1/*
2 * Copyright (C) 2009 Apple Inc. All Rights Reserved.
3 * Copyright (C) 2012 Igalia S.L.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in the
12 * documentation and/or other materials provided with the distribution.
13 *
14 * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
15 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
17 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR
18 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
19 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
20 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
21 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
22 * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
23 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
24 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
25 */
26
27#include "config.h"
28#include "DNSResolveQueue.h"
29
30#if USE(SOUP)
31#include "DNSResolveQueueSoup.h"
32#elif USE(CURL)
33#include "DNSResolveQueueCurl.h"
34#elif USE(CF)
35#include "DNSResolveQueueCFNet.h"
36#endif
37
38#include <wtf/CompletionHandler.h>
39#include <wtf/NeverDestroyed.h>
40
41namespace WebCore {
42
43// When resolve queue is empty, we fire async resolution requests immediately (which is important if the prefetch is triggered by hovering).
44// But during page parsing, we should coalesce identical requests to avoid stressing out the DNS resolver.
45static const int gNamesToResolveImmediately = 4;
46
47// Coalesce prefetch requests for this long before sending them out.
48static const Seconds coalesceDelay { 1_s };
49
50// Sending many DNS requests at once can overwhelm some gateways. See <rdar://8105550> for specific CFNET issues with CFHost throttling.
51static const int gMaxSimultaneousRequests = 8;
52
53// For a page has links to many outside sites, it is likely that the system DNS resolver won't be able to cache them all anyway, and we don't want
54// to negatively affect other applications' performance by pushing their cached entries out.
55// If we end up with lots of names to prefetch, some will be dropped.
56static const int gMaxRequestsToQueue = 64;
57
58// If there were queued names that couldn't be sent simultaneously, check the state of resolvers after this delay.
59static const Seconds resolvingRetryDelay { 100_ms };
60
61DNSResolveQueue& DNSResolveQueue::singleton()
62{
63 static NeverDestroyed<DNSResolveQueuePlatform> queue;
64
65 return queue;
66}
67
68DNSResolveQueue::DNSResolveQueue()
69 : m_timer(*this, &DNSResolveQueue::timerFired)
70 , m_requestsInFlight(0)
71{
72 // isUsingProxy will return the initial value of m_isUsingProxy at first on
73 // platforms that have an asynchronous implementation of updateIsUsingProxy,
74 // so initialize it to true so we won't prefetch before we know if we are using a proxy.
75}
76
77// Don't do DNS prefetch if proxies are involved. For many proxy types, the user agent is never
78// exposed to the IP address during normal operation. Querying an internal DNS server may not help
79// performance, as it doesn't necessarily look up the actual external IP. Also, if DNS returns a
80// fake internal address, local caches may keep it even after re-connecting to another network.
81bool DNSResolveQueue::isUsingProxy()
82{
83 MonotonicTime time = MonotonicTime::now();
84 static const Seconds minimumProxyCheckDelay = 5_s;
85 if (time - m_lastProxyEnabledStatusCheckTime > minimumProxyCheckDelay) {
86 m_lastProxyEnabledStatusCheckTime = time;
87 updateIsUsingProxy();
88 }
89 return m_isUsingProxy;
90}
91
92void DNSResolveQueue::add(const String& hostname)
93{
94 // If there are no names queued, and few enough are in flight, resolve immediately (the mouse may be over a link).
95 if (!m_names.size()) {
96 if (isUsingProxy())
97 return;
98 if (++m_requestsInFlight <= gNamesToResolveImmediately) {
99 platformResolve(hostname);
100 return;
101 }
102 --m_requestsInFlight;
103 }
104
105 // It's better to not prefetch some names than to clog the queue.
106 // Dropping the newest names, because on a single page, these are likely to be below oldest ones.
107 if (m_names.size() < gMaxRequestsToQueue) {
108 m_names.add(hostname);
109 if (!m_timer.isActive())
110 m_timer.startOneShot(coalesceDelay);
111 }
112}
113
114void DNSResolveQueue::timerFired()
115{
116 if (isUsingProxy()) {
117 m_names.clear();
118 return;
119 }
120
121 int requestsAllowed = gMaxSimultaneousRequests - m_requestsInFlight;
122
123 for (; !m_names.isEmpty() && requestsAllowed > 0; --requestsAllowed) {
124 ++m_requestsInFlight;
125 HashSet<String>::iterator currentName = m_names.begin();
126 platformResolve(*currentName);
127 m_names.remove(currentName);
128 }
129
130 if (!m_names.isEmpty())
131 m_timer.startOneShot(resolvingRetryDelay);
132}
133
134} // namespace WebCore
135