/*-*- mode:c;indent-tabs-mode:t;c-basic-offset:8;tab-width:8;coding:utf-8   -*-│
│ vi: set noet ft=c ts=8 sw=8 fenc=utf-8                                   :vi │
╚──────────────────────────────────────────────────────────────────────────────╝
│                                                                              │
│  Musl Libc                                                                   │
│  Copyright © 2005-2014 Rich Felker, et al.                                   │
│                                                                              │
│  Permission is hereby granted, free of charge, to any person obtaining       │
│  a copy of this software and associated documentation files (the             │
│  "Software"), to deal in the Software without restriction, including         │
│  without limitation the rights to use, copy, modify, merge, publish,         │
│  distribute, sublicense, and/or sell copies of the Software, and to          │
│  permit persons to whom the Software is furnished to do so, subject to       │
│  the following conditions:                                                   │
│                                                                              │
│  The above copyright notice and this permission notice shall be              │
│  included in all copies or substantial portions of the Software.             │
│                                                                              │
│  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,             │
│  EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF          │
│  MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.      │
│  IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY        │
│  CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,        │
│  TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE           │
│  SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                      │
│                                                                              │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "third_party/musl/resolv.h"
#include "libc/str/str.h"

/* RFC 1035 message compression */

/* label start offsets of a compressed domain name s */
static int getoffs(short *offs,
		   const unsigned char *base,
		   const unsigned char *s)
{
	int i=0;
	for (;;) {
		while (*s & 0xc0) {
			if ((*s & 0xc0) != 0xc0) return 0;
			s = base + ((s[0]&0x3f)<<8 | s[1]);
		}
		if (!*s) return i;
		if (s-base >= 0x4000) return 0;
		offs[i++] = s-base;
		s += *s + 1;
	}
}

/* label lengths of an ascii domain name s */
static int getlens(unsigned char *lens, const char *s, int l)
{
	int i=0,j=0,k=0;
	for (;;) {
		for (; j<l && s[j]!='.'; j++);
		if (j-k-1u > 62) return 0;
		lens[i++] = j-k;
		if (j==l) return i;
		k = ++j;
	}
}

/* longest suffix match of an ascii domain with a compressed domain name dn */
static int match(int *offset,
		 const unsigned char *base,
		 const unsigned char *dn,
		 const char *end,
		 const unsigned char *lens,
		 int nlen)
{
	int l, o, m=0;
	short offs[128];
	int noff = getoffs(offs, base, dn);
	if (!noff) return 0;
	for (;;) {
		l = lens[--nlen];
		o = offs[--noff];
		end -= l;
		if (l != base[o] || memcmp(base+o+1, end, l))
			return m;
		*offset = o;
		m += l;
		if (nlen) m++;
		if (!nlen || !noff) return m;
		end--;
	}
}

int dn_comp(const char *src,
	    unsigned char *dst,
	    int space,
	    unsigned char **dnptrs,
	    unsigned char **lastdnptr)
{
	int i, j, n, m=0, offset, bestlen=0, bestoff=0;
	unsigned char lens[127];
	unsigned char **p;
	const char *end;
	size_t l = strnlen(src, 255);
	if (l && src[l-1] == '.') l--;
	if (l>253 || space<=0) return -1;
	if (!l) {
		*dst = 0;
		return 1;
	}
	end = src+l;
	n = getlens(lens, src, l);
	if (!n) return -1;

	p = dnptrs;
	if (p && *p) for (p++; *p; p++) {
		m = match(&offset, *dnptrs, *p, end, lens, n);
		if (m > bestlen) {
			bestlen = m;
			bestoff = offset;
			if (m == l)
				break;
		}
	}

	/* encode unmatched part */
	if (space < l-bestlen+2+(bestlen-1 < l-1)) return -1;
	memcpy(dst+1, src, l-bestlen);
	for (i=j=0; i<l-bestlen; i+=lens[j++]+1)
		dst[i] = lens[j];

	/* add tail */
	if (bestlen) {
		dst[i++] = 0xc0 | bestoff>>8;
		dst[i++] = bestoff;
	} else
		dst[i++] = 0;

	/* save dst pointer */
	if (i>2 && lastdnptr && dnptrs && *dnptrs) {
		while (*p) p++;
		if (p+1 < lastdnptr) {
			*p++ = dst;
			*p=0;
		}
	}
	return i;
}