net/url_request/url_request_throttler_entry.cc

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "net/url_request/url_request_throttler_entry.h"
   6
   7 #include <cmath>
   8
   9 #include "base/logging.h"
  10 #include "base/metrics/field_trial.h"
  11 #include "base/metrics/histogram_macros.h"
  12 #include "base/rand_util.h"
  13 #include "base/strings/string_number_conversions.h"
  14 #include "base/values.h"
  15 #include "net/base/load_flags.h"
  16 #include "net/log/net_log.h"
  17 #include "net/url_request/url_request.h"
  18 #include "net/url_request/url_request_context.h"
  19 #include "net/url_request/url_request_throttler_manager.h"
  20
  21 namespace net {
  22
  23 const int URLRequestThrottlerEntry::kDefaultSlidingWindowPeriodMs = 2000;
  24 const int URLRequestThrottlerEntry::kDefaultMaxSendThreshold = 20;
  25
  26 // This set of back-off parameters will (at maximum values, i.e. without
  27 // the reduction caused by jitter) add 0-41% (distributed uniformly
  28 // in that range) to the "perceived downtime" of the remote server, once
  29 // exponential back-off kicks in and is throttling requests for more than
  30 // about a second at a time.  Once the maximum back-off is reached, the added
  31 // perceived downtime decreases rapidly, percentage-wise.
  32 //
  33 // Another way to put it is that the maximum additional perceived downtime
  34 // with these numbers is a couple of seconds shy of 15 minutes, and such
  35 // a delay would not occur until the remote server has been actually
  36 // unavailable at the end of each back-off period for a total of about
  37 // 48 minutes.
  38 //
  39 // Ignoring the first couple of errors is just a conservative measure to
  40 // avoid false positives.  It should help avoid back-off from kicking in e.g.
  41 // on flaky connections.
  42 const int URLRequestThrottlerEntry::kDefaultNumErrorsToIgnore = 2;
  43 const int URLRequestThrottlerEntry::kDefaultInitialDelayMs = 700;
  44 const double URLRequestThrottlerEntry::kDefaultMultiplyFactor = 1.4;
  45 const double URLRequestThrottlerEntry::kDefaultJitterFactor = 0.4;
  46 const int URLRequestThrottlerEntry::kDefaultMaximumBackoffMs = 15 * 60 * 1000;
  47 const int URLRequestThrottlerEntry::kDefaultEntryLifetimeMs = 2 * 60 * 1000;
  48
  49 // Returns NetLog parameters when a request is rejected by throttling.
  50 scoped_ptr<base::Value> NetLogRejectedRequestCallback(
  51     const std::string* url_id,
  52     int num_failures,
  53     const base::TimeDelta& release_after,
  54     NetLogCaptureMode /* capture_mode */) {
  55   scoped_ptr<base::DictionaryValue> dict(new base::DictionaryValue());
  56   dict->SetString("url", *url_id);
  57   dict->SetInteger("num_failures", num_failures);
  58   dict->SetInteger("release_after_ms",
  59                    static_cast<int>(release_after.InMilliseconds()));
  60   return dict.Pass();
  61 }
  62
  63 URLRequestThrottlerEntry::URLRequestThrottlerEntry(
  64     URLRequestThrottlerManager* manager,
  65     const std::string& url_id)
  66     : sliding_window_period_(
  67           base::TimeDelta::FromMilliseconds(kDefaultSlidingWindowPeriodMs)),
  68       max_send_threshold_(kDefaultMaxSendThreshold),
  69       is_backoff_disabled_(false),
  70       backoff_entry_(&backoff_policy_),
  71       manager_(manager),
  72       url_id_(url_id),
  73       net_log_(BoundNetLog::Make(
  74           manager->net_log(), NetLog::SOURCE_EXPONENTIAL_BACKOFF_THROTTLING)) {
  75   DCHECK(manager_);
  76   Initialize();
  77 }
  78
  79 URLRequestThrottlerEntry::URLRequestThrottlerEntry(
  80     URLRequestThrottlerManager* manager,
  81     const std::string& url_id,
  82     int sliding_window_period_ms,
  83     int max_send_threshold,
  84     int initial_backoff_ms,
  85     double multiply_factor,
  86     double jitter_factor,
  87     int maximum_backoff_ms)
  88     : sliding_window_period_(
  89           base::TimeDelta::FromMilliseconds(sliding_window_period_ms)),
  90       max_send_threshold_(max_send_threshold),
  91       is_backoff_disabled_(false),
  92       backoff_entry_(&backoff_policy_),
  93       manager_(manager),
  94       url_id_(url_id) {
  95   DCHECK_GT(sliding_window_period_ms, 0);
  96   DCHECK_GT(max_send_threshold_, 0);
  97   DCHECK_GE(initial_backoff_ms, 0);
  98   DCHECK_GT(multiply_factor, 0);
  99   DCHECK_GE(jitter_factor, 0.0);
 100   DCHECK_LT(jitter_factor, 1.0);
 101   DCHECK_GE(maximum_backoff_ms, 0);
 102   DCHECK(manager_);
 103
 104   Initialize();
 105   backoff_policy_.initial_delay_ms = initial_backoff_ms;
 106   backoff_policy_.multiply_factor = multiply_factor;
 107   backoff_policy_.jitter_factor = jitter_factor;
 108   backoff_policy_.maximum_backoff_ms = maximum_backoff_ms;
 109   backoff_policy_.entry_lifetime_ms = -1;
 110   backoff_policy_.num_errors_to_ignore = 0;
 111   backoff_policy_.always_use_initial_delay = false;
 112 }
 113
 114 bool URLRequestThrottlerEntry::IsEntryOutdated() const {
 115   // This function is called by the URLRequestThrottlerManager to determine
 116   // whether entries should be discarded from its url_entries_ map.  We
 117   // want to ensure that it does not remove entries from the map while there
 118   // are clients (objects other than the manager) holding references to
 119   // the entry, otherwise separate clients could end up holding separate
 120   // entries for a request to the same URL, which is undesirable.  Therefore,
 121   // if an entry has more than one reference (the map will always hold one),
 122   // it should not be considered outdated.
 123   //
 124   // We considered whether to make URLRequestThrottlerEntry objects
 125   // non-refcounted, but since any means of knowing whether they are
 126   // currently in use by others than the manager would be more or less
 127   // equivalent to a refcount, we kept them refcounted.
 128   if (!HasOneRef())
 129     return false;
 130
 131   // If there are send events in the sliding window period, we still need this
 132   // entry.
 133   if (!send_log_.empty() &&
 134       send_log_.back() + sliding_window_period_ > ImplGetTimeNow()) {
 135     return false;
 136   }
 137
 138   return GetBackoffEntry()->CanDiscard();
 139 }
 140
 141 void URLRequestThrottlerEntry::DisableBackoffThrottling() {
 142   is_backoff_disabled_ = true;
 143 }
 144
 145 void URLRequestThrottlerEntry::DetachManager() {
 146   manager_ = NULL;
 147 }
 148
 149 bool URLRequestThrottlerEntry::ShouldRejectRequest(
 150     const URLRequest& request) const {
 151   bool reject_request = false;
 152   if (!is_backoff_disabled_ && !ExplicitUserRequest(request.load_flags()) &&
 153       GetBackoffEntry()->ShouldRejectRequest()) {
 154     net_log_.AddEvent(
 155         NetLog::TYPE_THROTTLING_REJECTED_REQUEST,
 156         base::Bind(&NetLogRejectedRequestCallback,
 157                    &url_id_,
 158                    GetBackoffEntry()->failure_count(),
 159                    GetBackoffEntry()->GetTimeUntilRelease()));
 160     reject_request = true;
 161   }
 162
 163   int reject_count = reject_request ? 1 : 0;
 164   UMA_HISTOGRAM_ENUMERATION(
 165       "Throttling.RequestThrottled", reject_count, 2);
 166
 167   return reject_request;
 168 }
 169
 170 int64 URLRequestThrottlerEntry::ReserveSendingTimeForNextRequest(
 171     const base::TimeTicks& earliest_time) {
 172   base::TimeTicks now = ImplGetTimeNow();
 173
 174   // If a lot of requests were successfully made recently,
 175   // sliding_window_release_time_ may be greater than
 176   // exponential_backoff_release_time_.
 177   base::TimeTicks recommended_sending_time =
 178       std::max(std::max(now, earliest_time),
 179                std::max(GetBackoffEntry()->GetReleaseTime(),
 180                         sliding_window_release_time_));
 181
 182   DCHECK(send_log_.empty() ||
 183          recommended_sending_time >= send_log_.back());
 184   // Log the new send event.
 185   send_log_.push(recommended_sending_time);
 186
 187   sliding_window_release_time_ = recommended_sending_time;
 188
 189   // Drop the out-of-date events in the event list.
 190   // We don't need to worry that the queue may become empty during this
 191   // operation, since the last element is sliding_window_release_time_.
 192   while ((send_log_.front() + sliding_window_period_ <=
 193           sliding_window_release_time_) ||
 194          send_log_.size() > static_cast<unsigned>(max_send_threshold_)) {
 195     send_log_.pop();
 196   }
 197
 198   // Check if there are too many send events in recent time.
 199   if (send_log_.size() == static_cast<unsigned>(max_send_threshold_))
 200     sliding_window_release_time_ = send_log_.front() + sliding_window_period_;
 201
 202   return (recommended_sending_time - now).InMillisecondsRoundedUp();
 203 }
 204
 205 base::TimeTicks
 206     URLRequestThrottlerEntry::GetExponentialBackoffReleaseTime() const {
 207   // If a site opts out, it's likely because they have problems that trigger
 208   // the back-off mechanism when it shouldn't be triggered, in which case
 209   // returning the calculated back-off release time would probably be the
 210   // wrong thing to do (i.e. it would likely be too long).  Therefore, we
 211   // return "now" so that retries are not delayed.
 212   if (is_backoff_disabled_)
 213     return ImplGetTimeNow();
 214
 215   return GetBackoffEntry()->GetReleaseTime();
 216 }
 217
 218 void URLRequestThrottlerEntry::UpdateWithResponse(int status_code) {
 219   GetBackoffEntry()->InformOfRequest(IsConsideredSuccess(status_code));
 220 }
 221
 222 void URLRequestThrottlerEntry::ReceivedContentWasMalformed(int response_code) {
 223   // A malformed body can only occur when the request to fetch a resource
 224   // was successful.  Therefore, in such a situation, we will receive one
 225   // call to ReceivedContentWasMalformed() and one call to
 226   // UpdateWithResponse() with a response categorized as "good".  To end
 227   // up counting one failure, we need to count two failures here against
 228   // the one success in UpdateWithResponse().
 229   //
 230   // We do nothing for a response that is already being considered an error
 231   // based on its status code (otherwise we would count 3 errors instead of 1).
 232   if (IsConsideredSuccess(response_code)) {
 233     GetBackoffEntry()->InformOfRequest(false);
 234     GetBackoffEntry()->InformOfRequest(false);
 235   }
 236 }
 237
 238 URLRequestThrottlerEntry::~URLRequestThrottlerEntry() {
 239 }
 240
 241 void URLRequestThrottlerEntry::Initialize() {
 242   sliding_window_release_time_ = base::TimeTicks::Now();
 243   backoff_policy_.num_errors_to_ignore = kDefaultNumErrorsToIgnore;
 244   backoff_policy_.initial_delay_ms = kDefaultInitialDelayMs;
 245   backoff_policy_.multiply_factor = kDefaultMultiplyFactor;
 246   backoff_policy_.jitter_factor = kDefaultJitterFactor;
 247   backoff_policy_.maximum_backoff_ms = kDefaultMaximumBackoffMs;
 248   backoff_policy_.entry_lifetime_ms = kDefaultEntryLifetimeMs;
 249   backoff_policy_.always_use_initial_delay = false;
 250 }
 251
 252 bool URLRequestThrottlerEntry::IsConsideredSuccess(int response_code) {
 253   // We throttle only for the status codes most likely to indicate the server
 254   // is failing because it is too busy or otherwise are likely to be
 255   // because of DDoS.
 256   //
 257   // 500 is the generic error when no better message is suitable, and
 258   //     as such does not necessarily indicate a temporary state, but
 259   //     other status codes cover most of the permanent error states.
 260   // 503 is explicitly documented as a temporary state where the server
 261   //     is either overloaded or down for maintenance.
 262   // 509 is the (non-standard but widely implemented) Bandwidth Limit Exceeded
 263   //     status code, which might indicate DDoS.
 264   //
 265   // We do not back off on 502 or 504, which are reported by gateways
 266   // (proxies) on timeouts or failures, because in many cases these requests
 267   // have not made it to the destination server and so we do not actually
 268   // know that it is down or busy.  One degenerate case could be a proxy on
 269   // localhost, where you are not actually connected to the network.
 270   return !(response_code == 500 || response_code == 503 ||
 271            response_code == 509);
 272 }
 273
 274 base::TimeTicks URLRequestThrottlerEntry::ImplGetTimeNow() const {
 275   return base::TimeTicks::Now();
 276 }
 277
 278 const BackoffEntry* URLRequestThrottlerEntry::GetBackoffEntry() const {
 279   return &backoff_entry_;
 280 }
 281
 282 BackoffEntry* URLRequestThrottlerEntry::GetBackoffEntry() {
 283   return &backoff_entry_;
 284 }
 285
 286 // static
 287 bool URLRequestThrottlerEntry::ExplicitUserRequest(const int load_flags) {
 288   return (load_flags & LOAD_MAYBE_USER_GESTURE) != 0;
 289 }
 290
 291 }  // namespace net