Function parseCacheControl

http/unstable_cache_control.ts:241–360

(value: string | null)

 * `max-age=abc`) or a required value is missing (e.g. bare `max-age`).
 */
export function parseCacheControl(value: string | null): CacheControl {
  const result: CacheControl = {};
  if (value === null || value.trim() === "") {
    return result as CacheControl;
  }

  const seen = new Set<string>();
  const parts = splitDirectives(value);
  for (const part of parts) {
    const trimmed = part.trim();
    if (trimmed === "") continue;

    const eq = trimmed.indexOf("=");
    const name = (eq === -1 ? trimmed : trimmed.slice(0, eq)).trim()
      .toLowerCase();
    const rawValue = eq === -1 ? undefined : trimmed.slice(eq + 1).trim();

    // RFC 9111 §4.2.1: when a directive appears more than once, use the first
    // occurrence. Track seen directive names to skip subsequent duplicates.
    if (seen.has(name)) continue;
    seen.add(name);

    switch (name) {
      case "max-age":
        if (rawValue === undefined) {
          throw new SyntaxError(
            `Cache-Control: ${name} requires an integer value`,
          );
        }
        result.maxAge = parseNonNegativeInt(rawValue, name);
        break;
      case "max-stale":
        result.maxStale = rawValue === undefined
          ? true
          : parseNonNegativeInt(rawValue, name);
        break;
      case "min-fresh":
        if (rawValue === undefined) {
          throw new SyntaxError(
            `Cache-Control: ${name} requires an integer value`,
          );
        }
        result.minFresh = parseNonNegativeInt(rawValue, name);
        break;
      case "no-cache": {
        const noCacheFields = rawValue === undefined
          ? undefined
          : parseFieldNames(rawValue);
        result.noCache =
          noCacheFields === undefined || noCacheFields.length === 0
            ? true
            : noCacheFields;
        break;
      }
      case "no-store":
        result.noStore = true;
        break;
      case "no-transform":