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