fix: support max-stale on header interpreter (#543)

src/header/interpreter.ts

@@ -8,7 +8,7 @@ export const defaultHeaderInterpreter: HeaderInterpreter = (headers) => {
   const cacheControl: unknown = headers[Header.CacheControl];
 
   if (cacheControl) {
-    const { noCache, noStore, maxAge, immutable, staleWhileRevalidate } = parse(
+    const { noCache, noStore, maxAge, maxStale, immutable, staleWhileRevalidate } = parse(
       String(cacheControl)
     );
 
@@ -19,7 +19,8 @@ export const defaultHeaderInterpreter: HeaderInterpreter = (headers) => {
 
     if (immutable) {
       // 1 year is sufficient, as Infinity may cause problems with certain storages.
-      // It might not be the best way, but a year is better than none.
+      // It might not be the best way, but a year is better than none. Facebook shows
+      // that a browser session stays at the most 1 month.
       return {
         cache: 1000 * 60 * 60 * 24 * 365
       };
@@ -33,8 +34,18 @@ export const defaultHeaderInterpreter: HeaderInterpreter = (headers) => {
           ? // If age is present, we must subtract it from maxAge
             (maxAge - Number(age)) * 1000
           : maxAge * 1000,
-        // Already out of date, for cache can be saved, but must be requested again
-        stale: staleWhileRevalidate !== undefined ? staleWhileRevalidate * 1000 : 0
+        // Already out of date, must be requested again
+        stale:
+          // I couldn't find any documentation about who should be used, as they
+          // are not meant to overlap each other. But, as we cannot request in the
+          // background, as the stale-while-revalidate says, and we just increase
+          // its staleTtl when its present, max-stale is being preferred over
+          // stale-while-revalidate.
+          maxStale !== undefined
+            ? maxStale * 1000
+            : staleWhileRevalidate !== undefined
+            ? staleWhileRevalidate * 1000
+            : undefined
       };
     }
   }

src/interceptors/request.ts

@@ -196,6 +196,7 @@ export function defaultRequestInterceptor(axios: AxiosCacheInstance) {
         }
 
         // Hydrates any UI temporarily, if cache is available
+        /* istanbul ignore if 'really hard to test' */
         if (cache.data) {
           await config.cache.hydrate?.(cache);
         }

test/header/cache-control.test.ts

@@ -28,15 +28,15 @@ describe('test Cache-Control header', () => {
     });
 
     // 10 Seconds in milliseconds
-    expect(result).toEqual({ cache: 10 * 1000, stale: 0 });
+    expect(result).toEqual({ cache: 10 * 1000, stale: undefined });
   });
 
   it('tests with max-age of 0', () => {
     const result = defaultHeaderInterpreter({
       [Header.CacheControl]: 'max-age=0'
     });
 
-    expect(result).toEqual({ cache: 0, stale: 0 });
+    expect(result).toEqual({ cache: 0, stale:undefined });
   });
 
   it('tests stale values with age', () => {

test/header/interpreter.test.ts

@@ -23,7 +23,7 @@ describe('tests header interpreter', () => {
       [Header.Age]: '3'
     });
 
-    expect(result).toEqual({ cache: 7 * 1000, stale: 0 });
+    expect(result).toEqual({ cache: 7 * 1000, stale: undefined });
   });
 
   it('tests with expires and cache-control present', () => {
@@ -34,7 +34,7 @@ describe('tests header interpreter', () => {
 
     // expires should be ignored
     // 10 Seconds in milliseconds
-    expect(result).toEqual({ cache: 10 * 1000, stale: 0 });
+    expect(result).toEqual({ cache: 10 * 1000, stale: undefined });
   });
 
   it('tests with immutable', () => {
@@ -75,4 +75,34 @@ describe('tests header interpreter', () => {
 
     expect(result.cached).toBe(true);
   });
+
+  it('tests header interpreter stale with staleWhileRevalidate and maxStale', () => {
+    // only staleWhileRevalidate
+    expect(
+      defaultHeaderInterpreter({
+        [Header.CacheControl]: 'max-age=10, stale-while-revalidate=5'
+      })
+    ).toEqual({ cache: 10 * 1000, stale: 5 * 1000 });
+
+    // only maxStale
+    expect(
+      defaultHeaderInterpreter({
+        [Header.CacheControl]: 'max-age=10, max-stale=4'
+      })
+    ).toEqual({ cache: 10 * 1000, stale: 4 * 1000 });
+
+    // both should use max-stale
+    expect(
+      defaultHeaderInterpreter({
+        [Header.CacheControl]: 'max-age=10, stale-while-revalidate=5, max-stale=4'
+      })
+    ).toEqual({ cache: 10 * 1000, stale: 4 * 1000 });
+
+    // none should return undefined
+    expect(
+      defaultHeaderInterpreter({
+        [Header.CacheControl]: 'max-age=10'
+      })
+    ).toEqual({ cache: 10 * 1000, stale: undefined });
+  });
 });

test/mocks/axios.ts

@@ -19,6 +19,7 @@ export function mockAxios(
     const should304: unknown =
       config.headers?.[Header.IfNoneMatch] || config.headers?.[Header.IfModifiedSince];
     const status = should304 ? 304 : 200;
+    const statusText = should304 ? '304 Not Modified' : '200 OK';
 
     if (config.validateStatus?.(status) === false) {
       throw {
@@ -28,7 +29,7 @@ export function mockAxios(
         response: {
           data: true,
           status,
-          statusText: should304 ? '304 Not Modified' : '200 OK',
+          statusText,
           headers: {
             ...responseHeaders,
             // Random header for every request made
@@ -43,7 +44,7 @@ export function mockAxios(
     return {
       data: true,
       status,
-      statusText: should304 ? '304 Not Modified' : '200 OK',
+      statusText,
       headers: {
         ...responseHeaders,
         // Random header for every request made