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// 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.
// This class helps to remember what domains may be needed to be resolved when a
// navigation takes place to a given URL. This information is gathered when a
// navigation resolution was not foreseen by identifying the referrer field that
// induced the navigation. When future navigations take place to known referrer
// sites, then we automatically pre-resolve the expected set of useful domains.
// All access to this class is performed via the DnsMaster class, and is
// protected by the its lock.
#ifndef CHROME_BROWSER_NET_REFERRER_H_
#define CHROME_BROWSER_NET_REFERRER_H_
#include <map>
#include <string>
#include "base/basictypes.h"
#include "base/time.h"
#include "base/values.h"
#include "googleurl/src/gurl.h"
namespace chrome_browser_net {
//------------------------------------------------------------------------------
// For each hostname in a Referrer, we have a ReferrerValue. It indicates
// exactly how much value (re: latency reduction) has resulted from having this
// entry.
class ReferrerValue {
public:
ReferrerValue() : birth_time_(base::Time::Now()) {}
base::TimeDelta latency() const { return latency_; }
base::Time birth_time() const { return birth_time_; }
void AccrueValue(const base::TimeDelta& delta) { latency_ += delta; }
// Reduce the latency figure by a factor of 2, and return true if any latency
// remains.
bool Trim();
private:
base::TimeDelta latency_; // Accumulated latency savings.
const base::Time birth_time_;
};
//------------------------------------------------------------------------------
// A list of domain names to pre-resolve. The names are the keys to this map,
// and the values indicate the amount of benefit derived from having each name
// around.
typedef std::map<std::string, ReferrerValue> HostNameMap;
//------------------------------------------------------------------------------
// There is one Referrer instance for each hostname that has acted as an HTTP
// referer (note mispelling is intentional) for a hostname that was otherwise
// unexpectedly navgated towards ("unexpected" in the sense that the hostname
// was probably needed as a subresource of a page, and was not otherwise
// predictable until the content with the reference arrived). Most typically,
// an outer page was a page fetched by the user, and this instance lists names
// in HostNameMap which are subresources and that were needed to complete the
// rendering of the outer page.
class Referrer : public HostNameMap {
public:
// Add the indicated host to the list of hosts that are resolved via DNS when
// the user navigates to this referrer. Note that if the list is long, an
// entry may be discarded to make room for this insertion.
void SuggestHost(const std::string& host);
// Record additional usefulness of having this host name in the list.
// Value is expressed as positive latency of amount delta.
void AccrueValue(const base::TimeDelta& delta, const std::string host);
// Trim the Referrer, by first diminishing (scaling down) the latency for each
// ReferredValue.
// Returns true if there are any referring names with some latency left.
bool Trim();
// Provide methods for persisting, and restoring contents into a Value class.
Value* Serialize() const;
void Deserialize(const Value& referrers);
private:
// Helper function for pruning list. Metric for usefulness is "large accrued
// value," in the form of latency_ savings associated with a host name. We
// also give credit for a name being newly added, by scalling latency per
// lifetime (time since birth). For instance, when two names have accrued
// the same latency_ savings, the older one is less valuable as it didn't
// accrue savings as quickly.
void DeleteLeastUseful();
// We put these into a std::map<>, so we need copy constructors.
// DISALLOW_COPY_AND_ASSIGN(Referrer);
// TODO(jar): Consider optimization to use pointers to these instances, and
// avoid deep copies during re-alloc of the containing map.
};
} // namespace chrome_browser_net
#endif // CHROME_BROWSER_NET_REFERRER_H_
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