Support RDF/XML and Turtle content negotiation; fix wildcard Accept 500

[Copilot]

Accept: */* and no-Accept requests were returning 500 due to Rails unsafe-redirect protection blocking cross-host redirects in the format.html branch. Additionally, application/rdf+xml and text/turtle were not supported as representations — both redirected 303 instead of returning content.

Changes

• Unsafe redirect fix (app/controllers/index_controller.rb)

  • Added allow_other_host: true to format.html redirect — matches the already-correct rescue branch; eliminates 500 for wildcard/no-Accept requests

• RDF/XML + Turtle MIME registration (config/initializers/mime_types.rb)

  • application/rdf+xml → :rdf_xml
  • text/turtle → :turtle (with application/x-turtle as alias)
  • Renderers call obj.rdf_xml / obj.turtle from Bolognese's RdfXmlWriter/TurtleWriter, already included in Doi via Crosscitable — no network calls, no new dependencies

• Controller wiring (app/controllers/index_controller.rb)

  • Added :rdf_xml and :turtle to the format.any(...) block

• Link-form routes (config/routes.rb)

  get "/application/rdf+xml/:id",  to: "index#show", constraints: { id: /.+/ }, defaults: { format: :rdf_xml }
  get "/application/x-turtle/:id", to: "index#show", constraints: { id: /.+/ }, defaults: { format: :turtle }
  get "/text/turtle/:id",          to: "index#show", constraints: { id: /.+/ }, defaults: { format: :turtle }

• Request specs (spec/requests/index_spec.rb)

  • Header-based and link-form tests for application/rdf+xml, text/turtle, application/x-turtle
  • Wildcard Accept: */* guard (must not return 500)

Original prompt

Create a PR in datacite/lupo to fully support RDF/XML and Turtle content negotiation (both header-based and link-form routes) without making network calls, and fix wildcard/no-Accept redirect failures.

Context / current behavior (stage testing):

• Most content negotiation formats already work.
• Accept: */* and requests with no Accept header currently return 500 due to Rails unsafe redirect protection when redirecting to doi.url.
• Accept: application/rdf+xml and Accept: text/turtle currently redirect (303) instead of returning RDF.

Requirements:

1. Fix unsafe redirect for HTML fallback in app/controllers/index_controller.rb:

   • In format.html branch of IndexController#show, redirect to doi.url must include allow_other_host: true (to avoid 500).
   • Keep status :see_other.

2. Add RDF/XML + Turtle response support in Lupo (no network calls):

   • Support RDF/XML application/rdf+xml (format symbol :rdf_xml).
   • Support Turtle for BOTH text/turtle and legacy application/x-turtle (format symbol :turtle).
   • Implement header-based negotiation (GET /:doi with Accept:) and link-form routes (GET /application/rdf+xml/:id, GET /application/x-turtle/:id, GET /text/turtle/:id).

3. No network calls:

   • Do not fetch metadata from external APIs.
   • Use the DOI record already available in Lupo, converting it to RDF using local code.

4. Implementation approach guidance:

   • Lupo already depends on RDF-related gems (rdf, rdf-rdfxml, rdf-turtle) per Gemfile.lock, and DataCite uses Bolognese writers in the legacy CN service.
   • Prefer leveraging existing Bolognese conversion if already present in Lupo, but do not add external HTTP calls.
   • If Bolognese is not currently a dependency, you may add it as a gem dependency if needed and reasonable, but keep change minimal.

5. Update MIME types and renderers:

   • Ensure config/initializers/mime_types.rb registers:
     • application/rdf+xml => :rdf_xml
     • application/x-turtle => :turtle
     • text/turtle => :turtle
   • Add renderers for :rdf_xml and :turtle.

6. Update IndexController#show:

   • Include :rdf_xml and :turtle in the format.any(...) block that renders render request.format.to_sym => doi.

7. Add routes for link-form content negotiation:

   • In config/routes.rb, add GET routes mapping to IndexController#show with defaults:
     • /application/rdf+xml/:id => format :rdf_xml
     • /application/x-turtle/:id => format :turtle
     • /text/turtle/:id => format :turtle
   • Ensure constraints: { id: /.+/ } consistent with other CN routes.

8. Tests:

   • Add request specs that cover:
     • GET /:doi with Accept: application/rdf+xml returns 200 and Content-Type contains application/rdf+xml.
     • GET /:doi with Accept: application/x-turtle returns 200 and Content-Type contains application/x-turtle OR text/turtle (depending on mime registration) and body contains Turtle-like content (e.g., @prefix schema:).
     • GET /:doi with Accept: text/turtle returns 200 and turtle body.
     • Link-form routes return 200 and correct Content-Type:
       • /application/rdf+xml/:doi
       • /application/x-turtle/:doi
       • /text/turtle/:doi
     • GET /:doi with Accept: */* does not 500 and redirects (302/303) to doi.url.
     • GET /:doi with no Accept header does not 500 and redirects.

9. PR description requirements:

   • Do NOT include any prompt text.
   • PR description must explain what changed and why (parity with resolver, keep RDF/Turtle support, fix unsafe redirect regression).

Notes:

• Use DOI fixtures/factories already in Lupo tests; pick a findable DOI with a URL that is external host (e.g., http://datacite.org/) to exercise redirect behavior.
• Ensure that RDF/Turtle generation uses local DOI metadata and does not require network.

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

User: Running Lupo Content Negotiation Compliance Tests
Base: https://api.stage.datacite.org

======================================
Testing DOI: 10.81360/BIFURCATED
Base: https://api.stage.datacite.org
Require link routes: 0

✅ PASS: DataCite XML (header) (status=200)
✅ PASS: DataCite XML CT (header) (ct=application/vnd.datacite.datacite+xml; charset=utf-8)
✅ PASS: DataCite XML (link) supported
✅ PASS: DataCite JSON (header) (status=200)
✅ PASS: DataCite JSON CT (header) (ct=application/vnd.datacite.datacite+json; charset=utf-8)
✅ PASS: DataCite JSON (link) supported
✅ PASS: JSON-LD (header) (status=200)
✅ PASS: JSON-LD CT (header) (ct=application/vnd.schemaorg.ld+json; charset=utf-8)
✅ PASS: JSON-LD (link) supported
✅ PASS: CSL JSON (header) (status=200)
✅ PASS: CSL JSON CT (header) (ct=application/vnd.citationstyles.csl+json; charset=utf-8)
✅ PASS: CSL JSON (link) supported
✅ PASS: Codemeta (header) (status=200)
✅ PASS: Codemeta CT (header)...

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