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#include "chrome/browser/net/referrer.h" 6 7#include <limits.h> 8 9#include "base/compiler_specific.h" 10#include "base/logging.h" 11#include "base/message_loop/message_loop.h" 12#include "base/values.h" 13#include "chrome/browser/net/predictor.h" 14 15namespace chrome_browser_net { 16 17//------------------------------------------------------------------------------ 18// Smoothing parameter for updating subresource_use_rate_. 19 20// We always combine our old expected value, weighted by some factor W (we use 21// kWeightingForOldConnectsExpectedValue), with the new expected value Enew. 22// The new "expected value" is the number of actual connections made due to the 23// current navigations. 24// That means that IF we end up needing to connect, we should apply the formula: 25// Eupdated = Eold * W + Enew * (1 - W) 26// If we visit the containing url, but don't end up needing a connection, then 27// Enew == 0, so we use the formula: 28// Eupdated = Eold * W 29// To achieve the above updating algorithm, we end up doing the multiplication 30// by W every time we contemplate doing a preconnection (i.e., when we navigate 31// to the containing URL, and consider doing a preconnection), and then IFF we 32// learn that we really needed a connection to the subresource, we complete the 33// above algorithm by adding the (1 - W) for each connection we make. 34 35// We weight the new expected value by a factor which is in the range of 0.0 to 36// 1.0. 37static const double kWeightingForOldConnectsExpectedValue = 0.66; 38 39// To estimate the expected value of the number of connections that we'll need 40// when a referrer is navigated to, we start with the following low initial 41// value. 42// Each time we do indeed (again) need the subresource, this value will get 43// increased. 44// Each time we navigate to the refererrer but never end up needing this 45// subresource, the value will decrease. 46// Very conservative is 0.0, which will mean that we have to wait for a while 47// before doing much speculative acvtivity. We do persist results, so we'll 48// save the asymptotic (correct?) learned answer in the long run. 49// Some browsers blindly make 2 connections all the time, so we'll use that as 50// a starting point. 51static const double kInitialConnectsExpectedValue = 2.0; 52 53Referrer::Referrer() : use_count_(1) {} 54 55void Referrer::SuggestHost(const GURL& url) { 56 // Limit how large our list can get, in case we make mistakes about what 57 // hostnames are in sub-resources (example: Some advertisments have a link to 58 // the ad agency, and then provide a "surprising" redirect to the advertised 59 // entity, which then (mistakenly) appears to be a subresource on the page 60 // hosting the ad). 61 // TODO(jar): Do experiments to optimize the max count of suggestions. 62 static const size_t kMaxSuggestions = 10; 63 64 if (!url.has_host()) // TODO(jar): Is this really needed???? 65 return; 66 DCHECK(url == url.GetWithEmptyPath()); 67 SubresourceMap::iterator it = find(url); 68 if (it != end()) { 69 it->second.SubresourceIsNeeded(); 70 return; 71 } 72 73 if (kMaxSuggestions <= size()) { 74 DeleteLeastUseful(); 75 DCHECK(kMaxSuggestions > size()); 76 } 77 (*this)[url].SubresourceIsNeeded(); 78} 79 80void Referrer::DeleteLeastUseful() { 81 // Find the item with the lowest value. Most important is preconnection_rate, 82 // and least is lifetime (age). 83 GURL least_useful_url; 84 double lowest_rate_seen = 0.0; 85 // We use longs for durations because we will use multiplication on them. 86 int64 least_useful_lifetime = 0; // Duration in milliseconds. 87 88 const base::Time kNow(base::Time::Now()); // Avoid multiple calls. 89 for (SubresourceMap::iterator it = begin(); it != end(); ++it) { 90 int64 lifetime = (kNow - it->second.birth_time()).InMilliseconds(); 91 double rate = it->second.subresource_use_rate(); 92 if (least_useful_url.has_host()) { 93 if (rate > lowest_rate_seen) 94 continue; 95 if (lifetime <= least_useful_lifetime) 96 continue; 97 } 98 least_useful_url = it->first; 99 lowest_rate_seen = rate; 100 least_useful_lifetime = lifetime; 101 } 102 if (least_useful_url.has_host()) 103 erase(least_useful_url); 104} 105 106bool Referrer::Trim(double reduce_rate, double threshold) { 107 std::vector<GURL> discarded_urls; 108 for (SubresourceMap::iterator it = begin(); it != end(); ++it) { 109 if (!it->second.Trim(reduce_rate, threshold)) 110 discarded_urls.push_back(it->first); 111 } 112 for (size_t i = 0; i < discarded_urls.size(); ++i) 113 erase(discarded_urls[i]); 114 return size() > 0; 115} 116 117bool ReferrerValue::Trim(double reduce_rate, double threshold) { 118 subresource_use_rate_ *= reduce_rate; 119 return subresource_use_rate_ > threshold; 120} 121 122 123void Referrer::Deserialize(const base::Value& value) { 124 if (value.GetType() != base::Value::TYPE_LIST) 125 return; 126 const base::ListValue* subresource_list( 127 static_cast<const base::ListValue*>(&value)); 128 size_t index = 0; // Bounds checking is done by subresource_list->Get*(). 129 while (true) { 130 std::string url_spec; 131 if (!subresource_list->GetString(index++, &url_spec)) 132 return; 133 double rate; 134 if (!subresource_list->GetDouble(index++, &rate)) 135 return; 136 137 GURL url(url_spec); 138 // TODO(jar): We could be more direct, and change birth date or similar to 139 // show that this is a resurrected value we're adding in. I'm not yet sure 140 // of how best to optimize the learning and pruning (Trim) algorithm at this 141 // level, so for now, we just suggest subresources, which leaves them all 142 // with the same birth date (typically start of process). 143 SuggestHost(url); 144 (*this)[url].SetSubresourceUseRate(rate); 145 } 146} 147 148base::Value* Referrer::Serialize() const { 149 base::ListValue* subresource_list(new base::ListValue); 150 for (const_iterator it = begin(); it != end(); ++it) { 151 base::StringValue* url_spec(new base::StringValue(it->first.spec())); 152 base::FundamentalValue* rate(new base::FundamentalValue( 153 it->second.subresource_use_rate())); 154 155 subresource_list->Append(url_spec); 156 subresource_list->Append(rate); 157 } 158 return subresource_list; 159} 160 161//------------------------------------------------------------------------------ 162 163ReferrerValue::ReferrerValue() 164 : birth_time_(base::Time::Now()), 165 navigation_count_(0), 166 preconnection_count_(0), 167 preresolution_count_(0), 168 subresource_use_rate_(kInitialConnectsExpectedValue) { 169} 170 171void ReferrerValue::SubresourceIsNeeded() { 172 DCHECK_GE(kWeightingForOldConnectsExpectedValue, 0); 173 DCHECK_LE(kWeightingForOldConnectsExpectedValue, 1.0); 174 ++navigation_count_; 175 subresource_use_rate_ += 1 - kWeightingForOldConnectsExpectedValue; 176} 177 178void ReferrerValue::ReferrerWasObserved() { 179 subresource_use_rate_ *= kWeightingForOldConnectsExpectedValue; 180 // Note: the use rate is temporarilly possibly incorect, as we need to find 181 // out if we really end up connecting. This will happen in a few hundred 182 // milliseconds (when content arrives, etc.). 183 // Value of subresource_use_rate_ should be sampled before this call. 184} 185 186} // namespace chrome_browser_net 187