-extern bool meshlink_send(meshlink_handle_t *mesh, meshlink_node_t *destination, const void *data, unsigned int len);
+extern bool meshlink_send(meshlink_handle_t *mesh, meshlink_node_t *destination, const void *data, size_t len);
+
+/// Query the maximum packet size that can be sent to a node.
+/** This functions returns the maximum size of packets (path MTU) that can be sent to a specific node with meshlink_send().
+ * The path MTU is a property of the path packets will take to the destination node over the Internet.
+ * It can be different for different destination nodes.
+ * and the path MTU can change at any point in time due to changes in the Internet.
+ * Therefore, although this should only occur rarely, it can still happen that packets that do not exceed this size get dropped.
+ *
+ * @param mesh A handle which represents an instance of MeshLink.
+ * @param destination A pointer to a meshlink_node_t describing the destination for the data.
+ *
+ * @return The recommended maximum size of packets that are to be sent to the destination node, 0 if the node is unreachable,
+ * or a negative value in case of an error.
+ */
+extern ssize_t meshlink_get_pmtu(meshlink_handle_t *mesh, meshlink_node_t *destination);