dns_txt.c

   1 #include "stralloc.h"
   2 #include "uint16.h"
   3 #include "byte.h"
   4 #include "dns.h"
   5
   6 int dns_txt_packet(stralloc *out,const char *buf,unsigned int len)
   7 {
   8   unsigned int pos;
   9   char header[12];
  10   uint16 numanswers;
  11   uint16 datalen;
  12   char ch;
  13   unsigned int txtlen;
  14   int i;
  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_TXT))
  28       if (byte_equal(header + 2,2,DNS_C_IN)) {
  29         if (pos + datalen > len) return -1;
  30         txtlen = 0;
  31         for (i = 0;i < datalen;++i) {
  32           ch = buf[pos + i];
  33           if (!txtlen)
  34             txtlen = (unsigned char) ch;
  35           else {
  36             --txtlen;
  37             if (ch < 32) ch = '?';
  38             if (ch > 126) ch = '?';
  39             if (!stralloc_append(out,&ch)) return -1;
  40           }
  41         }
  42       }
  43     pos += datalen;
  44   }
  45
  46   return 0;
  47 }
  48
  49 static char *q = 0;
  50
  51 int dns_txt(stralloc *out,const stralloc *fqdn)
  52 {
  53   if (!dns_domain_fromdot(&q,fqdn->s,fqdn->len)) return -1;
  54   if (dns_resolve(q,DNS_T_TXT) == -1) return -1;
  55   if (dns_txt_packet(out,dns_resolve_tx.packet,dns_resolve_tx.packetlen) == -1) return -1;
  56   dns_transmit_free(&dns_resolve_tx);
  57   dns_domain_free(&q);
  58   return 0;
  59 }