core: add nm_match_spec_join() function

We have a special implemenation nm_match_spec_split() to split
a string. We also need the reverse operation to be able to convert
a list of specs to string without loss.

src/NetworkManagerUtils.c

@@ -1419,6 +1419,85 @@ nm_match_spec_split (const char *value)
 	return g_slist_reverse (pieces);
 }
 
+/**
+ * nm_match_spec_join:
+ * @specs: the device specs to join
+ *
+ * This is based on g_key_file_parse_string_as_value(), analog to
+ * nm_match_spec_split() which is based on g_key_file_parse_value_as_string().
+ *
+ * Returns: (transfer-full): a joined list of device specs that can be
+ *   split again with nm_match_spec_split(). Note that
+ *   nm_match_spec_split (nm_match_spec_join (specs)) yields the original
+ *   result (which is not true the other way around because there are multiple
+ *   ways to encode the same joined specs string).
+ */
+char *
+nm_match_spec_join (GSList *specs)
+{
+	const char *p;
+	GString *str;
+
+	str = g_string_new ("");
+
+	for (; specs; specs = specs->next) {
+		p = specs->data;
+
+		if (!p || !*p)
+			continue;
+
+		if (str->len > 0)
+			g_string_append_c (str, ',');
+
+		/* escape leading whitespace */
+		switch (*p) {
+		case ' ':
+			g_string_append (str, "\\s");
+			p++;
+			break;
+		case '\t':
+			g_string_append (str, "\\t");
+			p++;
+			break;
+		}
+
+		for (; *p; p++) {
+			switch (*p) {
+			case '\n':
+				g_string_append (str, "\\n");
+				break;
+			case '\r':
+				g_string_append (str, "\\r");
+				break;
+			case '\\':
+				g_string_append (str, "\\\\");
+				break;
+			case ',':
+				g_string_append (str, "\\,");
+				break;
+			case ';':
+				g_string_append (str, "\\;");
+				break;
+			default:
+				g_string_append_c (str, *p);
+				break;
+			}
+		}
+
+		/* escape trailing whitespaces */
+		switch (str->str[str->len - 1]) {
+		case ' ':
+			g_string_overwrite (str, str->len - 1, "\\s");
+			break;
+		case '\t':
+			g_string_overwrite (str, str->len - 1, "\\t");
+			break;
+		}
+	}
+
+	return g_string_free (str, FALSE);
+}
+
 const char *
 nm_utils_get_shared_wifi_permission (NMConnection *connection)
 {

src/NetworkManagerUtils.h

@@ -98,6 +98,7 @@ NMMatchSpecMatchType nm_match_spec_hwaddr (const GSList *specs, const char *hwad
 NMMatchSpecMatchType nm_match_spec_s390_subchannels (const GSList *specs, const char *subchannels);
 NMMatchSpecMatchType nm_match_spec_interface_name (const GSList *specs, const char *interface_name);
 GSList *nm_match_spec_split (const char *value);
+char *nm_match_spec_join (GSList *specs);
 
 const char *nm_utils_get_shared_wifi_permission (NMConnection *connection);
 

src/tests/test-general.c

@@ -674,13 +674,27 @@ static void
 test_match_spec_ifname (const char *spec_str, const char **matches, const char **neg_matches)
 {
 	const char *m;
-	GSList *specs, *specs_reverse = NULL;
+	GSList *specs, *specs_reverse = NULL, *specs_resplit, *specs_i, *specs_j;
 	guint i;
+	gs_free char *specs_joined = NULL;
 
 	g_assert (spec_str);
 
 	specs = nm_match_spec_split (spec_str);
 
+	/* assert that split(join(specs)) == specs */
+	specs_joined = nm_match_spec_join (specs);
+	specs_resplit = nm_match_spec_split (specs_joined);
+	specs_i = specs;
+	specs_j = specs_resplit;
+	while (specs_i && specs_j && g_strcmp0 (specs_i->data, specs_j->data) == 0) {
+		specs_i = specs_i->next;
+		specs_j = specs_j->next;
+	}
+	g_assert (!specs_i);
+	g_assert (!specs_j);
+	g_slist_free_full (specs_resplit, g_free);
+
 	/* also check the matches in the reverse order. They must yield the same result because
 	 * matches are inclusive -- except "except:" which always wins. */
 	specs_reverse = g_slist_reverse (g_slist_copy (specs));