// State manipulation
void odhcp6c_clear_state(enum odhcp6c_state state);
-void odhcp6c_add_state(enum odhcp6c_state state, const void *data, size_t len);
+int odhcp6c_add_state(enum odhcp6c_state state, const void *data, size_t len);
void odhcp6c_append_state(enum odhcp6c_state state, const void *data, size_t len);
int odhcp6c_insert_state(enum odhcp6c_state state, size_t offset, const void *data, size_t len);
size_t odhcp6c_remove_state(enum odhcp6c_state state, size_t offset, size_t len);