src/network/dn_comp.c

   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 */
   7 static 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 */
  23 static 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 */
  36 static 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
  57 int 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 }