An attempt at conservative default cache-control headers (#7587)

* An attempt at conservative default cache-control headers

* Reduce default cache-control max-age

app/lib/frontend/handlers.dart

@@ -11,6 +11,7 @@ import 'package:shelf_router/shelf_router.dart';
 import '../shared/handlers.dart';
 import '../shared/urls.dart';
 
+import 'handlers/headers.dart';
 import 'handlers/misc.dart';
 import 'handlers/pubapi.dart';
 import 'handlers/redirects.dart';
@@ -68,11 +69,21 @@ shelf.Handler createAppHandler() {
 
     final rs = await pubApiHandler(request);
     if (rs != Router.routeNotFound) {
+      if (rs.statusCode == 200 &&
+          request.method == 'GET' &&
+          !CacheHeaders.hasCacheHeader(rs.headers)) {
+        return rs.change(headers: CacheHeaders.defaultApi());
+      }
       return rs;
     }
 
     final res = await pubSiteHandler(request);
     if (res != Router.routeNotFound) {
+      if (rs.statusCode == 200 &&
+          request.method == 'GET' &&
+          !CacheHeaders.hasCacheHeader(rs.headers)) {
+        return rs.change(headers: CacheHeaders.defaultUI());
+      }
       return res;
     }
 

app/lib/frontend/handlers/account.dart

@@ -26,6 +26,7 @@ import '../../shared/urls.dart' as urls;
 import '../templates/admin.dart';
 import '../templates/consent.dart';
 import '../templates/misc.dart' show renderUnauthenticatedPage;
+import 'headers.dart';
 
 /// Handles requests for /authorized
 shelf.Response authorizedHandler(_) => htmlResponse(renderAuthorizedPage());
@@ -55,10 +56,13 @@ Future<shelf.Response> startSignInHandler(shelf.Request request) async {
   );
   return redirectResponse(
     oauth2Url.toString(),
-    headers: session_cookie.createClientSessionCookie(
-      sessionId: session.sessionId,
-      maxAge: session.maxAge,
-    ),
+    headers: {
+      ...session_cookie.createClientSessionCookie(
+        sessionId: session.sessionId,
+        maxAge: session.maxAge,
+      ),
+      ...CacheHeaders.privateZero(),
+    },
   );
 }
 
@@ -109,10 +113,13 @@ Future<shelf.Response> signInCompleteHandler(shelf.Request request) async {
   );
   return redirectResponse(
     go,
-    headers: session_cookie.createClientSessionCookie(
-      sessionId: newSession.sessionId,
-      maxAge: newSession.maxAge,
-    ),
+    headers: {
+      ...session_cookie.createClientSessionCookie(
+        sessionId: newSession.sessionId,
+        maxAge: newSession.maxAge,
+      ),
+      ...CacheHeaders.privateZero(),
+    },
   );
 }
 
@@ -174,6 +181,9 @@ Future<shelf.Response> consentPageHandler(
     // Consent pages have the consent ID in the URL. Browsers should not pass on
     // this ID to the pages that are linked from the consent page.
     noReferrer: true,
+    headers: {
+      ...CacheHeaders.privateZero(),
+    },
   );
 }
 

app/lib/frontend/handlers/headers.dart

@@ -43,7 +43,9 @@ class CacheHeaders {
           'private'
         else if (public)
           'public'
-        else if (requestContext.isNotAuthenticated)
+        else if (requestContext.isNotAuthenticated &&
+            requestContext.uiCacheEnabled &&
+            requestContext.sessionData == null)
           'public'
         else
           'private',
@@ -57,8 +59,26 @@ class CacheHeaders {
     return headers.containsKey(HttpHeaders.cacheControlHeader);
   }
 
-  /// Default private-only caching.
-  static final defaultPrivate = CacheHeaders._(Duration.zero, private: true);
+  /// Private-only max-age zero.
+  static final privateZero = CacheHeaders._(Duration.zero, private: true);
+
+  /// Default cache-control for public user-interface
+  static final defaultPublicUI = CacheHeaders._(
+    Duration(minutes: 10),
+    public: true,
+  );
+
+  /// Default cache-control for user-interface
+  static final defaultUI = CacheHeaders._(
+    Duration(minutes: 10),
+    // public / private is inferred from authentication + session header
+  );
+
+  /// Default cache-control for API responses
+  static final defaultApi = CacheHeaders._(
+    Duration(minutes: 10),
+    // public / private is inferred from authentication + session header
+  );
 
   /// Everything under the /documentation/ endpoint.
   static final dartdocAsset = CacheHeaders._(Duration(minutes: 15));

app/lib/frontend/handlers/misc.dart

@@ -68,9 +68,16 @@ Future<shelf.Response> securityPageHandler(shelf.Request request) async {
 /// Handles requests for /readiness_check
 Future<shelf.Response> readinessCheckHandler(shelf.Request request) async {
   if (nameTracker.isReady) {
-    return htmlResponse('OK');
+    return htmlResponse(
+      'OK',
+      headers: CacheHeaders.privateZero(),
+    );
   } else {
-    return htmlResponse('Service Unavailable', status: 503);
+    return htmlResponse(
+      'Service Unavailable',
+      status: 503,
+      headers: CacheHeaders.privateZero(),
+    );
   }
 }
 
@@ -182,6 +189,7 @@ Future<shelf.Response> staticsHandler(shelf.Request request) async {
         acceptsGzipEncoding ? staticFile.gzippedBytes : staticFile.bytes;
     final headers = <String, String>{
       if (acceptsGzipEncoding) HttpHeaders.contentEncodingHeader: 'gzip',
+      'Vary': 'Accept-Encoding',
       HttpHeaders.contentTypeHeader: staticFile.contentType,
       HttpHeaders.contentLengthHeader: bytes.length.toString(),
       HttpHeaders.lastModifiedHeader: formatHttpDate(staticFile.lastModified),
@@ -232,6 +240,7 @@ Future<shelf.Response> experimentalHandler(shelf.Request request) async {
       value: flags.encodedAsCookie(),
       maxAge: experimentalCookieDuration,
     ),
+    ...CacheHeaders.privateZero(),
   });
 }
 

app/lib/frontend/handlers/package.dart

@@ -231,6 +231,7 @@ Future<shelf.Response> packageScoreLogTxtHandler(
     body: log ?? 'no log',
     headers: {
       'content-type': 'text/plain;charset=UTF-8',
+      ...CacheHeaders.defaultPublicUI(),
     },
   );
 }

app/lib/frontend/handlers/report.dart

@@ -17,6 +17,7 @@ import '../../shared/handlers.dart';
 import '../../shared/utils.dart';
 import '../request_context.dart';
 import '../templates/report.dart';
+import 'headers.dart';
 
 /// Handles GET /report
 Future<shelf.Response> reportPageHandler(shelf.Request request) async {
@@ -29,9 +30,14 @@ Future<shelf.Response> reportPageHandler(shelf.Request request) async {
     return unauthenticatedRs;
   }
 
-  return htmlResponse(renderReportPage(
-    sessionData: requestContext.sessionData,
-  ));
+  return htmlResponse(
+    renderReportPage(
+      sessionData: requestContext.sessionData,
+    ),
+    headers: {
+      ...CacheHeaders.privateZero(),
+    },
+  );
 }
 
 /// Handles POST /api/report

app/lib/frontend/handlers/routes.dart

@@ -17,6 +17,7 @@ import '../../shared/handlers.dart';
 import 'account.dart';
 import 'atom_feed.dart';
 import 'documentation.dart';
+import 'headers.dart';
 import 'landing.dart';
 import 'listing.dart';
 import 'misc.dart';
@@ -35,7 +36,10 @@ class PubSiteService {
   // ****
 
   @Route.get('/liveness_check')
-  Future<Response> livenessCheck(Request request) async => htmlResponse('OK');
+  Future<Response> livenessCheck(Request request) async => htmlResponse(
+        'OK',
+        headers: CacheHeaders.privateZero(),
+      );
 
   @Route.get('/readiness_check')
   Future<Response> readinessCheck(Request request) async =>

app/lib/shared/handler_helpers.dart

@@ -136,7 +136,7 @@ shelf.Handler _requestContextWrapper(shelf.Handler handler) {
     if (!context.uiCacheEnabled && !CacheHeaders.hasCacheHeader(rs.headers)) {
       // Indicates that the response is intended for a single user and must not
       // be stored by a shared cache. A private cache may store the response.
-      rs = rs.change(headers: CacheHeaders.defaultPrivate());
+      rs = rs.change(headers: CacheHeaders.privateZero());
     }
     return rs;
   };

app/lib/task/handlers.dart

@@ -176,7 +176,10 @@ Future<shelf.Response> handleTaskResource(
   }
 
   if (request.method.toUpperCase() == 'HEAD') {
-    return htmlResponse('');
+    return htmlResponse(
+      '',
+      headers: CacheHeaders.defaultPublicUI(),
+    );
   }
 
   final acceptsGzip = request.acceptsGzipEncoding();
@@ -185,6 +188,8 @@ Future<shelf.Response> handleTaskResource(
     headers: {
       'Content-Type': mime,
       if (acceptsGzip) 'Content-Encoding': 'gzip',
+      'Vary': 'Accept-Encoding',
+      ...CacheHeaders.defaultPublicUI(),
     },
   );
 }