{
  "flavors": {
    "ok": "The control, fully correct: strong ETag, Last-Modified, cache-control: no-cache. If-Match (strong compare; * passes), If-Unmodified-Since, If-None-Match (weak compare, lists and * supported; match is 304), If-Modified-Since (ignored when If-None-Match is present, and ignored unless it is a valid HTTP-date). The 304 carries the ETag.",
    "weak": "The only validator is weak: W/\"…\". If-None-Match uses weak comparison, so revalidation works (304). If-Match requires strong comparison and a weak validator never strong-matches, so every If-Match gets 412 — except If-Match: *, which passes. Catches clients that treat W/ as part of the value.",
    "changing": "A different strong ETag on every response, and no Last-Modified (a changing resource with a frozen date would be a second lie). If-None-Match never matches, so a cache revalidates forever and re-downloads every time: thrash. Nondeterministic by design.",
    "ignore": "Sends a perfectly good ETag and Last-Modified, then ignores every conditional header: always 200, full body. (Violates a MUST. That is the point.) Your cache keeps asking; it keeps not listening.",
    "always-304": "Every GET is answered 304 — even the first, with no conditional headers at all. A cold cache is told \"you already have it\" about a body it has never seen. Broken proxies really do this.",
    "mismatch": "Revalidation \"succeeds\" — If-None-Match matches, 304 — but the 304 carries a different ETag than the one you sent. A cache that adopts it misses on its next revalidation (200, real validator restored) and then matches again: a permanent 304/200/304 thrash.",
    "no-validator-304": "If-None-Match matches and the 304 comes back bare: no ETag, no Last-Modified. A violation — RFC 9110 §15.4.5 says the 304 MUST carry the ETag its 200 would have — and hostile to caches that need the validator to know which stored response was confirmed.",
    "unquoted": "The ETag header is a bare token with no quotes (spec-invalid, common in the wild). The server matches If-None-Match sloppily — quoted, bare, weak-prefixed, anything goes — and If-Modified-Since works normally. What does your client send back, and does its parser cope?",
    "bad-date": "No ETag; Last-Modified is ISO 8601, not an HTTP-date (invalid). Revalidation is by exact string comparison of If-Modified-Since against that value — what a naive server does. Only a client that echoes the header back verbatim ever gets its 304; one that parses and reformats, or discards the unparseable date, refetches forever.",
    "future": "No ETag; Last-Modified is one year from today (a valid HTTP-date that is always in the future, moving at midnight UTC). The date comparison itself is honest, so a client that echoes today's header back verbatim still gets 304 — until the date rolls — while one that sends its own clock always gets 200. Which is yours? Nondeterministic across days by design."
  },
  "usage": "/etag/{flavor}",
  "caching": "Conditional requests over both validators, ETag and Last-Modified. Responses are cache-control: no-cache, no-transform (store, but revalidate every use), so a real cache can be pointed at these. Range and If-Range live at /range."
}