dns_txt.c

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#include "stralloc.h"
#include "uint_t.h"
#include "byte.h"
#include "dnsresolv.h"
 
int dns_txt_packet(stralloc *out,const char *buf,unsigned int len)
{
  unsigned int pos;
  char header[12];
  uint16 numanswers;
  uint16 datalen;
  char ch;
  unsigned int txtlen;
  int i;
  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_TXT))
      if (byte_equal(header + 2,2,DNS_C_IN)) {
        if (pos + datalen > len) return DNS_ERR;
        txtlen = (unsigned char) buf[pos];
        for (i = 1; i < datalen; ++i) {
          ch = buf[pos + i];
          if (i == txtlen + 1)     // next label
            txtlen += (unsigned char) ch + 1;
          else {
            if (ch < 32) ch = '?';
            if (ch > 126) ch = '?';
            if (!stralloc_append(out,&ch)) return DNS_MEM;
          }
        }
        if (txtlen) if (!stralloc_append(out,"\n")) return DNS_MEM;
      }
    pos += datalen;
    ++ranswers;
  }
 
  return ranswers;
}
 
static char *q = 0;
 
int dns_txt(stralloc *out,const stralloc *fqdn)
{
  int rc; 
 
  if (dns_domain_fromdot(&q,fqdn->s,fqdn->len) <= 0) return DNS_ERR;
  if (dns_resolve(q,DNS_T_TXT) < 0) return DNS_ERR;
  if ((rc = dns_txt_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;
}