#lang syndicate/actor
;; Example showing an interesting design flaw (?) (bug?) in the
;; old-school LLL demand-matcher when demand changes too quickly. The
;; port 6000 server is started, but by the time it starts monitoring
;; demand for its services, the demand is already gone, replaced with
;; demand for port 5999. This causes connections to be accepted on
;; port 6000 going nowhere.
;;
;; One fix is to use #:assertions to give the TCP listener actor some
;; initial interests, thus transferring responsibility atomically.
;; Another is to modify the demand-matcher to do something like
;; `during/spawn` is doing, using an auxiliary protocol to centralise
;; tracking of demand and supply at the demand-matcher rather than
;; delegating it to the services.

(require syndicate/protocol/advertise)
(require/activate syndicate/drivers/tcp)

(struct listen-port (number) #:prefab) ;; assertion

(define default-port 6000)

(spawn #:name 'connection-acceptor
       (define/query-value port default-port (listen-port $v) v)
       (assert (advertise (observe (tcp-channel _ (tcp-listener (port)) _))))
       (during (advertise (tcp-channel $c (tcp-listener (port)) _))
         (let ((accepted-port (port))) ;; capture field value at time of connect
           (assert (advertise (tcp-channel (tcp-listener accepted-port) c _)))
           (on-start
            (printf "Accepted connection from ~v on port ~a\n" c accepted-port)
            (send! (tcp-channel (tcp-listener accepted-port) c #"Hello!\n")))
           (on-stop
            (printf "Closed connection ~v on port ~a\n" c accepted-port)))))

(spawn #:name 'configuration-provider
       (assert (listen-port 5999)))