Prerender: Disable prefetch if there's an appcache.

chrome/browser/prerender/prerender_resource_throttle.cc

 // Copyright 2013 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 "chrome/browser/prerender/prerender_resource_throttle.h"
 
 #include "base/logging.h"
 #include "base/memory/ref_counted.h"
 #include "base/numerics/safe_conversions.h"
 #include "build/build_config.h"
 #include "chrome/browser/prerender/prerender_final_status.h"
 #include "chrome/browser/prerender/prerender_manager.h"
 #include "chrome/browser/prerender/prerender_util.h"
+#include "content/public/browser/appcache_service.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/web_contents.h"
 #include "net/base/load_flags.h"
 #include "net/http/http_response_headers.h"
 #include "net/url_request/redirect_info.h"
 #include "net/url_request/url_request.h"
 
 using content::BrowserThread;
 using content::ResourceRequestInfo;
 using content::ResourceType;
@@ skipping 60 matching lines @@
 
 PrerenderResourceThrottle::PrerenderResourceThrottle(net::URLRequest* request)
     : request_(request),
       load_flags_(net::LOAD_NORMAL),
       prerender_throttle_info_(new PrerenderThrottleInfo()) {}
 
 PrerenderResourceThrottle::~PrerenderResourceThrottle() {}
 
 void PrerenderResourceThrottle::WillStartRequest(bool* defer) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
-  const content::ResourceRequestInfo* info =
-      content::ResourceRequestInfo::ForRequest(request_);
+  const ResourceRequestInfo* info = ResourceRequestInfo::ForRequest(request_);
   *defer = true;
   BrowserThread::PostTask(
       BrowserThread::UI, FROM_HERE,
       base::Bind(&PrerenderResourceThrottle::WillStartRequestOnUI, AsWeakPtr(),
                  request_->method(), info->GetResourceType(), request_->url(),
                  info->GetWebContentsGetterForRequest(),
                  prerender_throttle_info_));
 }
 
 void PrerenderResourceThrottle::WillRedirectRequest(
     const net::RedirectInfo& redirect_info,
     bool* defer) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
-  const content::ResourceRequestInfo* info =
-      content::ResourceRequestInfo::ForRequest(request_);
+  const ResourceRequestInfo* info = ResourceRequestInfo::ForRequest(request_);
   *defer = true;
   std::string header;
   request_->GetResponseHeaderByName(kFollowOnlyWhenPrerenderShown, &header);
 
   BrowserThread::PostTask(
       BrowserThread::UI, FROM_HERE,
       base::Bind(&PrerenderResourceThrottle::WillRedirectRequestOnUI,
                  AsWeakPtr(), header, info->GetResourceType(), info->IsAsync(),
                  IsNoStoreResponse(*request_), redirect_info.new_url,
                  info->GetWebContentsGetterForRequest()));
 }
 
 void PrerenderResourceThrottle::WillProcessResponse(bool* defer) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
-  const content::ResourceRequestInfo* info =
-      content::ResourceRequestInfo::ForRequest(request_);
+
+  const ResourceRequestInfo* info = ResourceRequestInfo::ForRequest(request_);
   if (!info)
     return;
 
+  bool has_appcache =
+      content::AppCacheService::URLRequestHasActiveAppCache(request_);
+
   DCHECK_GT(request_->url_chain().size(), 0u);
   int redirect_count =
       base::saturated_cast<int>(request_->url_chain().size()) - 1;
 
   BrowserThread::PostTask(
       BrowserThread::UI, FROM_HERE,
       base::Bind(&PrerenderResourceThrottle::WillProcessResponseOnUI,
+                 AsWeakPtr(),
                  content::IsResourceTypeFrame(info->GetResourceType()),
-                 IsNoStoreResponse(*request_), redirect_count,
+                 IsNoStoreResponse(*request_), redirect_count, has_appcache,
+                 info->GetWebContentsGetterForRequest(),
                  prerender_throttle_info_));
 }
 
 const char* PrerenderResourceThrottle::GetNameForLogging() const {
   return "PrerenderResourceThrottle";
 }
 
 void PrerenderResourceThrottle::ResumeHandler() {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
   request_->SetLoadFlags(request_->load_flags() | load_flags_);
@@ skipping 101 matching lines @@
   }
 
   BrowserThread::PostTask(
       BrowserThread::IO, FROM_HERE,
       base::Bind(cancel ? &PrerenderResourceThrottle::Cancel
                         : &PrerenderResourceThrottle::ResumeHandler,
                  throttle));
 }
 
 // static
 void PrerenderResourceThrottle::WillProcessResponseOnUI(

[michaeln, 2017/03/27 23:27:45]

Since this call on the UI thread is advisory only, the io thread and renderer
will be racing ahead with (pre)loading while the task to invoke this method is
in-flight. I think many preload requests could get processed prior to the
Cancel() call making its way back to the IO thread (depending on how
busy/scheduled various threads are relative to one another).

+    const base::WeakPtr<PrerenderResourceThrottle>& throttle,
     bool is_main_resource,
     bool is_no_store,
     int redirect_count,
+    bool has_appcache,
+    const ResourceRequestInfo::WebContentsGetter& web_contents_getter,
     scoped_refptr<PrerenderThrottleInfo> prerender_throttle_info) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
   DCHECK(prerender_throttle_info);
   if (!prerender_throttle_info->manager())
     return;
 
   if (prerender_throttle_info->mode() != PREFETCH_ONLY)
     return;
 
+  // Check for an AppCache. If there is one, the AppCache fetcher (?) may not
+  // have been properly initialized for a prefetch-only resource, so the request
+  // is canceled. If there is no appcache, it is appropriate to go to the
+  // network: even if the main resource lists a manifest, its AppCache has not
+  // yet been initialized, and a network fetch would have happened in any case.
+  if (has_appcache) {
+    BrowserThread::PostTask(
+        BrowserThread::IO, FROM_HERE,
+        base::Bind(&PrerenderResourceThrottle::Cancel, throttle));
+
+    PrerenderContents* prerender_contents =
+        PrerenderContentsFromGetter(web_contents_getter);
+    if (prerender_contents)
+      prerender_contents->Destroy(FINAL_STATUS_CANCELLED_FOR_APPCACHE);
+    return;
+  }
+
   prerender_throttle_info->manager()->RecordPrefetchResponseReceived(
       prerender_throttle_info->origin(), is_main_resource,
       false /* is_redirect */, is_no_store);
   prerender_throttle_info->manager()->RecordPrefetchRedirectCount(
       prerender_throttle_info->origin(), is_main_resource, redirect_count);
 }
 
 // static
 PrerenderContents* PrerenderResourceThrottle::PrerenderContentsFromGetter(
     const ResourceRequestInfo::WebContentsGetter& web_contents_getter) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
   if (g_prerender_contents_for_testing)
     return g_prerender_contents_for_testing;
   return PrerenderContents::FromWebContents(web_contents_getter.Run());
 }
 
 void PrerenderResourceThrottle::SetPrerenderMode(PrerenderMode mode) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
   load_flags_ = (mode == PREFETCH_ONLY) ? net::LOAD_PREFETCH : net::LOAD_NORMAL;
 }
 
 }  // namespace prerender