/* vi: set sw=4 ts=4: */
/*
 * Mini nslookup implementation for busybox
 *
 * Copyright (C) 1999,2000 by Lineo, inc. and John Beppu
 * Copyright (C) 1999,2000,2001 by John Beppu <beppu@codepoet.org>
 *
 * Correct default name server display and explicit name server option
 * added by Ben Zeckel <bzeckel@hmc.edu> June 2001
 *
 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
 */
//config:config NSLOOKUP
//config:       bool "nslookup"
//config:       default y
//config:       help
//config:         nslookup is a tool to query Internet name servers.

//applet:IF_NSLOOKUP(APPLET(nslookup, BB_DIR_USR_BIN, BB_SUID_DROP))

//kbuild:lib-$(CONFIG_NSLOOKUP) += nslookup.o

//usage:#define nslookup_trivial_usage
//usage:       "[HOST] [SERVER]"
//usage:#define nslookup_full_usage "\n\n"
//usage:       "Query the nameserver for the IP address of the given HOST\n"
//usage:       "optionally using a specified DNS server"
//usage:
//usage:#define nslookup_example_usage
//usage:       "$ nslookup localhost\n"
//usage:       "Server:     default\n"
//usage:       "Address:    default\n"
//usage:       "\n"
//usage:       "Name:       debian\n"
//usage:       "Address:    127.0.0.1\n"

#include <resolv.h>
#include "libbb.h"

/*
 * I'm only implementing non-interactive mode;
 * I totally forgot nslookup even had an interactive mode.
 *
 * This applet is the only user of res_init(). Without it,
 * you may avoid pulling in _res global from libc.
 */

/* Examples of 'standard' nslookup output
 * $ nslookup yahoo.com
 * Server:         128.193.0.10
 * Address:        128.193.0.10#53
 *
 * Non-authoritative answer:
 * Name:   yahoo.com
 * Address: 216.109.112.135
 * Name:   yahoo.com
 * Address: 66.94.234.13
 *
 * $ nslookup 204.152.191.37
 * Server:         128.193.4.20
 * Address:        128.193.4.20#53
 *
 * Non-authoritative answer:
 * 37.191.152.204.in-addr.arpa     canonical name = 37.32-27.191.152.204.in-addr.arpa.
 * 37.32-27.191.152.204.in-addr.arpa       name = zeus-pub2.kernel.org.
 *
 * Authoritative answers can be found from:
 * 32-27.191.152.204.in-addr.arpa  nameserver = ns1.kernel.org.
 * 32-27.191.152.204.in-addr.arpa  nameserver = ns2.kernel.org.
 * 32-27.191.152.204.in-addr.arpa  nameserver = ns3.kernel.org.
 * ns1.kernel.org  internet address = 140.211.167.34
 * ns2.kernel.org  internet address = 204.152.191.4
 * ns3.kernel.org  internet address = 204.152.191.36
 */

static int print_host(const char *hostname, const char *header)
{
        /* We can't use xhost2sockaddr() - we want to get ALL addresses,
         * not just one */
        struct addrinfo *result = NULL;
        int rc;
        struct addrinfo hint;

        memset(&hint, 0 , sizeof(hint));
        /* hint.ai_family = AF_UNSPEC; - zero anyway */
        /* Needed. Or else we will get each address thrice (or more)
         * for each possible socket type (tcp,udp,raw...): */
        hint.ai_socktype = SOCK_STREAM;
        // hint.ai_flags = AI_CANONNAME;
        rc = getaddrinfo(hostname, NULL /*service*/, &hint, &result);

        if (rc == 0) {
                struct addrinfo *cur = result;
                unsigned cnt = 0;

                printf("%-10s %s\n", header, hostname);
                // puts(cur->ai_canonname); ?
                while (cur) {
                        char *dotted, *revhost;
                        dotted = xmalloc_sockaddr2dotted_noport(cur->ai_addr);
                        revhost = xmalloc_sockaddr2hostonly_noport(cur->ai_addr);

                        printf("Address %u: %s%c", ++cnt, dotted, revhost ? ' ' : '\n');
                        if (revhost) {
                                puts(revhost);
                                if (ENABLE_FEATURE_CLEAN_UP)
                                        free(revhost);
                        }
                        if (ENABLE_FEATURE_CLEAN_UP)
                                free(dotted);
                        cur = cur->ai_next;
                }
        } else {
#if ENABLE_VERBOSE_RESOLUTION_ERRORS
                bb_error_msg("can't resolve '%s': %s", hostname, gai_strerror(rc));
#else
                bb_error_msg("can't resolve '%s'", hostname);
#endif
        }
        if (ENABLE_FEATURE_CLEAN_UP && result)
                freeaddrinfo(result);
        return (rc != 0);
}

/* lookup the default nameserver and display it */
static void server_print(void)
{
        char *server;
        struct sockaddr *sa;

#if ENABLE_FEATURE_IPV6
        sa = (struct sockaddr*)_res._u._ext.nsaddrs[0];
        if (!sa)
#endif
                sa = (struct sockaddr*)&_res.nsaddr_list[0];
        server = xmalloc_sockaddr2dotted_noport(sa);

        print_host(server, "Server:");
        if (ENABLE_FEATURE_CLEAN_UP)
                free(server);
        bb_putchar('\n');
}

/* alter the global _res nameserver structure to use
   an explicit dns server instead of what is in /etc/resolv.conf */
static void set_default_dns(const char *server)
{
        len_and_sockaddr *lsa;

        if (!server)
                return;

        /* NB: this works even with, say, "[::1]:5353"! :) */
        lsa = xhost2sockaddr(server, 53);

        if (lsa->u.sa.sa_family == AF_INET) {
                _res.nscount = 1;
                /* struct copy */
                _res.nsaddr_list[0] = lsa->u.sin;
        }
#if ENABLE_FEATURE_IPV6
        /* Hoped libc can cope with IPv4 address there too.
         * No such luck, glibc 2.4 segfaults even with IPv6,
         * maybe I misunderstand how to make glibc use IPv6 addr?
         * (uclibc 0.9.31+ should work) */
        if (lsa->u.sa.sa_family == AF_INET6) {
                // glibc neither SEGVs nor sends any dgrams with this
                // (strace shows no socket ops):
                //_res.nscount = 0;
                _res._u._ext.nscount = 1;
                /* store a pointer to part of malloc'ed lsa */
                _res._u._ext.nsaddrs[0] = &lsa->u.sin6;
                /* must not free(lsa)! */
        }
#endif
}

int nslookup_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int nslookup_main(int argc, char **argv)
{
        /* We allow 1 or 2 arguments.
         * The first is the name to be looked up and the second is an
         * optional DNS server with which to do the lookup.
         * More than 3 arguments is an error to follow the pattern of the
         * standard nslookup */
        if (!argv[1] || argv[1][0] == '-' || argc > 3)
                bb_show_usage();

        /* initialize DNS structure _res used in printing the default
         * name server and in the explicit name server option feature. */
        res_init();
        /* rfc2133 says this enables IPv6 lookups */
        /* (but it also says "may be enabled in /etc/resolv.conf") */
        /*_res.options |= RES_USE_INET6;*/

        set_default_dns(argv[2]);

        server_print();

        /* getaddrinfo and friends are free to request a resolver
         * reinitialization. Just in case, set_default_dns() again
         * after getaddrinfo (in server_print). This reportedly helps
         * with bug 675 "nslookup does not properly use second argument"
         * at least on Debian Wheezy and Openwrt AA (eglibc based).
         */
        set_default_dns(argv[2]);

        return print_host(argv[1], "Name:");
}