Cache the result of a metadata lookup on disk, but only when conclusive

The register is rendered from thousands of requests to external APIs, and rendering the same certificate repeatedly re-runs the same lookups. Caching them keeps renders fast and stable, but caching a failed request would persist a gap in the register until the cache is cleared, which is how certificates lost their OpenAlex ID (register#185).

Usage

cached_lookup(key, dirs, lookup)

Arguments

key

List of values identifying the lookup

dirs

Cache subdirectory below the R.cache root

lookup

Function of no arguments returning a list with elements `status` ("found", "absent" or "failed") and `value`

Value

The `value` element of the lookup result

Details

Only conclusive results are stored: a value that was found, or an absence the API actually confirmed. Failed requests (network errors, rate limiting) are returned but not stored, so the next render retries them.

The cache lives under the R.cache root and is therefore removed by register_clear_cache, i.e. by `make clean`.