/* MasqMail Copyright (C) Oliver Kurth,
 *
 * 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 2 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, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

#include <sys/types.h>
#include <netinet/in.h>
#include <arpa/nameser.h>
#include <resolv.h>

#include "masqmail.h"

#ifdef RESOLV_TEST

#undef DEBUG
#define DEBUG(x) if(x > 0)

#define debugf g_print
#endif

#ifdef ENABLE_RESOLVER

static union {
  HEADER hdr;
  unsigned char buf[PACKETSZ];
} response;
static unsigned char *resp_end;
static unsigned char *resp_pos;

static int num_answers;
static char name[MAX_DNSNAME];

unsigned short rr_type;
unsigned short rr_dlen;

static
unsigned short getshort(unsigned char *c)
{
  unsigned short u;
  u = c[0];
  return (u << 8) + c[1];
}

static
int dns_resolve(char *domain, int type, gboolean do_search)
{
  int n;
  int i;

  int resp_len;
  /*errno = 0;*/

  /*
  if (!stralloc_copy(&glue,domain)) return DNS_MEM;
  if (!stralloc_0(&glue)) return DNS_MEM;
  */

  //  resp_len = res_query(domain, C_IN, type, response.buf, sizeof(response));
  DEBUG(5) debugf("DNS: before res_search()\n");
  if(do_search)
    resp_len = res_search(domain, C_IN, type, response.buf, sizeof(response));
  else
    resp_len = res_query(domain, C_IN, type, response.buf, sizeof(response));
  DEBUG(5) debugf("DBG: after res_search()\n");

  if (resp_len <= 0){
    /*
    if (errno == ECONNREFUSED) return DNS_SOFT;
    if (h_errno == TRY_AGAIN) return DNS_SOFT;
    return DNS_HARD;
    */
    return -1;
  }
  if (resp_len >= sizeof(response))
    resp_len = sizeof(response);

  resp_end = response.buf + resp_len;
  resp_pos = response.buf + sizeof(HEADER);
  n = ntohs(response.hdr.qdcount);

  while (n-- > 0){
    i = dn_expand(response.buf, resp_end, resp_pos, name, MAX_DNSNAME);
    if (i < 0)
      return -1;
    DEBUG(5) debugf("DBG: resolve name = %s\n", name);
    resp_pos += i;
    i = resp_end - resp_pos;
    if (i < QFIXEDSZ)
      return -1;
    resp_pos += QFIXEDSZ;
  }
  num_answers = ntohs(response.hdr.ancount);

  return 0;
}

static int dns_next()
{
  int i;

  if (num_answers <= 0) return 2;
  num_answers--;

  if (resp_pos == resp_end)
    return -1 /* soft */;

  i = dn_expand(response.buf, resp_end, resp_pos, name, 256);
  if (i < 0)
    return -1; /* soft */
  resp_pos += i;

  i = resp_end - resp_pos;
  if (i < 4 + 3 * 2)
    return -1; /* soft */
   
  rr_type = getshort(resp_pos);
  rr_dlen = getshort(resp_pos + 8);
  resp_pos += 10;

  return 0;
}

static
int dns_getip(guint32 *ip)
{
  int ret;

  if((ret = dns_next())) return ret;

  if (rr_type == T_A){
    if (rr_dlen < 4)
      return -1; /* soft */
    *ip = *(guint32 *)(resp_pos);
    DEBUG(5) debugf("DNS: dns_getip(): ip = %s\n", inet_ntoa(*(struct in_addr*)ip));
    resp_pos += rr_dlen;

    return 1;
  }
  resp_pos += rr_dlen;
  return 0;
}

static
int dns_getmx(int *pref)
{
  int ret;

  if((ret = dns_next())) return ret;

  if (rr_type == T_MX){
    if (rr_dlen < 3)
      return -1; /* soft */

    *pref = (resp_pos[0] << 8) + resp_pos[1];
    if (dn_expand(response.buf, resp_end, resp_pos + 2, name, MAX_DNSNAME) < 0)
      return -1;
   
    resp_pos += rr_dlen;

    return 1;
  }
  resp_pos += rr_dlen;
  return 0;
}

/*
static
int dns_getname(int type)
{
  int ret;

  if((ret = dns_next())) return ret;

  if (rr_type == type){
    if (dn_expand(response.buf, resp_end, resp_pos, name, MAX_DNSNAME) < 0)
      return -1;
   
    resp_pos += rr_dlen;

    return 1;
  }
  resp_pos += rr_dlen;
  return 0;
}
*/

static
int dns_look_ip(gchar *domain, guint32 *ip)
{
  gchar *n = domain;

  while(TRUE){
    if(dns_resolve(n, T_A, FALSE) == 0){
      dns_next();
      if(rr_type == T_A){
	if (rr_dlen < 4)
	  return -1; /* soft */
	*ip = *(guint32 *)(resp_pos);
	
	DEBUG(5) debugf("DNS: dns_look_ip(): ip = %s\n",
			inet_ntoa(*(struct in_addr*)ip));
	
	resp_pos += rr_dlen;
	return 0;
      }else if(rr_type == T_CNAME){
	if (dn_expand(response.buf, resp_end, resp_pos, name, MAX_DNSNAME) < 0)
	  return -1;

	DEBUG(5) debugf("DNS: (CNAME) dns_look_ip(): name = %s\n", name);
	
	resp_pos += rr_dlen;
	n = name;
      }else
	return -1;
    }else
      return -1;
  }
}

GList *resolve_dns_a(GList *list, gchar *domain)
{
  int ret;

  DEBUG(5) debugf("DNS: resolve_dns_a entered\n");

  if(dns_resolve(domain, T_A, TRUE) == 0){
    mxip_addr mxip;
    while((ret = dns_getip(&(mxip.ip))) != 2){
      if(ret == 1){
	mxip.name = g_strdup(name);
	mxip.pref = 0;
	list = g_list_append(list, g_memdup(&mxip, sizeof(mxip)));
      }
    }
  }
  return list;
}

static
gint _mx_sort_func(gconstpointer aa, gconstpointer bb)
{
  const mxip_addr *a = (mxip_addr *)aa;
  const mxip_addr *b = (mxip_addr *)bb;

  if(a->pref == b->pref)
    return a->ip - b->ip;
  else
    return a->pref - b->pref;
}

GList *resolve_dns_mx(GList *list, gchar *domain)
{
  GList *node;
  int ret;
  int cnt = 0;

  DEBUG(5) debugf("DNS: resolve_dns_mx entered\n");

  if(dns_resolve(domain, T_MX, TRUE) == 0){
    GList *node_next;
    mxip_addr mxip;
    while((ret = dns_getmx(&(mxip.pref))) != 2){
      if(ret == 1){
	mxip.name = g_strdup(name);
	mxip.ip = rand();
	list = g_list_append(list, g_memdup(&mxip, sizeof(mxip)));
	cnt++;
      }
    }

    DEBUG(5) debugf("DNS: found %d mx records\n", cnt);

    /* to randomize sequences with equal pref values,
       we temporarily 'misused' the ip field and
       put a random number in it as a secondary sort key.
    */
    list = g_list_sort(list, _mx_sort_func);

    /* CNAME resolving has to be added as well. */

    for(node = g_list_first(list);
	node != NULL;
	node = node_next){

      mxip_addr *p_mxip = (mxip_addr *)(node->data);
      node_next = g_list_next(node);

      if(dns_look_ip(p_mxip->name, &(p_mxip->ip)) != 0){
	DEBUG(1) debugf("DNS: could not resolve target of mx %s\n", p_mxip->name);
	list = g_list_remove_link(list, node);
	g_free(node->data);
	g_list_free_1(node);
      }
    }
  }
  return list;
}

#endif

/* now something completely different... */

GList *resolve_byname(GList *list, gchar *domain)
{
  struct hostent *hent;

  DEBUG(5) debugf("DNS: resolve_byname entered\n");

  if((hent = gethostbyname(domain))){
    char *haddr;
    int i = 0;
    while((haddr = hent->h_addr_list[i++])){
      mxip_addr mxip;
      mxip.ip = *(guint32 *)(haddr);
      mxip.pref = 0;
      mxip.name = g_strdup(hent->h_name);
      list = g_list_append(list, g_memdup(&mxip, sizeof(mxip)));
    }
  }
  return list;
}

#ifdef RESOLV_TEST
int main(int argc, char *argv[])
{
  GList *addr_list = NULL, *node;

  g_print("starting res_init()\n");

  g_print("retrans = %d, retry = %d\n", _res.retrans, _res.retry);

  if(res_init() == 0){
    
    addr_list = resolve_dns_a(NULL, argv[1]);
    g_print("A:\n");

    foreach(addr_list, node){
      mxip_addr *p_mxip = (mxip_addr *)(node->data);
    
      printf("name = %s\n IP = %s\n",
	     p_mxip->name,
	     inet_ntoa(*(struct in_addr *)&(p_mxip->ip)));
    }
    addr_list = resolve_dns_mx(NULL, argv[1]);
    g_print("MX:\n");

    foreach(addr_list, node){
      mxip_addr *p_mxip = (mxip_addr *)(node->data);
    
      printf("name = %s\n IP = %s pref = %d\n",
	     p_mxip->name,
	     inet_ntoa(*(struct in_addr *)&(p_mxip->ip)),
	     p_mxip->pref);
    }
    {
      guint32 ip;
      dns_look_ip(argv[1], &ip);
      printf("dns_look_ip: %s\n", inet_ntoa(*((struct in_addr *)(&ip))));
    }
  }else
    printf("res_init() failed.\n");
  
}
#endif