2 The software in this package is distributed under the GNU General
3 Public License version 2 (with a special exception described below).
5 A copy of GNU General Public License (GPL) is included in this distribution,
6 in the file COPYING.GPL.
8 As a special exception, if other files instantiate templates or use macros
9 or inline functions from this file, or you compile this file and link it
10 with other works to produce a work based on this file, this file
11 does not by itself cause the resulting work to be covered
12 by the GNU General Public License.
14 However the source code for this file must still be made available
15 in accordance with section (3) of the GNU General Public License.
17 This exception does not invalidate any other reasons why a work based
18 on this file might be covered by the GNU General Public License.
20 Christian Herdtweck, Intra2net AG 2015
24 * Two in one: a DNS resolver factory and a DNS cache
26 * Put these two things into one class because it is easier this way to avoid
27 * sync problems if e.g. there are 2 resolvers for the same host name
29 * This class is a Singleton. In case there are problems with this approach,
30 * there is an alternative:
31 * give every ResolverBase object a DnsMasterItem as variable, that is set
32 * during construction and call update / get_cached_results on that instance
39 #include <utility> // pair
41 #include <boost/shared_ptr.hpp>
42 #include <boost/noncopyable.hpp>
43 #include <boost/net/dns.hpp>
45 #include "host/pinger.h" // for IoserviceItem
46 #include "host/pingprotocol.h"
47 #include "dns/dnsipprotocol.h"
48 #include "dns/dnscache.h"
49 #include "dns/resolverbase.h"
53 typedef boost::shared_ptr<DnsMaster> DnsMasterItem;
55 typedef std::pair<std::string, DnsIpProtocol> resolver_key_type;
56 typedef std::map<resolver_key_type, ResolverItem> resolver_map_type;
59 * Factory and Cache of DNS resolvers
61 * to avoid having several resolvers resolving the same hostname which might
62 * result in conflicts with caching, this class is a singleton factory and the
63 * only place where Resolvers are constructed. They are remembered in an
64 * internal cache by hostname and IP version requested (v4, v6 or both).
66 * During resolving, several different name servers will have to be queried for
67 * the same hostname. These recursive resolvers are created using
68 * get_recursor_for and are NOT cached, so they should only be used from another
69 * "regular" resolver (created using get_resolver_for)
71 * The DnsMaster also remembers a few global variables that can be queried
72 * using public getter functions and it creates the DnsCache used by all its
75 class DnsMaster : boost::noncopyable
79 ResolverItem& get_resolver_for(const std::string &hostname,
80 const PingProtocol &ping_protocol);
81 ResolverItem& get_resolver_for(const std::string &hostname,
82 const DnsIpProtocol &protocol);
84 // implementation of singleton
86 static DnsMasterItem TheOnlyInstance;
88 DnsMaster(const IoServiceItem &io_serv,
89 const boost::asio::ip::address &default_name_server,
90 const int resolved_ip_ttl_threshold,
91 const int max_address_resolution_attempts,
92 const int max_recursion_count,
93 const DnsCacheItem &cache);
95 static void create_master(const IoServiceItem &io_serv,
96 const boost::asio::ip::address &default_name_server,
97 const int resolved_ip_ttl_threshold,
98 const int min_time_between_resolves,
99 const int max_address_resolution_attempts,
100 const int max_recursion_count,
101 const std::string &cache_file);
102 static void create_master(const IoServiceItem &io_serv,
103 const boost::asio::ip::address &default_name_server,
104 const int resolved_ip_ttl_threshold,
105 const int max_address_resolution_attempts,
106 const int max_recursion_count,
107 const DnsCacheItem &cache); // needed for unit test
108 static DnsMasterItem& get_instance();
111 // storage of global variables
113 //boost::asio::ip::address &get_default_name_server() const; // unused
114 int get_resolved_ip_ttl_threshold() const;
115 int get_max_address_resolution_attempts() const;
116 int get_max_recursion_count() const;
119 static std::string get_cname_chain_str(const std::string &hostname);
123 IoServiceItem IoService;
124 const boost::asio::ip::address DefaultNameServer;
125 const int ResolvedIpTtlThreshold;
126 const int MaxAddressResolutionAttempts;
127 const int MaxRecursionCount;
129 resolver_map_type ResolverMap;
131 // internal helper functions
133 bool is_ip(const std::string &hostname) const;