RDF convertors should not read or write plain JSON

[RubenVerborgh]

As discovered by @joepio in #275

Terminal 1

git checkout 3c32466d8873e73328f678acce1260fea02cabc9 # latest main
npm ci
npm start

Terminal 2

echo '{}' | curl -T - -H "Content-Type: application/json" http://localhost:3000/test
curl -H "Accept: text/turtle" http://localhost:3000/test

Log

2022-03-28T20:27:59.225Z [BaseHttpServerFactory] info: Received GET request for /test
2022-03-28T20:27:59.241Z [WebAclReader] info: Reading ACL statements from http://localhost:3000/.acl
2022-03-28T20:27:59.249Z [StreamUtil] warn: Piped stream errored with Missing context link header for media type application/json on http://localhost:3000/test
2022-03-28T20:27:59.250Z [StreamUtil] warn: Piped stream errored with Missing context link header for media type application/json on http://localhost:3000/test
2022-03-28T20:27:59.252Z [StreamUtil] warn: Piped stream errored with Missing context link header for media type application/json on http://localhost:3000/test
2022-03-28T20:27:59.252Z [BasicResponseWriter] error: Writing to HttpResponse failed with message Missing context link header for media type application/json on http://localhost:3000/test
2022-03-28T20:28:00.255Z [GuardedStream] error: No error listener was attached but error was thrown: aborted

Expected

200 or 406

[RubenVerborgh]

Conceptually, we need to extend RdfToQuadConverter with

  public async canHandle(args: RepresentationConverterArgs): Promise<void> {
    await super.canHandle(args);

    const { metadata } = args.representation;
    if (metadata.contentType === APPLICATION_JSON) {
      // Check if the Link header for the context is present
    }
  }

Whereas we can assume that our backend will always use application/ld+json, clients unfortunately may not.

In that sense, this converter has an interesting issue:

CommunitySolidServer/src/storage/conversion/RdfToQuadConverter.ts

Line 25 in 9ac00ca

const data = pipeSafely(rawQuads, pass, (error): Error => new BadRequestHttpError(error.message));

Who says it's the client making the error? In this case, it's the server, so it would be a 500 (see #1243).

[joachimvh]

I thought there was an issue about this somewhere but I couldn't find it so maybe I'm wrong. But yes, that's an issue if you use an RDF accept header on a JSON document. The getOutputTypes function should also be updated so it doesn't return results if the input type is JSON. Easiest is to just drop JSON from the input types being passed to the base class in the constructor.

[RubenVerborgh]

Easiest is to just drop JSON from the input types being passed to the base class in the constructor.

But then clients sending valid JSON-LD might will be in trouble.

[joachimvh]

But then clients sending valid JSON-LD might will be in trouble.

...if they are using application/json as content-type. And our server does not support this anyway as this would require us to parse the context header and put it in metadata to be used later by the converter.

[RubenVerborgh]

Perfect. But then we need to reject it.

[joachimvh]

That is going to require a MetadataParser that instead of putting header data into metadata throws an error if it sees a context header (specifically with application/json content type perhaps).

[RubenVerborgh]

Split off that task at #1244

[joachimvh]

Done in #1359