Move MimeTypeResourceHandler before ThrottlingResourceHandler

content/browser/loader/resource_dispatcher_host_impl.cc

 // Copyright (c) 2012 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.
 
 // See http://dev.chromium.org/developers/design-documents/multi-process-resource-loading
 
 #include "content/browser/loader/resource_dispatcher_host_impl.h"
 
 #include <stddef.h>
 
@@ skipping 31 matching lines @@
 #include "content/browser/download/download_resource_handler.h"
 #include "content/browser/download/save_file_manager.h"
 #include "content/browser/download/save_file_resource_handler.h"
 #include "content/browser/frame_host/frame_tree.h"
 #include "content/browser/frame_host/navigation_request_info.h"
 #include "content/browser/frame_host/navigator.h"
 #include "content/browser/loader/async_resource_handler.h"
 #include "content/browser/loader/async_revalidation_manager.h"
 #include "content/browser/loader/cross_site_resource_handler.h"
 #include "content/browser/loader/detachable_resource_handler.h"
-#include "content/browser/loader/mime_type_resource_handler.h"
+#include "content/browser/loader/intercepting_resource_handler.h"
+#include "content/browser/loader/mime_sniffing_resource_handler.h"
 #include "content/browser/loader/navigation_resource_handler.h"
 #include "content/browser/loader/navigation_resource_throttle.h"
 #include "content/browser/loader/navigation_url_loader_impl_core.h"
 #include "content/browser/loader/power_save_block_resource_throttle.h"
 #include "content/browser/loader/redirect_to_file_resource_handler.h"
 #include "content/browser/loader/resource_message_filter.h"
 #include "content/browser/loader/resource_request_info_impl.h"
 #include "content/browser/loader/stream_resource_handler.h"
 #include "content/browser/loader/sync_resource_handler.h"
 #include "content/browser/loader/throttling_resource_handler.h"
@@ skipping 1616 matching lines @@
   if (IsBrowserSideNavigationEnabled() && IsResourceTypeFrame(resource_type) &&
       child_id != -1) {
     DCHECK(request->url().SchemeIs(url::kBlobScheme));
     return handler;
   }
 
   PluginService* plugin_service = nullptr;
 #if defined(ENABLE_PLUGINS)
   plugin_service = PluginService::GetInstance();
 #endif
-  // Insert a buffered event handler before the actual one.
-  handler.reset(new MimeTypeResourceHandler(std::move(handler), this,
-                                            plugin_service, request));
+
+  // The InterceptingResourceHandler will replace its next handler with an
+  // appropriate one based on the MIME type of the response if needed. It
+  // should be placed at the end of the chain, just before |handler|.
+  handler.reset(new InterceptingResourceHandler(std::move(handler), this,
+                                                plugin_service, request));
 
   ScopedVector<ResourceThrottle> throttles;
 
   // Add a NavigationResourceThrottle for navigations.
   // PlzNavigate: the throttle is unnecessary as communication with the UI
   // thread is handled by the NavigationURLloader.
   if (!IsBrowserSideNavigationEnabled() && IsResourceTypeFrame(resource_type))
     throttles.push_back(new NavigationResourceThrottle(request, delegate()));
 
   if (delegate_) {
@@ skipping 11 matching lines @@
   }
 
   // TODO(ricea): Stop looking this up so much.
   ResourceRequestInfoImpl* info = ResourceRequestInfoImpl::ForRequest(request);
   throttles.push_back(scheduler_->ScheduleRequest(child_id, route_id,
                                                   info->IsAsync(), request));
 
   handler.reset(new ThrottlingResourceHandler(std::move(handler), request,
                                               std::move(throttles)));
 
+  // Insert a buffered event handler to sniff the mime type first.
+  handler.reset(new MimeSniffingResourceHandler(std::move(handler), request));

[asanka, 2016/06/23 02:30:13]

Note that this ResourceHandler is special. Every resource handler behind it has
to be prepared to service OnWillRead *before* OnResponseStarted. It used to be
an exception that only the last ResourceHandler needed to handle, but it's now
the norm for all ResourceHandlers due to MimeSniffingResourceHandler being at
the head of the chain.

Maybe we should document it.

[clamy, 2016/06/28 16:20:41]

Added documentation about this behavior in the comment.

+
   return handler;
 }
 
 void ResourceDispatcherHostImpl::OnReleaseDownloadedFile(int request_id) {
   UnregisterDownloadedTempFile(filter_->child_id(), request_id);
 }
 
 void ResourceDispatcherHostImpl::OnDidChangePriority(
     int request_id,
     net::RequestPriority new_priority,
@@ skipping 907 matching lines @@
   ssl.cert_id = GetCertStore()->StoreCert(ssl_info.cert.get(), child_id);
   response->head.security_info = SerializeSecurityInfo(ssl);
 }
 
 CertStore* ResourceDispatcherHostImpl::GetCertStore() {
   return cert_store_for_testing_ ? cert_store_for_testing_
                                  : CertStore::GetInstance();
 }
 
 }  // namespace content