prescriptive caching headers for conditional GET support

[catkins-miso]

In order for local caching and conditional GET to work properly with the snapshot endpoints, I believe a TROLIE implementation needs to return the following response headers:

• MUST have the same Weak ETag header for all representations of the current version of the snapshot. CONSIDER using the period, e.g., ETag: W/"2025-09-17T01:00:00-0400"
• MUST use Caching directives:
  • Vary: Accept, Accept-Encoding for the media type and compression requested
  • Cache-Control: private, no-cache because the monitoring set is implicit in the request

If a snapshot request includes the ?monitoring-set=... query parameter, the response COULD have Cache-Control: public, no-cache. This would allow a reverse proxy to be setup as a caching intermediary for the client.

[getorymckeag]

Yeah I think this sounds good. I suppose we could put the guidance directly in the spec for this. Is this kind of what you're thinking?

[catkins-miso]

we could put the guidance directly in the spec for this. Is this kind of what you're thinking?

Yeah, update the header documentation of the appropriate responses in the spec itself and update the Conditional GET article to be specific about this guidance. Also, what about an ADR for why monitoring-set is not a required parameter with some of this caching stuff in the consequences?