dns-srv.cpp
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3  * Copyright (c) 2014-2024, Regents of the University of California,
4  * Arizona Board of Regents,
5  * Colorado State University,
6  * University Pierre & Marie Curie, Sorbonne University,
7  * Washington University in St. Louis,
8  * Beijing Institute of Technology,
9  * The University of Memphis.
10  *
11  * This file is part of NFD (Named Data Networking Forwarding Daemon).
12  * See AUTHORS.md for complete list of NFD authors and contributors.
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25 
26 #include "dns-srv.hpp"
27 
28 #include <sys/types.h>
29 #include <arpa/nameser.h>
30 #include <netinet/in.h>
31 #include <resolv.h>
32 
33 #ifdef __APPLE__
34 #include <arpa/nameser_compat.h>
35 #endif
36 
37 #include <ndn-cxx/util/backports.hpp>
38 #include <ndn-cxx/util/exception.hpp>
39 
40 #include <iostream>
41 
42 #include <boost/endian/conversion.hpp>
43 
44 namespace ndn::autoconfig {
45 
46 using namespace std::string_literals;
47 
48 union QueryAnswer
49 {
50  HEADER header;
51  uint8_t buf[NS_PACKETSZ];
52 };
53 
58 static std::string
59 parseSrvRr(const QueryAnswer& queryAnswer, int answerSize)
60 {
61  // The references of the next classes are:
62  // http://www.diablotin.com/librairie/networking/dnsbind/ch14_02.htm
63 
64  struct rechdr
65  {
66  uint16_t type;
67  uint16_t iclass;
68  uint32_t ttl;
69  uint16_t length;
70  };
71 
72  struct srv_t
73  {
74  uint16_t priority;
75  uint16_t weight;
76  uint16_t port;
77  uint8_t* target;
78  };
79 
80  uint16_t ancount = queryAnswer.header.ancount;
81  if (boost::endian::big_to_native(ancount) == 0) {
82  NDN_THROW(DnsSrvError("SRV record cannot be parsed"));
83  }
84 
85  const uint8_t* blob = queryAnswer.buf + NS_HFIXEDSZ;
86  blob += dn_skipname(blob, queryAnswer.buf + answerSize) + NS_QFIXEDSZ;
87 
88  char srvName[NS_MAXDNAME];
89  int serverNameSize = dn_expand(queryAnswer.buf, // message pointer
90  queryAnswer.buf + answerSize, // end of message
91  blob, // compressed server name
92  srvName, // expanded server name
93  NS_MAXDNAME);
94  if (serverNameSize <= 0) {
95  NDN_THROW(DnsSrvError("SRV record cannot be parsed (error decoding domain name)"));
96  }
97 
98  const srv_t* server = reinterpret_cast<const srv_t*>(&blob[sizeof(rechdr)]);
99  uint16_t port = boost::endian::big_to_native(server->port);
100 
101  blob += serverNameSize + NS_HFIXEDSZ + NS_QFIXEDSZ;
102 
103  char hostName[NS_MAXDNAME];
104  int hostNameSize = dn_expand(queryAnswer.buf, // message pointer
105  queryAnswer.buf + answerSize, // end of message
106  blob, // compressed host name
107  hostName, // expanded host name
108  NS_MAXDNAME);
109  if (hostNameSize <= 0) {
110  NDN_THROW(DnsSrvError("SRV record cannot be parsed (error decoding host name)"));
111  }
112 
113  return "udp://"s + hostName + ":" + std::to_string(port);
114 }
115 
116 std::string
117 querySrvRr(const std::string& fqdn)
118 {
119  std::string srvDomain = "_ndn._udp." + fqdn;
120  std::cerr << "Sending DNS query for SRV record for " << srvDomain << std::endl;
121 
122  res_init();
123 
124  _res.retrans = 1;
125  _res.retry = 2;
126  _res.ndots = 10;
127 
128  QueryAnswer queryAnswer;
129  int answerSize = res_query(srvDomain.data(),
130  ns_c_in,
131  ns_t_srv,
132  queryAnswer.buf,
133  sizeof(queryAnswer));
134  if (answerSize == 0) {
135  NDN_THROW(DnsSrvError("No DNS SRV records found for " + srvDomain));
136  }
137  return parseSrvRr(queryAnswer, answerSize);
138 }
139 
143 std::string
145 {
146  std::cerr << "Sending DNS query for SRV record for _ndn._udp" << std::endl;
147 
148  QueryAnswer queryAnswer;
149 
150  res_init();
151 
152  _res.retrans = 1;
153  _res.retry = 2;
154  _res.ndots = 10;
155 
156  int answerSize = res_search("_ndn._udp",
157  ns_c_in,
158  ns_t_srv,
159  queryAnswer.buf,
160  sizeof(queryAnswer));
161 
162  if (answerSize == 0) {
163  NDN_THROW(DnsSrvError("No DNS SRV records found for _ndn._udp"));
164  }
165 
166  return parseSrvRr(queryAnswer, answerSize);
167 }
168 
169 } // namespace ndn::autoconfig
provide synchronous DNS SRV record querying
std::string querySrvRr(const std::string &fqdn)
Send DNS SRV request for fqdn.
Definition: dns-srv.cpp:117
std::string querySrvRrSearch()
Send DNS SRV request using search domain list.
Definition: dns-srv.cpp:144
static std::string parseSrvRr(const QueryAnswer &queryAnswer, int answerSize)
Parse SRV record.
Definition: dns-srv.cpp:59