- if (n_variable <= 0) {
- a = message_extend_body(m, 1, 0, add_offset, false);
+ if (isempty(c->signature)) {
+ /* The unary type is encoded as fixed 1 byte padding */
+ a = message_extend_body(m, 1, 1, add_offset, false);
+ if (!a)
+ return -ENOMEM;
+
+ *a = 0;
+ } else if (n_variable <= 0) {
+ int alignment = 1;
+
+ /* Structures with fixed-size members only have to be
+ * fixed-size themselves. But gvariant requires all fixed-size
+ * elements to be sized a multiple of their alignment. Hence,
+ * we must *always* add final padding after the last member so
+ * the overall size of the structure is properly aligned. */
+ if (fixed_size)
+ alignment = bus_gvariant_get_alignment(strempty(c->signature));
+
+ assert(alignment > 0);
+
+ a = message_extend_body(m, alignment, 0, add_offset, false);