1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
|
// Copyright (c) 2010 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_
#include <queue>
#include <string>
#include "base/basictypes.h"
#include "net/url_request/url_request_throttler_entry_interface.h"
namespace net {
// 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;
// Initial delay for exponential back-off.
static const int kDefaultInitialBackoffMs;
// Additional constant to adjust back-off.
static const int kDefaultAdditionalConstantMs;
// 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[];
URLRequestThrottlerEntry();
// The life span of instances created with this constructor is set to
// infinite.
// It is only used by unit tests.
URLRequestThrottlerEntry(int sliding_window_period_ms,
int max_send_threshold,
int initial_backoff_ms,
int additional_constant_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;
// Implementation of URLRequestThrottlerEntryInterface.
virtual bool IsDuringExponentialBackoff() const;
virtual int64 ReserveSendingTimeForNextRequest(
const base::TimeTicks& earliest_time);
virtual base::TimeTicks GetExponentialBackoffReleaseTime() const;
virtual void UpdateWithResponse(
const URLRequestThrottlerHeaderInterface* response);
virtual void ReceivedContentWasMalformed();
protected:
virtual ~URLRequestThrottlerEntry();
void Initialize();
// Calculates the release time for exponential back-off.
base::TimeTicks CalculateExponentialBackoffReleaseTime();
// 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 by tests.
void set_exponential_backoff_release_time(
const base::TimeTicks& release_time) {
exponential_backoff_release_time_ = release_time;
}
// 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;
}
// Used by tests.
void set_failure_count(int failure_count) {
failure_count_ = failure_count;
}
private:
// Timestamp calculated by the exponential back-off algorithm at which we are
// allowed to start sending requests again.
base::TimeTicks exponential_backoff_release_time_;
// Number of times we encounter server errors or malformed response bodies.
int failure_count_;
// If true, the last request response was a failure.
// Note that this member can be false at the same time as failure_count_ can
// be greater than 0, since we gradually decrease failure_count_, instead of
// resetting it to 0 directly, when we receive successful responses.
bool latest_response_was_failure_;
// 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_;
const int initial_backoff_ms_;
const int additional_constant_ms_;
const double multiply_factor_;
const double jitter_factor_;
const int maximum_backoff_ms_;
// Set to -1 if the entry never expires.
const int entry_lifetime_ms_;
DISALLOW_COPY_AND_ASSIGN(URLRequestThrottlerEntry);
};
} // namespace net
#endif // NET_URL_REQUEST_URL_REQUEST_THROTTLER_ENTRY_H_
|
