Remove unnecessary RestHandler#supportsBulkContent

[DaveCTurner]

This method only exists to add some additional Content-type
validation, but we can do all the validation needed using
RestHandler#mediaTypesValid instead.

[elasticsearchmachine]

Pinging @elastic/es-distributed-coordination (Team:Distributed Coordination)

[mhl-b]

LGTM.

But I would slap this check on XContentType enum.

    public static boolean isAnyOf(XContentType t, List<XContentType> ts) {
        if (t == null) return false;
        return ts.contains(t);
    }

    public static boolean isJsonOrSmile(XContentType t) {
        return isAnyOf(t, List.of(JSON, SMILE));
    }

Also remove indirection of hasValidMediaTypeForBulkRequest, saying isJsonOrSmile. RestBulkAction imports look odd here.

    public boolean mediaTypesValid(RestRequest request) {
        return XContentType.isJsonOrSmile(request.getXContentType());
    }

[DaveCTurner]

Yeah fair point this isn't just about RestBulkHandler and derivatives really. Slightly different approach, see d282db9.

[mhl-b]

Neat

[mhl-b]

A new version will return a generic unsupported type error rather than "stream parsing" error, right?

[DaveCTurner]

Yeah it will say Content-Type header [...] is not supported instead, with a (technically incorrect) 406 Not Acceptable either way.