chrome/browser/net/referrer.h

   1 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 // This class helps to remember what domains may be needed to be resolved when a
   6 // navigation takes place to a given URL.  This information is gathered when a
   7 // navigation to a subresource identifies a referring URL.
   8 // When future navigations take place to known referrer sites, then we
   9 // speculatively either pre-warm a TCP/IP conneciton, or at a minimum, resolve
  10 // the host name via DNS.
  11
  12 // All access to this class is performed via the Predictor class, which only
  13 // operates on the IO thread.
  14
  15 #ifndef CHROME_BROWSER_NET_REFERRER_H_
  16 #define CHROME_BROWSER_NET_REFERRER_H_
  17
  18 #include <map>
  19
  20 #include "base/basictypes.h"
  21 #include "base/time/time.h"
  22 #include "net/base/host_port_pair.h"
  23 #include "url/gurl.h"
  24
  25 namespace base {
  26 class Value;
  27 }
  28
  29 namespace chrome_browser_net {
  30
  31 //------------------------------------------------------------------------------
  32 // For each hostname in a Referrer, we have a ReferrerValue.  It indicates
  33 // exactly how much value (re: latency reduction, or connection use) has
  34 // resulted from having this entry.
  35 class ReferrerValue {
  36  public:
  37   ReferrerValue();
  38
  39   // Used during deserialization.
  40   void SetSubresourceUseRate(double rate) { subresource_use_rate_ = rate; }
  41
  42   base::Time birth_time() const { return birth_time_; }
  43
  44   // Record the fact that we navigated to the associated subresource URL.  This
  45   // will increase the value of the expected subresource_use_rate_
  46   void SubresourceIsNeeded();
  47
  48   // Record the fact that the referrer of this subresource was observed. This
  49   // will diminish the expected subresource_use_rate_ (and will only be
  50   // counteracted later if we really needed this subresource as a consequence
  51   // of our associated referrer.)
  52   void ReferrerWasObserved();
  53
  54   int64 navigation_count() const { return navigation_count_; }
  55   double subresource_use_rate() const { return subresource_use_rate_; }
  56
  57   int64 preconnection_count() const { return preconnection_count_; }
  58   void IncrementPreconnectionCount() { ++preconnection_count_; }
  59
  60   int64 preresolution_count() const { return preresolution_count_; }
  61   void preresolution_increment() { ++preresolution_count_; }
  62
  63   // Reduce the subresource_use_rate_ by the supplied factor, and return true
  64   // if the result is still greater than the given threshold.
  65   bool Trim(double reduce_rate, double threshold);
  66
  67  private:
  68   const base::Time birth_time_;
  69
  70   // The number of times this item was navigated to with the fixed referrer.
  71   int64 navigation_count_;
  72
  73   // The number of times this item was preconnected as a consequence of its
  74   // referrer.
  75   int64 preconnection_count_;
  76
  77   // The number of times this item was pre-resolved (via DNS) as a consequence
  78   // of its referrer.
  79   int64 preresolution_count_;
  80
  81   // A smoothed estimate of the expected number of connections that will be made
  82   // to this subresource.
  83   double subresource_use_rate_;
  84 };
  85
  86 //------------------------------------------------------------------------------
  87 // A list of domain names to pre-resolve. The names are the keys to this map,
  88 // and the values indicate the amount of benefit derived from having each name
  89 // around.
  90 typedef std::map<GURL, ReferrerValue> SubresourceMap;
  91
  92 //------------------------------------------------------------------------------
  93 // There is one Referrer instance for each hostname that has acted as an HTTP
  94 // referer (note mispelling is intentional) for a hostname that was otherwise
  95 // unexpectedly navgated towards ("unexpected" in the sense that the hostname
  96 // was probably needed as a subresource of a page, and was not otherwise
  97 // predictable until the content with the reference arrived).  Most typically,
  98 // an outer page was a page fetched by the user, and this instance lists names
  99 // in SubresourceMap which are subresources and that were needed to complete the
 100 // rendering of the outer page.
 101 class Referrer : public SubresourceMap {
 102  public:
 103   Referrer();
 104   void IncrementUseCount() { ++use_count_; }
 105   int64 use_count() const { return use_count_; }
 106
 107   // Add the indicated url to the list that are resolved via DNS when the user
 108   // navigates to this referrer.  Note that if the list is long, an entry may be
 109   // discarded to make room for this insertion.
 110   void SuggestHost(const GURL& url);
 111
 112   // Trim the Referrer, by first diminishing (scaling down) the subresource
 113   // use expectation for each ReferredValue.
 114   // Returns true if expected use rate is greater than the threshold.
 115   bool Trim(double reduce_rate, double threshold);
 116
 117   // Provide methods for persisting, and restoring contents into a Value class.
 118   base::Value* Serialize() const;
 119   void Deserialize(const base::Value& referrers);
 120
 121  private:
 122   // Helper function for pruning list.  Metric for usefulness is "large accrued
 123   // value," in the form of latency_ savings associated with a host name.  We
 124   // also give credit for a name being newly added, by scalling latency per
 125   // lifetime (time since birth).  For instance, when two names have accrued
 126   // the same latency_ savings, the older one is less valuable as it didn't
 127   // accrue savings as quickly.
 128   void DeleteLeastUseful();
 129
 130   // The number of times this referer had its subresources scanned for possible
 131   // preconnection or DNS preresolution.
 132   int64 use_count_;
 133
 134   // We put these into a std::map<>, so we need copy constructors.
 135   // DISALLOW_COPY_AND_ASSIGN(Referrer);
 136   // TODO(jar): Consider optimization to use pointers to these instances, and
 137   // avoid deep copies during re-alloc of the containing map.
 138 };
 139
 140 }  // namespace chrome_browser_net
 141
 142 #endif  // CHROME_BROWSER_NET_REFERRER_H_