content::ResourceDispatcherHostImpl changes for stale-while-revalidate

content/browser/loader/async_revalidation_manager.cc

+// Copyright 2015 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/async_revalidation_manager.h"
+
+#include <tuple>
+#include <utility>
+
+#include "base/logging.h"
+#include "content/browser/loader/async_revalidation_driver.h"
+#include "content/browser/loader/resource_message_filter.h"
+#include "content/browser/loader/resource_request_info_impl.h"
+#include "content/browser/loader/resource_scheduler.h"
+#include "content/common/resource_messages.h"
+#include "content/public/browser/resource_throttle.h"
+#include "net/base/load_flags.h"
+#include "net/http/http_transaction_factory.h"
+#include "net/http/http_util.h"
+#include "net/url_request/url_request.h"
+#include "net/url_request/url_request_context.h"
+#include "url/gurl.h"
+
+namespace content {
+
+AsyncRevalidationManager::AsyncRevalidationKey::AsyncRevalidationKey(
+    const ResourceContext* resource_context,
+    const net::HttpCache* http_cache,
+    const GURL& url)
+    : resource_context(resource_context),
+      http_cache(http_cache),
+      url_key(net::HttpUtil::SpecForRequest(url)) {}
+
+AsyncRevalidationManager::AsyncRevalidationKey::AsyncRevalidationKey(
+    const ResourceContext* resource_context)
+    : resource_context(resource_context), http_cache(nullptr), url_key() {}
+
+AsyncRevalidationManager::AsyncRevalidationKey::~AsyncRevalidationKey() {}
+
+bool AsyncRevalidationManager::AsyncRevalidationKey::LessThan::operator()(
+    const AsyncRevalidationKey& lhs,
+    const AsyncRevalidationKey& rhs) const {
+  return std::tie(lhs.resource_context, lhs.http_cache, lhs.url_key) <
+         std::tie(rhs.resource_context, rhs.http_cache, rhs.url_key);
+}
+
+AsyncRevalidationManager::AsyncRevalidationManager() {}
+
+AsyncRevalidationManager::~AsyncRevalidationManager() {
+  DCHECK(in_progress_.empty());
+}
+
+void AsyncRevalidationManager::BeginAsyncRevalidation(
+    const net::URLRequest& for_request,
+    ResourceScheduler* scheduler) {
+  DCHECK_EQ(for_request.url_chain().size(), 1u);
+  const ResourceRequestInfoImpl* info =
+      ResourceRequestInfoImpl::ForRequest(&for_request);
+  DCHECK(info);
+  if (!info->filter()) {
+    // The child has gone away and we can no longer get ResourceContext and
+    // URLRequestContext to perform async revalidation.
+    // This can happen in the following cases, ordered from bad to not-so-bad
+    //
+    // 1. PlzNavigate (but enabling PlzNavigate automatically disables
+    //    stale-while-revalidate; see crbug.com/561609)
+    // 2. <link rel=prefetch> may read a stale cache entry without a
+    //    revalidation being performed if the original renderer goes away. This
+    //    is a lost optimisation opportunity.
+    //
+    // Not an issue:
+    // 1. Implicit downloads. This method is called before
+    //    MimeTypeResourceHandler calls set_is_download, so the renderer process
+    //    must still exist for the request not to have been canceled.
+    // 2. Explicit downloads (ie. started via "Save As"). These never use
+    //    stale-while-revalidate.
+    // 3. Non-PlzNavigate navigations between renderers. The old renderer
+    //    still exists when this method is called.
+    // 4. <a ping>, navigation.sendBeacon() and Content-Security-Policy reports
+    //    are POST requests, so they never use stale-while-revalidate.
+    //
+    // TODO(ricea): Resolve these lifetime issues. crbug.com/561591
+    return;
+  }
+
+  ResourceContext* resource_context = nullptr;
+  net::URLRequestContext* request_context = nullptr;
+
+  // The embedder of //content needs to ensure that the URLRequestContext object
+  // remains valid until after the ResourceContext object is destroyed.
+  info->filter()->GetContexts(info->GetResourceType(), info->GetOriginPID(),
+                              &resource_context, &request_context);
+
+  AsyncRevalidationKey async_revalidation_key(
+      resource_context, request_context->http_transaction_factory()->GetCache(),
+      for_request.url());
+  std::pair<AsyncRevalidationMap::iterator, bool> insert_result =
+      in_progress_.insert(AsyncRevalidationMap::value_type(
+          async_revalidation_key, scoped_ptr<AsyncRevalidationDriver>()));
+  if (!insert_result.second) {
+    // A matching async revalidation is already in progress for this cache; we
+    // don't need another one. An async revalidation is never triggered when a
+    // Vary mismatch occurs. This means that the response will be usable even if
+    // the request headers differ.

[davidben, 2015/12/07 23:56:04]

Huh? What does this comment even mean?

I would, like the in the header file, leave a TODO about the missing HttpCache
logic. (Or maybe just remove these couple of sentences in favor of the header
talking about the problem.)

[Adam Rice, 2015/12/08 18:05:35]

Removed in favour of the comment in the header.

+    return;
+  }
+
+  net::HttpRequestHeaders headers;
+  headers.AddHeadersFromString(info->original_headers());
+
+  // Construct the request.
+  scoped_ptr<net::URLRequest> new_request = request_context->CreateRequest(
+      for_request.url(), net::MINIMUM_PRIORITY, nullptr);
+
+  new_request->set_method(for_request.method());
+  new_request->set_first_party_for_cookies(
+      for_request.first_party_for_cookies());
+  new_request->set_first_party_url_policy(
+      for_request.first_party_url_policy());
+
+  new_request->SetReferrer(for_request.referrer());
+  new_request->set_referrer_policy(for_request.referrer_policy());
+
+  new_request->SetExtraRequestHeaders(headers);
+
+  // Remove LOAD_SUPPORT_ASYNC_REVALIDATION and LOAD_MAIN_FRAME flags.
+  // Also remove things which shouldn't have been there to begin with,
+  // and unrecognised flags.
+  int load_flags =
+      for_request.load_flags() &
+      (net::LOAD_DO_NOT_SAVE_COOKIES | net::LOAD_BYPASS_PROXY |
+       net::LOAD_VERIFY_EV_CERT | net::LOAD_DO_NOT_SEND_COOKIES |
+       net::LOAD_DO_NOT_SEND_AUTH_DATA | net::LOAD_PREFETCH |
+       net::LOAD_MAYBE_USER_GESTURE | net::LOAD_DO_NOT_USE_EMBEDDED_IDENTITY);

[davidben, 2015/12/07 23:56:04]

Carrying over LOAD_PREFETCH seems wrong. That turns on various interesting cache
behaviors.

[Adam Rice, 2015/12/08 18:05:35]

I added LOAD_PREFETCH to the prohibited flags in QualifiesForAsyncRevalidation()
too,
since otherwise an async revalidation could trick the cache into thinking the
prefetched resource had been used.

Since prefetch is already an asynchronous operation, it doesn't seem useful to
try to
make it more asynchronous, so an argument can be made that this is the "correct"
behaviour. Though I suppose it will also have to be explicitly standardised.

+  new_request->SetLoadFlags(load_flags);
+
+  // These values would be -1 if the request was created by PlzNavigate. This
+  // would cause the async revalidation to start immediately.
+  // stale-while-revalidate is disabled when PlzNavigate is enabled
+  // to prevent this and other issues. See crbug.com/561610.
+  int child_id = info->GetChildID();
+  int route_id = info->GetRouteID();
+
+  scoped_ptr<ResourceThrottle> throttle =
+      scheduler->ScheduleRequest(child_id, route_id, false, new_request.get());
+
+  // AsyncRevalidationDriver does not outlive its entry in |in_progress_|,
+  // so the iterator and |this| may be passed to base::Bind directly.
+  insert_result.first->second.reset(new AsyncRevalidationDriver(
+      std::move(new_request), std::move(throttle),
+      base::Bind(&AsyncRevalidationManager::OnAsyncRevalidationComplete,
+                 base::Unretained(this), insert_result.first)));
+  insert_result.first->second->StartRequest();
+}
+
+void AsyncRevalidationManager::CancelAsyncRevalidationsForResourceContext(
+    ResourceContext* resource_context) {
+  // |resource_context| is the first part of the key, so elements to be
+  // cancelled are contiguous in the map.
+  AsyncRevalidationKey partial_key(resource_context);
+  for (auto it = in_progress_.lower_bound(partial_key);
+       it != in_progress_.end() &&
+       it->first.resource_context == resource_context;) {
+    it->second->CancelRequest();
+    it = in_progress_.erase(it);
+  }
+}
+
+bool AsyncRevalidationManager::QualifiesForAsyncRevalidation(
+    const ResourceHostMsg_Request& request) {
+  if (request.load_flags &
+      (net::LOAD_BYPASS_CACHE | net::LOAD_DISABLE_CACHE |
+       net::LOAD_VALIDATE_CACHE | net::LOAD_PREFERRING_CACHE |
+       net::LOAD_ONLY_FROM_CACHE | net::LOAD_IGNORE_LIMITS)) {
+    return false;
+  }
+  if (request.method != "GET")
+    return false;
+  // A GET request should not have a body.
+  if (request.request_body.get())
+    return false;
+  if (!request.url.SchemeIsHTTPOrHTTPS())
+    return false;
+
+  return true;
+}
+
+void AsyncRevalidationManager::OnAsyncRevalidationComplete(
+    AsyncRevalidationMap::iterator it) {
+  in_progress_.erase(it);
+}
+
+}  // namespace content