General-purpose broker-style relay from js-marketplace
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#lang racket/base
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;; Generic relay for WebSockets/TCP/etc-based participation in a network.
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(provide spawn-websocket-relay)
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(require racket/set)
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(require racket/match)
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(require net/rfc6455)
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(require "main.rkt")
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(require "demand-matcher.rkt")
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(require "drivers/timer.rkt")
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(require "drivers/websocket.rkt")
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(require json)
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; Main: start WebSocket server
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;; Depends on timer driver and websocket driver running at metalevel 1.
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(define (spawn-websocket-relay port [ssl-options #f])
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(define server-id (websocket-local-server port ssl-options))
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(spawn-demand-matcher (websocket-message (?! (websocket-remote-client ?)) server-id ?)
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#:meta-level 1
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(lambda (c) (spawn-connection-handler c server-id))))
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; Wire protocol representation of events and actions
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(define (drop-json-action j)
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(match j
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["ping" 'ping]
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["pong" 'pong]
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[`("routes" ,gj) (routing-update (jsexpr->gestalt gj (lambda (v) (set 'peer))))]
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[`("message" ,body ,meta-level ,feedback?) (message body meta-level feedback?)]))
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(define (lift-json-event j)
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(match j
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['ping "ping"]
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['pong "pong"]
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[(routing-update g) `("routes" ,(gestalt->jsexpr g (lambda (v) #t)))]
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[(message body meta-level feedback?) `("message" ,body ,meta-level ,feedback?)]))
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; Connections
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(struct connection-state (client-id tunnelled-gestalt) #:transparent)
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(define (ping-interval) (* 1000 (max (- (ws-idle-timeout) 10) (* (ws-idle-timeout) 0.8))))
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(define (spawn-connection-handler c server-id)
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(define (send-event e s)
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(send (websocket-message server-id
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(connection-state-client-id s)
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(jsexpr->string (lift-json-event e)))
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#:meta-level 1))
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(define ((handle-connection-routing-change g) s)
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(if (gestalt-empty? g)
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(transition s (quit)) ;; websocket connection closed
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#f))
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(define ((handle-tunnelled-routing-change g) s)
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(transition s (send-event (routing-update g) s)))
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(define ((handle-tunnellable-message m) s)
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(if (gestalt-accepts? (connection-state-tunnelled-gestalt s) m)
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(transition s (send-event m s))
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(transition s '())))
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(define relay-connections
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(gestalt-union (sub (timer-expired c ?) #:meta-level 1)
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(sub (websocket-message c server-id ?) #:meta-level 1)
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(sub (websocket-message c server-id ?) #:meta-level 1 #:level 1)
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(pub (websocket-message server-id c ?) #:meta-level 1)))
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(define (connection-handler e s)
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(match e
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[(routing-update g)
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(sequence-transitions
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(transition s '())
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(handle-connection-routing-change (gestalt-filter g relay-connections))
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(handle-tunnelled-routing-change
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(gestalt-filter g (connection-state-tunnelled-gestalt s))))]
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[(? message? m)
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(sequence-transitions
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(match m
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[(message (websocket-message from to data) 1 #f)
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(match (drop-json-action (string->jsexpr data))
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[(routing-update g-unfiltered)
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(define g (gestalt-transform g-unfiltered
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(lambda (ml l p) (if (zero? ml) p '(#f . #f)))))
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(transition (struct-copy connection-state s [tunnelled-gestalt g])
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(routing-update (gestalt-union g relay-connections)))]
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[(? message? m)
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(transition s (if (zero? (message-meta-level m)) m '()))]
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['ping
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(transition s (send-event 'pong s))]
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['pong
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(transition s '())])]
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[(message (timer-expired _ _) 1 #f)
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(transition s (list (send (set-timer c (ping-interval) 'relative) #:meta-level 1)
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(send-event 'ping s)))]
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[_
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(transition s '())])
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(handle-tunnellable-message m))]
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[#f #f]))
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(list (send (set-timer c (ping-interval) 'relative) #:meta-level 1)
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(spawn connection-handler
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(connection-state c (gestalt-empty))
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relay-connections)))
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