1#include <string.h>
  2#include <resolv.h>
  3
  4/* RFC 1035 message compression */
  5
  6/* label start offsets of a compressed domain name s */
  7static int getoffs(short *offs, const unsigned char *base, const unsigned char *s)
  8{
  9	int i=0;
 10	for (;;) {
 11		while (*s & 0xc0) {
 12			if ((*s & 0xc0) != 0xc0) return 0;
 13			s = base + ((s[0]&0x3f)<<8 | s[1]);
 14		}
 15		if (!*s) return i;
 16		if (s-base >= 0x4000) return 0;
 17		offs[i++] = s-base;
 18		s += *s + 1;
 19	}
 20}
 21
 22/* label lengths of an ascii domain name s */
 23static int getlens(unsigned char *lens, const char *s, int l)
 24{
 25	int i=0,j=0,k=0;
 26	for (;;) {
 27		for (; j<l && s[j]!='.'; j++);
 28		if (j-k-1u > 62) return 0;
 29		lens[i++] = j-k;
 30		if (j==l) return i;
 31		k = ++j;
 32	}
 33}
 34
 35/* longest suffix match of an ascii domain with a compressed domain name dn */
 36static int match(int *offset, const unsigned char *base, const unsigned char *dn,
 37	const char *end, const unsigned char *lens, int nlen)
 38{
 39	int l, o, m=0;
 40	short offs[128];
 41	int noff = getoffs(offs, base, dn);
 42	if (!noff) return 0;
 43	for (;;) {
 44		l = lens[--nlen];
 45		o = offs[--noff];
 46		end -= l;
 47		if (l != base[o] || memcmp(base+o+1, end, l))
 48			return m;
 49		*offset = o;
 50		m += l;
 51		if (nlen) m++;
 52		if (!nlen || !noff) return m;
 53		end--;
 54	}
 55}
 56
 57int dn_comp(const char *src, unsigned char *dst, int space, unsigned char **dnptrs, unsigned char **lastdnptr)
 58{
 59	int i, j, n, m=0, offset, bestlen=0, bestoff;
 60	unsigned char lens[127];
 61	unsigned char **p;
 62	const char *end;
 63	size_t l = strnlen(src, 255);
 64	if (l && src[l-1] == '.') l--;
 65	if (l>253 || space<=0) return -1;
 66	if (!l) {
 67		*dst = 0;
 68		return 1;
 69	}
 70	end = src+l;
 71	n = getlens(lens, src, l);
 72	if (!n) return -1;
 73
 74	p = dnptrs;
 75	if (p && *p) for (p++; *p; p++) {
 76		m = match(&offset, *dnptrs, *p, end, lens, n);
 77		if (m > bestlen) {
 78			bestlen = m;
 79			bestoff = offset;
 80			if (m == l)
 81				break;
 82		}
 83	}
 84
 85	/* encode unmatched part */
 86	if (space < l-bestlen+2+(bestlen-1 < l-1)) return -1;
 87	memcpy(dst+1, src, l-bestlen);
 88	for (i=j=0; i<l-bestlen; i+=lens[j++]+1)
 89		dst[i] = lens[j];
 90
 91	/* add tail */
 92	if (bestlen) {
 93		dst[i++] = 0xc0 | bestoff>>8;
 94		dst[i++] = bestoff;
 95	} else
 96		dst[i++] = 0;
 97
 98	/* save dst pointer */
 99	if (i>2 && lastdnptr && dnptrs && *dnptrs) {
100		while (*p) p++;
101		if (p+1 < lastdnptr) {
102			*p++ = dst;
103			*p=0;
104		}
105	}
106	return i;
107}