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}