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- // 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/bind.h"
- #include "base/check_op.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.
- base::Value NetLogRejectedRequestParams(const std::string* url_id,
- int num_failures,
- const base::TimeDelta& release_after) {
- base::Value::Dict dict;
- dict.Set("url", *url_id);
- dict.Set("num_failures", num_failures);
- dict.Set("release_after_ms",
- static_cast<int>(release_after.InMilliseconds()));
- return base::Value(std::move(dict));
- }
- URLRequestThrottlerEntry::URLRequestThrottlerEntry(
- URLRequestThrottlerManager* manager,
- const std::string& url_id)
- : sliding_window_period_(base::Milliseconds(kDefaultSlidingWindowPeriodMs)),
- max_send_threshold_(kDefaultMaxSendThreshold),
- backoff_entry_(&backoff_policy_),
- manager_(manager),
- url_id_(url_id),
- net_log_(NetLogWithSource::Make(
- manager->net_log(),
- NetLogSourceType::EXPONENTIAL_BACKOFF_THROTTLING)) {
- DCHECK(manager_);
- Initialize();
- }
- URLRequestThrottlerEntry::URLRequestThrottlerEntry(
- 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_(base::Milliseconds(sliding_window_period_ms)),
- max_send_threshold_(max_send_threshold),
- backoff_entry_(&backoff_policy_),
- manager_(manager),
- 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);
- DCHECK(manager_);
- Initialize();
- 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_ = nullptr;
- }
- bool URLRequestThrottlerEntry::ShouldRejectRequest(
- const URLRequest& request) const {
- bool reject_request = false;
- if (!is_backoff_disabled_ && GetBackoffEntry()->ShouldRejectRequest()) {
- net_log_.AddEvent(NetLogEventType::THROTTLING_REJECTED_REQUEST, [&] {
- return NetLogRejectedRequestParams(
- &url_id_, GetBackoffEntry()->failure_count(),
- GetBackoffEntry()->GetTimeUntilRelease());
- });
- reject_request = true;
- }
- int reject_count = reject_request ? 1 : 0;
- UMA_HISTOGRAM_ENUMERATION(
- "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),
- std::max(GetBackoffEntry()->GetReleaseTime(),
- sliding_window_release_time_));
- DCHECK(send_log_.empty() ||
- recommended_sending_time >= send_log_.back());
- // Log the new send event.
- send_log_.push(recommended_sending_time);
- 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_)) {
- send_log_.pop();
- }
- // 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();
- }
- base::TimeTicks
- 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) {
- GetBackoffEntry()->InformOfRequest(IsConsideredSuccess(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)) {
- GetBackoffEntry()->InformOfRequest(false);
- GetBackoffEntry()->InformOfRequest(false);
- }
- }
- URLRequestThrottlerEntry::~URLRequestThrottlerEntry() = default;
- 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
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