blob: f81e1b532d30865be87ceac005bff9d92fe82cb9 [file] [log] [blame]
// 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.
#include "net/url_request/url_request_throttler_entry.h"
#include <cmath>
#include <utility>
#include "base/logging.h"
#include "base/metrics/field_trial.h"
#include "base/metrics/histogram_macros.h"
#include "base/rand_util.h"
#include "base/strings/string_number_conversions.h"
#include "base/values.h"
#include "net/base/load_flags.h"
#include "net/log/net_log_capture_mode.h"
#include "net/log/net_log_event_type.h"
#include "net/log/net_log_source_type.h"
#include "net/url_request/url_request.h"
#include "net/url_request/url_request_context.h"
#include "net/url_request/url_request_throttler_manager.h"
namespace net {
const int URLRequestThrottlerEntry::kDefaultSlidingWindowPeriodMs = 2000;
const int URLRequestThrottlerEntry::kDefaultMaxSendThreshold = 20;
// This set of back-off parameters will (at maximum values, i.e. without
// the reduction caused by jitter) add 0-41% (distributed uniformly
// in that range) to the "perceived downtime" of the remote server, once
// exponential back-off kicks in and is throttling requests for more than
// about a second at a time. Once the maximum back-off is reached, the added
// perceived downtime decreases rapidly, percentage-wise.
// Another way to put it is that the maximum additional perceived downtime
// with these numbers is a couple of seconds shy of 15 minutes, and such
// a delay would not occur until the remote server has been actually
// unavailable at the end of each back-off period for a total of about
// 48 minutes.
// Ignoring the first couple of errors is just a conservative measure to
// avoid false positives. It should help avoid back-off from kicking in e.g.
// on flaky connections.
const int URLRequestThrottlerEntry::kDefaultNumErrorsToIgnore = 2;
const int URLRequestThrottlerEntry::kDefaultInitialDelayMs = 700;
const double URLRequestThrottlerEntry::kDefaultMultiplyFactor = 1.4;
const double URLRequestThrottlerEntry::kDefaultJitterFactor = 0.4;
const int URLRequestThrottlerEntry::kDefaultMaximumBackoffMs = 15 * 60 * 1000;
const int URLRequestThrottlerEntry::kDefaultEntryLifetimeMs = 2 * 60 * 1000;
// Returns NetLog parameters when a request is rejected by throttling.
std::unique_ptr<base::Value> NetLogRejectedRequestCallback(
const std::string* url_id,
int num_failures,
const base::TimeDelta& release_after,
NetLogCaptureMode /* capture_mode */) {
std::unique_ptr<base::DictionaryValue> dict(new base::DictionaryValue());
dict->SetString("url", *url_id);
dict->SetInteger("num_failures", num_failures);
return std::move(dict);
URLRequestThrottlerManager* manager,
const std::string& url_id)
: sliding_window_period_(
URLRequestThrottlerManager* manager,
const std::string& url_id,
int sliding_window_period_ms,
int max_send_threshold,
int initial_backoff_ms,
double multiply_factor,
double jitter_factor,
int maximum_backoff_ms)
: sliding_window_period_(
url_id_(url_id) {
DCHECK_GT(sliding_window_period_ms, 0);
DCHECK_GT(max_send_threshold_, 0);
DCHECK_GE(initial_backoff_ms, 0);
DCHECK_GT(multiply_factor, 0);
DCHECK_GE(jitter_factor, 0.0);
DCHECK_LT(jitter_factor, 1.0);
DCHECK_GE(maximum_backoff_ms, 0);
backoff_policy_.initial_delay_ms = initial_backoff_ms;
backoff_policy_.multiply_factor = multiply_factor;
backoff_policy_.jitter_factor = jitter_factor;
backoff_policy_.maximum_backoff_ms = maximum_backoff_ms;
backoff_policy_.entry_lifetime_ms = -1;
backoff_policy_.num_errors_to_ignore = 0;
backoff_policy_.always_use_initial_delay = false;
bool URLRequestThrottlerEntry::IsEntryOutdated() const {
// This function is called by the URLRequestThrottlerManager to determine
// whether entries should be discarded from its url_entries_ map. We
// want to ensure that it does not remove entries from the map while there
// are clients (objects other than the manager) holding references to
// the entry, otherwise separate clients could end up holding separate
// entries for a request to the same URL, which is undesirable. Therefore,
// if an entry has more than one reference (the map will always hold one),
// it should not be considered outdated.
// We considered whether to make URLRequestThrottlerEntry objects
// non-refcounted, but since any means of knowing whether they are
// currently in use by others than the manager would be more or less
// equivalent to a refcount, we kept them refcounted.
if (!HasOneRef())
return false;
// If there are send events in the sliding window period, we still need this
// entry.
if (!send_log_.empty() &&
send_log_.back() + sliding_window_period_ > ImplGetTimeNow()) {
return false;
return GetBackoffEntry()->CanDiscard();
void URLRequestThrottlerEntry::DisableBackoffThrottling() {
is_backoff_disabled_ = true;
void URLRequestThrottlerEntry::DetachManager() {
manager_ = NULL;
bool URLRequestThrottlerEntry::ShouldRejectRequest(
const URLRequest& request) const {
bool reject_request = false;
if (!is_backoff_disabled_ && GetBackoffEntry()->ShouldRejectRequest()) {
base::Bind(&NetLogRejectedRequestCallback, &url_id_,
reject_request = true;
int reject_count = reject_request ? 1 : 0;
"Throttling.RequestThrottled", reject_count, 2);
return reject_request;
int64_t URLRequestThrottlerEntry::ReserveSendingTimeForNextRequest(
const base::TimeTicks& earliest_time) {
base::TimeTicks now = ImplGetTimeNow();
// If a lot of requests were successfully made recently,
// sliding_window_release_time_ may be greater than
// exponential_backoff_release_time_.
base::TimeTicks recommended_sending_time =
std::max(std::max(now, earliest_time),
DCHECK(send_log_.empty() ||
recommended_sending_time >= send_log_.back());
// Log the new send event.
sliding_window_release_time_ = recommended_sending_time;
// Drop the out-of-date events in the event list.
// We don't need to worry that the queue may become empty during this
// operation, since the last element is sliding_window_release_time_.
while ((send_log_.front() + sliding_window_period_ <=
sliding_window_release_time_) ||
send_log_.size() > static_cast<unsigned>(max_send_threshold_)) {
// Check if there are too many send events in recent time.
if (send_log_.size() == static_cast<unsigned>(max_send_threshold_))
sliding_window_release_time_ = send_log_.front() + sliding_window_period_;
return (recommended_sending_time - now).InMillisecondsRoundedUp();
URLRequestThrottlerEntry::GetExponentialBackoffReleaseTime() const {
// If a site opts out, it's likely because they have problems that trigger
// the back-off mechanism when it shouldn't be triggered, in which case
// returning the calculated back-off release time would probably be the
// wrong thing to do (i.e. it would likely be too long). Therefore, we
// return "now" so that retries are not delayed.
if (is_backoff_disabled_)
return ImplGetTimeNow();
return GetBackoffEntry()->GetReleaseTime();
void URLRequestThrottlerEntry::UpdateWithResponse(int status_code) {
void URLRequestThrottlerEntry::ReceivedContentWasMalformed(int response_code) {
// A malformed body can only occur when the request to fetch a resource
// was successful. Therefore, in such a situation, we will receive one
// call to ReceivedContentWasMalformed() and one call to
// UpdateWithResponse() with a response categorized as "good". To end
// up counting one failure, we need to count two failures here against
// the one success in UpdateWithResponse().
// We do nothing for a response that is already being considered an error
// based on its status code (otherwise we would count 3 errors instead of 1).
if (IsConsideredSuccess(response_code)) {
URLRequestThrottlerEntry::~URLRequestThrottlerEntry() {
void URLRequestThrottlerEntry::Initialize() {
sliding_window_release_time_ = base::TimeTicks::Now();
backoff_policy_.num_errors_to_ignore = kDefaultNumErrorsToIgnore;
backoff_policy_.initial_delay_ms = kDefaultInitialDelayMs;
backoff_policy_.multiply_factor = kDefaultMultiplyFactor;
backoff_policy_.jitter_factor = kDefaultJitterFactor;
backoff_policy_.maximum_backoff_ms = kDefaultMaximumBackoffMs;
backoff_policy_.entry_lifetime_ms = kDefaultEntryLifetimeMs;
backoff_policy_.always_use_initial_delay = false;
bool URLRequestThrottlerEntry::IsConsideredSuccess(int response_code) {
// We throttle only for the status codes most likely to indicate the server
// is failing because it is too busy or otherwise are likely to be
// because of DDoS.
// 500 is the generic error when no better message is suitable, and
// as such does not necessarily indicate a temporary state, but
// other status codes cover most of the permanent error states.
// 503 is explicitly documented as a temporary state where the server
// is either overloaded or down for maintenance.
// 509 is the (non-standard but widely implemented) Bandwidth Limit Exceeded
// status code, which might indicate DDoS.
// We do not back off on 502 or 504, which are reported by gateways
// (proxies) on timeouts or failures, because in many cases these requests
// have not made it to the destination server and so we do not actually
// know that it is down or busy. One degenerate case could be a proxy on
// localhost, where you are not actually connected to the network.
return !(response_code == 500 || response_code == 503 ||
response_code == 509);
base::TimeTicks URLRequestThrottlerEntry::ImplGetTimeNow() const {
return base::TimeTicks::Now();
const BackoffEntry* URLRequestThrottlerEntry::GetBackoffEntry() const {
return &backoff_entry_;
BackoffEntry* URLRequestThrottlerEntry::GetBackoffEntry() {
return &backoff_entry_;
} // namespace net