Hydra is a machine readable description for APIs. Kopflos extends the API description with links to the actual code, which provides the API. Kopflos will use such an API description to create an express middleware which provides the API and dynamically loads the required code for it.
@kopflos-cms/core
uses an object that implements the RDF/JS Store interface to read resources and find types of resources to identify matching operations.
The resource is read using the IRI as named graph filter.
Here an example for a store on the local file system using rdf-store-fs
:
import FlatMultiFileStore from 'rdf-store-fs/FlatMultiFileStore.js'
const store = new FlatMultiFileStore({
baseIRI: 'http://localhost:9000/',
path: 'store'
})
An Api
object contains the dataset of the API documentation, where to find it and where to find the code.
The static method .fromFile
reads the dataset from the given file and creates an Api
object with the given options.
import rdf from '@zazuko/env-node'
const api = await Api.fromFile('api.ttl', {
factory: rdf,
path: '/api',
codePath: __dirname
})
The factory
parameter is required, and must be an RDF/JS Environment, providing the following factories compatible with the following:
- DatasetCoreFactory
- DataFactory
- NamespaceFactory
- TermSetFactory
- ClownfaceFactory
- NsBuildersFactory
- FsUtilsFactory
Once both objects are created, the middleware can be used:
const app = express()
app.use(hydraBox(api, store))
app.listen(9000)
The operations must implement a Express routing handler interface ((req, res, next) => {}
).
@kopflos-cms/core adds the @rdfjs/express-handler to handle incoming and outgoing RDF data.
For GET
requests with a matching IRI Template, the .dataset()
and .quadStream()
as defined by express-handler
are also available to read the given variables.
Additionally, there is a hydra
property assigned to req
that contains more data about the request:
req.hydra = {
// Api object given as argument to the middleware
api,
// RDF/JS Store object given as argument to the middleware
store,
// requested URL as RDF/JS NamedNode
term,
// the selected hydra:Operation as Graph Pointer
operation,
// resource this request is about
// This can be the requested URL for the case that a class operation is called.
// For the case that a property operation is called, this is the subject of the triple used to link to the property.
resource: {
// IRI of the resource as RDF/JS NamedNode
term,
// content of the resource read from the store as RDF/JS Dataset
dataset,
// rdf:types of the resource as @rdfjs/term-set
types
}
}