Add support for fallback content for the frame. This includes main and subframes.

content/browser/loader/navigation_url_loader_network_service.cc

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/loader/navigation_url_loader_network_service.h"
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/memory/ptr_util.h"
 #include "base/trace_event/trace_event.h"
@@ skipping 87 matching lines @@
     : public mojom::URLLoaderClient {
  public:
   URLLoaderRequestController(
       std::unique_ptr<ResourceRequest> resource_request,
       ResourceContext* resource_context,
       scoped_refptr<URLLoaderFactoryGetter> default_url_loader_factory_getter,
       const base::WeakPtr<NavigationURLLoaderNetworkService>& owner)
       : resource_request_(std::move(resource_request)),
         resource_context_(resource_context),
         default_url_loader_factory_getter_(default_url_loader_factory_getter),
-        owner_(owner) {}
+        owner_(owner),
+        response_loader_binding_(this) {}
 
   ~URLLoaderRequestController() override {
     DCHECK_CURRENTLY_ON(BrowserThread::IO);
   }
 
   void Start(
       ServiceWorkerNavigationHandleCore* service_worker_navigation_handle_core,
       AppCacheNavigationHandleCore* appcache_handle_core,
       std::unique_ptr<NavigationRequestInfo> request_info,
       mojom::URLLoaderFactoryPtrInfo factory_for_webui,
@@ skipping 87 matching lines @@
                          base::Unretained(this)));
       return;
     }
 
     mojom::URLLoaderFactory* factory = nullptr;
     DCHECK_EQ(handlers_.size(), handler_index_);
     if (resource_request_->url.SchemeIs(url::kBlobScheme)) {
       factory = default_url_loader_factory_getter_->GetBlobFactory()->get();
     } else {
       factory = default_url_loader_factory_getter_->GetNetworkFactory()->get();
+      default_loader_used_ = true;
     }
     url_loader_ = ThrottlingURLLoader::CreateLoaderAndStart(
         factory,
         GetContentClient()->browser()->CreateURLLoaderThrottles(
             web_contents_getter_),
         0 /* routing_id? */, 0 /* request_id? */,
         mojom::kURLLoadOptionSendSSLInfo | mojom::kURLLoadOptionSniffMimeType,
         *resource_request_, this, kTrafficAnnotation);
   }
 
   void FollowRedirect() {
     DCHECK_CURRENTLY_ON(BrowserThread::IO);
     DCHECK(url_loader_);
 
     url_loader_->FollowRedirect();

[kinuko, 2017/07/28 09:50:29]

It doesn't seem to happen in the current appcache code but actually
FollowRedirect should call response_url_loader_->FollowRedirect() if there's the
one, right?

Should we at least DCHECK(!response_url_loader_) here?

[ananta, 2017/07/28 22:59:22]

Thanks. Done

   }
 
   // Ownership of the URLLoaderFactoryPtrInfo instance is transferred to the
   // caller.
   mojom::URLLoaderFactoryPtrInfo GetSubresourceURLLoaderFactory() {
     return std::move(subresource_url_loader_factory_ptr_info_);
   }
 
  private:
   // mojom::URLLoaderClient implementation:
   void OnReceiveResponse(
       const ResourceResponseHead& head,
       const base::Optional<net::SSLInfo>& ssl_info,
       mojom::DownloadedTempFilePtr downloaded_file) override {
+    response_ = head;
+    // If the default loader (network) was used to handle the URL load request
+    // we need to see if the handlers want to potentially create a new loader
+    // for the response. e.g. AppCache.
+    if (MaybeCreateLoaderForResponse(head))
+      return;
+
     BrowserThread::PostTask(
         BrowserThread::UI, FROM_HERE,
         base::Bind(&NavigationURLLoaderNetworkService::OnReceiveResponse,
                    owner_, head, ssl_info, base::Passed(&downloaded_file)));
   }
 
   void OnReceiveRedirect(const net::RedirectInfo& redirect_info,
                          const ResourceResponseHead& head) override {
+    response_ = head;
+
     BrowserThread::PostTask(
         BrowserThread::UI, FROM_HERE,
         base::Bind(&NavigationURLLoaderNetworkService::OnReceiveRedirect,
                    owner_, redirect_info, head));
   }
 
   void OnDataDownloaded(int64_t data_length, int64_t encoded_length) override {}
 
   void OnUploadProgress(int64_t current_position,
                         int64_t total_size,
                         OnUploadProgressCallback callback) override {}
 
   void OnReceiveCachedMetadata(const std::vector<uint8_t>& data) override {}
 
   void OnTransferSizeUpdated(int32_t transfer_size_diff) override {}
 
   void OnStartLoadingResponseBody(
       mojo::ScopedDataPipeConsumerHandle body) override {
     BrowserThread::PostTask(
         BrowserThread::UI, FROM_HERE,
         base::Bind(
             &NavigationURLLoaderNetworkService::OnStartLoadingResponseBody,
             owner_, base::Passed(&body)));
   }
 
   void OnComplete(
       const ResourceRequestCompletionStatus& completion_status) override {
+    // If the default loader (network) was used to handle the URL load request
+    // we need to see if the handlers want to potentially create a new loader
+    // for the response. e.g. AppCache.
+    if (MaybeCreateLoaderForResponse(response_))

[michaeln, 2017/07/28 19:11:02]

I think we should only call MaybeCreateLoaderForResponse() once for each
MaybeCreateLoader() call, but it looks like we can/will call it twice in most
cases: first from OnReceivedResponse and again from OnComplete. If i understand
properly, we're calling MaybeCreateLoaderForResponse() to cover the case where
we did not receive a response at all. If that's right, I think we could make it
more clear somehow...

 if (!recieved_response_)
    MaybeCreateLoaderForResposne(NORESPONSE);

We'd have to reset recieved_response_ in Restart() for this to work.

Also, I think the only case this applied to is when completion_status is !OK.

 if (completion_status != OK && !recieved_response_)
    MaybeCreateLoaderForResposne(NORESPONSE);

... at least i think?

[ananta, 2017/07/28 22:59:22]

Thanks. I added a received_response_ flag which defaults to false and is set to
true in OnReceiveResponse(). It resets to false in Restart().

+      return;
+
     BrowserThread::PostTask(
         BrowserThread::UI, FROM_HERE,
         base::Bind(&NavigationURLLoaderNetworkService::OnComplete, owner_,
                    completion_status));
   }
 
+  // Returns true if a handler wants to handle the response, i.e. return a
+  // different response. For e.g. AppCache may have fallback content to be
+  // returned for a TLD.
+  bool MaybeCreateLoaderForResponse(const ResourceResponseHead& response) {
+    if (!default_loader_used_)
+      return false;
+
+    for (size_t index = 0; index < handlers_.size(); ++index) {
+      if (handlers_[index]->MaybeCreateLoaderForResponse(
+              response, &response_url_loader_, &response_client_request_)) {
+        OnResponseHandlerFound();
+        return true;
+      }
+    }
+    return false;
+  }
+
+  // Called if we find a handler who delivers different content for the URL.
+  void OnResponseHandlerFound() {
+    response_loader_binding_.Bind(std::move(response_client_request_));
+    // We reset this flag as we expect a new response from the handler.
+    default_loader_used_ = false;
+    // Disconnect from the network loader to stop receiving further data
+    // or notifications for the URL.
+    url_loader_->DisconnectClient();
+  }
+
   std::vector<std::unique_ptr<URLLoaderRequestHandler>> handlers_;
   size_t handler_index_ = 0;
 
   std::unique_ptr<ResourceRequest> resource_request_;
   ResourceContext* resource_context_;
   base::Callback<WebContents*()> web_contents_getter_;
 
   scoped_refptr<URLLoaderFactoryGetter> default_url_loader_factory_getter_;
 
   mojom::URLLoaderFactoryPtr webui_factory_ptr_;
 
   std::unique_ptr<ThrottlingURLLoader> url_loader_;
 
   BlobHandles blob_handles_;
 
   // Currently used by the AppCache loader to pass its factory to the
   // renderer which enables it to handle subresources.
   mojom::URLLoaderFactoryPtrInfo subresource_url_loader_factory_ptr_info_;
 
   // This is referenced only on the UI thread.
   base::WeakPtr<NavigationURLLoaderNetworkService> owner_;
 
+  // Set to true if the default URLLoader (network service) was used for the
+  // current navigation.
+  bool default_loader_used_ = false;
+
+  // Contains a copy of the response.
+  ResourceResponseHead response_;
+
+  // URLLoaderClient binding for loaders created for responses received from the
+  // network loader.
+  mojo::Binding<mojom::URLLoaderClient> response_loader_binding_;
+
+  // URLLoader instance for response loaders, i.e loaders created for handing
+  // responses received from the network URLLoader.
+  mojom::URLLoaderPtr response_url_loader_;
+
+  // URLLoaderClient request pointer for response loaders, i.e loaders created
+  // for handing responses received from the network URLLoader.
+  mojom::URLLoaderClientRequest response_client_request_;

[kinuko, 2017/07/28 09:50:29]

Does this need to be kept in this field?  Can we just stack-allocate this before
calling MaybeCreateLoaderForResponse and pass it in OnResponseHandlerFound()?

[ananta, 2017/07/28 22:59:22]

Done.

+
   DISALLOW_COPY_AND_ASSIGN(URLLoaderRequestController);
 };
 
 NavigationURLLoaderNetworkService::NavigationURLLoaderNetworkService(
     ResourceContext* resource_context,
     StoragePartition* storage_partition,
     std::unique_ptr<NavigationRequestInfo> request_info,
     std::unique_ptr<NavigationUIData> navigation_ui_data,
     ServiceWorkerNavigationHandle* service_worker_navigation_handle,
     AppCacheNavigationHandle* appcache_handle,
@@ skipping 135 matching lines @@
     TRACE_EVENT_ASYNC_END2("navigation", "Navigation timeToResponseStarted",
                            this, "&NavigationURLLoaderNetworkService", this,
                            "success", false);
 
     delegate_->OnRequestFailed(completion_status.exists_in_cache,
                                completion_status.error_code);
   }
 }
 
 }  // namespace content