Linked Data Fetch: a HTTP client for RDF resources

For both the browser as the NodeJS framework it adds features specifically for getting RDF resources.

Supports these features over standard fetch:

• Prefers to read TriG, yet also reads N3, Turtle, N-Triples, N-Quads, RDFa, JSON-LD snippets hidden in the HTML or just plain JSON-LD (uses content-negotiation to get an RDF representation)
• Returns the Triples/Quads containing the data in the RDFJS triple representation
• Returns the URL of the document after redirects
• Emits events for: request, response, redirect, cache-hit, cache-miss and parsed

Features for the NodeJS framework in specific:

• Automatically follows redirects
• Able to be configured with HTTP caching
• Able to limit the amount of concurrent requests and schedule these

Features for the Command Line:

• Writes data on any URL in TriG on stdout
• Extra features to automatically follow links (see ldfetch --help after npm install -g ldfetch)

Install it in your project:

npm install ldfetch

And using webpack you can also compile it for browser purposes:

npm run build

<script src="dist/main.js"></script>
<script>
  var fetch = new window.ldfetch();
  //use it as described bellow
</script>

How to use it

A small example fetching the next page of a paged collection and returning the url

  var ldfetch = require('../lib/ldfetch.js');
  try {
    var url = 'https://graph.irail.be/sncb/connections/';
    var options = ""; //{headers: {'Accept-Datetime': '2017-03-11T17:00:00.000Z'}}; // optional -- and then we’d have to look for the next page in a more advanced way
    var fetch = new ldfetch(options);
    fetch.addPrefix("hydra","http://www.w3.org/ns/hydra/core#");
    var response = await fetch.get(url); 
    for (var i = 0; i < response.triples.length; i ++) {
      var triple = response.triples[i];
      if (triple.subject.value === response.url && triple.predicate.value === 'http://www.w3.org/ns/hydra/core#next') {
        console.error('The next page is: ', triple.object.value);
      }
    }
  } catch (e) {
    console.error(e);
  }

If HTTP requests with specific headers are needed, the options object may be used by defining an object inside of it, named headers containig HTTP header names and values.

The response object will look like this:

{
  "responseCode": 200,
  "triples": [{},{},{}],
  "prefixes": {"hydra": "http://www.w3.org/ns/hydra/core#"},
  "url": "https://{url after redirects}"
}

License and copyright

This library was developed by Pieter Colpaert and contributors. The source code is available under an MIT license.