/* * 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(SOUP) #include "DNSResolveQueueSoup.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