dns_packet.c

   1 /*
   2 DNS should have used LZ77 instead of its own sophomoric compression algorithm.
   3 */
   4
   5 #include "error.h"
   6 #include "dns.h"
   7
   8 unsigned int dns_packet_copy(const char *buf,unsigned int len,unsigned int pos,char *out,unsigned int outlen)
   9 {
  10   while (outlen) {
  11     if (pos >= len) { errno = error_proto; return 0; }
  12     *out = buf[pos++];
  13     ++out; --outlen;
  14   }
  15   return pos;
  16 }
  17
  18 unsigned int dns_packet_skipname(const char *buf,unsigned int len,unsigned int pos)
  19 {
  20   unsigned char ch;
  21
  22   for (;;) {
  23     if (pos >= len) break;
  24     ch = buf[pos++];
  25     if (ch >= 192) return pos + 1;
  26     if (ch >= 64) break;
  27     if (!ch) return pos;
  28     pos += ch;
  29   }
  30
  31   errno = error_proto;
  32   return 0;
  33 }
  34
  35 unsigned int dns_packet_getname(const char *buf,unsigned int len,unsigned int pos,char **d)
  36 {
  37   unsigned int loop = 0;
  38   unsigned int state = 0;
  39   unsigned int firstcompress = 0;
  40   unsigned int where;
  41   unsigned char ch;
  42   char name[255];
  43   unsigned int namelen = 0;
  44
  45   for (;;) {
  46     if (pos >= len) goto PROTO; ch = buf[pos++];
  47     if (++loop >= 1000) goto PROTO;
  48
  49     if (state) {
  50       if (namelen + 1 > sizeof name) goto PROTO; name[namelen++] = ch;
  51       --state;
  52     }
  53     else {
  54       while (ch >= 192) {
  55         where = ch; where -= 192; where <<= 8;
  56         if (pos >= len) goto PROTO; ch = buf[pos++];
  57         if (!firstcompress) firstcompress = pos;
  58         pos = where + ch;
  59         if (pos >= len) goto PROTO; ch = buf[pos++];
  60         if (++loop >= 1000) goto PROTO;
  61       }
  62       if (ch >= 64) goto PROTO;
  63       if (namelen + 1 > sizeof name) goto PROTO; name[namelen++] = ch;
  64       if (!ch) break;
  65       state = ch;
  66     }
  67   }
  68
  69   if (!dns_domain_copy(d,name)) return 0;
  70
  71   if (firstcompress) return firstcompress;
  72   return pos;
  73
  74   PROTO:
  75   errno = error_proto;
  76   return 0;
  77 }