feat: immutable cache support

src/header/interpreter.ts

@@ -22,13 +22,19 @@ const interpretExpires: HeaderInterpreter = (expires) => {
 };
 
 const interpretCacheControl: HeaderInterpreter = (cacheControl, headers) => {
-  const { noCache, noStore, mustRevalidate, maxAge } = parse(cacheControl);
+  const { noCache, noStore, mustRevalidate, maxAge, immutable } = parse(cacheControl);
 
   // Header told that this response should not be cached.
   if (noCache || noStore) {
     return false;
   }
 
+  if (immutable) {
+    // 1 year is sufficient, as Infinity may cause more problems.
+    // It might not be the best way, but a year is better than none.
+    return 1000 * 60 * 60 * 24 * 365;
+  }
+
   // Already out of date, for cache can be saved, but must be requested again
   if (mustRevalidate) {
     return 0;

test/header/interpreter.test.ts

@@ -68,6 +68,15 @@ describe('tests header interpreter', () => {
     expect(result).toBe(false);
   });
 
+  it('tests with immutable', () => {
+    const result = defaultHeaderInterpreter({
+      [Header.CacheControl]: 'immutable'
+    });
+
+    // 1 year
+    expect(result).toBe(1000 * 60 * 60 * 24 * 365);
+  });
+
   it('tests with future expires', () => {
     const date = new Date(new Date().getFullYear() + 1, 1, 1);