/*-
 * SPDX-License-Identifier: BSD-2-Clause
 *
 * Copyright (c) 2012-2013 Baptiste Daroussin <bapt@FreeBSD.org>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer,
 *    without modification, immediately at the beginning of the file.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include <sys/cdefs.h>
#include <stdlib.h>
#include <string.h>
#include <netinet/in.h>
#include <resolv.h>

#include "dns_utils.h"

typedef union {
        HEADER hdr;
        unsigned char buf[1024];
} dns_query;

static int
srv_priority_cmp(const void *a, const void *b)
{
        const struct dns_srvinfo *da, *db;
        unsigned int r, l;

        da = *(struct dns_srvinfo * const *)a;
        db = *(struct dns_srvinfo * const *)b;

        l = da->priority;
        r = db->priority;

        return ((l > r) - (l < r));
}

static int
srv_final_cmp(const void *a, const void *b)
{
        const struct dns_srvinfo *da, *db;
        unsigned int r, l, wr, wl;
        int res;

        da = *(struct dns_srvinfo * const *)a;
        db = *(struct dns_srvinfo * const *)b;

        l = da->priority;
        r = db->priority;

        res = ((l > r) - (l < r));

        if (res == 0) {
                wl = da->finalweight;
                wr = db->finalweight;
                res = ((wr > wl) - (wr < wl));
        }

        return (res);
}

static void
compute_weight(struct dns_srvinfo **d, int first, int last)
{
        int i, j, totalweight;
        int *chosen;

        totalweight = 0;

        for (i = 0; i <= last; i++)
                totalweight += d[i]->weight;

        if (totalweight == 0)
                return;

        chosen = malloc(sizeof(int) * (last - first + 1));

        for (i = 0; i <= last; i++) {
                for (;;) {
                        chosen[i] = arc4random_uniform(d[i]->weight * 100 /
                            totalweight);
                        for (j = 0; j < i; j++) {
                                if (chosen[i] == chosen[j])
                                        break;
                        }
                        if (j == i) {
                                d[i]->finalweight = chosen[i];
                                break;
                        }
                }
        }

        free(chosen);
}

struct dns_srvinfo *
dns_getsrvinfo(const char *zone)
{
        struct dns_srvinfo **res, *first;
        unsigned char *end, *p;
        char host[MAXHOSTNAMELEN];
        dns_query q;
        int len, qdcount, ancount, n, i, f, l;
        unsigned int type, class, ttl, priority, weight, port;

        if ((len = res_query(zone, C_IN, T_SRV, q.buf, sizeof(q.buf))) == -1 ||
            len < (int)sizeof(HEADER))
                return (NULL);

        qdcount = ntohs(q.hdr.qdcount);
        ancount = ntohs(q.hdr.ancount);

        end = q.buf + len;
        p = q.buf + sizeof(HEADER);

        while(qdcount > 0 && p < end) {
                qdcount--;
                if((len = dn_expand(q.buf, end, p, host, MAXHOSTNAMELEN)) < 0)
                        return (NULL);
                p += len + NS_QFIXEDSZ;
        }

        res = calloc(ancount, sizeof(struct dns_srvinfo *));
        if (res == NULL)
                return (NULL);

        n = 0;
        while (ancount > 0 && p < end) {
                ancount--;
                len = dn_expand(q.buf, end, p, host, MAXHOSTNAMELEN);
                if (len < 0) {
                        for (i = 0; i < n; i++)
                                free(res[i]);
                        free(res);
                        return NULL;
                }

                p += len;

                NS_GET16(type, p);
                NS_GET16(class, p);
                NS_GET32(ttl, p);
                NS_GET16(len, p);

                if (type != T_SRV) {
                        p += len;
                        continue;
                }

                NS_GET16(priority, p);
                NS_GET16(weight, p);
                NS_GET16(port, p);

                len = dn_expand(q.buf, end, p, host, MAXHOSTNAMELEN);
                if (len < 0) {
                        for (i = 0; i < n; i++)
                                free(res[i]);
                        free(res);
                        return (NULL);
                }

                res[n] = malloc(sizeof(struct dns_srvinfo));
                if (res[n] == NULL) {
                        for (i = 0; i < n; i++)
                                free(res[i]);
                        free(res);
                        return (NULL);
                }
                res[n]->type = type;
                res[n]->class = class;
                res[n]->ttl = ttl;
                res[n]->priority = priority;
                res[n]->weight = weight;
                res[n]->port = port;
                res[n]->next = NULL;
                strlcpy(res[n]->host, host, MAXHOSTNAMELEN);

                p += len;
                n++;
        }

        qsort(res, n, sizeof(res[0]), srv_priority_cmp);

        priority = f = l = 0;
        for (i = 0; i < n; i++) {
                if (res[i]->priority != priority) {
                        if (f != l)
                                compute_weight(res, f, l);
                        f = i;
                        priority = res[i]->priority;
                }
                l = i;
        }

        qsort(res, n, sizeof(res[0]), srv_final_cmp);

        for (i = 0; i < n - 1; i++)
                res[i]->next = res[i + 1];

        first = res[0];
        free(res);

        return (first);
}