1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
|
/* Copyright (C) 2020 C. McEnroe <june@causal.agency>
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <https://www.gnu.org/licenses/>.
*
* Additional permission under GNU GPL version 3 section 7:
*
* If you modify this Program, or any covered work, by linking or
* combining it with OpenSSL (or a modified version of that library),
* containing parts covered by the terms of the OpenSSL License and the
* original SSLeay license, the licensors of this Program grant you
* additional permission to convey the resulting work. Corresponding
* Source for a non-source form of such a combination shall include the
* source code for the parts of OpenSSL used as well as that of the
* covered work.
*/
#include <netdb.h>
#include <netinet/in.h>
#include <resolv.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#ifndef EAI_BADHINTS
#define EAI_BADHINTS EAI_BADFLAGS
#endif
#ifndef EAI_PROTOCOL
#define EAI_PROTOCOL EAI_BADFLAGS
#endif
/* A wrapper around getaddrinfo(3) which first performs SRV record (RFC 2782)
* lookup. hints must be provided and hints->ai_protocol must be set. SRV
* lookup is skipped if servname is numerical. If SRV lookup is successful, the
* ai_canonname field of the first addrinfo structure returned is set to the
* target name. Only the first SRV record is used. Priority and weight are
* ignored.
*/
int getservinfo(
const char *hostname, const char *servname,
const struct addrinfo *hints, struct addrinfo **res
) {
if (!hints) return EAI_BADHINTS;
if (!hints->ai_protocol) return EAI_PROTOCOL;
char *rest;
strtoul(servname, &rest, 10);
if (!*rest || hints->ai_flags & (AI_NUMERICHOST | AI_NUMERICSERV)) {
return getaddrinfo(hostname, servname, hints, res);
}
struct protoent *proto = getprotobynumber(hints->ai_protocol);
if (!proto) return EAI_PROTOCOL;
char dname[256];
int len = snprintf(
dname, sizeof(dname), "_%s._%s.%s",
servname, proto->p_name, hostname
);
if ((size_t)len >= sizeof(dname)) return EAI_OVERFLOW;
uint8_t msg[512];
len = res_query(dname, 1 /* IN */, 33 /* SRV */, msg, sizeof(msg));
if (len < 12) return getaddrinfo(hostname, servname, hints, res);
uint8_t *ptr = &msg[12];
#define NAME_SKIP \
for (uint8_t n; ptr < &msg[len] && (n = *ptr++); ptr += n) { \
if (n & 0xC0) { \
ptr++; \
break; \
} \
}
uint16_t qdcount = msg[4] << 8 | msg[5];
for (uint16_t q = 0; ptr < &msg[len] && q < qdcount; ++q) {
NAME_SKIP; // QNAME
ptr += 4; // QTYPE, QCLASS
}
NAME_SKIP; // NAME
ptr += 14; // TYPE, CLASS, TTL, RDLENGTH, Priority, Weight
if (&msg[len] < ptr + 3) {
return getaddrinfo(hostname, servname, hints, res);
}
char port[sizeof("65535")];
snprintf(port, sizeof(port), "%d", ptr[0] << 8 | ptr[1]);
ptr += 2;
// Name compression is not used for Target.
if (!ptr[0]) return EAI_NONAME;
hostname = (const char *)&ptr[1];
for (uint8_t n; ptr < &msg[len] && (n = *ptr); ptr += n) {
*ptr++ = '.';
}
struct addrinfo myHints = *hints;
myHints.ai_flags |= AI_NUMERICSERV;
myHints.ai_flags &= ~AI_CANONNAME;
int error = getaddrinfo(hostname, port, &myHints, res);
if (error) return error;
(*res)->ai_canonname = strdup(hostname);
if (!(*res)->ai_canonname) {
freeaddrinfo(*res);
return EAI_MEMORY;
}
return 0;
}
|