Check MIME-Type before parsing body content

[BenjaminHofstetter]

Problem:
checkResponse(res) is checking for HTTP Status Code 200 OK. This is not enough. Stardog is answering with Status Code OK on failure but the content is JSON with an Error description.

In the code ... https://github.com/zazuko/sparql-http-client/blob/b8575ba15260ff3f038326bc757c3bf9f6dff10b/StreamQuery.js#L56

we check checkResponse(res) for HTTP 200 and then the body is parsed with N3Parser.

    await checkResponse(res)

    const parser = new N3Parser({ factory: this.factory })

    return parser.import(res.body)

Because Stardog is sending HTTP 200 on error parser.import(res.body) tries to parse a JSON body. This leads to a parsing error.
To avoid this we should check if the content type is application/n-triples or text/turtle before parsing it.

[tpluscode]

This should totally be fixed by Stardog too xd

[ktk]

Not sure what the conclusion is so far. I think we can agree that 200 is not very helpful in this case, the question is should there be a way to have an override of an error-handler so we can catch particularities like what Stardog is doing?

@mielvds if I get you correctly you cannot get the JSON returned from Stardog at the moment? At least not in a parsable way

[mielvds]

The error I had turned out unrelated, so I removed the comments.

[ktk]

@tpluscode do you have a proposal for what I should report @ Stardog?

[tpluscode]

We already have, haven't we?

Regardless of this particular scenario, it is possible that the body is ini whatever way malformed and would fail to parse. Is it so that parser errors are not handled gracefully?