1 files changed, 102 insertions, 1 deletions
diff --git a/src/network/dn_comp.c b/src/network/dn_comp.c
index 4f4452aa..a17d434d 100644
--- a/src/network/dn_comp.c
+++ b/src/network/dn_comp.c
@@ -1,9 +1,110 @@
+#include <string.h>
 #include <resolv.h>
 #include "libc.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)
 {
-	return -1;
+	int i, j, n, m=0, offset, bestlen=0, bestoff;
+	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;
 }
 
 weak_alias(__dn_comp, dn_comp);