feat: interpreter also handles Expires header (and tests)

src/header/interpreter.ts

@@ -2,16 +2,30 @@ import { parse } from '@tusbar/cache-control';
 import { HeaderInterpreter } from './types';
 
 export const defaultHeaderInterpreter: HeaderInterpreter = (headers) => {
-  const cacheControl = headers?.['cache-control'];
+  const cacheControl = headers?.['Cache-Control'];
 
   if (!cacheControl) {
+    // Checks if Expires header is present
+    // https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Expires
+    const expires = headers?.['Expires'];
+
+    if (expires) {
+      const milliseconds = Date.parse(expires) - Date.now();
+
+      if (milliseconds > 0) {
+        return milliseconds;
+      } else {
+        return false;
+      }
+    }
+
     return undefined;
   }
 
-  const { noCache, noStore, maxAge } = parse(cacheControl);
+  const { noCache, noStore, mustRevalidate, maxAge } = parse(cacheControl);
 
   // Header told that this response should not be cached.
-  if (noCache || noStore) {
+  if (noCache || noStore || mustRevalidate) {
     return false;
   }
 
@@ -19,5 +33,5 @@ export const defaultHeaderInterpreter: HeaderInterpreter = (headers) => {
     return undefined;
   }
 
-  return Date.now() + maxAge * 1000;
+  return maxAge * 1000;
 };

src/header/types.ts

@@ -5,8 +5,6 @@
  *
  * @returns `false` if cache should not be used. `undefined` when provided
  * headers was not enough to determine a valid value. Or a `number` containing
- * the number of **seconds** to cache the response.
+ * the number of **milliseconds** to cache the response.
  */
-export type HeaderInterpreter = (
-  headers: Record<string, string> | undefined
-) => false | undefined | number;
+export type HeaderInterpreter = (headers?: Record<string, string>) => false | undefined | number;

test/header/interpreter.test.ts

@@ -0,0 +1,71 @@
+import { defaultHeaderInterpreter } from '../../src/header';
+
+describe('tests header interpreter', () => {
+  it('tests without cache-control header', () => {
+    const noHeader = defaultHeaderInterpreter({});
+    expect(noHeader).toBeUndefined();
+
+    const emptyHeader = defaultHeaderInterpreter({ 'Cache-Control': 'public' });
+    expect(emptyHeader).toBeUndefined();
+  });
+
+  it('tests with cache preventing headers', () => {
+    const noStore = defaultHeaderInterpreter({
+      'Cache-Control': 'no-store'
+    });
+
+    expect(noStore).toBe(false);
+
+    const noCache = defaultHeaderInterpreter({
+      'Cache-Control': 'no-cache'
+    });
+
+    expect(noCache).toBe(false);
+
+    const mustRevalidate = defaultHeaderInterpreter({
+      'Cache-Control': 'must-revalidate'
+    });
+
+    expect(mustRevalidate).toBe(false);
+  });
+
+  it('tests with maxAge header for 10 seconds', () => {
+    const result = defaultHeaderInterpreter({
+      'Cache-Control': 'max-age=10'
+    });
+
+    // 10 Seconds in milliseconds
+    expect(result).toBe(10 * 1000);
+  });
+
+  it('tests with Expires and Cache-Control present', () => {
+    const result = defaultHeaderInterpreter({
+      'Cache-Control': 'max-age=10',
+      Expires: new Date(new Date().getFullYear() + 1, 1, 1).toISOString()
+    });
+
+    // Expires should be ignored
+    // 10 Seconds in milliseconds
+    expect(result).toBe(10 * 1000);
+  });
+
+  it('tests with past Expires', () => {
+    const result = defaultHeaderInterpreter({
+      Expires: new Date(new Date().getFullYear() - 1, 1, 1).toISOString()
+    });
+
+    // Past means cache invalid
+    expect(result).toBe(false);
+  });
+
+  it('tests with future Expires', () => {
+    const date = new Date(new Date().getFullYear() + 1, 1, 1);
+    const result = defaultHeaderInterpreter({
+      Expires: date.toISOString()
+    });
+
+    // the result should be what the date is in milliseconds
+    // minus the actual epoch milliseconds
+    expect(result).toBeCloseTo(date.getTime() - Date.now());
+  });
+});