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// Copyright (c) 2011 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.
// A RendererDnsPrefetch instance is maintained for each RenderThread.
// URL strings are typically added to the embedded queue during rendering.
// The first addition to the queue (transitioning from empty to having
// some names) causes a processing task to be added to the Renderer Thread.
// The processing task gathers all buffered names, and send them via IPC
// to the browser, so that DNS lookups can be performed before the user attempts
// to traverse a link.
// This class removed some duplicates, and discards numeric IP addresss
// (which wouldn't looked up in DNS anyway).
// To limit the time during the processing task (and avoid stalling the Render
// thread), several limits are placed on how much of the queue to process.
// If the processing task is not able to completely empty the queue, it
// schedules a future continuation of the task, and keeps the map of already
// sent names. If the entire queue is processed, then the list of "sent names"
// is cleared so that future gatherings might again pass along the same names.
#ifndef COMPONENTS_NETWORK_HINTS_RENDERER_RENDERER_DNS_PREFETCH_H_
#define COMPONENTS_NETWORK_HINTS_RENDERER_RENDERER_DNS_PREFETCH_H_
#include <stddef.h>
#include <map>
#include <string>
#include "base/macros.h"
#include "base/memory/weak_ptr.h"
#include "components/network_hints/renderer/dns_prefetch_queue.h"
namespace network_hints {
// An internal interface to the network_hints component for efficiently sending
// DNS prefetch requests to the net stack.
class RendererDnsPrefetch {
public:
RendererDnsPrefetch();
~RendererDnsPrefetch();
// Push a name into the queue to be resolved.
void Resolve(const char* name, size_t length);
// SubmitHosts processes the buffered names, and submits them for DNS
// prefetching.
// Note that browser process may decide which names should be looked up (to
// pre-warm the cache) based on what has been (or not been) looked up
// recently.
// If sending for DNS lookup is incomplete (queue is not empty, or not all
// names in map are sent, or ...) then a task to continue processing is
// sent to our thread loop.
void SubmitHostnames();
// The following is private, but exposed for testing purposes only.
static bool is_numeric_ip(const char* name, size_t length);
private:
// ExtractBufferedNames pulls names from queue into the map, reducing or
// eliminating a waiting queue.
// The size_goal argument can be used to reduce the amount of
// processing done in this method, and can leave some data
// in the buffer under some circumstances.
// If size_goal is zero, then extraction proceeds until
// the queue is empty. If size goal is positive, then
// extraction continues until the domain_map_ contains
// at least the specified number of names, or the buffer is empty.
void ExtractBufferedNames(size_t size_goal = 0);
// DnsPrefetchNames does not check the buffer, and just sends names
// that are already collected in the domain_map_ for DNS lookup.
// If max_count is zero, then all available names are sent; and
// if positive, then at most max_count names will be sent.
void DnsPrefetchNames(size_t max_count = 0);
// Reset() restores initial state provided after construction.
// This discards ALL queue entries, and map entries.
void Reset();
// We use c_string_queue_ to hold lists of names supplied typically) by the
// renderer. It queues the names, at minimal cost to the renderer's thread,
// and allows this class to process them when time permits (in a later task).
DnsQueue c_string_queue_;
// domain_map_ contains (for each domain) one of the next two constants,
// depending on whether we have asked the browser process to do the actual
// DNS lookup.
static const int kLookupRequested = 0x1;
static const int kPending = 0x0;
typedef std::map<std::string, int> DomainUseMap;
DomainUseMap domain_map_;
// Cache a tally of the count of names that haven't yet been sent
// for DNS pre-fetching. Note that we *could* recalculate this
// count by iterating over domain_map_, looking for even values.
size_t new_name_count_;
// We have some metrics to examine performance. We might use
// these metrics to modify buffer counts etc. some day.
int buffer_full_discard_count_;
int numeric_ip_discard_count_;
base::WeakPtrFactory<RendererDnsPrefetch> weak_factory_;
DISALLOW_COPY_AND_ASSIGN(RendererDnsPrefetch);
}; // class RendererDnsPrefetch
} // namespace network_hints
#endif // COMPONENTS_NETWORK_HINTS_RENDERER_RENDERER_DNS_PREFETCH_H_
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