Niven is a C++17 library that simplifies the task of creating a REST-based API.

It is inspired by the C# Nancy framework and uses similar techniques for declaring routes and responses.

Niven is designed to be self-hosted and is built upon the libmicrohttpd C library.

class SimpleModule : public Module
{
	public:

		SimpleModule()
		{
			Get["/"] = [](auto) {
				return "The moon's a balloon";
			};
		}
};

REGISTER_MODULE(SimpleModule)

Routes can contain literal segments as well as named captures.

Get["/person/{id}"] = [](auto &c) {
	return "Someone with an ID of " + c["id"];
};

A number of response types are supported simply by returning the appropriate value. As seen above you can return a string which will result in a "text/plain" content type and a status of Http::Ok. Other responses include:

• HTTP status code, e.g. return Http::Unauthorized;
• A path which will return a file on disk if it exists, e.g. return std::filesystem::path(filename);
• Entity or tree which will be automatically serialised to JSON, e.g. return tree {{ "name", "Test" }};

Additionally, by explicitly returning a Response object you can manipulate the headers and cookies using a fluent syntax.

Get["/"] = [](auto) {
	return Response()
		.WithHeader("Content-Type", "application/json")
		.WithCookie({ "niven-test", "chocolate chip", DateTime::Now().AddSeconds(30) });
};

Niven contains a basic dependency container implementation.

Register a singleton with the host by passing in a shared_ptr:

host.Register<MyType>(std::make_shared<MyDerivedType>());

Register a concrete class type with the host to be constructed each time it is resolved with the given parameters:

host.Register<MyType, MyDerivedType>(param1, param2...);

Within a request handler the dependency can be resolved via the context:

Get["/{key}"] = [](Context &c) {
	return c.Resolve<MyType>()->Get(c["key"]);
};

Niven uses libentity for dealing with request/response JSON.

If you return either an object derived from ent::entity or an ent::tree as a response it will be automatically serialised as a JSON string and the response content type set to "application/json".

Incoming JSON can be bound to an object, for example

Post["/bind"] = [](Context &c) {
	return "The name is: " + c.Bind<MyEntity>().name;
};

Please take a look in the src/examples directory to see how to set up the host and in include/examples for some simple commented modules.

• libmicrohttpd - the HTTP host back-end.
• libgcrypt - for hashing and SSL.
• libemergent - type registration, file paths, datetime helper, logging, string helpers.
• libentity - entity serialisation/deserialisation, trees.

A modern compiler that supports C++17 such as clang and premake v5.0.

$ sudo apt-get install libmicrohttpd-dev libgcrypt20-dev

Ensure that the headers for libemergent and libentity can be found on the standard paths (for example /usr/local/include).

$ premake5 gmake
$ make

To build the examples:

$ cd src/examples
$ premake5 gmake
$ make

When building an application with niven you must link against libniven and pthread.