content::ResourceDispatcherHostImpl changes for stale-while-revalidate

content/browser/loader/async_revalidation_driver.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_driver.h"
+
+#include <utility>
+
+#include "base/callback_helpers.h"
+#include "base/location.h"
+#include "base/logging.h"
+#include "base/memory/ref_counted.h"
+#include "base/metrics/user_metrics_action.h"
+#include "base/single_thread_task_runner.h"
+#include "base/thread_task_runner_handle.h"
+#include "base/time/time.h"
+#include "content/public/browser/user_metrics.h"
+#include "net/base/net_errors.h"
+#include "net/url_request/url_request_status.h"
+
+namespace content {
+
+namespace {
+// This matches the maximum allocation size of AsyncResourceHandler.
+const int kReadBufSize = 32 * 1024;
+
+// The time to wait for a response. Since this includes the time taken to
+// connect, this has been set to match the connect timeout
+// kTransportConnectJobTimeoutInSeconds.
+const int kResponseTimeoutInSeconds = 240;  // 4 minutes.
+
+// This value should not be too large, as this request may be tying up a socket
+// that could be used for something better. However, if it is too small, the
+// cache entry will be truncated for no good reason.
+// TODO(ricea): Find a more scientific way to set this timeout.
+const int kReadTimeoutInSeconds = 30;
+}  // namespace
+
+AsyncRevalidationDriver::AsyncRevalidationDriver(
+    scoped_ptr<net::URLRequest> request,
+    scoped_ptr<ResourceThrottle> throttle,
+    const base::Closure& completion_callback)
+    : request_(std::move(request)),
+      throttle_(std::move(throttle)),
+      completion_callback_(completion_callback),
+      weak_ptr_factory_(this) {
+  request_->set_delegate(this);
+  throttle_->set_controller(this);
+}
+
+AsyncRevalidationDriver::~AsyncRevalidationDriver() {}
+
+void AsyncRevalidationDriver::StartRequest() {
+  RecordAction(base::UserMetricsAction("AsyncRevalidationCreated"));
+  // Give the handler a chance to delay the URLRequest from being started.
+  bool defer_start = false;
+  throttle_->WillStartRequest(&defer_start);
+
+  if (defer_start) {
+    RecordDefer();
+  } else {
+    StartRequestInternal();
+  }
+}
+
+void AsyncRevalidationDriver::CancelRequest() {
+  CancelRequestInternal(net::ERR_ABORTED);
+}
+
+void AsyncRevalidationDriver::OnReceivedRedirect(
+    net::URLRequest* request,
+    const net::RedirectInfo& redirect_info,
+    bool* defer) {
+  DCHECK_EQ(request_.get(), request);
+
+  // The async revalidation should not follow redirects, because caching is
+  // a property of an individual HTTP resource.
+  DVLOG(1) << "OnReceivedRedirect: " << request_->url().spec();
+  RecordAction(base::UserMetricsAction("AsyncRevalidationRedirected"));
+  CancelRequest();
+}
+
+void AsyncRevalidationDriver::OnAuthRequired(
+    net::URLRequest* request,
+    net::AuthChallengeInfo* auth_info) {
+  DCHECK_EQ(request_.get(), request);
+  // This error code doesn't have exactly the right semantics, but it should
+  // be sufficient to narrow down the problem in net logs.
+  request_->CancelWithError(net::ERR_ACCESS_DENIED);
+}
+
+void AsyncRevalidationDriver::OnBeforeNetworkStart(net::URLRequest* request,
+                                                   bool* defer) {
+  DCHECK_EQ(request_.get(), request);
+
+  // Verify that the ResourceScheduler does not defer here.
+  throttle_->WillStartUsingNetwork(defer);
+  DCHECK(!*defer);
+
+  // Start the response timer. This use of base::Unretained() is guaranteed safe
+  // by the semantics of base::OneShotTimer.
+  timer_.Start(FROM_HERE,
+               base::TimeDelta::FromSeconds(kResponseTimeoutInSeconds),
+               base::Bind(&AsyncRevalidationDriver::OnTimeout,
+                          base::Unretained(this), RESPONSE_TIMEOUT));
+}
+
+void AsyncRevalidationDriver::OnResponseStarted(net::URLRequest* request) {
+  DCHECK_EQ(request_.get(), request);
+
+  DVLOG(1) << "OnResponseStarted: " << request_->url().spec();
+
+  // We have the response. No need to wait any longer.
+  timer_.Stop();
+
+  if (!request_->status().is_success()) {
+    ResponseCompleted();
+    return;
+  }
+
+  const net::HttpResponseInfo& response_info = request_->response_info();
+  if (!response_info.response_time.is_null() && response_info.was_cached) {
+    // The cached entry was revalidated. No need to read it in.
+    ResponseCompleted();
+    return;
+  }
+
+  bool defer = false;
+  throttle_->WillProcessResponse(&defer);
+  DCHECK(!defer);
+
+  // Set up the timer for reading the body. This use of base::Unretained() is
+  // guaranteed safe by the semantics of base::OneShotTimer.
+  timer_.Start(FROM_HERE, base::TimeDelta::FromSeconds(kReadTimeoutInSeconds),
+               base::Bind(&AsyncRevalidationDriver::OnTimeout,
+                          base::Unretained(this), READ_TIMEOUT));
+  StartReading(false);  // Read the first chunk.
+}
+
+void AsyncRevalidationDriver::OnReadCompleted(net::URLRequest* request,
+                                              int bytes_read) {
+  DCHECK_EQ(request_.get(), request);
+  DCHECK(!is_deferred_);
+  DVLOG(1) << "OnReadCompleted: \"" << request_->url().spec() << "\""
+           << " bytes_read = " << bytes_read;
+
+  // bytes_read == -1 is an error.
+  // bytes_read == 0 is EOF.
+  if (bytes_read == -1 || bytes_read == 0 || !request_->status().is_success()) {
+    ResponseCompleted();
+    return;
+  }
+
+  DCHECK_GT(bytes_read, 0);
+  StartReading(true);  // Read the next chunk.
+}
+
+void AsyncRevalidationDriver::Resume() {
+  DCHECK(is_deferred_);
+  is_deferred_ = false;
+  request_->LogUnblocked();
+  StartRequestInternal();
+}
+
+void AsyncRevalidationDriver::Cancel() {
+  NOTREACHED();
+}
+
+void AsyncRevalidationDriver::CancelAndIgnore() {
+  NOTREACHED();
+}
+
+void AsyncRevalidationDriver::CancelWithError(int error_code) {
+  NOTREACHED();
+}
+
+void AsyncRevalidationDriver::StartRequestInternal() {
+  DCHECK(!request_->is_pending());
+
+  // This can happen if Resume() is called after CancelRequest().
+  // Since CancelRequest() will have called ResponseCompleted() asynchronously,
+  // it's not necessary to call it again.
+  if (!request_->status().is_success())
+    return;
+
+  request_->Start();
+}
+
+void AsyncRevalidationDriver::CancelRequestInternal(int error) {
+  DVLOG(1) << "CancelRequestInternal: " << request_->url().spec();
+
+  bool was_pending = request_->is_pending();
+
+  request_->CancelWithError(error);
+
+  if (!was_pending) {
+    // If the request isn't in flight, then we won't get an asynchronous
+    // notification from the request, so we have to signal ourselves to finish
+    // this request.
+    scoped_refptr<base::SingleThreadTaskRunner> single_thread_task_runner =
+        base::ThreadTaskRunnerHandle::Get();

[davidben, 2015/12/07 23:56:03]

Nit: Why the change? The old one seems shorter.
(base::TTRH::Get()->PostTask(...))

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

I got tired of people asking me why I need the single_thread_task_runner.h
include file. So I made the usage explicit.

I don't have any better ideas.

+    single_thread_task_runner->PostTask(
+        FROM_HERE, base::Bind(&AsyncRevalidationDriver::ResponseCompleted,
+                              weak_ptr_factory_.GetWeakPtr()));
+  }
+}
+
+void AsyncRevalidationDriver::StartReading(bool is_continuation) {
+  int bytes_read = 0;
+  ReadMore(&bytes_read);
+
+  // If IO is pending, wait for the URLRequest to call OnReadCompleted.
+  if (request_->status().is_io_pending())
+    return;
+
+  if (!is_continuation || bytes_read <= 0) {
+    OnReadCompleted(request_.get(), bytes_read);
+  } else {
+    // Else, trigger OnReadCompleted asynchronously to avoid starving the IO
+    // thread in case the URLRequest can provide data synchronously.
+    scoped_refptr<base::SingleThreadTaskRunner> single_thread_task_runner =
+        base::ThreadTaskRunnerHandle::Get();

[davidben, 2015/12/07 23:56:03]

Ditto.

+    single_thread_task_runner->PostTask(
+        FROM_HERE,
+        base::Bind(&AsyncRevalidationDriver::OnReadCompleted,
+                   weak_ptr_factory_.GetWeakPtr(), request_.get(), bytes_read));
+  }
+}
+
+void AsyncRevalidationDriver::ReadMore(int* bytes_read) {
+  DCHECK(!is_deferred_);
+
+  if (!read_buffer_)
+    read_buffer_ = new net::IOBuffer(kReadBufSize);
+
+  timer_.Reset();
+  request_->Read(read_buffer_.get(), kReadBufSize, bytes_read);
+
+  // No need to check the return value here as we'll detect errors by
+  // inspecting the URLRequest's status.
+}
+
+void AsyncRevalidationDriver::ResponseCompleted() {
+  DVLOG(1) << "ResponseCompleted: " << request_->url().spec();
+  DCHECK(!completion_callback_.is_null());
+  base::ResetAndReturn(&completion_callback_).Run();
+  // |this| may be deleted after this point.
+}
+
+void AsyncRevalidationDriver::OnTimeout(TimeoutType type) {

[davidben, 2015/12/07 23:56:03]

Since you allow for the object to be in a canceled but not yet destroyed state,
OnTimeout may trigger after you call CancelRequest, which seems poor. But it
doesn't seem like you actually need that state.

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

The object can still be in a zombie state if it calls completion_callback_.Run()
and isn't immediately deleted. I modified the tests so they always delete it
immediately, so now this never happens in practice.

+  // UserMetricsAction must be passed a literal string otherwise
+  // //tools/metrics/actions/extract_actions.py won't understand it.
+  switch (type) {
+    case RESPONSE_TIMEOUT:
+      RecordAction(base::UserMetricsAction("AsyncRevalidationResponseTimeout"));
+      break;
+
+    case READ_TIMEOUT:
+      RecordAction(base::UserMetricsAction("AsyncRevalidationReadTimeout"));
+      break;
+  }
+  CancelRequestInternal(net::ERR_TIMED_OUT);
+}
+
+void AsyncRevalidationDriver::RecordDefer() {
+  request_->LogBlockedBy(throttle_->GetNameForLogging());
+  DCHECK(!is_deferred_);
+  is_deferred_ = true;
+}
+
+}  // namespace content