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// Copyright (c) 2012 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 UrlInfo object is used to store prediction related information about a host
// port and scheme triplet. When performing DNS pre-resolution of the host/port
// pair, its state is monitored as it is resolved.
// It includes progress, from placement in the Predictor's queue, to resolution
// by the DNS service as either FOUND or NO_SUCH_NAME. Each instance may also
// hold records of previous resolution times, which might later be shown to be
// savings relative to resolution time during a navigation.
// UrlInfo objects are also used to describe frames, and additional instances
// may describe associated subresources, for future speculative connections to
// those expected subresources.
#include <string>
#include <vector>
#include "base/time/time.h"
#include "net/base/host_port_pair.h"
#include "url/gurl.h"
namespace chrome_browser_net {
// Use command line switch to enable detailed logging.
void EnablePredictorDetailedLog(bool enable);
class UrlInfo {
// Reasons for a domain to be resolved.
enum ResolutionMotivation {
MOUSE_OVER_MOTIVATED, // Mouse-over link induced resolution.
PAGE_SCAN_MOTIVATED, // Scan of rendered page induced resolution.
LINKED_MAX_MOTIVATED, // enum demarkation above motivation from links.
OMNIBOX_MOTIVATED, // Omni-box suggested resolving this.
STARTUP_LIST_MOTIVATED, // Startup list caused this resolution.
EARLY_LOAD_MOTIVATED, // In some cases we use the prefetcher to warm up
// the connection in advance of issuing the real
// request.
NO_PREFETCH_MOTIVATION, // Browser navigation info (not prefetch related).
// The following involve predictive prefetching, triggered by a navigation.
// The referrinrg_url_ is also set when these are used.
// TODO(jar): Support STATIC_REFERAL_MOTIVATED API and integration.
STATIC_REFERAL_MOTIVATED, // External database suggested this resolution.
LEARNED_REFERAL_MOTIVATED, // Prior navigation taught us this resolution.
SELF_REFERAL_MOTIVATED, // Guess about need for a second connection.
MAX_MOTIVATED // Beyond all enums, for use in histogram bounding.
enum DnsProcessingState {
// When processed by our prefetching system, the states are:
PENDING, // Constructor has completed.
QUEUED, // In name queue but not yet being resolved.
ASSIGNED, // Being resolved (or being reset to earlier state)
ASSIGNED_BUT_MARKED, // Needs to be deleted as soon as it's resolved.
FOUND, // DNS resolution completed.
NO_SUCH_NAME, // DNS resolution completed.
typedef std::vector<UrlInfo> UrlInfoTable;
static base::TimeDelta NullDuration() {
return base::TimeDelta::FromMilliseconds(-1);
// UrlInfo are usually made by the default constructor during
// initializing of the Predictor's map (of info for Hostnames).
// NeedDnsUpdate decides, based on our internal info,
// if it would be valuable to attempt to update (prefectch)
// DNS data for hostname. This decision is based
// on how recently we've done DNS prefetching for hostname.
bool NeedsDnsUpdate();
// FOR TEST ONLY: The following access the otherwise constant values.
static void set_cache_expiration(base::TimeDelta time);
static base::TimeDelta get_cache_expiration();
// The prefetching lifecycle.
void SetQueuedState(ResolutionMotivation motivation);
void SetAssignedState();
void RemoveFromQueue();
void SetPendingDeleteState();
void SetFoundState();
void SetNoSuchNameState();
// Finish initialization. Must only be called once.
void SetUrl(const GURL& url);
bool was_linked() const { return was_linked_; }
GURL referring_url() const { return referring_url_; }
void SetReferringHostname(const GURL& url) {
referring_url_ = url;
bool was_found() const { return FOUND == state_; }
bool was_nonexistent() const { return NO_SUCH_NAME == state_; }
bool is_assigned() const {
return ASSIGNED == state_ || ASSIGNED_BUT_MARKED == state_;
bool is_marked_to_delete() const { return ASSIGNED_BUT_MARKED == state_; }
const GURL url() const { return url_; }
bool HasUrl(const GURL& url) const {
return url_ == url;
base::TimeDelta resolve_duration() const { return resolve_duration_;}
base::TimeDelta queue_duration() const { return queue_duration_;}
void DLogResultsStats(const char* message) const;
static void GetHtmlTable(const UrlInfoTable& host_infos,
const char* description,
bool brief,
std::string* output);
// For testing, and use in printing tables of info, we sometimes need to
// adjust the time manually. Usually, this value is maintained by state
// transition, and this call is not made.
void set_time(const base::TimeTicks& time) { time_ = time; }
base::TimeDelta GetDuration() {
base::TimeTicks old_time = time_;
time_ = base::TimeTicks::Now();
return time_ - old_time;
// IsStillCached() guesses if the DNS cache still has IP data.
bool IsStillCached() const;
// Record why we created, or have updated (reqested pre-resolution) of this
// instance.
void SetMotivation(ResolutionMotivation motivation);
// Helper function for about:dns printing.
std::string GetAsciiMotivation() const;
// The current state of this instance.
DnsProcessingState state_;
// Record the state prior to going to a queued state, in case we have to back
// out of the queue.
DnsProcessingState old_prequeue_state_;
GURL url_; // Host, port and scheme for this info.
// When was last state changed (usually lookup completed).
base::TimeTicks time_;
// Time needed for DNS to resolve.
base::TimeDelta resolve_duration_;
// Time spent in queue.
base::TimeDelta queue_duration_;
int sequence_number_; // Used to calculate potential of cache eviction.
static int sequence_counter; // Used to allocate sequence_number_'s.
// Motivation for creation of this instance.
ResolutionMotivation motivation_;
// Record if the motivation for prefetching was ever a page-link-scan.
bool was_linked_;
// If this instance holds data about a navigation, we store the referrer.
// If this instance hold data about a prefetch, and the prefetch was
// instigated by a referrer, we store it here (for use in about:dns).
GURL referring_url_;
// We put these objects into a std::map, and hence we
// need some "evil" constructors.
} // namespace chrome_browser_net