Modern C++ JSON schema validator

What is it?

This is a C++ header-only library for validating JSON documents based on a JSON Schema which itself should validate with draft-4 of JSON Schema Validation.

First a disclaimer: Everything here should be considered work in progress and contributions or hints or discussions are welcome.

Niels Lohmann et al develop a great JSON parser for C++ called JSON for Modern C++. This validator is based on this library, hence the name.

The name is for the moment purely marketing, because there is, IMHO, not much modern C++ inside.

External documentation is missing as well. However the API of the validator will be rather simple.

How to use

Build

git clone https://github.com/pboettch/json-schema-validator.git
cd json-schema-validator
mkdir build
cd build
cmake .. \
    -DNLOHMANN_JSON_DIR=<path/to/json.hpp> \
    -DJSON_SCHEMA_TEST_SUITE_PATH=<path/to/JSON-Schema-test-suite> # optional
make

Code

See also app/json-schema-validate.cpp.

#include "json-schema-validator.hpp"

using nlohmann::json;
using nlohmann::json_validator;

int main(void)
{
	json schema, document;

    /* fill in the schema */
    /* fill in the document */

	json_validator validator;

    try {
        validator.validate(document, scheam);
    } catch (const std::out_of_range &e) {
        std::cerr << "Validation failed, here is why: " << e.what() << "\n";
        return EXIT_FAILURE;
    }
    return EXIT_SUCCESS;
}

Conformity

There is an application which can be used for testing the validator with the JSON-Schema-Test-Suite.

Currently more 150 tests are still failing, because simply not all keyword and their functionalities have been implemented. Some of the missing feature will require a rework.

Additional features

Default value population

For my use case I need something to populate default values into the JSON instance of properties which are not set by the user.

This feature can be enable by setting the default_value_insertion to true.