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.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/base/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_header_interface.h"
  20 #include "net/url_request/url_request_throttler_manager.h"
  21
  22 namespace net {
  23
  24 const int URLRequestThrottlerEntry::kDefaultSlidingWindowPeriodMs = 2000;
  25 const int URLRequestThrottlerEntry::kDefaultMaxSendThreshold = 20;
  26
  27 // This set of back-off parameters will (at maximum values, i.e. without
  28 // the reduction caused by jitter) add 0-41% (distributed uniformly
  29 // in that range) to the "perceived downtime" of the remote server, once
  30 // exponential back-off kicks in and is throttling requests for more than
  31 // about a second at a time.  Once the maximum back-off is reached, the added
  32 // perceived downtime decreases rapidly, percentage-wise.
  33 //
  34 // Another way to put it is that the maximum additional perceived downtime
  35 // with these numbers is a couple of seconds shy of 15 minutes, and such
  36 // a delay would not occur until the remote server has been actually
  37 // unavailable at the end of each back-off period for a total of about
  38 // 48 minutes.
  39 //
  40 // Ignoring the first couple of errors is just a conservative measure to
  41 // avoid false positives.  It should help avoid back-off from kicking in e.g.
  42 // on flaky connections.
  43 const int URLRequestThrottlerEntry::kDefaultNumErrorsToIgnore = 2;
  44 const int URLRequestThrottlerEntry::kDefaultInitialDelayMs = 700;
  45 const double URLRequestThrottlerEntry::kDefaultMultiplyFactor = 1.4;
  46 const double URLRequestThrottlerEntry::kDefaultJitterFactor = 0.4;
  47 const int URLRequestThrottlerEntry::kDefaultMaximumBackoffMs = 15 * 60 * 1000;
  48 const int URLRequestThrottlerEntry::kDefaultEntryLifetimeMs = 2 * 60 * 1000;
  49 const char URLRequestThrottlerEntry::kExponentialThrottlingHeader[] =
  50     "X-Chrome-Exponential-Throttling";
  51 const char URLRequestThrottlerEntry::kExponentialThrottlingDisableValue[] =
  52     "disable";
  53
  54 // Returns NetLog parameters when a request is rejected by throttling.
  55 base::Value* NetLogRejectedRequestCallback(const std::string* url_id,
  56                                            int num_failures,
  57                                            const base::TimeDelta& release_after,
  58                                            NetLog::LogLevel /* log_level */) {
  59   base::DictionaryValue* dict = new base::DictionaryValue();
  60   dict->SetString("url", *url_id);
  61   dict->SetInteger("num_failures", num_failures);
  62   dict->SetInteger("release_after_ms",
  63                    static_cast<int>(release_after.InMilliseconds()));
  64   return dict;
  65 }
  66
  67 URLRequestThrottlerEntry::URLRequestThrottlerEntry(
  68     URLRequestThrottlerManager* manager,
  69     const std::string& url_id)
  70     : sliding_window_period_(
  71           base::TimeDelta::FromMilliseconds(kDefaultSlidingWindowPeriodMs)),
  72       max_send_threshold_(kDefaultMaxSendThreshold),
  73       is_backoff_disabled_(false),
  74       backoff_entry_(&backoff_policy_),
  75       manager_(manager),
  76       url_id_(url_id),
  77       net_log_(BoundNetLog::Make(
  78           manager->net_log(), NetLog::SOURCE_EXPONENTIAL_BACKOFF_THROTTLING)) {
  79   DCHECK(manager_);
  80   Initialize();
  81 }
  82
  83 URLRequestThrottlerEntry::URLRequestThrottlerEntry(
  84     URLRequestThrottlerManager* manager,
  85     const std::string& url_id,
  86     int sliding_window_period_ms,
  87     int max_send_threshold,
  88     int initial_backoff_ms,
  89     double multiply_factor,
  90     double jitter_factor,
  91     int maximum_backoff_ms)
  92     : sliding_window_period_(
  93           base::TimeDelta::FromMilliseconds(sliding_window_period_ms)),
  94       max_send_threshold_(max_send_threshold),
  95       is_backoff_disabled_(false),
  96       backoff_entry_(&backoff_policy_),
  97       manager_(manager),
  98       url_id_(url_id) {
  99   DCHECK_GT(sliding_window_period_ms, 0);
 100   DCHECK_GT(max_send_threshold_, 0);
 101   DCHECK_GE(initial_backoff_ms, 0);
 102   DCHECK_GT(multiply_factor, 0);
 103   DCHECK_GE(jitter_factor, 0.0);
 104   DCHECK_LT(jitter_factor, 1.0);
 105   DCHECK_GE(maximum_backoff_ms, 0);
 106   DCHECK(manager_);
 107
 108   Initialize();
 109   backoff_policy_.initial_delay_ms = initial_backoff_ms;
 110   backoff_policy_.multiply_factor = multiply_factor;
 111   backoff_policy_.jitter_factor = jitter_factor;
 112   backoff_policy_.maximum_backoff_ms = maximum_backoff_ms;
 113   backoff_policy_.entry_lifetime_ms = -1;
 114   backoff_policy_.num_errors_to_ignore = 0;
 115   backoff_policy_.always_use_initial_delay = false;
 116 }
 117
 118 bool URLRequestThrottlerEntry::IsEntryOutdated() const {
 119   // This function is called by the URLRequestThrottlerManager to determine
 120   // whether entries should be discarded from its url_entries_ map.  We
 121   // want to ensure that it does not remove entries from the map while there
 122   // are clients (objects other than the manager) holding references to
 123   // the entry, otherwise separate clients could end up holding separate
 124   // entries for a request to the same URL, which is undesirable.  Therefore,
 125   // if an entry has more than one reference (the map will always hold one),
 126   // it should not be considered outdated.
 127   //
 128   // We considered whether to make URLRequestThrottlerEntry objects
 129   // non-refcounted, but since any means of knowing whether they are
 130   // currently in use by others than the manager would be more or less
 131   // equivalent to a refcount, we kept them refcounted.
 132   if (!HasOneRef())
 133     return false;
 134
 135   // If there are send events in the sliding window period, we still need this
 136   // entry.
 137   if (!send_log_.empty() &&
 138       send_log_.back() + sliding_window_period_ > ImplGetTimeNow()) {
 139     return false;
 140   }
 141
 142   return GetBackoffEntry()->CanDiscard();
 143 }
 144
 145 void URLRequestThrottlerEntry::DisableBackoffThrottling() {
 146   is_backoff_disabled_ = true;
 147 }
 148
 149 void URLRequestThrottlerEntry::DetachManager() {
 150   manager_ = NULL;
 151 }
 152
 153 bool URLRequestThrottlerEntry::ShouldRejectRequest(
 154     const URLRequest& request,
 155     NetworkDelegate* network_delegate) const {
 156   bool reject_request = false;
 157   if (!is_backoff_disabled_ && !ExplicitUserRequest(request.load_flags()) &&
 158       (!network_delegate || network_delegate->CanThrottleRequest(request)) &&
 159       GetBackoffEntry()->ShouldRejectRequest()) {
 160     net_log_.AddEvent(
 161         NetLog::TYPE_THROTTLING_REJECTED_REQUEST,
 162         base::Bind(&NetLogRejectedRequestCallback,
 163                    &url_id_,
 164                    GetBackoffEntry()->failure_count(),
 165                    GetBackoffEntry()->GetTimeUntilRelease()));
 166     reject_request = true;
 167   }
 168
 169   int reject_count = reject_request ? 1 : 0;
 170   UMA_HISTOGRAM_ENUMERATION(
 171       "Throttling.RequestThrottled", reject_count, 2);
 172
 173   return reject_request;
 174 }
 175
 176 int64 URLRequestThrottlerEntry::ReserveSendingTimeForNextRequest(
 177     const base::TimeTicks& earliest_time) {
 178   base::TimeTicks now = ImplGetTimeNow();
 179
 180   // If a lot of requests were successfully made recently,
 181   // sliding_window_release_time_ may be greater than
 182   // exponential_backoff_release_time_.
 183   base::TimeTicks recommended_sending_time =
 184       std::max(std::max(now, earliest_time),
 185                std::max(GetBackoffEntry()->GetReleaseTime(),
 186                         sliding_window_release_time_));
 187
 188   DCHECK(send_log_.empty() ||
 189          recommended_sending_time >= send_log_.back());
 190   // Log the new send event.
 191   send_log_.push(recommended_sending_time);
 192
 193   sliding_window_release_time_ = recommended_sending_time;
 194
 195   // Drop the out-of-date events in the event list.
 196   // We don't need to worry that the queue may become empty during this
 197   // operation, since the last element is sliding_window_release_time_.
 198   while ((send_log_.front() + sliding_window_period_ <=
 199           sliding_window_release_time_) ||
 200          send_log_.size() > static_cast<unsigned>(max_send_threshold_)) {
 201     send_log_.pop();
 202   }
 203
 204   // Check if there are too many send events in recent time.
 205   if (send_log_.size() == static_cast<unsigned>(max_send_threshold_))
 206     sliding_window_release_time_ = send_log_.front() + sliding_window_period_;
 207
 208   return (recommended_sending_time - now).InMillisecondsRoundedUp();
 209 }
 210
 211 base::TimeTicks
 212     URLRequestThrottlerEntry::GetExponentialBackoffReleaseTime() const {
 213   // If a site opts out, it's likely because they have problems that trigger
 214   // the back-off mechanism when it shouldn't be triggered, in which case
 215   // returning the calculated back-off release time would probably be the
 216   // wrong thing to do (i.e. it would likely be too long).  Therefore, we
 217   // return "now" so that retries are not delayed.
 218   if (is_backoff_disabled_)
 219     return ImplGetTimeNow();
 220
 221   return GetBackoffEntry()->GetReleaseTime();
 222 }
 223
 224 void URLRequestThrottlerEntry::UpdateWithResponse(
 225     const std::string& host,
 226     const URLRequestThrottlerHeaderInterface* response) {
 227   if (IsConsideredError(response->GetResponseCode())) {
 228     GetBackoffEntry()->InformOfRequest(false);
 229   } else {
 230     GetBackoffEntry()->InformOfRequest(true);
 231
 232     std::string throttling_header = response->GetNormalizedValue(
 233         kExponentialThrottlingHeader);
 234     if (!throttling_header.empty())
 235       HandleThrottlingHeader(throttling_header, host);
 236   }
 237 }
 238
 239 void URLRequestThrottlerEntry::ReceivedContentWasMalformed(int response_code) {
 240   // A malformed body can only occur when the request to fetch a resource
 241   // was successful.  Therefore, in such a situation, we will receive one
 242   // call to ReceivedContentWasMalformed() and one call to
 243   // UpdateWithResponse() with a response categorized as "good".  To end
 244   // up counting one failure, we need to count two failures here against
 245   // the one success in UpdateWithResponse().
 246   //
 247   // We do nothing for a response that is already being considered an error
 248   // based on its status code (otherwise we would count 3 errors instead of 1).
 249   if (!IsConsideredError(response_code)) {
 250     GetBackoffEntry()->InformOfRequest(false);
 251     GetBackoffEntry()->InformOfRequest(false);
 252   }
 253 }
 254
 255 URLRequestThrottlerEntry::~URLRequestThrottlerEntry() {
 256 }
 257
 258 void URLRequestThrottlerEntry::Initialize() {
 259   sliding_window_release_time_ = base::TimeTicks::Now();
 260   backoff_policy_.num_errors_to_ignore = kDefaultNumErrorsToIgnore;
 261   backoff_policy_.initial_delay_ms = kDefaultInitialDelayMs;
 262   backoff_policy_.multiply_factor = kDefaultMultiplyFactor;
 263   backoff_policy_.jitter_factor = kDefaultJitterFactor;
 264   backoff_policy_.maximum_backoff_ms = kDefaultMaximumBackoffMs;
 265   backoff_policy_.entry_lifetime_ms = kDefaultEntryLifetimeMs;
 266   backoff_policy_.always_use_initial_delay = false;
 267 }
 268
 269 bool URLRequestThrottlerEntry::IsConsideredError(int response_code) {
 270   // We throttle only for the status codes most likely to indicate the server
 271   // is failing because it is too busy or otherwise are likely to be
 272   // because of DDoS.
 273   //
 274   // 500 is the generic error when no better message is suitable, and
 275   //     as such does not necessarily indicate a temporary state, but
 276   //     other status codes cover most of the permanent error states.
 277   // 503 is explicitly documented as a temporary state where the server
 278   //     is either overloaded or down for maintenance.
 279   // 509 is the (non-standard but widely implemented) Bandwidth Limit Exceeded
 280   //     status code, which might indicate DDoS.
 281   //
 282   // We do not back off on 502 or 504, which are reported by gateways
 283   // (proxies) on timeouts or failures, because in many cases these requests
 284   // have not made it to the destination server and so we do not actually
 285   // know that it is down or busy.  One degenerate case could be a proxy on
 286   // localhost, where you are not actually connected to the network.
 287   return (response_code == 500 ||
 288           response_code == 503 ||
 289           response_code == 509);
 290 }
 291
 292 base::TimeTicks URLRequestThrottlerEntry::ImplGetTimeNow() const {
 293   return base::TimeTicks::Now();
 294 }
 295
 296 void URLRequestThrottlerEntry::HandleThrottlingHeader(
 297     const std::string& header_value,
 298     const std::string& host) {
 299   if (header_value == kExponentialThrottlingDisableValue) {
 300     DisableBackoffThrottling();
 301     if (manager_)
 302       manager_->AddToOptOutList(host);
 303   }
 304 }
 305
 306 const BackoffEntry* URLRequestThrottlerEntry::GetBackoffEntry() const {
 307   return &backoff_entry_;
 308 }
 309
 310 BackoffEntry* URLRequestThrottlerEntry::GetBackoffEntry() {
 311   return &backoff_entry_;
 312 }
 313
 314 // static
 315 bool URLRequestThrottlerEntry::ExplicitUserRequest(const int load_flags) {
 316   return (load_flags & LOAD_MAYBE_USER_GESTURE) != 0;
 317 }
 318
 319 }  // namespace net