Valijson provides a simple validation API that allows you to load JSON Schemas, and validate documents loaded by one of several supported parser libraries.
The goal of this project is to support validation of all constraints available in JSON Schema v7, while being competitive with the performance of a hand-written schema validator.
Note that Valijson's `SchemaParser` and `Validator` classes expect you to pass in a `RapidJsonAdapter` rather than a `rapidjson::Document`. This is due to the fact that `SchemaParser` and `Validator` are template classes that can be used with any of the JSON parsers supported by Valijson.
By default, Valijson classes will not throw exceptions (e.g. when failing to parse a schema). To enable exceptions for these cases, `VALIJSON_USE_EXCEPTIONS` must be defined.
However note that `VALIJSON_USE_EXCEPTIONS` is defined as interface compile definition of the cmake target, and the definition populates all the targets linking Valijson with cmake.
Valijson has a notion of strong and weak typing. By default, strong typing is used. For example, the following will create a validator that uses strong typing:
```cpp
Validator validator;
```
This validator will not attempt to cast between types to satisfy a schema. So the string `"23"` will not be parsed as a number.
Alternatively, weak typing can be used:
```cpp
Validator validator(Validator::kWeakTypes);
```
This will create a validator that will attempt to cast values to satisfy a schema. The original motivation for this was to support the Boost Property Tree library, which can parse JSON, but stores values as strings.
Valijson has been designed to safely manage, and eventually free, the memory that is allocated while parsing a schema or validating a document. When working with an externally loaded schema (i.e. one that is populated using the `SchemaParser` class) you can rely on RAII semantics.
Things get more interesting when you build a schema using custom code, as illustrated in the following snippet. This code demonstrates how you would create a schema to verify that the value of a 'description' property (if present) is always a string:
The library includes support for local JSON References. Remote JSON References are supported only when the appropriate callback functions are provided.
Valijson's JSON Reference implementation requires that two callback functions are required. The first is expected to return a pointer to a newly fetched document. Valijson takes ownership of this pointer. The second callback function is used to release ownership of that pointer back to the application. Typically, this would immediately free the memory that was allocated for the document.
Valijson's' test suite currently contains several hand-crafted tests and uses the standard [JSON Schema Test Suite](https://github.com/json-schema/JSON-Schema-Test-Suite) to test support for parts of the JSON Schema feature set that have been implemented.
It is possible to install headers by running cmake's install command from the build tree. Once Valijson is installed, use it from other CMake projects using `find_package(Valijson)` in your CMakeLists.txt.
Building the Valijson Test Suite, using the instructions above, will also compile two example applications: `custom_schema` and `external_schema`.
`custom_schema` shows how you can hard-code a schema definition into an application, while `external_schema` builds on the example code above to show you how to validate and document and report on any validation errors.
Support for JSON References is in development. It is mostly working, however some of the test cases added to [JSON Schema Test Suite](https://github.com/json-schema/JSON-Schema-Test-Suite) for v6/v7 are still failing.
An example application based on Qt is also included under [inspector](./inspector). It can be used to experiment with JSON Schemas and target documents. JSON Inspector is a self-contained CMake project, so it must be built separately:
## Live Demo
A web-based demo can be found [here](https://letmaik.github.io/valijson-wasm), courtesy of [Maik Riechert](https://github.com/letmaik).
This demo uses Emscripten to compile Valijson and Nlohmann JSON (JSON for Modern C++) to WebAssembly. The source code can be found [here](https://github.com/letmaik/valijson-wasm) and is available under the MIT license.
Doxygen documentation can be built by running 'doxygen' from the project root directory. Generated documentation will be placed in 'doc/html'. Other relevant documentation such as schemas and specifications have been included in the 'doc' directory.
Valijson requires a compiler with full C++11 support. Please note that versions of GCC prior to 4.9.0 had incomplete `<regex>` support, so `pattern` constraints may not work. If using GCC, it is recommended that you use GCC 5.0 or later.
Other versions of these libraries may work, but have not been tested. In particular, versions of jsoncpp going back to 0.5.0 should also work correctly.
When compiling with older versions of Boost (<1.76.0)youmayseecompilerwarningsfromthe`boost::property_tree`headers.Thishasbeenaddressedinversion1.76.0ofBoost.
If you are using [vcpkg](https://github.com/Microsoft/vcpkg) on your project for external dependencies, then you can use the [valijson](https://github.com/microsoft/vcpkg/tree/master/ports/valijson) package. Please see the vcpkg project for any issues regarding the packaging.
You can also use [conan](https://conan.io/) as a package manager to handle [valijson](https://conan.io/center/valijson/0.3/) package. Please see the [conan recipe](https://github.com/conan-io/conan-center-index/tree/master/recipes/valijson) for any issues regarding the packaging via conan.
When building Valijson using CMake on macOS, with Qt 5 installed via Homebrew, you may need to set `CMAKE_PREFIX_PATH` so that CMake can find your Qt installation, e.g:
