@rdfjs/express-handler

@rdfjs/express-handler

The @rdfjs/express-handler middleware provides methods to parse incoming RDF data from request with content like POST or PUT requests. It also provides methods to serialize outgoing RDF data.

Usage

The package returns a factory function to create express middlewares.

Factory

Adding it to all routes of the app would look like this:

import express from 'express'
import rdfHandler from '@rdfjs/express-handler'

const app = express()

app.use(rdfHandler())

The factory accepts the following options:

• factory: The factory used to create Dataset instances. Default: require('rdf-ext')
• formats: An object with parsers and serializers, each given as @rdfjs/sink-map. Default: require('@rdfjs/formats-common')
• defaultMediaType: If an unknown Content-Type is given, this media type will be used. Default: undefined
• baseIriFromRequest: If true, will call absolute-url to get the requested IRI and pass as base IRI to the parser. It can also be a function async (req) => string which can be used to compute the base IRI for the parser.
• sendTriples: If true, the RDF/JS Quads sent using res.dataset() or res.quadStream() are converted to triples (default graph). Default undefined.

Request

Routes following the RDF Handler can access the parsed Quads from the request as a Stream or Dataset. The req.dataset() and req.quadStream() methods can be used for this. But the methods are only attached if the request contains content in a type supported by one of the parsers. The logic to access the Quads could look like this:

app.use((req, res) => {
  if (!req.dataset) {
    return res.status(406).end() // send 406 not acceptable if the content can't be parsed
  }

  const dataset = await req.dataset()
})

req.dataset() requires await as it's an async method. req.quadStream() is a sync method. Both methods accept an options object, which is forwarded to the parser.

Response

The RDF Handler middleware always attaches the res.dataset() and res.quadStream() methods. The methods must be called with the Dataset or Stream, which should be sent. A second options object can be given, which will be forwarded to the serializer. Sending a Dataset would look like this:

app.use((req, res) => {
  await res.dataset(dataset)
})

Both methods are async and finished once the response was sent.

Attaching

If you don't know if @rdfjs/express-handler is used earlier in the application, it's possible to attach it dynamically. That is useful inside of a middleware where you want to use an application RDF Handler instance and it's options, but fallback to a local instance if there is no RDF Handler earlier in the routes. The .attach() function can be used. await must be used, as it's an async function.

app.use((req, res) => {
  await rdfHandler.attach(req, res)

  if (req.dataset) {
    const dataset = await req.dataset()
  }

  await res.dataset(rdf.dataset())
})