rapidjson's assert IsObject() fails randomly while it shouldn't

Question

we are facing an issue where the RAPIDJSON_ASSERT(IsObject()) called by MemberEnd() which is called by HasMember() fails. However, that rapidjson::Value is guaranteed to be an object by other logic.

Here is the code snippet:

const std::string str = "{\"outer_key\":{\"inner_key\":\"value\", \"foo\":\"bar\"}}";
rapidjson::Document doc;
if (doc.Parse(str.c_str()).HasParseError()) {
    return -1;
}

rapidjson::Value::MemberIterator it = doc.FindMember("outer_key");
// make sure the member is of Object type
if (it == doc.MemberEnd() || !it->value.IsObject()) {
    return -1;
}

rapidjson::Value* p_json;
p_json = &(it->value);

rapidjson::Document new_doc;
rapidjson::Document::AllocatorType& new_doc_allocator = new_doc.GetAllocator();
// if SOME_FLAG is set and "outer_key" exists in the input JSON string,
// use "outer_key"'s value so that `new_doc` will have other properties such as `foo` for free.
if (SOME_FLAG && p_json != NULL) {
    new_doc.CopyFrom(*p_json, new_doc_allocator);

    // The value of "inner_key" will be re-added later, so remove it for now.
    // assert(IsObject()) fails here and core is dumped.
    if (new_doc.HasMember("inner_key")) {
        new_doc.RemoveMember("inner_key");
    }
} else {
    // Otherwise, start from an empty object.
    new_doc.SetObject();
}

// Add "inner_key" for both cases above.
const std::string new_value_str = "new_value";
new_doc.AddMember("inner_key", rapidjson::StringRef(new_value_str.c_str()), new_doc_allocator);

We suspect that the new_doc.CopyFrom(*p_json, new_doc_allocator); line is the culprit, but are kind of new to rapidjson and not sure whether it is the correct way to use new_doc_allocator to copy *p_json to new_doc.

The weird part is that this issue only happened online for a small number of requests. We extracted the input JSON string, checked that it is valid, but couldn't reproduce the failure offline.

It would be good if someone could point out where we did wrong. Thanks in advance.

rapidjson's assert IsObject() fails randomly while it shouldn't

0 Answers0