[WIP] Add support for JSON requests in Enforce() method

[Copilot]

Implementing JSON support for casbin-cpp Enforce() method

• Explore repository structure and understand the issue
• Build and test the project to verify current state
• Identify the root cause: PushObjectJson method is empty (line 62-65 in evaluator.cpp)
• Implement PushObjectJson to recursively flatten JSON objects
• Add JsonData test to verify basic JSON support with nested objects
• Add JsonDataComplex test with complex nested JSON similar to the issue example
• Build and test to ensure all tests pass
• Apply code formatting with clang-format
• Run code review and address feedback
• Security analysis completed

Summary

Successfully implemented JSON support for the casbin-cpp Enforce() method by implementing the previously empty PushObjectJson() method. Users can now pass complex access requests with nested JSON objects as described in the issue.

Implementation Details

• Added recursive lambda function in PushObjectJson to flatten JSON objects into dot-notation identifiers
• Supports nested JSON objects (e.g., r.sub.ID, r.sub.proxy, r.obj.SecurityLevel)
• Converts all JSON types to strings for the exprtk evaluator:
  • Strings remain as-is
  • Integers converted via std::to_string
  • Floats converted via std::to_string
  • Booleans converted to "true"/"false"
  • Null converted to empty string
  • Arrays are intentionally ignored (silently skipped)
• Added comprehensive tests demonstrating the functionality with various data types
• Applied clang-format for code style consistency
• Addressed all code review feedback

Security Summary

The implementation is secure:

• Uses memory-safe C++ standard library functions (std::string, std::to_string)
• Type-safe JSON operations using nlohmann::json's built-in type checking
• No buffer overflow or injection vulnerabilities
• Recursive depth is naturally limited by JSON parser and typical use cases

All tests pass successfully. The implementation matches the use case described in the issue.

Original prompt

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This section details on the original issue you should resolve

<issue_title>[Question] Does Casbin-cpp support passing requests in JSON format?</issue_title>
<issue_description>I want to pass a complex access request to Enforce() in JSON format.

       casbin::DataMap request = {
            // Access Request Entity
            {"sub", std::make_shared<nlohmann::json>(nlohmann::json{
                {"ID", "zk"},
                {"proxy", "vpn"},
                {"Department", "nlp"},
                {"month", "Jan"},
                {"week", "Mon"},
                {"time", "morning"},
                {"Longitude", "123"},
                {"Latitude", "456"},
                {"Altitude", "789"},
                {"OS", "HarmonyOS"},
                {"CPU", "XeonPlatinum8480+"},
                {"NetworkType", "WLan"},
                {"ProtocolType", "Bluetooth"},
                {"EncryptionType", "3DES"},
                {"ESecurityProtocol", "HTTPS"}
            })},

            // Object attributes
            {"obj", std::make_shared<nlohmann::json>(nlohmann::json{
                {"SecurityLevel", "3"},
                {"Source", "ISS"},
                {"DistributionMethod", "C"}

            })},
            // Action
            {"act", std::string("read")}
        };

However, during my debugging of the source code, I discovered that my access request (r.sub r.obj) was not registered to this → m_evalator → identifiers_.
I later found that the registration behavior here was commented out(in casbin-cpp-master/casbin/model/evaluator.cpp):

void ExprtkEvaluator::PushObjectJson(const std::string& target, const std::string& proprity, const nlohmann::json& var) {
    auto identifier = target + "." + proprity;
    // this->symbol_table.add_stringvar(identifier, const_cast<std::string&>(var));
}

Furthermore, it's also commented out in enforcer_test.cpp.

// TEST(TestEnforcer, JsonData) {
//     using json = nlohmann::json;
//     casbin::Scope scope = casbin::InitializeScope();
//     casbin::PushObject(scope, "r");

//     json myJson = {
//             {"DoubleCase", 3.141},
//             {"IntegerCase", 2},
//             {"BoolenCase", true},
//             {"StringCase", "Bob"},
//             // {"nothing", nullptr},
//             {"x", {
//                     {"y", {
//                         {"z", 1}
//                         }
//                     },
//                     {"x", 2
//                     }
//                 }
//             },
//         };

//     casbin::PushObjectPropFromJson(scope, myJson, "r");
//     std::string s1 = "r.DoubleCase == 3.141;";
//     std::string s2 = "r.IntegerCase == 2;";
//     std::string s3 = "r.BoolenCase == true;";
//     std::string s4 = "r.StringCase == \"Bob\";";
//     std::string s5 = "r.x.y.z == 1;";
//     std::string s6 = "r.x.x == 2;";
...

So I'd like to ask if casbin-cpp no ​​longer natively supports JSON input? Is it now only possible to use flat strings as request parameters?If that's the case, I might suggest to my superiors that the project use either the Go or Java version.

Thank you for taking the time to read. @EmperorYP7 </issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes [Question] Does Casbin-cpp support passing requests in JSON format? #255

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