sunet/nettime.scm

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;;; nettime.scm -- obtain the time on remote machines
;;
;; $Id: nettime.scm,v 1.3 2002/05/12 05:32:28 interp Exp $
;;
;; Please send suggestions and bug reports to <emarsden@mail.dotcom.fr>
;;; Overview ========================================================
;;
;; Most Unix hosts provide a Daytime service which sends the current
;; date and time as a human-readable character string. The daytime
;; service is typically served on port 13 as both TCP and UDP.
;;
;; The Time protocol provides a site-independent, machine readable
;; date and time. A "time" consists of the number of seconds since
;; midnight on 1st January 1900. The Time service is typically served
;; on port 37 as TCP and UDP. The idea is that you can confirm your
;; system's idea of the time by polling several independent sites on
;; the network.
;;; Related work ======================================================
;;
;; * Time.pm is a Perl module by Graham Barr
;; * rfc868 describes the Time protocol
;; * rfc867 describes the Daytime protocol in all its glory
;; * for a genuinely useful protocol look at the Network Time Protocol
;; defined in rfc1305, which allows for the synchronization of clocks
;; on networked computers.
;; args host protocol, where host may be an IP number or a fqdn. we
;; subtract 70 years' worth of seconds at the end, since the time
;; protocol returns the number of seconds since 1900, whereas Unix
;; time is since 1970.
(define (net-time host tcp/udp)
(let* ((hst-info (host-info host))
(srvc-info (service-info "time" "tcp"))
(sock (socket-connect protocol-family/internet
tcp/udp
(host-info:name hst-info)
(service-info:port srvc-info)))
(result (read-integer (socket:inport sock))))
(close-socket sock)
(- result 2208988800)))
(define (net-daytime host tcp/udp)
(let* ((hst-info (host-info host))
(srvc-info (service-info "daytime" "tcp"))
(sock (socket-connect protocol-family/internet
tcp/udp
(host-info:name hst-info)
(service-info:port srvc-info)))
(result (read-string 20 (socket:inport sock))))
(close-socket sock)
result))
;; read 4 bytes from fd and build an integer from them
(define (read-integer fd)
(let loop ((accum 0)
(remaining 4))
(if (zero? remaining)
accum
(loop (+ (arithmetic-shift accum 8) (read-byte fd))
(- remaining 1)))))
;; what about EOF??
(define (read-byte fd)
(char->ascii (read-char fd)))
;; EOF