This week at the HTTP reading group we discussed content negotiation (RFC 7231 § 3.4).
We already familiar with the idea of proactive negotiation (§ 3.4.1)—where the client sends an
Accept-Language, etc. header and the server responds with the correct representation—but reactive negotiation (§ 3.4.2) was new to us, especially the idea of sending a
300 (Multiple Choices) response with a list of possible representations and letting the user (or UA) decide.
It seems like this would be more useful if there was a standard way of sending the list of alternatives, so that the UA could pick one based on the user’s preferences. We talked about using HTML that looked something like this, but without built-in browser support it would still require user interaction:
<a href="en.html" rel="alternate" hreflang="en" type="text/html">HTML, English</a> <a href="fr.json" rel="alternate" hreflang="fr" type="application/json">JSON, French</a>
There is an experimental RFC from 1998 (RFC 2295) that defines an
Alternates headers that can be used to list the options in a 300 response, but according to a W3C HTTP Working Group mailing list post from 2009 it isn’t widely supported.
Has anyone seen a 300 in the wild, or used one in their own applications?
/cc @calleerlandsson @joelq @DeviousDuck