C++98 JSON Parser & Validator (Zod-like)

This project is a custom JSON parser and schema validator library written in C++98, designed without relying on modern C++ features or any external JSON libraries.

Due to the lack of built-in JSON support and modern language features in C++98, the project includes:

• A full JSON parser
• A custom JSON object model (JsonObject, JsonArray, etc.)
• A Zod-like schema validator with fluent validation rules

Why? 🤔

This project originally started as a fun side project, where I wanted to challenge myself to build a JSON parser and validator from scratch in C++98.

Later, I decided to integrate it into my 1337 (42) school webserv project to handle server configuration files using JSON instead of the more common .conf or YAML formats that most students choose.

Since the webserv project at 42 requires strict C++98 compliance, I couldn’t rely on any modern JSON libraries. This pushed me to design and implement my own:

• JSON Object Model
• JSON Parser
• JSON Schema Validator (inspired by tools like Zod in TypeScript)

Rather than taking the common path of writing an NGINX-style parser, I wanted something developer-friendly and schema-validated, making configuration parsing both fun and robust.

Features ✅

• JSON parsing from file or raw string
• Full JSON type system: Object, Array, String, Number, Bool, Null
• Chainable & type-safe JSON validation
• Schema definitions for complex nested JSON structures
• Default values support
• Optional fields
• Custom error reporting (Not fully supported 🗿)
• Supports constraints like min, max, string length, allowed values, etc.
• Object shape checking, array item validation, OR conditions, and more

Example: Server Configuration Schema ✅

Parsing JSON

AJsonValue* json = Json::parse("config.json");  // From file
AJsonValue* jsonRaw = Json::parse_raw("{ \"key\": \"value\" }");  // From string

Schema definition (like Zod in JS):

ArrayValidator ServerSchema = arr().item(
    obj()
        .property("server_name", str().notEmpty())
        .property("host", str().notEmpty())
        .property("port", arr().item(num().min(0).max(65535)).min(1))
        .property("redirects", obj().match(str().isStartWith('/'),str().isStartWith('/'))).optional()
        .property("error_pages", obj().match(str().isDigit(), str().notEmpty())).optional()
        .property("default_root", str().notEmpty().isValidDir())
        .property("default_index", arr().item(str().notEmpty()))
        .property("location", obj().match(str().notEmpty().isStartWith('/'), locationSchema))
        .property("list_dir", Bool().withDefault(false))
        .property("client_max_body_size", num().min(0).withDefault(1024)))
    .min(1);

Location schema example (nested object validation):

ObjectValidator locationSchema = obj()
    .property("allowed_methods", arr().item(Or()
        .addConditions(str().isEqual("GET"))
        .addConditions(str().isEqual("POST"))
        .addConditions(str().isEqual("DELETE"))
        .withMsg("Allowed methods must be GET, POST or DELETE!")).max(3))
    .property("auto_index", Bool().withDefault(false))
    .property("cgi", obj().match(str().notEmpty(), str().notEmpty().isValidPath()))
    .property("upload_dir", str().notEmpty()).optional();

Example Usage ✅

#include "Json.hpp"
#include "JsonValidator.hpp"

AJsonValue* config = Json::parse("config.json");

if (!ServerSchema.validate(config)) {
    const std::vector<ValidationError>& errors = ServerSchema.getErrors();
    for (size_t i = 0; i < errors.size(); ++i) {
        std::cout << errors[i].path << "': " << errors[i].msg << std::endl;
    }
} else {
    std::cout << "JSON config is valid!" << std::endl;
}

delete config;

Limitations ❌

• C++98: No modern C++ features like smart pointers, STL JSON libs, or variadic templates
• Manual Memory Management: You are responsible for deleting JSON values after use
• No Streaming / Incremental Parsing: Full JSON loads into memory

Building 🔨

Example (G++ or Clang with C++98 mode):

c++ -std=c++98 -Iincludes src/*.cpp -o json_validator main.cpp

Where main.cpp is your file that uses the library.

License 📜

This project is licensed under the MIT License ©️ Mohammed Hayyoun.