1// Copyright 2013 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_QUIC_PORT_SUGGESTER_H_
6#define NET_QUIC_PORT_SUGGESTER_H_
7
8#include "base/basictypes.h"
9#include "base/memory/ref_counted.h"
10#include "base/sha1.h"
11#include "net/base/net_export.h"
12
13namespace net {
14
15class HostPortPair;
16
17// We provide a pseudo-random number generator that is always seeded the same
18// way for a given destination host-port pair.  The generator is used to
19// consistently suggest (for that host-port pair) an ephemeral source port,
20// and hence increase the likelihood that a server's load balancer will direct
21// a repeated connection to the same server (with QUIC, further increasing the
22// chance of connection establishment with 0-RTT).
23class NET_EXPORT_PRIVATE PortSuggester
24    : public base::RefCounted<PortSuggester> {
25 public:
26  PortSuggester(const HostPortPair& server, uint64 seed);
27
28  // Generate a pseudo-random int in the inclusive range from |min| to |max|.
29  // Will (probably) return different numbers when called repeatedly.
30  int SuggestPort(int min, int max);
31
32  uint32 call_count() const { return call_count_; }
33  int previous_suggestion() const;
34
35 private:
36  friend class base::RefCounted<PortSuggester>;
37
38  virtual ~PortSuggester() {}
39
40  // We maintain the first 8 bytes of a hash as our seed_ state.
41  uint64 seed_;
42  uint32 call_count_;  // Number of suggestions made.
43  int previous_suggestion_;
44
45  DISALLOW_COPY_AND_ASSIGN(PortSuggester);
46};
47
48}  // namespace net
49
50#endif  // NET_QUIC_PORT_SUGGESTER_H_
51