Anti-DDoS enhancements: Log to net log, UMA stats, improved policy.

net/base/backoff_entry.cc

 // Copyright (c) 2011 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/base/backoff_entry.h"
 
 #include <algorithm>
 #include <cmath>
 
 #include "base/logging.h"
 #include "base/rand_util.h"
 
 namespace net {
 
 BackoffEntry::BackoffEntry(const BackoffEntry::Policy* const policy)
     : failure_count_(0),
       policy_(policy) {
   DCHECK(policy_);
 
-  // Can't use GetTimeNow() as it's virtual.
+  // Can't use ImplGetTimeNow() as it's virtual.

[wtc, 2011/05/25 23:12:06]

IMPORTANT: I wonder if the constructor should just initialize
exponential_backoff_release_time_ to 0 or some dummy value,
and we use Reset() to initialize exponential_backoff_release_time_
properly.

[Jói, 2011/05/26 14:53:42]

Good point, I fixed this so that the constructor calls Reset() and I modified
Reset() to not use the virtual function; it now sets the backoff release time as
follows, with this comment:

  // We leave exponential_backoff_release_time_ unset, meaning 0. We could
  // initialize to ImplGetTimeNow() but because it's a virtual method it's
  // not safe to call in the constructor (and the constructor calls Reset()).
  // The effects are the same, i.e. ShouldRejectRequest() will return false
  // right after Reset().
  exponential_backoff_release_time_ = base::TimeTicks();

   exponential_backoff_release_time_ = base::TimeTicks::Now();
 }
 
 BackoffEntry::~BackoffEntry() {
   // TODO(joi): Remove this once our clients (e.g. URLRequestThrottlerManager)
   // always destroy from the I/O thread.
   DetachFromThread();
 }
 
 void BackoffEntry::InformOfRequest(bool succeeded) {
   if (!succeeded) {
     ++failure_count_;
     exponential_backoff_release_time_ = CalculateReleaseTime();
   } else {
     // We slowly decay the number of times delayed instead of resetting it to 0
     // in order to stay stable if we receive successes interleaved between lots
     // of failures.
     //
     // TODO(joi): Revisit this; it might be most correct to go to zero
     // but have a way to go back to "old error count +1" if there is
     // another error soon after.
     if (failure_count_ > 0)
       --failure_count_;
 
-    // The reason why we are not just cutting the release time to GetTimeNow()
-    // is on the one hand, it would unset a release time set by
-    // SetCustomReleaseTime and on the other we would like to push every
-    // request up to our "horizon" when dealing with multiple in-flight
-    // requests. Ex: If we send three requests and we receive 2 failures and
-    // 1 success. The success that follows those failures will not reset the
-    // release time, further requests will then need to wait the delay caused
-    // by the 2 failures.
+    // The reason why we are not just cutting the release time to
+    // ImplGetTimeNow() is on the one hand, it would unset a release
+    // time set by SetCustomReleaseTime and on the other we would like
+    // to push every request up to our "horizon" when dealing with
+    // multiple in-flight requests. Ex: If we send three requests and
+    // we receive 2 failures and 1 success. The success that follows
+    // those failures will not reset the release time, further
+    // requests will then need to wait the delay caused by the 2
+    // failures.
     exponential_backoff_release_time_ = std::max(
-        GetTimeNow(), exponential_backoff_release_time_);
+        ImplGetTimeNow(), exponential_backoff_release_time_);
   }
 }
 
 bool BackoffEntry::ShouldRejectRequest() const {
-  return exponential_backoff_release_time_ > GetTimeNow();
+  return exponential_backoff_release_time_ > ImplGetTimeNow();
 }
 
 base::TimeTicks BackoffEntry::GetReleaseTime() const {
   return exponential_backoff_release_time_;
 }
 
 void BackoffEntry::SetCustomReleaseTime(const base::TimeTicks& release_time) {
   exponential_backoff_release_time_ = release_time;
 }
 
 bool BackoffEntry::CanDiscard() const {
   if (policy_->entry_lifetime_ms == -1)
     return false;
 
-  base::TimeTicks now = GetTimeNow();
+  base::TimeTicks now = ImplGetTimeNow();
 
   int64 unused_since_ms =
       (now - exponential_backoff_release_time_).InMilliseconds();
 
   // Release time is further than now, we are managing it.
   if (unused_since_ms < 0)
     return false;
 
   if (failure_count_ > 0) {
     // Need to keep track of failures until maximum back-off period
     // has passed (since further failures can add to back-off).
     return unused_since_ms >= std::max(policy_->maximum_backoff_ms,
                                        policy_->entry_lifetime_ms);
   }
 
   // Otherwise, consider the entry is outdated if it hasn't been used for the
   // specified lifetime period.
   return unused_since_ms >= policy_->entry_lifetime_ms;
 }
 
-base::TimeTicks BackoffEntry::GetTimeNow() const {
+void BackoffEntry::Reset() {
+  failure_count_ = 0;
+  exponential_backoff_release_time_ = ImplGetTimeNow();
+}
+
+int BackoffEntry::failure_count() const {
+  return failure_count_;
+}
+
+base::TimeTicks BackoffEntry::ImplGetTimeNow() const {
   return base::TimeTicks::Now();
 }
 
 base::TimeTicks BackoffEntry::CalculateReleaseTime() const {
   int effective_failure_count =
       std::max(0, failure_count_ - policy_->num_errors_to_ignore);
   if (effective_failure_count == 0) {
     // Never reduce previously set release horizon, e.g. due to Retry-After
     // header.
-    return std::max(GetTimeNow(), exponential_backoff_release_time_);
+    return std::max(ImplGetTimeNow(), exponential_backoff_release_time_);
   }
 
   // The delay is calculated with this formula:
   // delay = initial_backoff * multiply_factor^(
   //     effective_failure_count - 1) * Uniform(1 - jitter_factor, 1]
   double delay = policy_->initial_backoff_ms;
   delay *= pow(policy_->multiply_factor, effective_failure_count - 1);
   delay -= base::RandDouble() * policy_->jitter_factor * delay;
 
   // Ensure that we do not exceed maximum delay.
   int64 delay_int = static_cast<int64>(delay + 0.5);
   delay_int = std::min(delay_int,
                        static_cast<int64>(policy_->maximum_backoff_ms));
 
   // Never reduce previously set release horizon, e.g. due to Retry-After
   // header.
-  return std::max(GetTimeNow() + base::TimeDelta::FromMilliseconds(delay_int),
-                  exponential_backoff_release_time_);
+  return std::max(
+      ImplGetTimeNow() + base::TimeDelta::FromMilliseconds(delay_int),
+      exponential_backoff_release_time_);
 }
 
 }  // namespace net