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#include <string.h>
#include <resolv.h>
/* RFC 1035 message compression */
/* label start offsets of a compressed domain name s */
static int getoffs(short *offs, const unsigned char *base, const unsigned char *s)
{
int i=0;
for (;;) {
while (*s & 0xc0) {
if ((*s & 0xc0) != 0xc0) return 0;
s = base + ((s[0]&0x3f)<<8 | s[1]);
}
if (!*s) return i;
if (s-base >= 0x4000) return 0;
offs[i++] = s-base;
s += *s + 1;
}
}
/* label lengths of an ascii domain name s */
static int getlens(unsigned char *lens, const char *s, int l)
{
int i=0,j=0,k=0;
for (;;) {
for (; j<l && s[j]!='.'; j++);
if (j-k-1u > 62) return 0;
lens[i++] = j-k;
if (j==l) return i;
k = ++j;
}
}
/* longest suffix match of an ascii domain with a compressed domain name dn */
static int match(int *offset, const unsigned char *base, const unsigned char *dn,
const char *end, const unsigned char *lens, int nlen)
{
int l, o, m=0;
short offs[128];
int noff = getoffs(offs, base, dn);
if (!noff) return 0;
for (;;) {
l = lens[--nlen];
o = offs[--noff];
end -= l;
if (l != base[o] || memcmp(base+o+1, end, l))
return m;
*offset = o;
m += l;
if (nlen) m++;
if (!nlen || !noff) return m;
end--;
}
}
int dn_comp(const char *src, unsigned char *dst, int space, unsigned char **dnptrs, unsigned char **lastdnptr)
{
int i, j, n, m=0, offset, bestlen=0, bestoff;
unsigned char lens[127];
unsigned char **p;
const char *end;
size_t l = strnlen(src, 255);
if (l && src[l-1] == '.') l--;
if (l>253 || space<=0) return -1;
if (!l) {
*dst = 0;
return 1;
}
end = src+l;
n = getlens(lens, src, l);
if (!n) return -1;
p = dnptrs;
if (p && *p) for (p++; *p; p++) {
m = match(&offset, *dnptrs, *p, end, lens, n);
if (m > bestlen) {
bestlen = m;
bestoff = offset;
if (m == l)
break;
}
}
/* encode unmatched part */
if (space < l-bestlen+2+(bestlen-1 < l-1)) return -1;
memcpy(dst+1, src, l-bestlen);
for (i=j=0; i<l-bestlen; i+=lens[j++]+1)
dst[i] = lens[j];
/* add tail */
if (bestlen) {
dst[i++] = 0xc0 | bestoff>>8;
dst[i++] = bestoff;
} else
dst[i++] = 0;
/* save dst pointer */
if (i>2 && lastdnptr && dnptrs && *dnptrs) {
while (*p) p++;
if (p+1 < lastdnptr) {
*p++ = dst;
*p=0;
}
}
return i;
}
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