Support Link header when fetching remote contexts

[cheerfulstoic]

I referenced this bit of the documentation (thanks @gkellogg in this comment). The most relevant being part 5 (quoted below). I haven't implemented all of it, but started with the basic case that would fix the issue. I'll start playing around with more fully supporting the spec.

One question, though: that document is for JSON-LD 1.1, and as far as I can see, this library doesn't support beyond 1.0 yet. I'm not sure if the Link header is a 1.0 thing, but I also wasn't able to get any JSON-LD data from various webpages to work because of this issue, so 🤷

"If the retrieved resource's Content-Type is application/json or any media type with a +json suffix as defined in [RFC6839] except application/ld+json, and the response has an HTTP Link Header [RFC8288] using the http://www.w3.org/ns/json-ld#context link relation, set contextUrl to the associated href."

"If multiple HTTP Link Headers using the http://www.w3.org/ns/json-ld#context link relation are found, the promise is rejected with a JsonLdError whose code is set to multiple context link headers and processing is terminated."

"Processors MAY transform document to the internal representation."

"NOTE: The HTTP Link Header is ignored for documents served as application/ld+json, text/html, or application/xhtml+xml."

[marcelotto]

Sorry for the late reply.

One question, though: that document is for JSON-LD 1.1, and as far as I can see, this library doesn't support beyond 1.0 yet.

That's correct.

I'm not sure if the Link header is a 1.0 thing, but I also wasn't able to get any JSON-LD data from various webpages to work because of this issue, so 🤷

It seems to be supported in 1.0 already: https://www.w3.org/TR/2014/REC-json-ld-20140116/#interpreting-json-as-json-ld

[marcelotto]

CI doesn't pass yet.

[cheerfulstoic]

🤔 Is it passing on master? When I try to run it locally in master it fails. It seems to be that it's trying to connect to the http://json-ld.org/* URLs and they're failing to load.

[marcelotto]

🤔 Is it passing on master? When I try to run it locally in master it fails. It seems to be that it's trying to connect to the http://json-ld.org/* URLs and they're failing to load.

You're right. http://json-ld.org/ is currently down in general. json-ld/json-ld.org#802

[cheerfulstoic]

Seems like the site's back up. I re-pushed to see if I could get the tests to run, but maybe they're run manually. Anyway, hopefully they're working now 🤞

Might be worth trying out exvcr for these tests which connect to json-ld.org so that the tests can run even if the site is down (I think maybe you can re-generate the cassettes occasionally to make sure you're still matching to real data)

[marcelotto]

Seems like the site's back up. I re-pushed to see if I could get the tests to run, but maybe they're run manually. Anyway, hopefully they're working now 🤞

The problem was this: "First-time contributors need a maintainer to approve running workflows." So, your next PR should automatically trigger CI ;-)

I approved and it's passing now. 🚀

Might be worth trying out exvcr for these tests which connect to json-ld.org so that the tests can run even if the site is down (I think maybe you can re-generate the cassettes occasionally to make sure you're still matching to real data)

Yes, I agree. In the sparql_client I'm already using this. But the whole remote-context handling was not written by me and there are more things to improve on this front, eg. the hard dependency on Hackney for this. I would prefer Tesla to give users the option to choose the HTTP client they want. Unfortunately, I don't have time to look into all of this at the moment. PRs are welcome, however.