how to validate ipv4 with pattern in rapidjson

Question

(This question is not duplicate of regex to validate ipv4

It is not asking "somehow". It is asking to do that with rapidjson library:

rapidjson

I have already tried options of regex to validate ipv4, but with rapidjson did not work.)

I am using rapidjson and I want to validate JSON against schema.

rapidjson ignores "format" of "string" but it is indicated that it does support "pattern". So, I try this pattern to validate ipv4 format:

^((25[0-5]|(2[0-4]|1[0-9]|[1-9]|)[0-9])(\\.(?!$)|$)){4}$

This normally is able to validate ipv4 in a json (draft#4) (checked with other json validators).

However, rapidjson still fails: It returns OK for an invalid ip string.

Here is complete schema and test data of C++:

std::string strschema = R"({"type":"object","properties":{"ip":{"type":"string","pattern":"^((25[0-5]|(2[0-4]|1[0-9]|[1-9]|)[0-9])(\\.(?!$)|$)){4}$"}}, "required":["ip"]})";
std::string json = R"({"ip":"hahaha"})";

rapidjson::Document schema;
schema.Parse(strschema.c_str());
rapidjson::SchemaDocument schemaDocument(schema);
rapidjson::SchemaValidator schemaValidator(schemaDocument);

rapidjson::Document doc;
doc.Parse(json.c_str());

bool b = doc.Accept(schemaValidator);

How can I validate an ipv4 format in rapidjson using pattern, not with std::regex but with internal regex RAPIDJSON_SCHEMA_USE_INTERNALREGEX?