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
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
|
// Copyright 2015 The Chromium Authors
// 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_serializer.h"
#include <algorithm>
#include <ostream>
#include <utility>
#include "base/notreached.h"
#include "base/strings/string_number_conversions.h"
#include "base/time/tick_clock.h"
#include "base/values.h"
#include "net/base/backoff_entry.h"
namespace {
// This max defines how many times we are willing to call
// |BackoffEntry::InformOfRequest| in |DeserializeFromList|.
//
// This value is meant to large enough that the computed backoff duration can
// still be saturated. Given that the duration is an int64 and assuming 1.01 as
// a conservative lower bound for BackoffEntry::Policy::multiply_factor,
// ceil(log(2**63-1, 1.01)) = 4389.
const int kMaxFailureCount = 4389;
// This function returns true iff |duration| is finite and can be serialized and
// deserialized without becoming infinite. This function is aligned with the
// latest version.
bool BackoffDurationSafeToSerialize(const base::TimeDelta& duration) {
return !duration.is_inf() &&
!base::Microseconds(duration.InMicroseconds()).is_inf();
}
} // namespace
namespace net {
base::Value::List BackoffEntrySerializer::SerializeToList(
const BackoffEntry& entry,
base::Time time_now) {
base::Value::List serialized;
serialized.Append(SerializationFormatVersion::kVersion2);
serialized.Append(entry.failure_count());
// Convert both |base::TimeTicks| values into |base::TimeDelta| values by
// subtracting |kZeroTicks. This way, the top-level subtraction uses
// |base::TimeDelta::operator-|, which has clamping semantics.
const base::TimeTicks kZeroTicks;
const base::TimeDelta kReleaseTime = entry.GetReleaseTime() - kZeroTicks;
const base::TimeDelta kTimeTicksNow = entry.GetTimeTicksNow() - kZeroTicks;
base::TimeDelta backoff_duration;
if (!kReleaseTime.is_inf() && !kTimeTicksNow.is_inf()) {
backoff_duration = kReleaseTime - kTimeTicksNow;
}
if (!BackoffDurationSafeToSerialize(backoff_duration)) {
backoff_duration = base::TimeDelta();
}
base::Time absolute_release_time = backoff_duration + time_now;
// If the computed release time is infinite, default to zero. The deserializer
// should pick up on this.
if (absolute_release_time.is_inf()) {
absolute_release_time = base::Time();
}
// Redundantly stores both the remaining time delta and the absolute time.
// The delta is used to work around some cases where wall clock time changes.
serialized.Append(base::NumberToString(backoff_duration.InMicroseconds()));
serialized.Append(
base::NumberToString(absolute_release_time.ToInternalValue()));
return serialized;
}
std::unique_ptr<BackoffEntry> BackoffEntrySerializer::DeserializeFromList(
const base::Value::List& serialized,
const BackoffEntry::Policy* policy,
const base::TickClock* tick_clock,
base::Time time_now) {
if (serialized.size() != 4)
return nullptr;
if (!serialized[0].is_int())
return nullptr;
int version_number = serialized[0].GetInt();
if (version_number != kVersion1 && version_number != kVersion2)
return nullptr;
if (!serialized[1].is_int())
return nullptr;
int failure_count = serialized[1].GetInt();
if (failure_count < 0) {
return nullptr;
}
failure_count = std::min(failure_count, kMaxFailureCount);
base::TimeDelta original_backoff_duration;
switch (version_number) {
case kVersion1: {
if (!serialized[2].is_double())
return nullptr;
double original_backoff_duration_double = serialized[2].GetDouble();
original_backoff_duration =
base::Seconds(original_backoff_duration_double);
break;
}
case kVersion2: {
if (!serialized[2].is_string())
return nullptr;
std::string original_backoff_duration_string = serialized[2].GetString();
int64_t original_backoff_duration_us;
if (!base::StringToInt64(original_backoff_duration_string,
&original_backoff_duration_us)) {
return nullptr;
}
original_backoff_duration =
base::Microseconds(original_backoff_duration_us);
break;
}
default:
NOTREACHED() << "Unexpected version_number: " << version_number;
}
if (!serialized[3].is_string())
return nullptr;
int64_t absolute_release_time_us;
if (!base::StringToInt64(serialized[3].GetString(),
&absolute_release_time_us)) {
return nullptr;
}
auto entry = std::make_unique<BackoffEntry>(policy, tick_clock);
for (int n = 0; n < failure_count; n++)
entry->InformOfRequest(false);
base::Time absolute_release_time =
base::Time::FromInternalValue(absolute_release_time_us);
base::TimeDelta backoff_duration;
if (absolute_release_time == base::Time()) {
// When the serializer cannot compute a finite release time, it uses zero.
// When we see this, fall back to the redundant original_backoff_duration.
backoff_duration = original_backoff_duration;
} else {
// Before computing |backoff_duration|, throw out +/- infinity values for
// either operand. This way, we can use base::TimeDelta's saturated math.
if (absolute_release_time.is_inf() || time_now.is_inf())
return nullptr;
backoff_duration = absolute_release_time.ToDeltaSinceWindowsEpoch() -
time_now.ToDeltaSinceWindowsEpoch();
// In cases where the system wall clock is rewound, use the redundant
// original_backoff_duration to ensure the backoff duration isn't longer
// than it was before serializing (note that it's not possible to protect
// against the clock being wound forward).
if (backoff_duration > original_backoff_duration)
backoff_duration = original_backoff_duration;
}
if (!BackoffDurationSafeToSerialize(backoff_duration))
return nullptr;
const base::TimeTicks release_time =
entry->BackoffDurationToReleaseTime(backoff_duration);
if (release_time.is_inf())
return nullptr;
entry->SetCustomReleaseTime(release_time);
return entry;
}
} // namespace net
|
