Restore DOI content-negotiation redirect parity for wildcard and XML/RDF/Turtle Accept headers

[Copilot]

This updates DOI content negotiation to match current DataCite CN parity for unsupported XML/RDF/Turtle-style Accept headers. Requests with */*, application/xml, application/rdf+xml, text/turtle, and application/x-turtle now redirect to doi.url instead of attempting to render a body or failing with 500.

• Controller behavior

  • Treat unregistered/unknown negotiated formats as redirect cases before respond_to
  • Keep 303 See Other redirect behavior
  • Preserve safe cross-site redirect handling with allow_other_host: true

• Parity-aligned Accept handling

  • Accept: */* no longer falls into a 500 path
  • Accept: application/xml
  • Accept: application/rdf+xml
  • Accept: text/turtle
  • Accept: application/x-turtle
  • All now resolve to redirect behavior rather than RDF/XML or Turtle rendering

• Specs

  • Add request coverage asserting redirect behavior for the headers above
  • Leave existing supported content types unchanged

def show
  # ...
  if request.format.symbol.nil?
    redirect_to_doi(doi)
    return
  end

  respond_to do |format|
    format.html { redirect_to_doi(doi) }
    # supported formats unchanged
  end
rescue ActionController::UnknownFormat, ActionController::RoutingError
  redirect_to_doi(doi)
end

Original prompt

Update PR #1518 in repository datacite/lupo to match current DataCite Content Negotiation (CN) parity behavior.

Context / desired parity:

• Current CN behavior for https://api.datacite.org/[doi] with Accept headers like application/xml, application/rdf+xml, and text/turtle is a 303 See Other redirect (not a 200 response with RDF/Turtle bodies).
• Current production returns 500 for Accept: /; treat that as a bug and fix it in Lupo.
• Lupo should NOT generate RDF/XML or Turtle bodies in this PR. RDF/XML/Turtle output may be a future feature.
• doi.graph can be nil; do not call graph.dump(...) via rdf/turtle renderers.

Required changes:

1. Keep wildcard Accept handling: Accept: / must NOT return 500 and should fall back to normal redirect behavior (302/303 acceptable, prefer 303). Keep redirect safety (allow_other_host: true).
2. Ensure Accept: application/xml, application/rdf+xml, text/turtle, application/x-turtle all redirect like CN: status 303 See Other with Location header set to doi.url. Do not render bodies.
3. Remove RDF/Turtle support introduced by this PR:
   • Remove MIME registrations for application/rdf+xml and text/turtle/application/x-turtle.
   • Remove ActionController renderers for :rdf_xml and :turtle.
   • Remove link-form routes for RDF/Turtle (/application/rdf+xml/:id, /text/turtle/:id, /application/x-turtle/:id).
   • Remove controller wiring that renders :rdf_xml or :turtle.
   • Remove Doi model methods ensure_bolognese_meta!, rdf_xml, turtle (and any RDF-related meta population added for this).
4. Update specs:
   • Remove specs expecting 200 for RDF/XML/Turtle and any body expectations (rdf:RDF, @Prefix schema:).
   • Add/update specs asserting redirect behavior for Accept: application/xml, application/rdf+xml, text/turtle, application/x-turtle.
   • Keep/add spec for Accept: / asserting no 500 and redirect.
   • Do not require DOI fixture to have non-nil graph to pass parity tests.

Notes:

• The existing unsafe redirect fix in IndexController#show format.html should be kept.
• Keep allow_other_host: true for redirects.
• Keep behavior for existing supported formats (datacite XML/JSON, schemaorg, etc.) unchanged.

Acceptance criteria:

• Request specs should reflect redirect parity for the formats above.
• Wildcard Accept should not return 500.
• No RDF/Turtle bodies are generated or rendered in controller/renderers.
• All tests pass.

The following is the prior conversation context from the user's chat exploration (may be truncated):

User: i have not applied crosssite solution

Assistant: Apply the Crosscitable require fix; that’s the single change that consistently eliminates NameError: uninitialized constant JSON::LD::Context in your request-spec runtime (where initializers weren’t reliably helping).

1) Update app/models/concerns/crosscitable.rb

Add these requires at the very top of the file (before the module definition). This guarantees the constants bolognese references are loaded whenever Doi is loaded.

# frozen_string_literal: true

# Ensure RDF + JSON-LD dependencies used by Bolognese::MetadataUtils#graph are loaded
# in all runtimes (incl. request specs where initializers may not be executed).
require "rdf"
require "json/ld"
require "json/ld/context"
require "json/ld/api"

# Ensure RDF::Graph#dump supports the serialization formats used by bolognese writers
require "rdf/rdfxml"
require "rdf/turtle"

module Crosscitable
  extend ActiveSupport::Concern

  included do
    include Bolognese::MetadataUtils
    # ... keep the rest of your existing includes/code here unchanged ...
  end

  # ... rest of the file unchanged ...
end

Notes:

• If your file already has # frozen_string_literal: true, keep it once.
• If the file already starts with other requires, place these with them.
• If require "rdf/rdfxml" raises LoadError, you’ll need to add gem rdf-rdfxml to the Gemfile. Try first.

2) Remove any temporary “debug graph” monkeypatches

Delete any initializer or override you added that redefines Bolognese::MetadataUtils#graph to “not rescue NameError”. That debug code will now cause 500s and is no longer needed.

3) Keep Doi#rdf_xml and #turtle returning 406 when graph can’t be built

Make sure you have (or revert to) this:

def rdf_xml
  ensure_bolognese_meta!
  raise ActionController::UnknownFormat, "RDF representation is not available for this DOI" if graph.nil?
  super
end

def turtle
  ensure_bolognese_meta!
  raise ActionController::UnknownFormat, "RDF representation is not available for this DOI" if graph.nil?
  super
end

4) Re-run the failing specs

bundle exec rspec spec/requests/index_spec.rb:351

If it still fails after this, paste the new failure output; at that point the most likely remaining issue will be either:

• missing rdf-rdfxml gem (LoadError from rdf/rdfxml), or
• the...

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