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/*
* Copyright (C) 2009 Apple Inc. All Rights Reserved.
* Copyright (C) 2012 Igalia S.L.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
* OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include "config.h"
#include "DNSResolveQueue.h"
#if USE(GLIB)
#include "DNSResolveQueueGLib.h"
#elif USE(CURL)
#include "DNSResolveQueueCurl.h"
#elif USE(CF)
#include "DNSResolveQueueCFNet.h"
#endif
#include <wtf/CompletionHandler.h>
#include <wtf/NeverDestroyed.h>
namespace WebCore {
// When resolve queue is empty, we fire async resolution requests immediately (which is important if the prefetch is triggered by hovering).
// But during page parsing, we should coalesce identical requests to avoid stressing out the DNS resolver.
static const int gNamesToResolveImmediately = 4;
// Coalesce prefetch requests for this long before sending them out.
static const Seconds coalesceDelay { 1_s };
// Sending many DNS requests at once can overwhelm some gateways. See <rdar://8105550> for specific CFNET issues with CFHost throttling.
static const int gMaxSimultaneousRequests = 8;
// 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
// to negatively affect other applications' performance by pushing their cached entries out.
// If we end up with lots of names to prefetch, some will be dropped.
static const int gMaxRequestsToQueue = 64;
// If there were queued names that couldn't be sent simultaneously, check the state of resolvers after this delay.
static const Seconds resolvingRetryDelay { 100_ms };
DNSResolveQueue& DNSResolveQueue::singleton()
{
static NeverDestroyed<DNSResolveQueuePlatform> queue;
return queue;
}
DNSResolveQueue::DNSResolveQueue()
: m_timer(*this, &DNSResolveQueue::timerFired)
, m_requestsInFlight(0)
{
// isUsingProxy will return the initial value of m_isUsingProxy at first on
// platforms that have an asynchronous implementation of updateIsUsingProxy,
// so initialize it to true so we won't prefetch before we know if we are using a proxy.
}
// Don't do DNS prefetch if proxies are involved. For many proxy types, the user agent is never
// exposed to the IP address during normal operation. Querying an internal DNS server may not help
// performance, as it doesn't necessarily look up the actual external IP. Also, if DNS returns a
// fake internal address, local caches may keep it even after re-connecting to another network.
bool DNSResolveQueue::isUsingProxy()
{
MonotonicTime time = MonotonicTime::now();
static const Seconds minimumProxyCheckDelay = 5_s;
if (time - m_lastProxyEnabledStatusCheckTime > minimumProxyCheckDelay) {
m_lastProxyEnabledStatusCheckTime = time;
updateIsUsingProxy();
}
return m_isUsingProxy;
}
void DNSResolveQueue::add(const String& hostname)
{
// If there are no names queued, and few enough are in flight, resolve immediately (the mouse may be over a link).
if (!m_names.size()) {
if (isUsingProxy())
return;
if (++m_requestsInFlight <= gNamesToResolveImmediately) {
platformResolve(hostname);
return;
}
--m_requestsInFlight;
}
// It's better to not prefetch some names than to clog the queue.
// Dropping the newest names, because on a single page, these are likely to be below oldest ones.
if (m_names.size() < gMaxRequestsToQueue) {
m_names.add(hostname);
if (!m_timer.isActive())
m_timer.startOneShot(coalesceDelay);
}
}
void DNSResolveQueue::timerFired()
{
if (isUsingProxy()) {
m_names.clear();
return;
}
int requestsAllowed = gMaxSimultaneousRequests - m_requestsInFlight;
for (; !m_names.isEmpty() && requestsAllowed > 0; --requestsAllowed) {
++m_requestsInFlight;
HashSet<String>::iterator currentName = m_names.begin();
platformResolve(*currentName);
m_names.remove(currentName);
}
if (!m_names.isEmpty())
m_timer.startOneShot(resolvingRetryDelay);
}
} // namespace WebCore
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