From 22ae65d05e0186da587d632da513b4421da3eeb7 Mon Sep 17 00:00:00 2001
From: Tony Garnock-Jones <tonygarnockjones@gmail.com>
Date: Sat, 14 Jun 2014 20:52:38 -0400
Subject: [PATCH] General-purpose broker-style relay from js-marketplace

---
 minimart/relay.rkt | 104 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 104 insertions(+)
 create mode 100644 minimart/relay.rkt

diff --git a/minimart/relay.rkt b/minimart/relay.rkt
new file mode 100644
index 0000000..bc63358
--- /dev/null
+++ b/minimart/relay.rkt
@@ -0,0 +1,104 @@
+#lang racket/base
+;; Generic relay for WebSockets/TCP/etc-based participation in a network.
+
+(provide spawn-websocket-relay)
+
+(require racket/set)
+(require racket/match)
+(require net/rfc6455)
+(require "main.rkt")
+(require "demand-matcher.rkt")
+(require "drivers/timer.rkt")
+(require "drivers/websocket.rkt")
+(require json)
+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; Main: start WebSocket server
+
+;; Depends on timer driver and websocket driver running at metalevel 1.
+(define (spawn-websocket-relay port [ssl-options #f])
+  (define server-id (websocket-local-server port ssl-options))
+  (spawn-demand-matcher (websocket-message (?! (websocket-remote-client ?)) server-id ?)
+			#:meta-level 1
+			(lambda (c) (spawn-connection-handler c server-id))))
+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; Wire protocol representation of events and actions
+
+(define (drop-json-action j)
+  (match j
+    ["ping" 'ping]
+    ["pong" 'pong]
+    [`("routes" ,gj) (routing-update (jsexpr->gestalt gj (lambda (v) (set 'peer))))]
+    [`("message" ,body ,meta-level ,feedback?) (message body meta-level feedback?)]))
+
+(define (lift-json-event j)
+  (match j
+    ['ping "ping"]
+    ['pong "pong"]
+    [(routing-update g) `("routes" ,(gestalt->jsexpr g (lambda (v) #t)))]
+    [(message body meta-level feedback?) `("message" ,body ,meta-level ,feedback?)]))
+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; Connections
+
+(struct connection-state (client-id tunnelled-gestalt) #:transparent)
+
+(define (ping-interval) (* 1000 (max (- (ws-idle-timeout) 10) (* (ws-idle-timeout) 0.8))))
+
+(define (spawn-connection-handler c server-id)
+  (define (send-event e s)
+    (send (websocket-message server-id
+			     (connection-state-client-id s)
+			     (jsexpr->string (lift-json-event e)))
+	  #:meta-level 1))
+  (define ((handle-connection-routing-change g) s)
+    (if (gestalt-empty? g)
+	(transition s (quit)) ;; websocket connection closed
+	#f))
+  (define ((handle-tunnelled-routing-change g) s)
+    (transition s (send-event (routing-update g) s)))
+  (define ((handle-tunnellable-message m) s)
+    (if (gestalt-accepts? (connection-state-tunnelled-gestalt s) m)
+	(transition s (send-event m s))
+	(transition s '())))
+  (define relay-connections
+    (gestalt-union (sub (timer-expired c ?) #:meta-level 1)
+		   (sub (websocket-message c server-id ?) #:meta-level 1)
+		   (sub (websocket-message c server-id ?) #:meta-level 1 #:level 1)
+		   (pub (websocket-message server-id c ?) #:meta-level 1)))
+  (define (connection-handler e s)
+    (match e
+      [(routing-update g)
+       (sequence-transitions
+	(transition s '())
+	(handle-connection-routing-change (gestalt-filter g relay-connections))
+	(handle-tunnelled-routing-change
+	 (gestalt-filter g (connection-state-tunnelled-gestalt s))))]
+      [(? message? m)
+       (sequence-transitions
+	(match m
+	  [(message (websocket-message from to data) 1 #f)
+	   (match (drop-json-action (string->jsexpr data))
+	     [(routing-update g-unfiltered)
+	      (define g (gestalt-transform g-unfiltered
+					   (lambda (ml l p) (if (zero? ml) p '(#f . #f)))))
+	      (transition (struct-copy connection-state s [tunnelled-gestalt g])
+			  (routing-update (gestalt-union g relay-connections)))]
+	     [(? message? m)
+	      (transition s (if (zero? (message-meta-level m)) m '()))]
+	     ['ping
+	      (transition s (send-event 'pong s))]
+	     ['pong
+	      (transition s '())])]
+	  [(message (timer-expired _ _) 1 #f)
+	   (transition s (list (send (set-timer c (ping-interval) 'relative) #:meta-level 1)
+			       (send-event 'ping s)))]
+	  [_
+	   (transition s '())])
+	(handle-tunnellable-message m))]
+      [#f #f]))
+  (list (send (set-timer c (ping-interval) 'relative) #:meta-level 1)
+	(spawn connection-handler
+	       (connection-state c (gestalt-empty))
+	       relay-connections)))