#include "byte.h"
#include "dnsresolv.h"
#include "stralloc.h"
#include "uint_t.h"

/**
  @file dns_mx.c
  @author djb
  @ref qmail
  @brief dns MX query
  @param (on output) stralloc out
*/

static char *q = 0;

int dns_mx_packet(stralloc *out, const char *buf, unsigned int len)
{
  unsigned int pos;
  char header[12];
  char pref[2];
  uint16 numanswers;
  uint16 datalen;
  int ranswers = 0;

  if (!stralloc_copys(out, "")) return DNS_MEM;

  pos = dns_packet_copy(buf, len, 0, header, 12);
  if (!pos) return DNS_ERR;
  uint16_unpack_big(header + 6, &numanswers);
  pos = dns_packet_skipname(buf, len, pos);
  if (!pos) return DNS_ERR;
  pos += 4;

  while (numanswers--) {
    pos = dns_packet_skipname(buf, len, pos);
    if (!pos) return DNS_ERR;
    pos = dns_packet_copy(buf, len, pos, header, 10);
    if (!pos) return DNS_ERR;
    uint16_unpack_big(header + 8, &datalen);
    if (byte_equal(header, 2, DNS_T_MX)) {
      if (byte_equal(header + 2, 2, DNS_C_IN)) {
        if (!dns_packet_copy(buf, len, pos, pref, 2)) return DNS_ERR;
        if (!dns_packet_getname(buf, len, pos + 2, &q)) return DNS_ERR;
        if (!stralloc_catb(out, pref, 2)) return DNS_MEM;
        if (dns_domain_todot_cat(out, q) <= 0) return DNS_ERR;
        if (!stralloc_0(out)) return DNS_MEM;
      }
    }
    pos += datalen;
    ++ranswers;
  }

  return ranswers;
}

int dns_mx(stralloc *out, const stralloc *fqdn)
{
  int rc = 0;

  if (dns_domain_fromdot(&q, fqdn->s, fqdn->len) <= 0) return DNS_ERR;
  if (dns_resolve(q, DNS_T_MX) >= 0) {
    if ((rc = dns_mx_packet(out, dns_resolve_tx.packet, dns_resolve_tx.packetlen)) < 0) return DNS_ERR;
    dns_transmit_free(&dns_resolve_tx);
    dns_domain_free(&q);
  }

  return rc;
}