Support "application/problem+json" Content Type

[Maxouwell]

What version of React Router are you using?

6.17.0

Steps to Reproduce

RFC 7807/9457 introduced a extensible format for json error response, and a dedicated Content-Type : "application/problem+json".
Some server framework start to respond with this Content-Type on error (Spring Framework 6 for example).

When these responses are returned on a loader or action, the resulting response is used as text instead of a json:
(packages/router/router.ts#L3925)

    let contentType = result.headers.get("Content-Type");
    // Check between word boundaries instead of startsWith() due to the last
    // paragraph of https://httpwg.org/specs/rfc9110.html#field.content-type
    if (contentType && /\bapplication\/json\b/.test(contentType)) {
      data = await result.json();
    } else {
      data = await result.text();
    }

Would it be possible to add the new Content Type ?

Expected Behavior

useLoaderData or useActionData returns a Javascript object

Actual Behavior

useLoaderData or useActionData returns a string

[timdorr]

It's probably best to wait until this has advanced beyond the Proposed Standard stage, which is the introductory level for IETF RFCs.

[brophdawg11]

I'm going to convert this to a Proposal for consideration. However I will say that as part of our ongoing work for single fetch we are already looking into on some ways to let the React Router consumer customize the response parsing: #11029.

So I think that will eventually be your solution here - rather than RR trying to internally handle every content type under the sun.