valijson/README.md

# Valijson [![Build Status](https://travis-ci.org/tristanpenman/valijson.svg?branch=master)](https://travis-ci.org/tristanpenman/valijson) #

## Overview ##

Valijson is a header-only [JSON Schema](http://json-schema.org/) Validation library for C++11.

Valijson provides a simple validation API that allows you load JSON Schemas, and validate documents loaded by one of several supported parser libraries.

## Project Goals ##

The goal of this project is to support validation of all constraints available in JSON Schema v4, while being competitive with the performance of a hand-written schema validator.

## Usage ##

The following code snippets show how you might implement a simple validator using RapidJson as the underlying JSON Parser.

Include the necessary headers:

    #include <rapidjson/document.h>

    #include <valijson/adapters/rapidjson_adapter.hpp>
    #include <valijson/utils/rapidjson_utils.hpp>
    #include <valijson/schema.hpp>
    #include <valijson/schema_parser.hpp>
    #include <valijson/validator.hpp>

These are the classes that we'll be using:

    using valijson::Schema;
    using valijson::SchemaParser;
    using valijson::Validator;
    using valijson::adapters::RapidJsonAdapter;

We are going to use RapidJSON to load the schema and the target document:

    // Load JSON document using RapidJSON with Valijson helper function
    rapidjson::Document mySchemaDoc;
    if (!valijson::utils::loadDocument("mySchema.json", mySchemaDoc)) {
        throw std::runtime_error("Failed to load schema document");
    }

    // Parse JSON schema content using valijson
    Schema mySchema;
    SchemaParser parser;
    RapidJsonAdapter mySchemaAdapter(mySchemaDoc);
    parser.populateSchema(mySchemaAdapter, mySchema);

Load a document to validate:

    rapidjson::Document myTargetDoc;
    if (!valijson::utils::loadDocument("myTarget.json", myTargetDoc)) {
        throw std::runtime_error("Failed to load target document");
    }

Validate a document:

    Validator validator;
    RapidJsonAdapter myTargetAdapter(myTargetDoc);
    if (!validator.validate(mySchema, myTargetAdapter, NULL)) {
        std::runtime_error("Validation failed.");
    }

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.

## Memory Management ##

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:

    {
        // Root schema object that manages memory allocated for
        // constraints or sub-schemas
        Schema schema;

        // Allocating memory for a sub-schema returns a const pointer
        // which allows inspection but not mutation. This memory will be
        // freed only when the root schema goes out of scope
        const Subschema *subschema = schema.createSubschema();

        {   // Limited scope, for example purposes

            // Construct a constraint on the stack
            TypeConstraint typeConstraint;
            typeConstraint.addNamedType(TypeConstraint::kString);

            // Constraints are added to a sub-schema via the root schema,
            // which will make a copy of the constraint
            schema.addConstraintToSubschema(typeConstraint, subschema);

            // Constraint on the stack goes out of scope, but the copy
            // held by the root schema continues to exist
        }

        // Include subschema in properties constraint
        PropertiesConstraint propertiesConstraint;
        propertiesConstraint.addPropertySubschema("description", subschema);

        // Add the properties constraint
        schema.addConstraint(propertiesConstraint);

        // Root schema goes out of scope and all allocated memory is freed
    }

## JSON References ##

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.

## Test Suite ##

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.

### cmake ###

The examples and test suite can be built using cmake:

    # Build examples and test suite
    mkdir build
    cd build
    cmake ..
    make

    # Run test suite (from build directory)
    ./test_suite

### Xcode ###

An Xcode project has also been provided, in the 'xcode' directory. Note that in order to run the test suite, you may need to configure the working directory for the 'test\_suite' scheme. It is recommended that you use the 'xcode' directory as the working directory.

The Xcode project has been configured so that /usr/local/include is in the include path, and /usr/local/lib is in the library path. These are the locations that homebrew installed Boost on my test system.

## Examples ##

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.

## JSON Schema Support ##

Valijson supports most of the constraints defined in [Draft 3](http://tools.ietf.org/search/draft-zyp-json-schema-03) and [Draft 4](http://tools.ietf.org/search/draft-zyp-json-schema-04) of the JSON Schema specification.

The exceptions for Draft 3 are:

 - disallow
 - extends
 - format (optional)
 - readonly

The exceptions for Draft 4 are:

 - format (optional)

Support for JSON References is in development.

## Documentation ##

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.

## Dependencies ##

Valijson requires a compiler with robust C++11 support.

## Supported Parsers ##

Valijson supports JSON documents loaded using JsonCpp, RapidJson, Boost Property Tree and PicoJSON. It has been tested against the following versions of these libraries:

 - [boost::property_tree 1.54](http://www.boost.org/doc/libs/1_54_0/doc/html/boost_propertytree/synopsis.html)
 - [json11 (commit afcc8d0)](https://github.com/dropbox/json11/tree/afcc8d0d82b1ce2df587a7a0637d05ba493bf5e6)
 - [jsoncpp 0.9.4](https://github.com/open-source-parsers/jsoncpp/archive/0.9.4.tar.gz)
 - [nlohmann/json 1.1.0](https://github.com/nlohmann/json/archive/v1.1.0.tar.gz)
 - [rapidjson 1.0.2](https://github.com/miloyip/rapidjson/releases/tag/v1.0.2)
 - [PicoJSON 1.3.0](https://github.com/kazuho/picojson/archive/v1.3.0.tar.gz)

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, but versions from 1.0 onwards have not yet been tested.

## Test Suite Requirements ##

Supported versions of these libraries have been included in the 'thirdparty' directory so as to support Valijson's examples and test suite. 

The only exception to this is boost, which due to its sheer size must be installed to a location that CMake can find.

## Known Issues ##

Note that when using PicoJSON, it may be necessary to include the `picojson.h` before other headers to ensure that the appropriate macros have been enabled.

## License ##

Valijson is licensed under the Simplified BSD License.

See the LICENSE file for more information.