shared: add new API to validate a string as hostname or IP address

src/shared/dns-domain.c

@@ -1324,3 +1324,15 @@ int dns_name_apply_idna(const char *name, char **ret) {
 
         return (int) n;
 }
+
+int dns_name_is_valid_or_address(const char *name) {
+        /* Returns > 0 if the specified name is either a valid IP address formatted as string or a valid DNS name */
+
+        if (isempty(name))
+                return 0;
+
+        if (in_addr_from_string_auto(name, NULL, NULL) >= 0)
+                return 1;
+
+        return dns_name_is_valid(name);
+}

src/shared/dns-domain.h

@@ -107,3 +107,5 @@ int dns_name_equal_skip(const char *a, unsigned n_labels, const char *b);
 int dns_name_common_suffix(const char *a, const char *b, const char **ret);
 
 int dns_name_apply_idna(const char *name, char **ret);
+
+int dns_name_is_valid_or_address(const char *name);

src/test/test-dns-domain.c

@@ -627,6 +627,18 @@ static void test_dns_name_apply_idna(void) {
         test_dns_name_apply_idna_one("föö.bär.", "xn--f-1gaa.xn--br-via");
 }
 
+static void test_dns_name_is_valid_or_address(void) {
+        assert_se(dns_name_is_valid_or_address(NULL) == 0);
+        assert_se(dns_name_is_valid_or_address("") == 0);
+        assert_se(dns_name_is_valid_or_address("foobar") > 0);
+        assert_se(dns_name_is_valid_or_address("foobar.com") > 0);
+        assert_se(dns_name_is_valid_or_address("foobar..com") == 0);
+        assert_se(dns_name_is_valid_or_address("foobar.com.") > 0);
+        assert_se(dns_name_is_valid_or_address("127.0.0.1") > 0);
+        assert_se(dns_name_is_valid_or_address("::") > 0);
+        assert_se(dns_name_is_valid_or_address("::1") > 0);
+}
+
 int main(int argc, char *argv[]) {
 
         test_dns_label_unescape();
@@ -654,6 +666,7 @@ int main(int argc, char *argv[]) {
         test_dns_name_compare_func();
         test_dns_name_common_suffix();
         test_dns_name_apply_idna();
+        test_dns_name_is_valid_or_address();
 
         return 0;
 }