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#ifndef NET_DNS_DNS_SESSION_H_
6#define NET_DNS_DNS_SESSION_H_
7
8#include <vector>
9
10#include "base/lazy_instance.h"
11#include "base/memory/ref_counted.h"
12#include "base/memory/scoped_ptr.h"
13#include "base/memory/scoped_vector.h"
14#include "base/metrics/bucket_ranges.h"
15#include "base/time/time.h"
16#include "net/base/net_export.h"
17#include "net/base/rand_callback.h"
18#include "net/dns/dns_config_service.h"
19#include "net/dns/dns_socket_pool.h"
20
21namespace base {
22class BucketRanges;
23class SampleVector;
24}
25
26namespace net {
27
28class ClientSocketFactory;
29class DatagramClientSocket;
30class NetLog;
31class StreamSocket;
32
33// Session parameters and state shared between DNS transactions.
34// Ref-counted so that DnsClient::Request can keep working in absence of
35// DnsClient. A DnsSession must be recreated when DnsConfig changes.
36class NET_EXPORT_PRIVATE DnsSession
37    : NON_EXPORTED_BASE(public base::RefCounted<DnsSession>) {
38 public:
39  typedef base::Callback<int()> RandCallback;
40
41  class NET_EXPORT_PRIVATE SocketLease {
42   public:
43    SocketLease(scoped_refptr<DnsSession> session,
44                unsigned server_index,
45                scoped_ptr<DatagramClientSocket> socket);
46    ~SocketLease();
47
48    unsigned server_index() const { return server_index_; }
49
50    DatagramClientSocket* socket() { return socket_.get(); }
51
52   private:
53    scoped_refptr<DnsSession> session_;
54    unsigned server_index_;
55    scoped_ptr<DatagramClientSocket> socket_;
56
57    DISALLOW_COPY_AND_ASSIGN(SocketLease);
58  };
59
60  DnsSession(const DnsConfig& config,
61             scoped_ptr<DnsSocketPool> socket_pool,
62             const RandIntCallback& rand_int_callback,
63             NetLog* net_log);
64
65  const DnsConfig& config() const { return config_; }
66  NetLog* net_log() const { return net_log_; }
67
68  // Return the next random query ID.
69  int NextQueryId() const;
70
71  // Return the index of the first configured server to use on first attempt.
72  unsigned NextFirstServerIndex();
73
74  // Start with |server_index| and find the index of the next known good server
75  // to use on this attempt. Returns |server_index| if this server has no
76  // recorded failures, or if there are no other servers that have not failed
77  // or have failed longer time ago.
78  unsigned NextGoodServerIndex(unsigned server_index);
79
80  // Record that server failed to respond (due to SRV_FAIL or timeout).
81  void RecordServerFailure(unsigned server_index);
82
83  // Record that server responded successfully.
84  void RecordServerSuccess(unsigned server_index);
85
86  // Record how long it took to receive a response from the server.
87  void RecordRTT(unsigned server_index, base::TimeDelta rtt);
88
89  // Record suspected loss of a packet for a specific server.
90  void RecordLostPacket(unsigned server_index, int attempt);
91
92  // Record server stats before it is destroyed.
93  void RecordServerStats();
94
95  // Return the timeout for the next query. |attempt| counts from 0 and is used
96  // for exponential backoff.
97  base::TimeDelta NextTimeout(unsigned server_index, int attempt);
98
99  // Allocate a socket, already connected to the server address.
100  // When the SocketLease is destroyed, the socket will be freed.
101  scoped_ptr<SocketLease> AllocateSocket(unsigned server_index,
102                                         const NetLog::Source& source);
103
104  // Creates a StreamSocket from the factory for a transaction over TCP. These
105  // sockets are not pooled.
106  scoped_ptr<StreamSocket> CreateTCPSocket(unsigned server_index,
107                                           const NetLog::Source& source);
108
109 private:
110  friend class base::RefCounted<DnsSession>;
111  ~DnsSession();
112
113  // Release a socket.
114  void FreeSocket(unsigned server_index,
115                  scoped_ptr<DatagramClientSocket> socket);
116
117  // Return the timeout using the TCP timeout method.
118  base::TimeDelta NextTimeoutFromJacobson(unsigned server_index, int attempt);
119
120  // Compute the timeout using the histogram method.
121  base::TimeDelta NextTimeoutFromHistogram(unsigned server_index, int attempt);
122
123  const DnsConfig config_;
124  scoped_ptr<DnsSocketPool> socket_pool_;
125  RandCallback rand_callback_;
126  NetLog* net_log_;
127
128  // Current index into |config_.nameservers| to begin resolution with.
129  int server_index_;
130
131  struct ServerStats;
132
133  // Track runtime statistics of each DNS server.
134  ScopedVector<ServerStats> server_stats_;
135
136  // Buckets shared for all |ServerStats::rtt_histogram|.
137  struct RttBuckets : public base::BucketRanges {
138    RttBuckets();
139  };
140  static base::LazyInstance<RttBuckets>::Leaky rtt_buckets_;
141
142  DISALLOW_COPY_AND_ASSIGN(DnsSession);
143};
144
145}  // namespace net
146
147#endif  // NET_DNS_DNS_SESSION_H_
148