dns_packet.c

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/*
DNS should have used LZ77 instead of its own sophomoric compression algorithm.
*/
 
#include "error.h"
#include "dns.h"
 
unsigned int dns_packet_copy(const char *buf,unsigned int len,unsigned int pos,char *out,unsigned int outlen)
{
  while (outlen) {
    if (pos >= len) { errno = EPROTO ; return 0; }
    *out = buf[pos++];
    ++out; --outlen;
  }
  return pos;
}
 
unsigned int dns_packet_skipname(const char *buf,unsigned int len,unsigned int pos)
{
  unsigned char ch;
 
  for (;;) {
    if (pos >= len) break;
    ch = buf[pos++];
    if (ch >= 192) return pos + 1;
    if (ch >= 64) break;
    if (!ch) return pos;
    pos += ch;
  }
 
  errno = EPROTO;
  return 0;
}
 
unsigned int dns_packet_getname(const char *buf,unsigned int len,unsigned int pos,char **d)
{
  unsigned int loop = 0;
  unsigned int state = 0;
  unsigned int firstcompress = 0;
  unsigned int where;
  unsigned char ch;
  char name[511];
  unsigned int namelen = 0;
 
  for (;;) {
    if (pos >= len) goto PROTO; 
    ch = buf[pos++];
    if (++loop >= 1000) goto PROTO;
 
    if (state) {
      if (namelen + 1 > sizeof(name)) goto PROTO; 
      name[namelen++] = ch;
      --state;
    } else {
      while (ch >= 192) {
        where = ch; where -= 192; where <<= 8;
        if (pos >= len) goto PROTO; 
        ch = buf[pos++];
        if (!firstcompress) firstcompress = pos;
        pos = where + ch;
        if (pos >= len) goto PROTO; 
        ch = buf[pos++];
        if (++loop >= 1000) goto PROTO;
      }
      if (ch >= 64) goto PROTO;
      if (namelen + 1 > sizeof(name)) goto PROTO; 
      name[namelen++] = ch;
      if (!ch) break;
      state = ch;
    }
  }
 
  if (!dns_domain_copy(d,name)) return 0;
 
  if (firstcompress) return firstcompress;
  return pos;
 
  PROTO:
  errno = EPROTO;
  return 0;
}