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
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
|
// Copyright (c) 2006-2008 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/host_resolver_proc.h"
#include "build/build_config.h"
#if defined(OS_LINUX)
#include <resolv.h>
#endif
#include "base/logging.h"
#include "base/time.h"
#include "net/base/address_list.h"
#include "net/base/net_errors.h"
#include "net/base/sys_addrinfo.h"
#if defined(OS_LINUX)
#include "base/singleton.h"
#include "base/thread_local_storage.h"
#endif
namespace net {
HostResolverProc* HostResolverProc::default_proc_ = NULL;
HostResolverProc::HostResolverProc(HostResolverProc* previous) {
set_previous_proc(previous);
// Implicitly fall-back to the global default procedure.
if (!previous)
set_previous_proc(default_proc_);
}
// static
HostResolverProc* HostResolverProc::SetDefault(HostResolverProc* proc) {
HostResolverProc* old = default_proc_;
default_proc_ = proc;
return old;
}
// static
HostResolverProc* HostResolverProc::GetDefault() {
return default_proc_;
}
int HostResolverProc::ResolveUsingPrevious(const std::string& host,
AddressFamily address_family,
AddressList* addrlist) {
if (previous_proc_)
return previous_proc_->Resolve(host, address_family, addrlist);
// Final fallback is the system resolver.
return SystemHostResolverProc(host, address_family, addrlist);
}
#if defined(OS_LINUX)
// On Linux changes to /etc/resolv.conf can go unnoticed thus resulting in
// DNS queries failing either because nameservers are unknown on startup
// or because nameserver info has changed as a result of e.g. connecting to
// a new network. Some distributions patch glibc to stat /etc/resolv.conf
// to try to automatically detect such changes but these patches are not
// universal and even patched systems such as Jaunty appear to need calls
// to res_ninit to reload the nameserver information in different threads.
//
// We adopt the Mozilla solution here which is to call res_ninit when
// lookups fail and to rate limit the reloading to once per second per
// thread.
// Keep a timer per calling thread to rate limit the calling of res_ninit.
class DnsReloadTimer {
public:
// Check if the timer for the calling thread has expired. When no
// timer exists for the calling thread, create one.
bool Expired() {
const base::TimeDelta kRetryTime = base::TimeDelta::FromSeconds(1);
base::TimeTicks now = base::TimeTicks::Now();
base::TimeTicks* timer_ptr =
static_cast<base::TimeTicks*>(tls_index_.Get());
if (!timer_ptr) {
timer_ptr = new base::TimeTicks();
*timer_ptr = base::TimeTicks::Now();
tls_index_.Set(timer_ptr);
// Return true to reload dns info on the first call for each thread.
return true;
} else if (now - *timer_ptr > kRetryTime) {
*timer_ptr = now;
return true;
} else {
return false;
}
}
// Free the allocated timer.
static void SlotReturnFunction(void* data) {
base::TimeTicks* tls_data = static_cast<base::TimeTicks*>(data);
delete tls_data;
}
private:
friend struct DefaultSingletonTraits<DnsReloadTimer>;
DnsReloadTimer() {
// During testing the DnsReloadTimer Singleton may be created and destroyed
// multiple times. Initialize the ThreadLocalStorage slot only once.
if (!tls_index_.initialized())
tls_index_.Initialize(SlotReturnFunction);
}
~DnsReloadTimer() {
}
// We use thread local storage to identify which base::TimeTicks to
// interact with.
static ThreadLocalStorage::Slot tls_index_ ;
DISALLOW_COPY_AND_ASSIGN(DnsReloadTimer);
};
// A TLS slot to the TimeTicks for the current thread.
// static
ThreadLocalStorage::Slot DnsReloadTimer::tls_index_(base::LINKER_INITIALIZED);
#endif // defined(OS_LINUX)
int SystemHostResolverProc(const std::string& host,
AddressFamily address_family,
AddressList* addrlist) {
// The result of |getaddrinfo| for empty hosts is inconsistent across systems.
// On Windows it gives the default interface's address, whereas on Linux it
// gives an error. We will make it fail on all platforms for consistency.
if (host.empty())
return ERR_NAME_NOT_RESOLVED;
struct addrinfo* ai = NULL;
struct addrinfo hints = {0};
switch (address_family) {
case ADDRESS_FAMILY_IPV4:
hints.ai_family = AF_INET;
break;
case ADDRESS_FAMILY_IPV6:
hints.ai_family = AF_INET6;
break;
case ADDRESS_FAMILY_UNSPECIFIED:
hints.ai_family = AF_UNSPEC;
break;
default:
NOTREACHED();
hints.ai_family = AF_UNSPEC;
}
#if defined(OS_WIN)
// DO NOT USE AI_ADDRCONFIG ON WINDOWS.
//
// The following comment in <winsock2.h> is the best documentation I found
// on AI_ADDRCONFIG for Windows:
// Flags used in "hints" argument to getaddrinfo()
// - AI_ADDRCONFIG is supported starting with Vista
// - default is AI_ADDRCONFIG ON whether the flag is set or not
// because the performance penalty in not having ADDRCONFIG in
// the multi-protocol stack environment is severe;
// this defaulting may be disabled by specifying the AI_ALL flag,
// in that case AI_ADDRCONFIG must be EXPLICITLY specified to
// enable ADDRCONFIG behavior
//
// Not only is AI_ADDRCONFIG unnecessary, but it can be harmful. If the
// computer is not connected to a network, AI_ADDRCONFIG causes getaddrinfo
// to fail with WSANO_DATA (11004) for "localhost", probably because of the
// following note on AI_ADDRCONFIG in the MSDN getaddrinfo page:
// The IPv4 or IPv6 loopback address is not considered a valid global
// address.
// See http://crbug.com/5234.
hints.ai_flags = 0;
#else
hints.ai_flags = AI_ADDRCONFIG;
#endif
// Restrict result set to only this socket type to avoid duplicates.
hints.ai_socktype = SOCK_STREAM;
int err = getaddrinfo(host.c_str(), NULL, &hints, &ai);
#if defined(OS_LINUX)
net::DnsReloadTimer* dns_timer = Singleton<net::DnsReloadTimer>::get();
// If we fail, re-initialise the resolver just in case there have been any
// changes to /etc/resolv.conf and retry. See http://crbug.com/11380 for info.
if (err && dns_timer->Expired()) {
res_nclose(&_res);
if (!res_ninit(&_res))
err = getaddrinfo(host.c_str(), NULL, &hints, &ai);
}
#endif
if (err)
return ERR_NAME_NOT_RESOLVED;
addrlist->Adopt(ai);
return OK;
}
} // namespace net
|
