--- a/src/lib-dns/Makefile.am	Wed Nov 16 21:36:17 2016 +0200
+++ b/src/lib-dns/Makefile.am	Fri Nov 11 13:13:29 2016 +0200
@@ -4,10 +4,12 @@
 	-I$(top_srcdir)/src/lib
 
 libdns_la_SOURCES = \
-	dns-lookup.c
+	dns-lookup.c \
+	dns-util.c
 
 headers = \
-	dns-lookup.h
+	dns-lookup.h \
+	dns-util.h
 
 pkginc_libdir=$(pkgincludedir)
 pkginc_lib_HEADERS = $(headers)

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/lib-dns/dns-util.c	Fri Nov 11 13:13:29 2016 +0200
@@ -0,0 +1,85 @@
+/* Copyright (c) 2010-2016 Dovecot authors, see the included COPYING file */
+#include "lib.h"
+#include "dns-util.h"
+
+/**
+  return first position from b->a of c or a if not found
+ */
+static inline
+const char *strchr_ba(const char *a, const char *b, char c)
+{
+	for(;b>a && *b != c; b--);
+	return b;
+}
+
+int dns_ncompare(const char *a, const char *b, size_t n)
+{
+	if (a == NULL && b == NULL) return 0;
+	if (a == NULL && b != NULL) return 1;
+	if (a != NULL && b == NULL) return -1;
+
+	for(size_t i = 0; i < n &&
+			  *a != '\0' &&
+			  *b != '\0' &&
+			  dns_tolower(*a) == dns_tolower(*b);
+	    i++, a++, b++);
+
+	return dns_tolower(*a) - dns_tolower(*b);
+}
+
+int dns_compare(const char *a, const char *b)
+{
+	return dns_ncompare(a, b, (size_t)-1);
+}
+
+int dns_compare_labels(const char *a, const char *b)
+{
+	if (a == NULL && b == NULL) return 0;
+	if (a == NULL && b != NULL) return 1;
+	if (a != NULL && b == NULL) return -1;
+
+	const char *ptr_a = a + strlen(a);
+	const char *ptr_b = b + strlen(b);
+	const char *label_a = ptr_a, *label_b = ptr_b;
+	int comp = 0;
+
+	while(comp == 0 && ptr_a > a && ptr_b > b) {
+		/* look for start of label, including dot */
+		label_a = strchr_ba(a, ptr_a, '.');
+		label_b = strchr_ba(b, ptr_b, '.');
+		if (ptr_a - label_a != ptr_b - label_b)
+			/* compare labels up to minimum length
+			   but include \0 to make sure that we
+			   don't consider alpha and alphabet
+			   equal */
+			return dns_ncompare(label_a, label_b,
+					   I_MIN(ptr_a - label_a,
+						 ptr_b - label_b)+1);
+		comp = dns_ncompare(label_a, label_b, ptr_a -label_a);
+		ptr_a = label_a - 1;
+		ptr_b = label_b - 1;
+	}
+
+	return dns_tolower(*label_a) - dns_tolower(*label_b);
+}
+
+int dns_match_wildcard(const char *name, const char *mask)
+{
+	i_assert(name != NULL && mask != NULL);
+
+	for(;*name != '\0' && *mask != '\0'; name++, mask++) {
+		switch(*mask) {
+		case '*':
+			name = strchr(name, '.');
+			if (name == NULL || mask[1] != '.') return -1;
+			mask++;
+			break;
+		case '?':
+			break;
+		default:
+			if (dns_tolower(*name) != dns_tolower(*mask)) return -1;
+		}
+	}
+	if (*mask == '*') mask++;
+	return dns_tolower(*name) == dns_tolower(*mask) ? 0 : -1;
+}

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/lib-dns/dns-util.h	Fri Nov 11 13:13:29 2016 +0200
@@ -0,0 +1,36 @@
+#ifndef DNS_UTIL_H
+#define DNS_UTIL_H 1
+
+static inline char
+dns_tolower(char c)
+{
+	if (c >= 'A' && c <= 'Z')
+		c+='a'-'A';
+	return c;
+}
+
+/**
+ * Will compare names in accordance with RFC4343
+ */
+int dns_compare(const char *a, const char *b) ATTR_PURE;
+int dns_ncompare(const char *a, const char *b, size_t n) ATTR_PURE;
+
+/**
+ * Same as above but done by labels from right to left
+ *
+ * www.example.org and www.example.net would be compared as
+ * org = net (return first difference)
+ * example = example
+ * www = www
+ */
+int dns_compare_labels(const char *a, const char *b) ATTR_PURE;
+
+/**
+ * Will match names in RFC4592 style
+ *
+ * this means *.foo.bar will match name.foo.bar
+ * but *DOES NOT* match something.name.foo.bar
+ */
+int dns_match_wildcard(const char *name, const char *mask) ATTR_PURE;
+
+#endif