dnl AC_C_DNS
 dnl Checks resolv.h presence and usability
 dnl Checks for specific lresolv exports
 dnl Checks for lresolve reentrance
 dnl
 dnl Note using AC_LINK_IFELSE instead of AC_CHECK_LIB
 dnl as symbols are often redefined in resolv.h
 
 AC_DEFUN([AC_C_DNS], [
 
 AC_ARG_ENABLE([dns],
     AC_HELP_STRING([--disable-dns], [disable support for database verification through DNS]),
     [want_dns=$enableval], [want_dns=yes]
 )
 if test $want_dns = yes; then
     AC_CHECK_HEADER([resolv.h],
 	[
 	    bklibs=$LIBS;
 	    LIBS=-lresolv;
 	    AC_CACHE_CHECK([for dn_expand in -lresolv], [ac_cv_have_lresolv], [
 	        ac_cv_have_lresolv=no;
 		AC_LINK_IFELSE([
 #include <sys/types.h>
 #include <netinet/in.h>
 #include <arpa/nameser.h>
 #include <resolv.h>
 int main() { return (int)dn_expand; }
     	     	],
 		[
 		    ac_cv_have_lresolv=yes;
 		])
 	    ])
 	    LIBS=$bklibs;
 	],
 	[],
 	[
 #include <sys/types.h>
 #include <netinet/in.h>
 #include <arpa/nameser.h>
     ])
     if test "x$ac_cv_have_lresolv" = "xyes"; then
     	FRESHCLAM_LIBS="$FRESHCLAM_LIBS -lresolv";
 	CLAMAV_MILTER_LIBS="$CLAMAV_MILTER_LIBS -lresolv";
 	bklibs=$LIBS;
 	LIBS=-lresolv;
 	AC_DEFINE([HAVE_RESOLV_H],1,[have resolv.h])
 	AC_CACHE_CHECK([for res_nquery in -lresolv], [ac_cv_have_lresolv_r], [
 	    ac_cv_have_lresolv_r=no;
 	    AC_LINK_IFELSE([
 #include <sys/types.h>
 #include <netinet/in.h>
 #include <arpa/nameser.h>
 #include <resolv.h>
 int main() { return (int)res_nquery; }
     	    ],
 	    [
 	        ac_cv_have_lresolv_r=yes;
 	    ]),
 	])
 	LIBS=$bklibs;
 	if test "x$ac_cv_have_lresolv_r" = "xyes"; then
 	    AC_DEFINE([HAVE_LRESOLV_R],1,[Define to 1 if -lresolv provides thread safe API's like res_nquery])
 	fi
     else
 	AC_MSG_WARN([****** DNS support disabled])
     fi
 fi
 
 ])