83 lines
2.8 KiB
Racket
83 lines
2.8 KiB
Racket
#lang racket/base
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;; Simple imperative UDP server harness.
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(require racket/match)
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(require racket/udp)
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(require "dump-bytes.rkt")
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(provide (struct-out udp-packet)
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event-handlers
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start-udp-service)
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;; A UdpPacket is a (udp-packet Bytes String Uint16), and represents
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;; either a received UDP packet and the source of the packet, or a UDP
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;; packet ready to be sent along with the address to which it should
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;; be sent.
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(struct udp-packet (body host port) #:prefab)
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;; TODO: Should packet-classifier be permitted to examine (or possibly
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;; even transform!) the ServerState?
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;; A Handler is a ClassifiedPacket ServerState -> ListOf<ClassifiedPacket> ServerState.
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(define-syntax event-handlers
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(syntax-rules ()
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((_ old-state-var (pattern body ...) ...)
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(list (cons (match-lambda (pattern #t) (_ #f))
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(lambda (v old-state-var)
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(match v
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(pattern body ...))))
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...))))
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;; Starts a generic request/reply UDP server on the given port.
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(define (start-udp-service
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port-number ;; Uint16
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packet-classifier ;; UdpPacket -> ClassifiedPacket
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event-handlers ;; ListOf<Pair<ClassifiedPacket -> Boolean, Handler>>
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default-handler ;; Handler
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initial-state ;; ServerState
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#:packet-size-limit
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[packet-size-limit 65536])
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(define s (udp-open-socket #f #f)) ;; the server socket
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(udp-bind! s #f port-number) ;; bind it to the port we were given
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(set! event-handlers ;; TEMPORARY while I figure out I/O
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(cons (cons udp-packet?
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(lambda (p state)
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(match-define (udp-packet body host port) p)
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(printf "<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<~n~v~n" body)
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(dump-bytes! body (bytes-length body))
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(flush-output)
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(udp-send-to s host port body)
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(values '() state)))
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event-handlers))
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(define (dispatch-events events old-state)
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(if (null? events)
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(read-and-dispatch old-state)
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(let ((classified-packet (car events)))
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(define-values (new-events new-state)
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(let search ((handlers event-handlers))
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(cond
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[(null? handlers) (default-handler classified-packet old-state)]
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[((caar handlers) classified-packet) ((cdar handlers) classified-packet old-state)]
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[else (search (cdr handlers))])))
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(dispatch-events (append (cdr events) new-events) new-state))))
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(define (read-and-dispatch old-state)
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(define buffer (make-bytes packet-size-limit))
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(define-values (packet-length source-hostname source-port)
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(udp-receive! s buffer))
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(define packet (subbytes buffer 0 packet-length))
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(printf ">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>~n~v~n" packet)
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(dump-bytes! buffer packet-length)
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(flush-output)
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(define packet-and-source (udp-packet packet source-hostname source-port))
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(define classified-packet (packet-classifier packet-and-source))
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(dispatch-events (list classified-packet) old-state))
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(read-and-dispatch initial-state))
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