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// 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.
#ifndef NET_URL_REQUEST_URL_REQUEST_THROTTLER_ENTRY_H_
#define NET_URL_REQUEST_URL_REQUEST_THROTTLER_ENTRY_H_
#pragma once
#include <queue>
#include <string>
#include "base/basictypes.h"
#include "net/base/backoff_entry.h"
#include "net/url_request/url_request_throttler_entry_interface.h"
namespace net {
class URLRequestThrottlerManager;
// URLRequestThrottlerEntry represents an entry of URLRequestThrottlerManager.
// It analyzes requests of a specific URL over some period of time, in order to
// deduce the back-off time for every request.
// The back-off algorithm consists of two parts. Firstly, exponential back-off
// is used when receiving 5XX server errors or malformed response bodies.
// The exponential back-off rule is enforced by URLRequestHttpJob. Any
// request sent during the back-off period will be cancelled.
// Secondly, a sliding window is used to count recent requests to a given
// destination and provide guidance (to the application level only) on whether
// too many requests have been sent and when a good time to send the next one
// would be. This is never used to deny requests at the network level.
class URLRequestThrottlerEntry : public URLRequestThrottlerEntryInterface {
public:
// Sliding window period.
static const int kDefaultSlidingWindowPeriodMs;
// Maximum number of requests allowed in sliding window period.
static const int kDefaultMaxSendThreshold;
// Number of initial errors to ignore before starting exponential back-off.
static const int kDefaultNumErrorsToIgnore;
// Initial delay for exponential back-off.
static const int kDefaultInitialBackoffMs;
// Factor by which the waiting time will be multiplied.
static const double kDefaultMultiplyFactor;
// Fuzzing percentage. ex: 10% will spread requests randomly
// between 90%-100% of the calculated time.
static const double kDefaultJitterFactor;
// Maximum amount of time we are willing to delay our request.
static const int kDefaultMaximumBackoffMs;
// Time after which the entry is considered outdated.
static const int kDefaultEntryLifetimeMs;
// Name of the header that servers can use to ask clients to delay their
// next request.
static const char kRetryHeaderName[];
// Name of the header that sites can use to opt out of exponential back-off
// throttling.
static const char kExponentialThrottlingHeader[];
// Value for exponential throttling header that can be used to opt out of
// exponential back-off throttling.
static const char kExponentialThrottlingDisableValue[];
// The manager object's lifetime must enclose the lifetime of this object.
explicit URLRequestThrottlerEntry(URLRequestThrottlerManager* manager);
// The life span of instances created with this constructor is set to
// infinite, and the number of initial errors to ignore is set to 0.
// It is only used by unit tests.
URLRequestThrottlerEntry(URLRequestThrottlerManager* manager,
int sliding_window_period_ms,
int max_send_threshold,
int initial_backoff_ms,
double multiply_factor,
double jitter_factor,
int maximum_backoff_ms);
// Used by the manager, returns true if the entry needs to be garbage
// collected.
bool IsEntryOutdated() const;
// Causes this entry to never reject requests due to back-off.
void DisableBackoffThrottling();
// Causes this entry to NULL its manager pointer.
void DetachManager();
// Implementation of URLRequestThrottlerEntryInterface.
virtual bool IsDuringExponentialBackoff() const;
virtual int64 ReserveSendingTimeForNextRequest(
const base::TimeTicks& earliest_time);
virtual base::TimeTicks GetExponentialBackoffReleaseTime() const;
virtual void UpdateWithResponse(
const std::string& host,
const URLRequestThrottlerHeaderInterface* response);
virtual void ReceivedContentWasMalformed();
protected:
virtual ~URLRequestThrottlerEntry();
void Initialize();
// Equivalent to TimeTicks::Now(), virtual to be mockable for testing purpose.
virtual base::TimeTicks GetTimeNow() const;
// Used internally to increase release time following a retry-after header.
void HandleCustomRetryAfter(const std::string& header_value);
// Used internally to handle the opt-out header.
void HandleThrottlingHeader(const std::string& header_value,
const std::string& host);
// Retrieves the back-off entry object we're using. Used to enable a
// unit testing seam for dependency injection in tests.
virtual const BackoffEntry* GetBackoffEntry() const;
virtual BackoffEntry* GetBackoffEntry();
// Used by tests.
base::TimeTicks sliding_window_release_time() const {
return sliding_window_release_time_;
}
// Used by tests.
void set_sliding_window_release_time(const base::TimeTicks& release_time) {
sliding_window_release_time_ = release_time;
}
// Valid and immutable after construction time.
BackoffEntry::Policy backoff_policy_;
private:
// Timestamp calculated by the sliding window algorithm for when we advise
// clients the next request should be made, at the earliest. Advisory only,
// not used to deny requests.
base::TimeTicks sliding_window_release_time_;
// A list of the recent send events. We use them to decide whether there are
// too many requests sent in sliding window.
std::queue<base::TimeTicks> send_log_;
const base::TimeDelta sliding_window_period_;
const int max_send_threshold_;
// True if DisableBackoffThrottling() has been called on this object.
bool is_backoff_disabled_;
// Access it through GetBackoffEntry() to allow a unit test seam.
BackoffEntry backoff_entry_;
// Weak back-reference to the manager object managing us.
URLRequestThrottlerManager* manager_;
DISALLOW_COPY_AND_ASSIGN(URLRequestThrottlerEntry);
};
} // namespace net
#endif // NET_URL_REQUEST_URL_REQUEST_THROTTLER_ENTRY_H_
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