1// Copyright (c) 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_DNS_MDNS_CACHE_H_
6#define NET_DNS_MDNS_CACHE_H_
7
8#include <map>
9#include <string>
10#include <vector>
11
12#include "base/callback.h"
13#include "base/memory/scoped_ptr.h"
14#include "base/time/time.h"
15#include "net/base/net_export.h"
16
17namespace net {
18
19class ParsedDnsRecord;
20class RecordParsed;
21
22// mDNS Cache
23// This is a cache of mDNS records. It keeps track of expiration times and is
24// guaranteed not to return expired records. It also has facilities for timely
25// record expiration.
26class NET_EXPORT_PRIVATE MDnsCache {
27 public:
28  // Key type for the record map. It is a 3-tuple of type, name and optional
29  // value ordered by type, then name, then optional value. This allows us to
30  // query for all records of a certain type and name, while also allowing us
31  // to set records of a certain type, name and optionally value as unique.
32  class Key {
33   public:
34    Key(unsigned type, const std::string& name, const std::string& optional);
35    Key(const Key&);
36    Key& operator=(const Key&);
37    ~Key();
38    bool operator<(const Key& key) const;
39    bool operator==(const Key& key) const;
40
41    unsigned type() const { return type_; }
42    const std::string& name() const  { return name_; }
43    const std::string& optional() const { return optional_; }
44
45    // Create the cache key corresponding to |record|.
46    static Key CreateFor(const RecordParsed* record);
47   private:
48    unsigned type_;
49    std::string name_;
50    std::string optional_;
51  };
52
53  typedef base::Callback<void(const RecordParsed*)> RecordRemovedCallback;
54
55  enum UpdateType {
56    RecordAdded,
57    RecordChanged,
58    RecordRemoved,
59    NoChange
60  };
61
62  MDnsCache();
63  ~MDnsCache();
64
65  // Return value indicates whether the record was added, changed
66  // (existed previously with different value) or not changed (existed
67  // previously with same value).
68  UpdateType UpdateDnsRecord(scoped_ptr<const RecordParsed> record);
69
70  // Check cache for record with key |key|. Return the record if it exists, or
71  // NULL if it doesn't.
72  const RecordParsed* LookupKey(const Key& key);
73
74  // Return records with type |type| and name |name|. Expired records will not
75  // be returned. If |type| is zero, return all records with name |name|.
76  void FindDnsRecords(unsigned type,
77                      const std::string& name,
78                      std::vector<const RecordParsed*>* records,
79                      base::Time now) const;
80
81  // Remove expired records, call |record_removed_callback| for every removed
82  // record.
83  void CleanupRecords(base::Time now,
84                      const RecordRemovedCallback& record_removed_callback);
85
86  // Returns a time less than or equal to the next time a record will expire.
87  // Is updated when CleanupRecords or UpdateDnsRecord are called. Returns
88  // base::Time when the cache is empty.
89  base::Time next_expiration() const { return next_expiration_; }
90
91  // Remove a record from the cache.  Returns a scoped version of the pointer
92  // passed in if it was removed, scoped null otherwise.
93  scoped_ptr<const RecordParsed> RemoveRecord(const RecordParsed* record);
94
95  void Clear();
96
97 private:
98  typedef std::map<Key, const RecordParsed*> RecordMap;
99
100  // Get the effective expiration of a cache entry, based on its creation time
101  // and TTL. Does adjustments so entries with a TTL of zero will have a
102  // nonzero TTL, as explained in RFC 6762 Section 10.1.
103  static base::Time GetEffectiveExpiration(const RecordParsed* entry);
104
105  // Get optional part of the DNS key for shared records. For example, in PTR
106  // records this is the pointed domain, since multiple PTR records may exist
107  // for the same name.
108  static std::string GetOptionalFieldForRecord(
109      const RecordParsed* record);
110
111  RecordMap mdns_cache_;
112
113  base::Time next_expiration_;
114
115  DISALLOW_COPY_AND_ASSIGN(MDnsCache);
116};
117
118}  // namespace net
119
120#endif  // NET_DNS_MDNS_CACHE_H_
121