TEST_ASSERT_EQUAL_STRING(short_valuestring, cJSON_GetObjectItem(root, "one")->valuestring);
+
     /* we needn't to free the original valuestring manually */
-    returnValue = cJSON_SetValuestringToObject(cJSON_GetObjectItem(root, "one"), newValuestring);
-    TEST_ASSERT_NOT_NULL(returnValue);
-    TEST_ASSERT_EQUAL_STRING(newValuestring, cJSON_GetObjectItem(root, "one")->valuestring);
-
-    returnValue = cJSON_SetValuestringToObject(cJSON_GetObjectItem(root, "two"), newValuestring);
-    TEST_ASSERT_NOT_NULL(returnValue);
-    TEST_ASSERT_EQUAL_STRING(newValuestring, cJSON_GetObjectItem(root, "two")->valuestring);
-    /* we must free the memory manually when the item's type is cJSON_IsReference */
-    cJSON_free(item2->valuestring);
+    ptr1 = item1->valuestring;
+    return_value = cJSON_SetValuestring(cJSON_GetObjectItem(root, "one"), long_valuestring);
+    TEST_ASSERT_NOT_NULL(return_value);
+    TEST_ASSERT_NOT_EQUAL_MESSAGE(ptr1, return_value, "new valuestring longer than old should reallocate memory")
+    TEST_ASSERT_EQUAL_STRING(long_valuestring, cJSON_GetObjectItem(root, "one")->valuestring);
+
+    return_value = cJSON_SetValuestring(cJSON_GetObjectItem(root, "two"), long_valuestring);
+    TEST_ASSERT_NULL_MESSAGE(return_value, "valuestring of reference object should not be changed");
+    TEST_ASSERT_EQUAL_STRING(reference_valuestring, cJSON_GetObjectItem(root, "two")->valuestring);
 
     cJSON_Delete(root);
 }