dns-srv.cpp
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1 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
2 /*
3  * Copyright (c) 2014-2019, 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.
13  *
14  * NFD is free software: you can redistribute it and/or modify it under the terms
15  * of the GNU General Public License as published by the Free Software Foundation,
16  * either version 3 of the License, or (at your option) any later version.
17  *
18  * NFD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
19  * without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
20  * PURPOSE. See the GNU General Public License for more details.
21  *
22  * You should have received a copy of the GNU General Public License along with
23  * NFD, e.g., in COPYING.md file. If not, see <http://www.gnu.org/licenses/>.
24  */
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 <iostream>
38 
39 #include <boost/endian/conversion.hpp>
40 
41 namespace ndn {
42 namespace tools {
43 namespace autoconfig {
44 
45 using namespace std::string_literals;
46 
47 union QueryAnswer
48 {
49  HEADER header;
50  uint8_t buf[NS_PACKETSZ];
51 };
52 
57 static std::string
58 parseSrvRr(const QueryAnswer& queryAnswer, int answerSize)
59 {
60  // The references of the next classes are:
61  // http://www.diablotin.com/librairie/networking/dnsbind/ch14_02.htm
62 
63  struct rechdr
64  {
65  uint16_t type;
66  uint16_t iclass;
67  uint32_t ttl;
68  uint16_t length;
69  };
70 
71  struct srv_t
72  {
73  uint16_t priority;
74  uint16_t weight;
75  uint16_t port;
76  uint8_t* target;
77  };
78 
79  uint16_t ancount = queryAnswer.header.ancount;
80  if (boost::endian::big_to_native(ancount) == 0) {
81  NDN_THROW(DnsSrvError("SRV record cannot be parsed"));
82  }
83 
84  const uint8_t* blob = queryAnswer.buf + NS_HFIXEDSZ;
85  blob += dn_skipname(blob, queryAnswer.buf + answerSize) + NS_QFIXEDSZ;
86 
87  char srvName[NS_MAXDNAME];
88  int serverNameSize = dn_expand(queryAnswer.buf, // message pointer
89  queryAnswer.buf + answerSize, // end of message
90  blob, // compressed server name
91  srvName, // expanded server name
92  NS_MAXDNAME);
93  if (serverNameSize <= 0) {
94  NDN_THROW(DnsSrvError("SRV record cannot be parsed (error decoding domain name)"));
95  }
96 
97  const srv_t* server = reinterpret_cast<const srv_t*>(&blob[sizeof(rechdr)]);
98  uint16_t port = boost::endian::big_to_native(server->port);
99 
100  blob += serverNameSize + NS_HFIXEDSZ + NS_QFIXEDSZ;
101 
102  char hostName[NS_MAXDNAME];
103  int hostNameSize = dn_expand(queryAnswer.buf, // message pointer
104  queryAnswer.buf + answerSize, // end of message
105  blob, // compressed host name
106  hostName, // expanded host name
107  NS_MAXDNAME);
108  if (hostNameSize <= 0) {
109  NDN_THROW(DnsSrvError("SRV record cannot be parsed (error decoding host name)"));
110  }
111 
112  return "udp://"s + hostName + ":" + to_string(port);
113 }
114 
115 std::string
116 querySrvRr(const std::string& fqdn)
117 {
118  std::string srvDomain = "_ndn._udp." + fqdn;
119  std::cerr << "Sending DNS query for SRV record for " << srvDomain << std::endl;
120 
121  res_init();
122 
123  _res.retrans = 1;
124  _res.retry = 2;
125  _res.ndots = 10;
126 
127  QueryAnswer queryAnswer;
128  int answerSize = res_query(srvDomain.data(),
129  ns_c_in,
130  ns_t_srv,
131  queryAnswer.buf,
132  sizeof(queryAnswer));
133  if (answerSize == 0) {
134  NDN_THROW(DnsSrvError("No DNS SRV records found for " + srvDomain));
135  }
136  return parseSrvRr(queryAnswer, answerSize);
137 }
138 
142 std::string
144 {
145  std::cerr << "Sending DNS query for SRV record for _ndn._udp" << std::endl;
146 
147  QueryAnswer queryAnswer;
148 
149  res_init();
150 
151  _res.retrans = 1;
152  _res.retry = 2;
153  _res.ndots = 10;
154 
155  int answerSize = res_search("_ndn._udp",
156  ns_c_in,
157  ns_t_srv,
158  queryAnswer.buf,
159  sizeof(queryAnswer));
160 
161  if (answerSize == 0) {
162  NDN_THROW(DnsSrvError("No DNS SRV records found for _ndn._udp"));
163  }
164 
165  return parseSrvRr(queryAnswer, answerSize);
166 }
167 
168 } // namespace autoconfig
169 } // namespace tools
170 } // namespace ndn
Copyright (c) 2014-2017, Regents of the University of California, Arizona Board of Regents...
Definition: dns-srv.cpp:41
static std::string parseSrvRr(const QueryAnswer &queryAnswer, int answerSize)
Parse SRV record.
Definition: dns-srv.cpp:58
provide synchronous DNS SRV record querying
std::string querySrvRr(const std::string &fqdn)
Send DNS SRV request for fqdn.
Definition: dns-srv.cpp:116
std::string querySrvRrSearch()
Send DNS SRV request using search domain list.
Definition: dns-srv.cpp:143