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. But I think the whole thing could be rewritten mode "modern".

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

How to use

Build

Directly

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 # install
ctest # if test-suite has been given

or from another CMakeLists.txt as a subdirectory:

# create an interface-target called json-hpp
add_library(json-hpp INTERFACE)
target_include_directories(json-hpp
    INTERFACE
        path/to/json.hpp)
set(JSON_SCHEMA_TEST_SUITE_PATH "path/to/json-schema-test-suite")

enable_testing() # if you want to inherit tests
add_subdirectory(path-to-this-project json-schema-validator)

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 72 of ~308 tests are still failing, because simply not all keywords and their functionalities have been implemented. Some of the missing feature will require a rework. Some will only work with external libraries. (remote references)

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.