syndicate-2017/racket/syndicate-monolithic/drivers/udp.rkt

91 lines
3.3 KiB
Racket

#lang racket/base
(require racket/match)
(require (prefix-in udp: racket/udp))
(require "../main.rkt")
(require "../demand-matcher.rkt")
(provide (struct-out udp-remote-address)
(struct-out udp-handle)
(struct-out udp-listener)
udp-address?
udp-local-address?
(struct-out udp-packet)
spawn-udp-driver)
;; A UdpAddress is one of
;; -- a (udp-address String Uint16), representing a remote socket
;; -- a (udp-handle Any), representing a local socket on a kernel-assigned port
;; -- a (udp-listener Uint16), representing a local socket on a user-assigned port
;; Note that udp-handle-ids must be chosen carefully: they are scoped
;; to the local VM, i.e. shared between processes in that VM, so
;; processes must make sure not to accidentally clash in handle ID
;; selection.
(struct udp-remote-address (host port) #:prefab)
(struct udp-handle (id) #:prefab)
(struct udp-listener (port) #:prefab)
(define (udp-address? x)
(or (udp-remote-address? x)
(udp-local-address? x)))
(define (udp-local-address? x)
(or (udp-handle? x)
(udp-listener? x)))
;; A UdpPacket is a (udp-packet UdpAddress UdpAddress Bytes), and
;; represents a packet appearing on our local "subnet" of the full UDP
;; network, complete with source, destination and contents.
(struct udp-packet (source destination body) #:prefab)
;; -> Action
;; Spawns a process acting as a UDP socket factory.
(define (spawn-udp-driver)
(spawn-demand-matcher (observe (udp-packet ? (?! (udp-listener ?)) ?))
(advertise (udp-packet ? (?! (udp-listener ?)) ?))
spawn-udp-socket))
;; UdpLocalAddress -> Action
(define (spawn-udp-socket local-addr)
(define socket (udp:udp-open-socket #f #f))
(match local-addr
[(udp-listener port) (udp:udp-bind! socket #f port)]
[(udp-handle _) (udp:udp-bind! socket #f 0)]) ;; kernel-allocated port number
(define control-ch (make-channel))
(thread (lambda () (udp-receiver-thread local-addr socket control-ch)))
(spawn (lambda (e s)
(match e
[(scn r)
(cond [(trie-non-empty? r) #f] ;; peer hasn't quit yet: do nothing.
[else (channel-put control-ch 'quit)
(quit)])]
[(message (at-meta (? udp-packet? p)))
(transition s (message p))]
[(message (udp-packet _ (udp-remote-address host port) body))
(udp:udp-send-to socket host port body)
#f]
[_ #f]))
(void)
(scn/union (subscription (udp-packet ? local-addr ?) #:meta-level 1)
(subscription (udp-packet local-addr (udp-remote-address ? ?) ?))
(advertisement (udp-packet (udp-remote-address ? ?) local-addr ?))
(subscription (observe (udp-packet (udp-remote-address ? ?) local-addr ?))))))
;; UdpLocalAddress UdpSocket Channel -> Void
(define (udp-receiver-thread local-addr socket control-ch)
(define buffer (make-bytes 65536))
(let loop ()
(sync (handle-evt control-ch (match-lambda ['quit (void)]))
(handle-evt (udp:udp-receive!-evt socket buffer)
(lambda (receive-results)
(match-define (list len source-hostname source-port) receive-results)
(send-ground-message
(udp-packet (udp-remote-address source-hostname source-port)
local-addr
(subbytes buffer 0 len)))
(loop)))))
(udp:udp-close socket))