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      1 // Copyright (c) 2012 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/url_info.h"
      6 
      7 #include <ctype.h>
      8 #include <math.h>
      9 
     10 #include <algorithm>
     11 #include <string>
     12 
     13 #include "base/format_macros.h"
     14 #include "base/lazy_instance.h"
     15 #include "base/logging.h"
     16 #include "base/metrics/histogram.h"
     17 #include "base/strings/stringprintf.h"
     18 
     19 using base::Time;
     20 using base::TimeDelta;
     21 using base::TimeTicks;
     22 
     23 namespace chrome_browser_net {
     24 
     25 namespace {
     26 
     27 // The number of OS cache entries we can guarantee(?) before cache eviction
     28 // might likely take place.
     29 const int kMaxGuaranteedDnsCacheSize = 50;
     30 
     31 // Common low end TTL for sites is 5 minutes.  However, DNS servers give us the
     32 // remaining time, not the original 5 minutes.  Hence it doesn't much matter
     33 // whether we found something in the local cache, or an ISP cache, it will on
     34 // average be 2.5 minutes before it expires.  We could try to model this with
     35 // 180 seconds, but simpler is just to do the lookups all the time (wasting OS
     36 // calls(?)), and let that OS cache decide what to do (with TTL in hand).  We
     37 // use a small time to help get some duplicate suppression, in case a page has
     38 // a TON of copies of the same domain name, so that we don't thrash the OS to
     39 // death.  Hopefully it is small enough that we're not hurting our cache hit
     40 // rate (i.e., we could always ask the OS).
     41 const int kDefaultCacheExpirationDuration = 5;
     42 
     43 TimeDelta MaxNonNetworkDnsLookupDuration() {
     44   return TimeDelta::FromMilliseconds(15);
     45 }
     46 
     47 bool detailed_logging_enabled = false;
     48 
     49 struct GlobalState {
     50   GlobalState() {
     51     cache_expiration_duration =
     52         TimeDelta::FromSeconds(kDefaultCacheExpirationDuration);
     53   }
     54   TimeDelta cache_expiration_duration;
     55 };
     56 
     57 base::LazyInstance<GlobalState>::Leaky global_state;
     58 
     59 }  // anonymous namespace
     60 
     61 // Use command line switch to enable detailed logging.
     62 void EnablePredictorDetailedLog(bool enable) {
     63   detailed_logging_enabled = enable;
     64 }
     65 
     66 // static
     67 int UrlInfo::sequence_counter = 1;
     68 
     69 UrlInfo::UrlInfo()
     70     : state_(PENDING),
     71       old_prequeue_state_(state_),
     72       resolve_duration_(NullDuration()),
     73       queue_duration_(NullDuration()),
     74       sequence_number_(0),
     75       motivation_(NO_PREFETCH_MOTIVATION),
     76       was_linked_(false) {
     77 }
     78 
     79 UrlInfo::~UrlInfo() {}
     80 
     81 bool UrlInfo::NeedsDnsUpdate() {
     82   switch (state_) {
     83     case PENDING:  // Just now created info.
     84       return true;
     85 
     86     case QUEUED:  // In queue.
     87     case ASSIGNED:  // It's being resolved.
     88     case ASSIGNED_BUT_MARKED:  // It's being resolved.
     89       return false;  // We're already working on it
     90 
     91     case NO_SUCH_NAME:  // Lookup failed.
     92     case FOUND:  // Lookup succeeded.
     93       return !IsStillCached();  // See if DNS cache expired.
     94 
     95     default:
     96       NOTREACHED();
     97       return false;
     98   }
     99 }
    100 
    101 // Used by test ONLY. The value is otherwise constant.
    102 // static
    103 void UrlInfo::set_cache_expiration(TimeDelta time) {
    104   global_state.Pointer()->cache_expiration_duration = time;
    105 }
    106 
    107 // static
    108 TimeDelta UrlInfo::get_cache_expiration() {
    109   return global_state.Get().cache_expiration_duration;
    110 }
    111 
    112 void UrlInfo::SetQueuedState(ResolutionMotivation motivation) {
    113   DCHECK(PENDING == state_ || FOUND == state_ || NO_SUCH_NAME == state_);
    114   old_prequeue_state_ = state_;
    115   state_ = QUEUED;
    116   queue_duration_ = resolve_duration_ = NullDuration();
    117   SetMotivation(motivation);
    118   GetDuration();  // Set time_
    119   DLogResultsStats("DNS Prefetch in queue");
    120 }
    121 
    122 void UrlInfo::SetAssignedState() {
    123   DCHECK(QUEUED == state_);
    124   state_ = ASSIGNED;
    125   queue_duration_ = GetDuration();
    126   DLogResultsStats("DNS Prefetch assigned");
    127   UMA_HISTOGRAM_TIMES("DNS.PrefetchQueue", queue_duration_);
    128 }
    129 
    130 void UrlInfo::RemoveFromQueue() {
    131   DCHECK(ASSIGNED == state_);
    132   state_ = old_prequeue_state_;
    133   DLogResultsStats("DNS Prefetch reset to prequeue");
    134   const TimeDelta kBoundary = TimeDelta::FromSeconds(2);
    135   if (queue_duration_ > kBoundary) {
    136     UMA_HISTOGRAM_MEDIUM_TIMES("DNS.QueueRecycledDeltaOver2",
    137                                queue_duration_ - kBoundary);
    138     return;
    139   }
    140   // Make a custom linear histogram for the region from 0 to boundary.
    141   static const size_t kBucketCount = 52;
    142   static base::HistogramBase* histogram(NULL);
    143   if (!histogram)
    144     histogram = base::LinearHistogram::FactoryTimeGet(
    145         "DNS.QueueRecycledUnder2", TimeDelta(), kBoundary, kBucketCount,
    146         base::HistogramBase::kUmaTargetedHistogramFlag);
    147   histogram->AddTime(queue_duration_);
    148 }
    149 
    150 void UrlInfo::SetPendingDeleteState() {
    151   DCHECK(ASSIGNED == state_  || ASSIGNED_BUT_MARKED == state_);
    152   state_ = ASSIGNED_BUT_MARKED;
    153 }
    154 
    155 void UrlInfo::SetFoundState() {
    156   DCHECK(ASSIGNED == state_);
    157   state_ = FOUND;
    158   resolve_duration_ = GetDuration();
    159   const TimeDelta max_duration = MaxNonNetworkDnsLookupDuration();
    160   if (max_duration <= resolve_duration_) {
    161     UMA_HISTOGRAM_CUSTOM_TIMES("DNS.PrefetchResolution", resolve_duration_,
    162         max_duration, TimeDelta::FromMinutes(15), 100);
    163   }
    164   sequence_number_ = sequence_counter++;
    165   DLogResultsStats("DNS PrefetchFound");
    166 }
    167 
    168 void UrlInfo::SetNoSuchNameState() {
    169   DCHECK(ASSIGNED == state_);
    170   state_ = NO_SUCH_NAME;
    171   resolve_duration_ = GetDuration();
    172   if (MaxNonNetworkDnsLookupDuration() <= resolve_duration_) {
    173     DHISTOGRAM_TIMES("DNS.PrefetchNotFoundName", resolve_duration_);
    174   }
    175   sequence_number_ = sequence_counter++;
    176   DLogResultsStats("DNS PrefetchNotFound");
    177 }
    178 
    179 void UrlInfo::SetUrl(const GURL& url) {
    180   if (url_.is_empty())  // Not yet initialized.
    181     url_ = url;
    182   else
    183     DCHECK_EQ(url_, url);
    184 }
    185 
    186 // IsStillCached() guesses if the DNS cache still has IP data,
    187 // or at least remembers results about "not finding host."
    188 bool UrlInfo::IsStillCached() const {
    189   DCHECK(FOUND == state_ || NO_SUCH_NAME == state_);
    190 
    191   // Default MS OS does not cache failures. Hence we could return false almost
    192   // all the time for that case.  However, we'd never try again to prefetch
    193   // the value if we returned false that way.  Hence we'll just let the lookup
    194   // time out the same way as FOUND case.
    195 
    196   if (sequence_counter - sequence_number_ > kMaxGuaranteedDnsCacheSize)
    197     return false;
    198 
    199   TimeDelta time_since_resolution = TimeTicks::Now() - time_;
    200   return time_since_resolution < global_state.Get().cache_expiration_duration;
    201 }
    202 
    203 void UrlInfo::DLogResultsStats(const char* message) const {
    204   if (!detailed_logging_enabled)
    205     return;
    206   DVLOG(1) << "\t" << message << "\tq=" << queue_duration().InMilliseconds()
    207            << "ms,\tr=" << resolve_duration().InMilliseconds()
    208            << "ms,\tp=" << sequence_number_ << "\t" << url_.spec();
    209 }
    210 
    211 //------------------------------------------------------------------------------
    212 // This last section supports HTML output, such as seen in about:dns.
    213 //------------------------------------------------------------------------------
    214 
    215 // Preclude any possibility of Java Script or markup in the text, by only
    216 // allowing alphanumerics, '.', '-', ':', and whitespace.
    217 static std::string RemoveJs(const std::string& text) {
    218   std::string output(text);
    219   size_t length = output.length();
    220   for (size_t i = 0; i < length; i++) {
    221     char next = output[i];
    222     if (isalnum(next) || isspace(next) || strchr(".-:/", next) != NULL)
    223       continue;
    224     output[i] = '?';
    225   }
    226   return output;
    227 }
    228 
    229 class MinMaxAverage {
    230  public:
    231   MinMaxAverage()
    232     : sum_(0), square_sum_(0), count_(0),
    233       minimum_(kint64max), maximum_(kint64min) {
    234   }
    235 
    236   // Return values for use in printf formatted as "%d"
    237   int sample(int64 value) {
    238     sum_ += value;
    239     square_sum_ += value * value;
    240     count_++;
    241     minimum_ = std::min(minimum_, value);
    242     maximum_ = std::max(maximum_, value);
    243     return static_cast<int>(value);
    244   }
    245   int minimum() const { return static_cast<int>(minimum_);    }
    246   int maximum() const { return static_cast<int>(maximum_);    }
    247   int average() const { return static_cast<int>(sum_/count_); }
    248   int     sum() const { return static_cast<int>(sum_);        }
    249 
    250   int standard_deviation() const {
    251     double average = static_cast<float>(sum_) / count_;
    252     double variance = static_cast<float>(square_sum_)/count_
    253                       - average * average;
    254     return static_cast<int>(floor(sqrt(variance) + .5));
    255   }
    256 
    257  private:
    258   int64 sum_;
    259   int64 square_sum_;
    260   int count_;
    261   int64 minimum_;
    262   int64 maximum_;
    263 
    264   // DISALLOW_COPY_AND_ASSIGN(MinMaxAverage);
    265 };
    266 
    267 static std::string HoursMinutesSeconds(int seconds) {
    268   std::string result;
    269   int print_seconds = seconds % 60;
    270   int minutes = seconds / 60;
    271   int print_minutes = minutes % 60;
    272   int print_hours = minutes/60;
    273   if (print_hours)
    274     base::StringAppendF(&result, "%.2d:",  print_hours);
    275   if (print_hours || print_minutes)
    276     base::StringAppendF(&result, "%2.2d:",  print_minutes);
    277   base::StringAppendF(&result, "%2.2d",  print_seconds);
    278   return result;
    279 }
    280 
    281 // static
    282 void UrlInfo::GetHtmlTable(const UrlInfoTable& host_infos,
    283                            const char* description,
    284                            bool brief,
    285                            std::string* output) {
    286   if (0 == host_infos.size())
    287     return;
    288   output->append(description);
    289   base::StringAppendF(output, "%" PRIuS " %s", host_infos.size(),
    290                       (1 == host_infos.size()) ? "hostname" : "hostnames");
    291 
    292   if (brief) {
    293     output->append("<br><br>");
    294     return;
    295   }
    296 
    297   output->append("<br><table border=1>"
    298       "<tr><th>Host name</th>"
    299       "<th>How long ago<br>(HH:MM:SS)</th>"
    300       "<th>Motivation</th>"
    301       "</tr>");
    302 
    303   const char* row_format = "<tr align=right><td>%s</td>"  // Host name.
    304                            "<td>%s</td>"                  // How long ago.
    305                            "<td>%s</td>"                  // Motivation.
    306                            "</tr>";
    307 
    308   // Print bulk of table, and gather stats at same time.
    309   MinMaxAverage queue, when;
    310   TimeTicks current_time = TimeTicks::Now();
    311   for (UrlInfoTable::const_iterator it(host_infos.begin());
    312        it != host_infos.end(); it++) {
    313     queue.sample((it->queue_duration_.InMilliseconds()));
    314     base::StringAppendF(
    315         output,
    316         row_format,
    317         RemoveJs(it->url_.spec()).c_str(),
    318                  HoursMinutesSeconds(when.sample(
    319                      (current_time - it->time_).InSeconds())).c_str(),
    320         it->GetAsciiMotivation().c_str());
    321   }
    322   output->append("</table>");
    323 
    324 #ifndef NDEBUG
    325   base::StringAppendF(
    326       output,
    327       "Prefetch Queue Durations: min=%d, avg=%d, max=%d<br><br>",
    328       queue.minimum(), queue.average(), queue.maximum());
    329 #endif
    330 
    331   output->append("<br>");
    332 }
    333 
    334 void UrlInfo::SetMotivation(ResolutionMotivation motivation) {
    335   motivation_ = motivation;
    336   if (motivation < LINKED_MAX_MOTIVATED)
    337     was_linked_ = true;
    338 }
    339 
    340 std::string UrlInfo::GetAsciiMotivation() const {
    341   switch (motivation_) {
    342     case MOUSE_OVER_MOTIVATED:
    343       return "[mouse-over]";
    344 
    345     case PAGE_SCAN_MOTIVATED:
    346       return "[page scan]";
    347 
    348     case OMNIBOX_MOTIVATED:
    349       return "[omnibox]";
    350 
    351     case STARTUP_LIST_MOTIVATED:
    352       return "[startup list]";
    353 
    354     case NO_PREFETCH_MOTIVATION:
    355       return "n/a";
    356 
    357     case STATIC_REFERAL_MOTIVATED:
    358       return RemoveJs(referring_url_.spec()) + "*";
    359 
    360     case LEARNED_REFERAL_MOTIVATED:
    361       return RemoveJs(referring_url_.spec());
    362 
    363     default:
    364       return std::string();
    365   }
    366 }
    367 
    368 }  // namespace chrome_browser_net
    369