accept trailing . and empty domain names

trailing . should be accepted in domain name strings by convention
(RFC 1034), host name lookup accepts "." but rejects empty "", res_*
interfaces also accept empty name following existing practice.

src/network/lookup_name.c

@@ -14,7 +14,7 @@
 static int is_valid_hostname(const char *host)
 {
 	const unsigned char *s;
-	if (strnlen(host, 254)-1 >= 253 || mbstowcs(0, host, 0) == -1) return 0;
+	if (strnlen(host, 255)-1 >= 254 || mbstowcs(0, host, 0) == -1) return 0;
 	for (s=(void *)host; *s>=0x80 || *s=='.' || *s=='-' || isalnum(*s); s++);
 	return !*s;
 }
@@ -152,8 +152,9 @@ int __lookup_name(struct address buf[static MAXADDRS], char canon[static 256], c
 
 	*canon = 0;
 	if (name) {
-		size_t l;
-		if ((l = strnlen(name, 254))-1 >= 253)
+		/* reject empty name and check len so it fits into temp bufs */
+		size_t l = strnlen(name, 255);
+		if (l-1 >= 254)
 			return EAI_NONAME;
 		memcpy(canon, name, l+1);
 	}

src/network/res_mkquery.c

@@ -10,13 +10,16 @@ int __res_mkquery(int op, const char *dname, int class, int type,
 	int id, i, j;
 	unsigned char q[280];
 	struct timespec ts;
-	size_t l = strnlen(dname, 254);
+	size_t l = strnlen(dname, 255);
+	int n;
 
-	if (l-1>=253 || buflen<18+l || op>15u || class>255u || type>255u)
+	if (l && dname[l-1]=='.') l--;
+	n = 17+l+!!l;
+	if (l>253 || buflen<n || op>15u || class>255u || type>255u)
 		return -1;
 
 	/* Construct query template - ID will be filled later */
-	memset(q, 0, 18+l);
+	memset(q, 0, n);
 	q[2] = op*8 + 1;
 	q[5] = 1;
 	memcpy((char *)q+13, dname, l);
@@ -34,8 +37,8 @@ int __res_mkquery(int op, const char *dname, int class, int type,
 	q[0] = id/256;
 	q[1] = id;
 
-	memcpy(buf, q, 18+l);
-	return 18+l;
+	memcpy(buf, q, n);
+	return n;
 }
 
 weak_alias(__res_mkquery, res_mkquery);

src/network/res_querydomain.c

@@ -3,10 +3,10 @@
 
 int res_querydomain(const char *name, const char *domain, int class, int type, unsigned char *dest, int len)
 {
-	char tmp[254];
-	size_t nl = strnlen(name, 254);
-	size_t dl = strnlen(domain, 254);
-	if (nl+dl+1 > 253) return -1;
+	char tmp[255];
+	size_t nl = strnlen(name, 255);
+	size_t dl = strnlen(domain, 255);
+	if (nl+dl+1 > 254) return -1;
 	memcpy(tmp, name, nl);
 	tmp[nl] = '.';
 	memcpy(tmp+nl+1, domain, dl+1);