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/dnscache.h"
48 #include "dns/resolverbase.h"
52 typedef boost::shared_ptr<DnsMaster> DnsMasterItem;
54 typedef boost::net::dns::type_t DnsIpProtocol;
55 const DnsIpProtocol DNS_IPv4 = boost::net::dns::type_a;
56 const DnsIpProtocol DNS_IPv6 = boost::net::dns::type_a6;
57 const DnsIpProtocol DNS_IPALL = boost::net::dns::type_all;
59 typedef std::pair<std::string, DnsIpProtocol> resolver_key_type;
60 typedef std::map<resolver_key_type, ResolverItem> resolver_map_type;
62 std::string to_string(const DnsIpProtocol &protocol);
65 * Factory and Cache of DNS resolvers
67 * to avoid having several resolvers resolving the same hostname which might
68 * result in conflicts with caching, this class is a singleton factory and the
69 * only place where Resolvers are constructed. They are remembered in an
70 * internal cache by hostname and IP version requested (v4, v6 or both).
72 * During resolving, several different name servers will have to be queried for
73 * the same hostname. These recursive resolvers are created using
74 * get_recursor_for and are NOT cached, so they should only be used from another
75 * "regular" resolver (created using get_resolver_for)
77 * The DnsMaster also remembers a few global variables that can be queried
78 * using public getter functions and it creates the DnsCache used by all its
81 class DnsMaster : boost::noncopyable
85 ResolverItem& get_resolver_for(const std::string &hostname,
86 const PingProtocol &ping_protocol);
87 ResolverItem& get_resolver_for(const std::string &hostname,
88 const DnsIpProtocol &protocol);
90 // implementation of singleton
92 static DnsMasterItem TheOnlyInstance;
94 DnsMaster(const IoServiceItem &io_serv,
95 const boost::asio::ip::address &default_name_server,
96 const int resolved_ip_ttl_threshold,
97 const int max_address_resolution_attempts,
98 const DnsCacheItem &cache);
100 static void create_master(const IoServiceItem &io_serv,
101 const boost::asio::ip::address &default_name_server,
102 const int resolved_ip_ttl_threshold,
103 const int max_address_resolution_attempts,
104 const std::string &cache_file);
105 static void create_master(const IoServiceItem &io_serv,
106 const boost::asio::ip::address &default_name_server,
107 const int resolved_ip_ttl_threshold,
108 const int max_address_resolution_attempts,
109 const DnsCacheItem &cache); // needed for unit test
110 static DnsMasterItem& get_instance();
113 // storage of global variables
115 //boost::asio::ip::address &get_default_name_server() const; // unused
116 int get_resolved_ip_ttl_threshold() const;
117 int get_max_address_resolution_attempts() const;
121 IoServiceItem IoService;
122 const boost::asio::ip::address DefaultNameServer;
123 const int ResolvedIpTtlThreshold;
124 const int MaxAddressResolutionAttempts;
126 resolver_map_type ResolverMap;
128 // internal helper functions
130 bool is_ip(const std::string &hostname) const;
131 static DnsIpProtocol ping2dns_protocol(const PingProtocol& pprot);
136 // (created using vim -- the world's best text editor)