net/dns/mdns_cache.h

   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.h"
  15 #include "net/base/net_export.h"
  16
  17 namespace net {
  18
  19 class ParsedDnsRecord;
  20 class 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.
  26 class 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     NoChange
  59   };
  60
  61   MDnsCache();
  62   ~MDnsCache();
  63
  64   // Return value indicates whether the record was added, changed
  65   // (existed previously with different value) or not changed (existed
  66   // previously with same value).
  67   UpdateType UpdateDnsRecord(scoped_ptr<const RecordParsed> record);
  68
  69   // Check cache for record with key |key|. Return the record if it exists, or
  70   // NULL if it doesn't.
  71   const RecordParsed* LookupKey(const Key& key);
  72
  73   // Return records with type |type| and name |name|. Expired records will not
  74   // be returned. If |name| is empty, return all records with type |type|.
  75   void FindDnsRecords(unsigned type,
  76                       const std::string& name,
  77                       std::vector<const RecordParsed*>* records,
  78                       base::Time now) const;
  79
  80   // Remove expired records, call |record_removed_callback| for every removed
  81   // record.
  82   void CleanupRecords(base::Time now,
  83                       const RecordRemovedCallback& record_removed_callback);
  84
  85   // Returns a time less than or equal to the next time a record will expire.
  86   // Is updated when CleanupRecords or UpdateDnsRecord are called. Returns
  87   // base::Time when the cache is empty.
  88   base::Time next_expiration() const { return next_expiration_; }
  89
  90   void Clear();
  91
  92 private:
  93   typedef std::map<Key, const RecordParsed*> RecordMap;
  94
  95   // Get the effective expiration of a cache entry, based on its creation time
  96   // and TTL. Does adjustments so entries with a TTL of zero will have a
  97   // nonzero TTL, as explained in RFC 6762 Section 10.1.
  98   static base::Time GetEffectiveExpiration(const RecordParsed* entry);
  99
 100   // Get optional part of the DNS key for shared records. For example, in PTR
 101   // records this is the pointed domain, since multiple PTR records may exist
 102   // for the same name.
 103   static std::string GetOptionalFieldForRecord(
 104       const RecordParsed* record);
 105
 106   RecordMap mdns_cache_;
 107
 108   base::Time next_expiration_;
 109
 110   DISALLOW_COPY_AND_ASSIGN(MDnsCache);
 111 };
 112
 113 }  // namespace net
 114
 115 #endif  // NET_DNS_MDNS_CACHE_H_