/*
 *  $Id: libnet_build_dns.c,v 1.10 2004/04/13 17:32:28 mike Exp $
 *
 *  libnet
 *  libnet_build_dns.c - DNS packet assembler
 *
 *  Copyright (c) 1998 - 2004 Mike D. Schiffman <mike@infonexus.com>
 *  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.
 * 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 AND CONTRIBUTORS ``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 OR CONTRIBUTORS 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 "common.h"


libnet_ptag_t
libnet_build_dnsv4(uint16_t h_len, uint16_t id, uint16_t flags,
            uint16_t num_q, uint16_t num_anws_rr, uint16_t num_auth_rr,
            uint16_t num_addi_rr, const uint8_t *payload, uint32_t payload_s,
            libnet_t *l, libnet_ptag_t ptag)
{

    uint32_t n, h;
    uint32_t offset;
    libnet_pblock_t *p;
    struct libnet_dnsv4_hdr dns_hdr;

    if (l == NULL)
    { 
        return (-1);
    } 

    if (h_len != LIBNET_UDP_DNSV4_H && h_len != LIBNET_TCP_DNSV4_H)
    {
        snprintf(l->err_buf, LIBNET_ERRBUF_SIZE,
                "%s(): invalid header length: %d", __func__, h_len);
       return (-1);
    }
    offset = (h_len == LIBNET_UDP_DNSV4_H ? sizeof(dns_hdr.h_len) : 0);
    n = h_len + payload_s;
    h = 0;          /* no checksum */

    /*
     *  Find the existing protocol block if a ptag is specified, or create
     *  a new one.
     */
    p = libnet_pblock_probe(l, ptag, n, LIBNET_PBLOCK_DNSV4_H);
    if (p == NULL)
    {
        return (-1);
    }

    /*
     * The sizeof(dns_hdr.h_len) is not counted is the packet size
     * for TCP packet.
     * And since this will be ignored for udp packets, let's compute it 
     * anyway.
     */
    memset(&dns_hdr, 0, sizeof(dns_hdr));
    dns_hdr.h_len       = htons((u_short)(n - sizeof (dns_hdr.h_len)));
    dns_hdr.id          = htons(id);
    dns_hdr.flags       = htons(flags);
    dns_hdr.num_q       = htons(num_q);
    dns_hdr.num_answ_rr = htons(num_anws_rr);
    dns_hdr.num_auth_rr = htons(num_auth_rr);
    dns_hdr.num_addi_rr = htons(num_addi_rr);

    /*
     * A dirty trick: DNS can be either TCP or UDP based, and depending on
     * that, the header changes. A 'length' field is present in TCP packets,
     * but not in UDP packets. As they are the first 2 bytes of the header,
     * they are skipped if the packet is UDP...
     */
    n = libnet_pblock_append(l, p, ((uint8_t *)&dns_hdr) + offset, h_len);
    if (n == -1)
    {
        goto bad;
    }

    /* boilerplate payload sanity check / append macro */
    LIBNET_DO_PAYLOAD(l, p);
 
    return (ptag ? ptag : libnet_pblock_update(l, p, h, LIBNET_PBLOCK_DNSV4_H));
bad:
    libnet_pblock_delete(l, p);
    return (-1);
}

/* EOF */
