shared,core: extend nm_utils_is_specific_hostname() and move to shared

nm_utils_is_specific_hostname() is basically to check whether the
hostname is localhost (and also handle "(null)").

In that sense, it's similar to systemd's is_localhost(). Extend or
variant to

  - be case insensitive (like is_localhost()).

  - accept more variants of localhost/localdomain names as special.

shared/nm-glib-aux/nm-shared-utils.c

@@ -5157,3 +5157,81 @@ _nm_utils_format_variant_attributes (GHashTable *attributes,
 	                                          key_value_separator);
 	return g_string_free (str, FALSE);
 }
+
+/*****************************************************************************/
+
+gboolean
+nm_utils_is_localhost (const char *name)
+{
+	static const char *const NAMES[] = {
+		"localhost",
+		"localhost4",
+		"localhost6",
+		"localhost.localdomain",
+		"localhost4.localdomain4",
+		"localhost6.localdomain6",
+	};
+	gsize name_len;
+	int i;
+
+	if (!name)
+		return FALSE;
+
+	/* This tries to identify local host and domain names
+	 * described in RFC6761 plus the redhatism of localdomain.
+	 *
+	 * Similar to systemd's is_localhost(). */
+
+	name_len = strlen (name);
+
+	if (name_len == 0)
+		return FALSE;
+
+	if (name[name_len - 1] == '.') {
+		/* one trailing dot is fine. Hide it. */
+		name_len--;
+	}
+
+	for (i = 0; i < (int) G_N_ELEMENTS (NAMES); i++) {
+		const char *n = NAMES[i];
+		gsize l = strlen (n);
+		gsize s;
+
+		if (name_len < l)
+			continue;
+
+		s = name_len - l;
+
+		if (g_ascii_strncasecmp (&name[s], n, l) != 0)
+			continue;
+
+		/* we accept the name if it is equal to one of the well-known names,
+		 * or if it is some prefix, a '.' and the well-known name. */
+		if (s == 0)
+			return TRUE;
+		if (name[s - 1] == '.')
+			return TRUE;
+	}
+
+	return FALSE;
+}
+
+gboolean
+nm_utils_is_specific_hostname (const char *name)
+{
+	if (nm_str_is_empty (name))
+		return FALSE;
+
+	if (nm_streq (name, "(none)")) {
+		/* This is not a special hostname. Probably an artefact by somebody wrongly
+		 * printing NULL. */
+		return FALSE;
+	}
+
+	if (nm_utils_is_localhost (name))
+		return FALSE;
+
+	/* FIXME: properly validate the hostname, like systemd's hostname_is_valid() */
+
+	return TRUE;
+}

shared/nm-glib-aux/nm-shared-utils.h

@@ -2195,4 +2195,10 @@ char *_nm_utils_format_variant_attributes (GHashTable *attributes,
                                            char attr_separator,
                                            char key_value_separator);
 
+/*****************************************************************************/
+
+gboolean nm_utils_is_localhost (const char *name);
+
+gboolean nm_utils_is_specific_hostname (const char *name);
+
 #endif /* __NM_SHARED_UTILS_H__ */

shared/nm-glib-aux/tests/test-shared-general.c

@@ -910,6 +910,37 @@ test_in_strset_ascii_case (void)
 
 /*****************************************************************************/
 
+static void
+test_is_specific_hostname (void)
+{
+	g_assert (!nm_utils_is_specific_hostname (NULL));
+	g_assert (!nm_utils_is_specific_hostname (""));
+	g_assert (!nm_utils_is_specific_hostname ("(none)"));
+	g_assert (nm_utils_is_specific_hostname ("(NONE)"));
+
+	g_assert (!nm_utils_is_specific_hostname ("localhost"));
+	g_assert (!nm_utils_is_specific_hostname ("lOcalHost"));
+	g_assert (!nm_utils_is_specific_hostname ("LOCALHOST"));
+
+	g_assert (!nm_utils_is_specific_hostname ("LOCALHOST.localdomain"));
+
+	g_assert (nm_utils_is_specific_hostname ("xlocalhost"));
+	g_assert (nm_utils_is_specific_hostname ("lOcalHxost"));
+	g_assert (nm_utils_is_specific_hostname ("LOCALxHOST"));
+
+	g_assert (!nm_utils_is_specific_hostname ("foo.LOCALHOST"));
+	g_assert (!nm_utils_is_specific_hostname ("foo.LOCALHOsT6."));
+	g_assert (!nm_utils_is_specific_hostname ("foo.LOCALHOsT6.localdomain6"));
+	g_assert (!nm_utils_is_specific_hostname (".LOCALHOsT6.localdomain6"));
+	g_assert (!nm_utils_is_specific_hostname ("LOCALHOsT6.localdomain6"));
+	g_assert (!nm_utils_is_specific_hostname ("LOCALHOsT6.localdomain6."));
+	g_assert (nm_utils_is_specific_hostname ("LOCALHOsT6.localdomain."));
+
+	g_assert (nm_utils_is_specific_hostname (" "));
+}
+
+/*****************************************************************************/
+
 NMTST_DEFINE ();
 
 int main (int argc, char **argv)
@@ -933,6 +964,7 @@ int main (int argc, char **argv)
 	g_test_add_func ("/general/test_nm_str_buf", test_nm_str_buf);
 	g_test_add_func ("/general/test_nm_utils_parse_next_line", test_nm_utils_parse_next_line);
 	g_test_add_func ("/general/test_in_strset_ascii_case", test_in_strset_ascii_case);
+	g_test_add_func ("/general/test_is_specific_hostname", test_is_specific_hostname);
 
 	return g_test_run ();
 }

src/nm-core-utils.c

@@ -2373,20 +2373,6 @@ NM_ASSERT_VALID_PATH_COMPONENT (const char *name)
 	g_assert_not_reached ();
 }
 
-gboolean
-nm_utils_is_specific_hostname (const char *name)
-{
-	if (!name)
-		return FALSE;
-	if (   strcmp (name, "(none)")
-	    && strcmp (name, "localhost")
-	    && strcmp (name, "localhost6")
-	    && strcmp (name, "localhost.localdomain")
-	    && strcmp (name, "localhost6.localdomain6"))
-		return TRUE;
-	return FALSE;
-}
-
 /*****************************************************************************/
 
 typedef struct {