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racket-dns-2012
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Add unparsing of packets, symmetrically with what used to be called classification.

This commit is contained in:
Tony Garnock-Jones 2011-12-16 11:30:18 -05:00
parent 5181e0fce0
commit 94486f4dba
2 changed files with 23 additions and 14 deletions
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23
simple-udp-service.rkt
View File

@ -17,7 +17,7 @@
;; be sent.
(struct udp-packet (body host port) #:prefab)
;; TODO: Should packet-classifier be permitted to examine (or possibly
;; TODO: Should parse-packet be permitted to examine (or possibly
;; even transform!) the ServerState?
;; A Handler is a ClassifiedPacket ServerState -> ListOf<ClassifiedPacket> ServerState.
@ -34,7 +34,11 @@
;; Starts a generic request/reply UDP server on the given port.
(define (start-udp-service
port-number ;; Uint16
packet-classifier ;; UdpPacket -> ClassifiedPacket
parse-packet ;; UdpPacket -> ClassifiedPacket
;--------------------------------------------------
unparse-packet? ;; ClassifiedPacket -> Boolean
unparse-packet ;; ClassifiedPacket -> UdpPacket
;--------------------------------------------------
event-handlers ;; ListOf<Pair<ClassifiedPacket -> Boolean, Handler>>
default-handler ;; Handler
initial-state ;; ServerState
@ -44,8 +48,9 @@
(udp-bind! s #f port-number) ;; bind it to the port we were given
(set! event-handlers ;; TEMPORARY while I figure out I/O
(cons (cons udp-packet?
(lambda (p state)
(cons (cons unparse-packet?
(lambda (event state)
(define p (unparse-packet event))
(match-define (udp-packet body host port) p)
(printf "<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<~n~v~n" body)
(dump-bytes! body (bytes-length body))
@ -57,12 +62,12 @@
(define (dispatch-events events next-events-rev old-state)
(if (null? events)
(check-for-io (reverse next-events-rev) old-state)
(let ((classified-packet (car events)))
(let ((event (car events)))
(define-values (new-events new-state)
(let search ((handlers event-handlers))
(cond
[(null? handlers) (default-handler classified-packet old-state)]
[((caar handlers) classified-packet) ((cdar handlers) classified-packet old-state)]
[(null? handlers) (default-handler event old-state)]
[((caar handlers) event) ((cdar handlers) event old-state)]
[else (search (cdr handlers))])))
(dispatch-events (cdr events)
(append-reverse new-events next-events-rev)
@ -81,8 +86,8 @@
(define packet-and-source
(udp-packet packet source-hostname source-port))
(define classified-packet (packet-classifier packet-and-source))
(list classified-packet)]))
(define event (parse-packet packet-and-source))
(list event)]))
(if (null? pending-events)
never-evt ;; Nothing waiting to be done, don't wake up until sth external arrives
(handle-evt (system-idle-evt)

14
simplified-driver.rkt
View File

@ -72,21 +72,21 @@
(start-udp-service
port-number
classify-dns-packet
parse-dns-event
dns-reply?
unparse-dns-event
(event-handlers old-state
[(? bad-dns-packet? p)
(pretty-print p)
(values '() old-state)]
[(? dns-request? r)
(values (handle-request soa-rr zone r) old-state)]
[(dns-reply message host port)
(values (list (udp-packet (dns-message->packet message) host port)) old-state)])
(values (handle-request soa-rr zone r) old-state)])
(lambda (unhandled state)
(error 'dns-server "Unhandled packet ~v" unhandled))
#f
#:packet-size-limit 512))
(define (classify-dns-packet packet)
(define (parse-dns-event packet)
(match-define (udp-packet body host port) packet)
(with-handlers ((exn? (lambda (e) (bad-dns-packet body host port 'unparseable))))
(define message (packet->dns-message body))
@ -94,6 +94,10 @@
((request) (dns-request message host port))
((response) (bad-dns-packet message host port 'unexpected-dns-response)))))
(define (unparse-dns-event event)
(match-define (dns-reply message host port) event)
(udp-packet (dns-message->packet message) host port))
(define (handle-request soa-rr zone request)
(match-define (dns-request request-message request-host request-port) request)