* @param fd A file descriptor from which data will be read.
* @param len The length of the data, or 0 if there is no data to send.
* @param cb A pointer to the function which will be called when MeshLink has finished using the filedescriptor.
* @param fd A file descriptor from which data will be read.
* @param len The length of the data, or 0 if there is no data to send.
* @param cb A pointer to the function which will be called when MeshLink has finished using the filedescriptor.