expiring with response headers

[sckott]

right now the only method we have is time based: number of seconds since the request was recorded.

perhaps we can use response headers, following https://github.com/sourcelevel/faraday-http-cache :

• cache-control: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Cache-Control
• age: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Age
• expires: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Expires
• last-modified: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Last-Modified
  • if-modified-since: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/If-Modified-Since
  • if-unmodified-since: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/If-Unmodified-Since
  • if-none-match: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/If-None-Match
• e-tag: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/ETag

p.s.

• pragma: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Pragma (only recommended for backwards compatibility with http 1.0 clients)

Seems that the folowing are often found together:

• cache-control and age
• last-modified, if-modified-since, if-unmodified-since
• etag

---

• canonical ref perhaps: rfc2616 https://tools.ietf.org/html/rfc2616#page-108
• how httr gathers caching info https://github.com/r-lib/httr/blob/master/R/cache.R - not used in normal http requests in the pkg though

[sckott]

APIs that send certain response headers to test against:

• cache-control/age:
  • GBIF API, eg., cache-control: public, max-age=3601 & age: 0/age: 478 (age header varies with each request)
  • CORE API, e.g., Cache-Control: no-cache
  • Wikimedia API, e.g., w/ wikitaxa::wk_wikispecies, e..g, cache-control: private, must-revalidate, max-age=0 & age: 0 (age field is always zero w/ each request)
  • BHL API, e.g., Cache-Control: private & ``
• cache-control/expires/pragma:
  • ORCID API, e.g., Cache-Control: no-cache, no-store, max-age=0, must-revalidate & Expires: 0 & Pragma: no-cache
• etag:
  • IUCN Redlist API, e.g., ETag: W/"3eb-ZLtsaPeDQHcASdzjqCxnUQ"