;WOL is based on the following principle: 
;When the PC shuts down, the NIC still gets power, and keeps listening on the network for a 'magic' packet to arrive. This packet must contain a certain byte-sequence, but can be encapsulated in any kind of packet (IPX, IP, anything). 

;This program uses UDP for sending the packet. The complete UDP packet, sent over an ethernet interface, looks something like this:
;[ethernet header][IP header][UDP header][Magic sequence][CRCS] 
;The only goal of the script is to send this packet over the network. It expects no returning data, since the NIC only listens, and does not reply anything.

;The Magic Packet is a broadcast frame, transmitted over port 7 or 9. It can be sent over a variety of connectionless protocols (UDP, IPX) but UDP is most commonly used. The data that is contained in a Magic Packet is the defined constant as represented in hexadecimal: FF FF FF FF FF FF followed by sixteen (I've also seen six) repetitions of the target computer's MAC address, possibly followed by a four or six byte password.         


(require (lib "pregexp.ss"))

(define port 57111)

(define s (udp-open-socket "127.0.0.1" port))


(define MACs (list
              ""
              "00:13:72:A2:A6:76" 
              "00:13:72:A2:B0:96"
              "00:13:72:A2:A9:5B"
              "00:13:72:A2:A9:33"
              "00:13:72:A2:A8:EE" 
              "00:13:72:A2:A8:BE"
              "00:13:72:A2:A9:01"
              "00:13:72:A2:9F:6E"                          
              "00:13:72:A2:A8:5E"                          
              "00:13:72:A2:B2:84"
              "00:13:72:A2:95:91"
              "00:13:72:A2:CC:DC"                           
              "00:13:72:A2:A9:0B"
              "00:13:72:A2:CB:D1"
              "00:13:72:A2:9A:31"
              "00:13:72:A2:A9:38"
              "00:13:72:A2:A8:CF"
              "00:13:72:87:C6:AE"                          
              "00:13:72:87:0F:D0"
              "00:13:72:87:A9:3F"))

;string->bytes : string(representing a mac address) -> byte string of the same
(define (string->bytes mac)
  (apply bytes-append (map string->bytes/utf-8 (pregexp-split ":" mac))))

;(string->bytes "00:13:72:A2:A6:76") #"001372A2A676"


;repeat: string (mac address) -> string (with repetition n times)
(define (repeat mac n)
  (cond
    [(= n 0) ""]
    [else
     (string-append mac (repeat mac (sub1 n)))])) 


;magic-packet: string (mac address) -> bytes
(define (magic-packet mac)
  (let ((mac (string->bytes (repeat mac 16))))
   (bytes-append (string->bytes/utf-8 "FFFFFFFFFFFF") mac)))


(define (wol-packet from to)
  (bytes-append (string->bytes to)
                (string->bytes from)
                (string->bytes/utf-8 "0842") ;packet type is 0x0842 
                (magic-packet to)))


(udp-send-to  s "pc03" port (wol-packet (list-ref MACs 11)(list-ref MACs 3)))
(udp-send-to  s "pc03" port (wol-packet (list-ref MACs 11)(list-ref MACs 3)))
(udp-send-to  s "pc03" port (wol-packet (list-ref MACs 11)(list-ref MACs 3)))
(udp-send-to  s "pc03" port (wol-packet (list-ref MACs 11)(list-ref MACs 3)))
(udp-send-to  s "pc03" port (wol-packet (list-ref MACs 11)(list-ref MACs 3)))