68 lines
2.2 KiB
Racket
68 lines
2.2 KiB
Racket
#lang racket/base
|
|
;; Simple "ping" responder. Nightmarishly oversimplified. We want to
|
|
;; look at overheads excluding Syndicate. See also
|
|
;; http://dunkels.com/adam/twip.html
|
|
|
|
(require packet-socket)
|
|
|
|
(require "dump-bytes.rkt")
|
|
|
|
(define device-name (or (getenv "PINGRESP_DEVICE") "eth0"))
|
|
(define self-ip (integer-bytes->integer (bytes 129 10 115 94) #f #t))
|
|
|
|
(define handle (raw-interface-open device-name))
|
|
(unless handle (error 'pingresp "Couldn't open ~a" device-name))
|
|
|
|
(let loop ()
|
|
(define eth-buffer (raw-interface-read handle))
|
|
(define buffer (subbytes eth-buffer 14))
|
|
(when (>= (bytes-length buffer) 20) ;; enough space for local and remote IP addresses
|
|
(define local-ip (integer-bytes->integer buffer #f #t 16 20))
|
|
(define remote-ip (integer-bytes->integer buffer #f #t 12 16))
|
|
(when (= local-ip self-ip)
|
|
;; (printf "Got ping from ~v\n" (bytes->list (subbytes buffer 12 16)))
|
|
;; (flush-output)
|
|
;; (dump-bytes! eth-buffer)
|
|
;; (newline)
|
|
|
|
(when (and (>= (bytes-length buffer) 28) ;; IP + ICMP headers
|
|
(= (bytes-ref buffer 9) 1) ;; IP protocol
|
|
(= (bytes-ref buffer 20) 8) ;; ICMP ECHO
|
|
)
|
|
|
|
(bytes-set! buffer 20 0) ;; ICMP ECHO_REPLY
|
|
(integer->integer-bytes (bitwise-and #xffff
|
|
(+ #x0800
|
|
(integer-bytes->integer buffer #f #t 22 24)))
|
|
2 #f #t buffer 22) ;; "fix" checksum
|
|
(integer->integer-bytes local-ip 4 #f #t buffer 12)
|
|
(integer->integer-bytes remote-ip 4 #f #t buffer 16)
|
|
|
|
(define reply
|
|
(bytes-append (subbytes eth-buffer 6 12)
|
|
(subbytes eth-buffer 0 6)
|
|
(subbytes eth-buffer 12 14)
|
|
buffer))
|
|
;; (displayln "Reply:")
|
|
;; (dump-bytes! reply)
|
|
;; (newline)
|
|
(raw-interface-write handle reply))))
|
|
(loop))
|
|
|
|
(raw-interface-close handle)
|
|
|
|
|
|
;; short s[70];
|
|
;; int *l = s;
|
|
;; int t;
|
|
;;
|
|
;; read(0, s, 140);
|
|
;; if((s[4] & 65280) == 256 & s[10] == 8) {
|
|
;; s[10] = 0;
|
|
;; s[11] += 8;
|
|
;; t = l[4];
|
|
;; l[4] = l[3];
|
|
;; l[3] = t;
|
|
;; write(1, s, 140);
|
|
;; }
|