[AppCache] Add feature to always fallback requests to the network.

This adds a (default enabled) feature AppCacheAlwaysFallbackToNetwork,
when enabled chrome will behave as if every manifest file included a
NETWORK: * line, indicating that all requests should fall back to the
network.

Bug: 1152226
Change-Id: I02f126a91d7061183274a66ad759cde58da533cb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2594235Reviewed-by: Marijn Kruisselbrink <mek@chromium.org>
Reviewed-by: Victor Costan <pwnall@chromium.org>
Commit-Queue: Marijn Kruisselbrink <mek@chromium.org>
Cr-Commit-Position: refs/heads/master@{#843607}

content/browser/appcache/appcache_request_handler.cc

@@ -9,6 +9,7 @@
 #include "base/bind.h"
 #include "base/callback_helpers.h"
 #include "base/command_line.h"
+#include "base/feature_list.h"
 #include "content/browser/appcache/appcache.h"
 #include "content/browser/appcache/appcache_backend_impl.h"
 #include "content/browser/appcache/appcache_host.h"
@@ -29,6 +30,12 @@
 
 namespace content {
 
+// If this feature is enabled, we behave as if all manifests include a
+// NETWORK: * line, indicating that all requests should fall back to the
+// network.
+const base::Feature kAppCacheAlwaysFallbackToNetwork{
+    "AppCacheAlwaysFallbackToNetwork", base::FEATURE_ENABLED_BY_DEFAULT};
+
 namespace {
 
 bool g_running_in_tests = false;
@@ -153,7 +160,8 @@ AppCacheURLLoader* AppCacheRequestHandler::MaybeLoadFallbackForRedirect(
     DeliverAppCachedResponse(found_fallback_entry_, found_cache_id_,
                              found_manifest_url_, true,
                              found_namespace_entry_url_);
-  } else if (!found_network_namespace_) {
+  } else if (!found_network_namespace_ &&
+             !base::FeatureList::IsEnabled(kAppCacheAlwaysFallbackToNetwork)) {
     // 7.9.6, step 6: Fail the resource load.
     loader = CreateLoader(network_delegate);
     DeliverErrorResponse();
@@ -515,7 +523,8 @@ void AppCacheRequestHandler::ContinueMaybeLoadSubResource() {
     return;
   }
 
-  if (found_network_namespace_) {
+  if (found_network_namespace_ ||
+      base::FeatureList::IsEnabled(kAppCacheAlwaysFallbackToNetwork)) {
     // Step 3 and 5: Fetch the resource normally.
     DCHECK(!found_entry_.has_response_id() &&
            !found_fallback_entry_.has_response_id());

content/browser/appcache/appcache_request_handler.h

@@ -36,6 +36,8 @@ class AppCacheRequest;
 class AppCacheRequestHandlerTest;
 class AppCacheHost;
 
+CONTENT_EXPORT extern const base::Feature kAppCacheAlwaysFallbackToNetwork;
+
 // An instance is created for each net::URLRequest. The instance survives all
 // http transactions involved in the processing of its net::URLRequest, and is
 // given the opportunity to hijack the request along the way. Callers

content/browser/appcache/appcache_request_handler_unittest.cc

@@ -21,6 +21,7 @@
 #include "base/stl_util.h"
 #include "base/strings/stringprintf.h"
 #include "base/synchronization/waitable_event.h"
+#include "base/test/scoped_feature_list.h"
 #include "base/threading/thread.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "content/browser/appcache/appcache.h"
@@ -64,6 +65,7 @@ class AppCacheRequestHandlerTest : public ::testing::Test {
   // Test harness --------------------------------------------------
 
   AppCacheRequestHandlerTest() : host_(nullptr), request_(nullptr) {
+    feature_list_.InitAndEnableFeature(kAppCacheAlwaysFallbackToNetwork);
     AppCacheRequestHandler::SetRunningInTests(true);
   }
 
@@ -369,7 +371,9 @@ class AppCacheRequestHandlerTest : public ::testing::Test {
 
   void SubResource_Miss_WithCacheSelected() {
     // A sub-resource load where the resource is not in an appcache, or
-    // in a network or fallback namespace, should result in a failed request.
+    // in a network or fallback namespace, should result in a fallback to the
+    // network rather than an error, as we treat all network namespaces as
+    // including '*'.
     host_->AssociateCompleteCache(MakeNewCache());
 
     CreateRequestAndHandler(GURL("http://blah/"), host_,
@@ -377,8 +381,7 @@ class AppCacheRequestHandlerTest : public ::testing::Test {
     EXPECT_TRUE(handler_.get());
 
     SetAppCacheURLLoader(handler_->MaybeLoadResource(nullptr));
-    EXPECT_TRUE(loader());
-    EXPECT_TRUE(loader()->IsDeliveringErrorResponse());
+    EXPECT_FALSE(loader());
 
     SetAppCacheURLLoader(handler_->MaybeLoadFallbackForRedirect(
         nullptr, GURL("http://blah/redirect")));
@@ -406,7 +409,7 @@ class AppCacheRequestHandlerTest : public ::testing::Test {
 
     host_->FinishCacheSelection(cache.get(), nullptr, base::DoNothing());
     EXPECT_FALSE(loader()->IsWaiting());
-    EXPECT_TRUE(loader()->IsDeliveringErrorResponse());
+    EXPECT_TRUE(loader()->IsDeliveringNetworkResponse());
 
     SetAppCacheURLLoader(handler_->MaybeLoadFallbackForRedirect(
         nullptr, GURL("http://blah/redirect")));
@@ -707,6 +710,7 @@ class AppCacheRequestHandlerTest : public ::testing::Test {
   }
 
   // Data members --------------------------------------------------
+  base::test::ScopedFeatureList feature_list_;
   BrowserTaskEnvironment task_environment_;
 
   base::OnceClosure test_finished_cb_;

third_party/blink/web_tests/VirtualTestSuites

@@ -594,7 +594,8 @@
   {
     "prefix": "appcache-origin-trial",
     "bases": ["http/tests/appcache"],
-    "args": ["--enable-features=AppCacheRequireOriginTrial"]
+    "args": ["--enable-features=AppCacheRequireOriginTrial",
+             "--disable-features=AppCacheAlwaysFallbackToNetwork"]
   },
   {
     "prefix": "async-script-scheduling-finished-parsing",