Firmware Over-the-Air (FOTA)

@DrAzzy, would below code fix the issue - if there ever was any (because the .substr() would not have not concatenated more to t than would have been left from the last piece of data - would it)?

    while (l > 0) {
        i=((i = this.pgsz-(add%this.pgsz)) > l) ? l : i;