Inconsistent HTTP caching: properties and SKOS endpoints missing check_last_modified

[alexskr]

Summary

While reviewing controllers, found that HTTP caching (check_last_modified / check_last_modified_segment / check_last_modified_collection) is applied inconsistently. Some read endpoints emit Last-Modified / Cache-Control and support 304 Not Modified revalidation; others don't, so clients re-fetch full payloads unnecessarily.

There are two distinct root causes — one is a controller-layer gap, the other is a model-layer gap.

Background

check_last_modified* lives in helpers/http_cache_helper.rb. It only works for models registered as cacheable resources — i.e. models that declare cache_timeout (and usually cache_segment_instance) in ontologies_linked_data. LinkedData::HTTPCache::CacheableResource is mixed into every model via base.rb, but max_age reads cache_settings[:cache_timeout].first, so a model that never calls cache_timeout is not a functioning cacheable resource.

Model	cache_timeout declared?	Controller calls check_last_modified*?
Class	yes (86400)	yes
Instance (named_individual)	yes (14400)	yes
OntologySubmission	yes (3600)	yes
SKOS::Collection	yes (14400)	no
SKOS::Scheme	yes (14400)	no
SKOS::Label (skosxl)	no	no
property models (object/datatype/annotation/ontology_property)	no	no

Gap 1 — controller layer (models already cacheable)

SKOS::Collection and SKOS::Scheme models already declare cache_timeout 14400, but collections_controller and schemes endpoints never call check_last_modified*. These were added in the 2025-06 SKOS batch (collections/schemes/labels) which landed without wiring caching into the controllers.

• Add check_last_modified* to the SKOS collections/schemes read endpoints (no model change required).

Gap 2 — model layer (not cacheable at all)

Neither the property models nor SKOS::Label declare cache_timeout, so they are not cacheable resources. The properties_controller has had no caching since it was created (2013); skos_xl_label_controller is new (2025) and the Label model was never made cacheable.

• Decide whether property reads and SKOS XL label reads should be HTTP-cached.
• If yes: add cache_timeout / cache_segment_instance to the relevant models in ncbo/ontologies_linked_data, then call check_last_modified* in the controllers here.

Notes

• Cross-repo: Gap 2 requires model changes in ncbo/ontologies_linked_data first.
• check_last_modified* must only be invoked on GET routes (it can short-circuit with 304); do not add it to mixed-method handlers blindly.
• Discovered while doing the before-filter / boilerplate dedup work on the classes/instances controllers.