[ios] Reload offline pages during fast WKBackForwardList navigations.

Offline pages can leave the WKBackForwardList current item as a placeholder with
no saved content.  In this case, trigger a retry on that navigation with an
updated NavigationItem url and NavigationContext error.

Bug: 875761
Change-Id: Iff5e2688b76da59755726097ac955efefded39d8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1573082
Commit-Queue: Justin Cohen <justincohen@chromium.org>
Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Reviewed-by: Eugene But <eugenebut@chromium.org>
Reviewed-by: Danyao Wang <danyao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#652266}

ios/chrome/browser/ui/reading_list/BUILD.gn

@@ -186,6 +186,7 @@ source_set("eg_tests") {
     "//ios/third_party/earl_grey:earl_grey+link",
     "//ios/third_party/material_components_ios",
     "//ios/web",
+    "//ios/web/common:common",
     "//ios/web/public",
     "//ios/web/public/test",
     "//ios/web/public/test/http_server",

ios/chrome/browser/ui/reading_list/reading_list_egtest.mm

@@ -36,6 +36,7 @@
 #import "ios/chrome/test/earl_grey/chrome_matchers.h"
 #import "ios/chrome/test/earl_grey/chrome_test_case.h"
 #import "ios/third_party/material_components_ios/src/components/Snackbar/src/MaterialSnackbar.h"
+#import "ios/web/common/features.h"
 #import "ios/web/public/navigation_manager.h"
 #import "ios/web/public/reload_type.h"
 #import "ios/web/public/test/web_view_content_test_util.h"
@@ -639,6 +640,13 @@ void AssertIsShowingDistillablePage(bool online, const GURL& distillable_url) {
       web::ReloadType::NORMAL, false);
   AssertIsShowingDistillablePage(false, distillableURL);
 
+  // TODO(crbug.com/954248) This DCHECK's (but works) with slimnav disabled.
+  if (base::FeatureList::IsEnabled(web::features::kSlimNavigationManager)) {
+    [ChromeEarlGrey goBack];
+    [ChromeEarlGrey goForward];
+    AssertIsShowingDistillablePage(false, distillableURL);
+  }
+
   // Start server to reload online error.
   self.serverRespondsWithContent = YES;
   base::test::ios::SpinRunLoopWithMinDelay(
@@ -678,6 +686,10 @@ void AssertIsShowingDistillablePage(bool online, const GURL& distillable_url) {
 
   AssertIsShowingDistillablePage(false, distillableURL);
 
+  [ChromeEarlGrey goBack];
+  [ChromeEarlGrey goForward];
+  AssertIsShowingDistillablePage(false, distillableURL);
+
   // Reload should load online page.
   chrome_test_util::GetCurrentWebState()->GetNavigationManager()->Reload(
       web::ReloadType::NORMAL, false);

ios/web/navigation/error_retry_state_machine.h

@@ -35,6 +35,9 @@ enum class ErrorRetryState {
   // This navigation item failed to load and is in the process of loading a
   // placeholder.
   kLoadingPlaceholder,
+  // This navigation item failed to load and was stored in the WKBackForwardList
+  // and is now being reloaded.
+  kRetryPlaceholderNavigation,
   // This navigation item has an entry in WKBackForwardList. Ready to present
   // error in native view.
   kReadyToDisplayErrorForFailedNavigation,
@@ -86,6 +89,9 @@ class ErrorRetryStateMachine {
   // Transitions the state machine to kDisplayingWebErrorForFailedNavigation.
   void SetDisplayingWebError();
 
+  // Transitions the state machine to kRetryPlaceholderNavigation.
+  void SetRetryPlaceholderNavigation();
+
   // Runs state transitions upon a failed provisional navigation.
   ErrorRetryCommand DidFailProvisionalNavigation(const GURL& web_view_url,
                                                  const GURL& error_url);

ios/web/navigation/error_retry_state_machine.mm

@@ -49,6 +49,11 @@ void ErrorRetryStateMachine::SetDisplayingWebError() {
   state_ = ErrorRetryState::kDisplayingWebErrorForFailedNavigation;
 }
 
+void ErrorRetryStateMachine::SetRetryPlaceholderNavigation() {
+  DCHECK(state_ == web::ErrorRetryState::kNoNavigationError);
+  state_ = ErrorRetryState::kRetryPlaceholderNavigation;
+}
+
 ErrorRetryCommand ErrorRetryStateMachine::DidFailProvisionalNavigation(
     const GURL& web_view_url,
     const GURL& error_url) {
@@ -82,6 +87,7 @@ ErrorRetryCommand ErrorRetryStateMachine::DidFailProvisionalNavigation(
       }
 
     case ErrorRetryState::kLoadingPlaceholder:
+    case ErrorRetryState::kRetryPlaceholderNavigation:
     case ErrorRetryState::kReadyToDisplayErrorForFailedNavigation:
     case ErrorRetryState::kNavigatingToFailedNavigationItem:
       NOTREACHED() << "Unexpected error retry state: "
@@ -108,6 +114,7 @@ ErrorRetryCommand ErrorRetryStateMachine::DidFailNavigation(
       return BackForwardOrReloadFailed(web_view_url, error_url);
 
     case ErrorRetryState::kLoadingPlaceholder:
+    case ErrorRetryState::kRetryPlaceholderNavigation:
     case ErrorRetryState::kReadyToDisplayErrorForFailedNavigation:
     case ErrorRetryState::kNavigatingToFailedNavigationItem:
       NOTREACHED() << "Unexpected error retry state: "
@@ -126,6 +133,20 @@ ErrorRetryCommand ErrorRetryStateMachine::DidFinishNavigation(
       state_ = ErrorRetryState::kReadyToDisplayErrorForFailedNavigation;
       return ErrorRetryCommand::kLoadErrorView;
 
+    case ErrorRetryState::kRetryPlaceholderNavigation:
+      if (wk_navigation_util::IsPlaceholderUrl(web_view_url)) {
+        // (11) Explicitly keep the state the same so after rewriting to the non
+        // placeholder url the else block will trigger.
+        DCHECK_EQ(web_view_url,
+                  wk_navigation_util::CreatePlaceholderUrlForUrl(url_));
+        state_ = ErrorRetryState::kRetryPlaceholderNavigation;
+        return ErrorRetryCommand::kRewriteWebViewURL;
+      } else {
+        // The url was written by kRewriteWebViewURL in the if block, so on
+        // this navigation load an error view.
+        state_ = ErrorRetryState::kReadyToDisplayErrorForFailedNavigation;
+        return ErrorRetryCommand::kLoadErrorView;
+      }
     case ErrorRetryState::kNewRequest:
       if (wk_navigation_util::IsRestoreSessionUrl(web_view_url)) {
         // (8) Initial load of restore_session.html. Don't change state or

ios/web/navigation/error_retry_state_machine_unittest.mm

@@ -248,5 +248,34 @@ TEST_F(ErrorRetryStateMachineTest, OfflineAfterColdStart) {
             machine.state());
 }
 
+// Tests retrying a placeholder navigation.
+TEST_F(ErrorRetryStateMachineTest, RetryPlaceholderNavigation) {
+  GURL test_url(kTestUrl);
+  ErrorRetryStateMachine machine;
+  machine.SetURL(test_url);
+  ASSERT_EQ(ErrorRetryState::kNewRequest, machine.state());
+
+  // First trigger the cached placeholder load.
+  const GURL placeholder_url =
+      wk_navigation_util::CreatePlaceholderUrlForUrl(test_url);
+  ASSERT_EQ(ErrorRetryCommand::kDoNothing,
+            machine.DidFinishNavigation(placeholder_url));
+  ASSERT_EQ(ErrorRetryState::kNoNavigationError, machine.state());
+
+  // Then trigger a retry.
+  machine.SetRetryPlaceholderNavigation();
+  ASSERT_EQ(ErrorRetryCommand::kRewriteWebViewURL,
+            machine.DidFinishNavigation(placeholder_url));
+  ASSERT_EQ(ErrorRetryState::kRetryPlaceholderNavigation, machine.state());
+
+  // Lastly trigger the error view.
+  const GURL target_url =
+      wk_navigation_util::ExtractUrlFromPlaceholderUrl(placeholder_url);
+  ASSERT_EQ(ErrorRetryCommand::kLoadErrorView,
+            machine.DidFinishNavigation(target_url));
+  ASSERT_EQ(ErrorRetryState::kReadyToDisplayErrorForFailedNavigation,
+            machine.state());
+}
+
 }  // namespace
 }  // namespace web

ios/web/web_state/ui/crw_web_controller.mm

@@ -4955,6 +4955,23 @@ typedef void (^ViewportStateCompletion)(const web::PageViewportState*);
         if (web::features::StorePendingItemInContext() && context->GetItem()) {
           self.navigationManagerImpl->SetPendingItem(context->ReleaseItem());
         }
+      } else if (web::GetWebClient()->IsSlimNavigationManagerEnabled() &&
+                 item->error_retry_state_machine().state() ==
+                     web::ErrorRetryState::kNoNavigationError) {
+        // Offline pages can leave the WKBackForwardList current item as a
+        // placeholder with no saved content.  In this case, trigger a retry
+        // on that navigation with an update |item| url and |context| error.
+        item->SetURL(
+            ExtractUrlFromPlaceholderUrl(net::GURLWithNSURL(self.webView.URL)));
+        item->SetVirtualURL(item->GetURL());
+        context->SetError([NSError
+            errorWithDomain:NSURLErrorDomain
+                       code:NSURLErrorNetworkConnectionLost
+                   userInfo:@{
+                     NSURLErrorFailingURLStringErrorKey :
+                         base::SysUTF8ToNSString(item->GetURL().spec())
+                   }]);
+        item->error_retry_state_machine().SetRetryPlaceholderNavigation();
       }
     }