github.com/afumu/libc@v0.0.6/musl/src/network/dn_comp.c (about)

     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  }