Function determineDeleteAt

lib/handler/cache-handler.js:494–526

* @param {number} baseTime * @param {number} cachedAt * @param {import('../../types/cache-interceptor.d.ts').default.CacheControlDirectives} cacheControlDirectives * @param {number} staleAt

(baseTime, cachedAt, cacheControlDirectives, staleAt)

 * @param {number} staleAt
 */
function determineDeleteAt (baseTime, cachedAt, cacheControlDirectives, staleAt) {
  let staleWhileRevalidate = -Infinity
  let staleIfError = -Infinity
  let immutable = -Infinity

  if (cacheControlDirectives['stale-while-revalidate']) {
    staleWhileRevalidate = staleAt + (cacheControlDirectives['stale-while-revalidate'] * 1000)
  }

  if (cacheControlDirectives['stale-if-error']) {
    staleIfError = staleAt + (cacheControlDirectives['stale-if-error'] * 1000)
  }

  if (cacheControlDirectives.immutable && staleWhileRevalidate === -Infinity && staleIfError === -Infinity) {
    immutable = cachedAt + 31536000000
  }

  // When no stale directives or immutable flag, add a revalidation buffer
  // equal to the freshness lifetime so the entry survives past staleAt long
  // enough to be revalidated instead of silently disappearing.
  //
  // Response Date headers only have second precision, so baseTime can trail the
  // actual cache insertion time by up to ~1s. Pad the buffer by that bounded
  // skew so short-lived entries do not disappear exactly when they should be
  // revalidated.
  if (staleWhileRevalidate === -Infinity && staleIfError === -Infinity && immutable === -Infinity) {
    const freshnessLifetime = staleAt - baseTime
    const datePrecisionPadding = Math.min(Math.max(cachedAt - baseTime, 0), 1000)
    return staleAt + freshnessLifetime + datePrecisionPadding
  }

  return Math.max(staleAt, staleWhileRevalidate, staleIfError, immutable)
}

/**
 * Strips headers required to be removed in cached responses