dns_mx.c

   1 #include "stralloc.h"
   2 #include "byte.h"
   3 #include "uint16.h"
   4 #include "dns.h"
   5
   6 static char *q = 0;
   7
   8 int dns_mx_packet(stralloc *out,const char *buf,unsigned int len)
   9 {
  10   unsigned int pos;
  11   char header[12];
  12   char pref[2];
  13   uint16 numanswers;
  14   uint16 datalen;
  15
  16   if (!stralloc_copys(out,"")) return -1;
  17
  18   pos = dns_packet_copy(buf,len,0,header,12); if (!pos) return -1;
  19   uint16_unpack_big(header + 6,&numanswers);
  20   pos = dns_packet_skipname(buf,len,pos); if (!pos) return -1;
  21   pos += 4;
  22
  23   while (numanswers--) {
  24     pos = dns_packet_skipname(buf,len,pos); if (!pos) return -1;
  25     pos = dns_packet_copy(buf,len,pos,header,10); if (!pos) return -1;
  26     uint16_unpack_big(header + 8,&datalen);
  27     if (byte_equal(header,2,DNS_T_MX))
  28       if (byte_equal(header + 2,2,DNS_C_IN)) {
  29         if (!dns_packet_copy(buf,len,pos,pref,2)) return -1;
  30         if (!dns_packet_getname(buf,len,pos + 2,&q)) return -1;
  31         if (!stralloc_catb(out,pref,2)) return -1;
  32         if (!dns_domain_todot_cat(out,q)) return -1;
  33         if (!stralloc_0(out)) return -1;
  34       }
  35     pos += datalen;
  36   }
  37
  38   return 0;
  39 }
  40
  41 int dns_mx(stralloc *out,const stralloc *fqdn)
  42 {
  43   if (!dns_domain_fromdot(&q,fqdn->s,fqdn->len)) return -1;
  44   if (dns_resolve(q,DNS_T_MX) == -1) return -1;
  45   if (dns_mx_packet(out,dns_resolve_tx.packet,dns_resolve_tx.packetlen) == -1) return -1;
  46   dns_transmit_free(&dns_resolve_tx);
  47   dns_domain_free(&q);
  48   return 0;
  49 }