text: // 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.
  
  #ifndef NET_DNS_DNS_CONFIG_SERVICE_H_
  #define NET_DNS_DNS_CONFIG_SERVICE_H_
  
  #include <map>
  #include <string>
  #include <vector>
  
  #include "base/gtest_prod_util.h"
  #include "base/memory/scoped_ptr.h"
  #include "base/threading/non_thread_safe.h"
  #include "base/time.h"
  #include "base/timer.h"
  // Needed on shared build with MSVS2010 to avoid multiple definitions of
  // std::vector<IPEndPoint>.
  #include "net/base/address_list.h"
  #include "net/base/ip_endpoint.h"  // win requires size of IPEndPoint
  #include "net/base/net_export.h"
  #include "net/dns/dns_hosts.h"
  
  namespace base {
  class Value;
  }
  
  namespace net {
  
  // Always use 1 second timeout (followed by binary exponential backoff).
  // TODO(szym): Remove code which reads timeout from system.
  const unsigned kDnsTimeoutSeconds = 1;
  
  // DnsConfig stores configuration of the system resolver.
  struct NET_EXPORT_PRIVATE DnsConfig {
    DnsConfig();
    virtual ~DnsConfig();
  
    bool Equals(const DnsConfig& d) const;
  
    bool EqualsIgnoreHosts(const DnsConfig& d) const;
  
    void CopyIgnoreHosts(const DnsConfig& src);
  
    // Returns a Value representation of |this|.  Caller takes ownership of the
    // returned Value.  For performance reasons, the Value only contains the
    // number of hosts rather than the full list.
    base::Value* ToValue() const;
  
    bool IsValid() const {
      return !nameservers.empty();
    }
  
    // List of name server addresses.
    std::vector<IPEndPoint> nameservers;
    // Suffix search list; used on first lookup when number of dots in given name
    // is less than |ndots|.
    std::vector<std::string> search;
  
    DnsHosts hosts;
  
    // AppendToMultiLabelName: is suffix search performed for multi-label names?
    // True, except on Windows where it can be configured.
    bool append_to_multi_label_name;
  
    // Indicates that source port randomization is required. This uses additional
    // resources on some platforms.
    bool randomize_ports;
  
    // Resolver options; see man resolv.conf.
  
    // Minimum number of dots before global resolution precedes |search|.
    int ndots;
    // Time between retransmissions, see res_state.retrans.
    base::TimeDelta timeout;
    // Maximum number of attempts, see res_state.retry.
    int attempts;
    // Round robin entries in |nameservers| for subsequent requests.
    bool rotate;
    // Enable EDNS0 extensions.
    bool edns0;
  };
  
  
  // Service for reading system DNS settings, on demand or when signalled by
  // internal watchers and NetworkChangeNotifier.
  class NET_EXPORT_PRIVATE DnsConfigService
      : NON_EXPORTED_BASE(public base::NonThreadSafe) {
   public:
    // Callback interface for the client, called on the same thread as
    // ReadConfig() and WatchConfig().
    typedef base::Callback<void(const DnsConfig& config)> CallbackType;
  
    // Creates the platform-specific DnsConfigService.
    static scoped_ptr<DnsConfigService> CreateSystemService();
  
    DnsConfigService();
    virtual ~DnsConfigService();
  
    // Attempts to read the configuration. Will run |callback| when succeeded.
    // Can be called at most once.
    void ReadConfig(const CallbackType& callback);
  
    // Registers systems watchers. Will attempt to read config after watch starts,
    // but only if watchers started successfully. Will run |callback| iff config
    // changes from last call or has to be withdrawn. Can be called at most once.
    // Might require MessageLoopForIO.
    void WatchConfig(const CallbackType& callback);
  
   protected:
    enum WatchStatus {
      DNS_CONFIG_WATCH_STARTED = 0,
      DNS_CONFIG_WATCH_FAILED_TO_START_CONFIG,
      DNS_CONFIG_WATCH_FAILED_TO_START_HOSTS,
      DNS_CONFIG_WATCH_FAILED_CONFIG,
      DNS_CONFIG_WATCH_FAILED_HOSTS,
      DNS_CONFIG_WATCH_MAX,
    };
  
   // Immediately attempts to read the current configuration.
    virtual void ReadNow() = 0;
    // Registers system watchers. Returns true iff succeeds.
    virtual bool StartWatching() = 0;
  
    // Called when the current config (except hosts) has changed.
    void InvalidateConfig();
    // Called when the current hosts have changed.
    void InvalidateHosts();
  
    // Called with new config. |config|.hosts is ignored.
    void OnConfigRead(const DnsConfig& config);
    // Called with new hosts. Rest of the config is assumed unchanged.
    void OnHostsRead(const DnsHosts& hosts);
  
    void set_watch_failed(bool value) { watch_failed_ = value; }
  
   private:
    // The timer counts from the last Invalidate* until complete config is read.
    void StartTimer();
    void OnTimeout();
    // Called when the config becomes complete. Stops the timer.
    void OnCompleteConfig();
  
    CallbackType callback_;
  
    DnsConfig dns_config_;
  
    // True if any of the necessary watchers failed. In that case, the service
    // will communicate changes via OnTimeout, but will only send empty DnsConfig.
    bool watch_failed_;
    // True after On*Read, before Invalidate*. Tells if the config is complete.
    bool have_config_;
    bool have_hosts_;
    // True if receiver needs to be updated when the config becomes complete.
    bool need_update_;
    // True if the last config sent was empty (instead of |dns_config_|).
    // Set when |timer_| expires.
    bool last_sent_empty_;
  
    // Initialized and updated on Invalidate* call.
    base::TimeTicks last_invalidate_config_time_;
    base::TimeTicks last_invalidate_hosts_time_;
    // Initialized and updated when |timer_| expires.
    base::TimeTicks last_sent_empty_time_;
  
    // Started in Invalidate*, cleared in On*Read.
    base::OneShotTimer<DnsConfigService> timer_;
  
    DISALLOW_COPY_AND_ASSIGN(DnsConfigService);
  };
  
  }  // namespace net
  
  #endif  // NET_DNS_DNS_CONFIG_SERVICE_H_
  