1/* vi: set sw=4 ts=4: */
2/*
3 * Mini nslookup implementation for busybox
4 *
5 * Copyright (C) 1999,2000 by Lineo, inc. and John Beppu
6 * Copyright (C) 1999,2000,2001 by John Beppu <beppu@codepoet.org>
7 *
8 * Correct default name server display and explicit name server option
9 * added by Ben Zeckel <bzeckel@hmc.edu> June 2001
10 *
11 * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
12 */
13
14#include <resolv.h>
15#include "libbb.h"
16
17/*
18 *  I'm only implementing non-interactive mode;
19 *  I totally forgot nslookup even had an interactive mode.
20 */
21
22/* Examples of 'standard' nslookup output
23 * $ nslookup yahoo.com
24 * Server:         128.193.0.10
25 * Address:        128.193.0.10#53
26 *
27 * Non-authoritative answer:
28 * Name:   yahoo.com
29 * Address: 216.109.112.135
30 * Name:   yahoo.com
31 * Address: 66.94.234.13
32 *
33 * $ nslookup 204.152.191.37
34 * Server:         128.193.4.20
35 * Address:        128.193.4.20#53
36 *
37 * Non-authoritative answer:
38 * 37.191.152.204.in-addr.arpa     canonical name = 37.32-27.191.152.204.in-addr.arpa.
39 * 37.32-27.191.152.204.in-addr.arpa       name = zeus-pub2.kernel.org.
40 *
41 * Authoritative answers can be found from:
42 * 32-27.191.152.204.in-addr.arpa  nameserver = ns1.kernel.org.
43 * 32-27.191.152.204.in-addr.arpa  nameserver = ns2.kernel.org.
44 * 32-27.191.152.204.in-addr.arpa  nameserver = ns3.kernel.org.
45 * ns1.kernel.org  internet address = 140.211.167.34
46 * ns2.kernel.org  internet address = 204.152.191.4
47 * ns3.kernel.org  internet address = 204.152.191.36
48 */
49
50static int print_host(const char *hostname, const char *header)
51{
52	/* We can't use xhost2sockaddr() - we want to get ALL addresses,
53	 * not just one */
54
55	struct addrinfo *result = NULL;
56	int rc;
57	struct addrinfo hint;
58
59	memset(&hint, 0 , sizeof(hint));
60	/* hint.ai_family = AF_UNSPEC; - zero anyway */
61	/* Needed. Or else we will get each address thrice (or more)
62	 * for each possible socket type (tcp,udp,raw...): */
63	hint.ai_socktype = SOCK_STREAM;
64	// hint.ai_flags = AI_CANONNAME;
65	rc = getaddrinfo(hostname, NULL /*service*/, &hint, &result);
66
67	if (!rc) {
68		struct addrinfo *cur = result;
69		unsigned cnt = 0;
70
71		printf("%-10s %s\n", header, hostname);
72		// printf("%s\n", cur->ai_canonname); ?
73		while (cur) {
74			char *dotted, *revhost;
75			dotted = xmalloc_sockaddr2dotted_noport(cur->ai_addr);
76			revhost = xmalloc_sockaddr2hostonly_noport(cur->ai_addr);
77
78			printf("Address %u: %s%c", ++cnt, dotted, revhost ? ' ' : '\n');
79			if (revhost) {
80				puts(revhost);
81				if (ENABLE_FEATURE_CLEAN_UP)
82					free(revhost);
83			}
84			if (ENABLE_FEATURE_CLEAN_UP)
85				free(dotted);
86			cur = cur->ai_next;
87		}
88	} else {
89#if ENABLE_VERBOSE_RESOLUTION_ERRORS
90		bb_error_msg("can't resolve '%s': %s", hostname, gai_strerror(rc));
91#else
92		bb_error_msg("can't resolve '%s'", hostname);
93#endif
94	}
95	if (ENABLE_FEATURE_CLEAN_UP)
96		freeaddrinfo(result);
97	return (rc != 0);
98}
99
100/* lookup the default nameserver and display it */
101static void server_print(void)
102{
103	char *server;
104
105	server = xmalloc_sockaddr2dotted_noport((struct sockaddr*)&_res.nsaddr_list[0]);
106	/* I honestly don't know what to do if DNS server has _IPv6 address_.
107	 * Probably it is listed in
108	 * _res._u._ext_.nsaddrs[MAXNS] (of type "struct sockaddr_in6*" each)
109	 * but how to find out whether resolver uses
110	 * _res.nsaddr_list[] or _res._u._ext_.nsaddrs[], or both?
111	 * Looks like classic design from hell, BIND-grade. Hard to surpass. */
112	print_host(server, "Server:");
113	if (ENABLE_FEATURE_CLEAN_UP)
114		free(server);
115	puts("");
116}
117
118/* alter the global _res nameserver structure to use
119   an explicit dns server instead of what is in /etc/resolv.h */
120static void set_default_dns(char *server)
121{
122	struct in_addr server_in_addr;
123
124	if (inet_pton(AF_INET, server, &server_in_addr) > 0) {
125		_res.nscount = 1;
126		_res.nsaddr_list[0].sin_addr = server_in_addr;
127	}
128}
129
130int nslookup_main(int argc, char **argv);
131int nslookup_main(int argc, char **argv)
132{
133	/* We allow 1 or 2 arguments.
134	 * The first is the name to be looked up and the second is an
135	 * optional DNS server with which to do the lookup.
136	 * More than 3 arguments is an error to follow the pattern of the
137	 * standard nslookup */
138
139	if (argc < 2 || *argv[1] == '-' || argc > 3)
140		bb_show_usage();
141
142	/* initialize DNS structure _res used in printing the default
143	 * name server and in the explicit name server option feature. */
144	res_init();
145	/* rfc2133 says this enables IPv6 lookups */
146	/* (but it also says "may be enabled in /etc/resolv.conf|) */
147	/*_res.options |= RES_USE_INET6;*/
148
149	if (argc == 3)
150		set_default_dns(argv[2]);
151
152	server_print();
153	return print_host(argv[1], "Name:");
154}
155