+So, you want to write a networked actor!
+Well, luckily that's pretty easy, especially with all you know so far.
+
+#+BEGIN_SRC scheme
+ (use-modules (oop goops)
+ (8sync)
+ (ice-9 rdelim) ; line delineated i/o
+ (ice-9 match)) ; pattern matching
+
+ (define-actor <telcmd> (<actor>)
+ ((*init* telcmd-init)
+ (*cleanup* telcmd-cleanup)
+ (new-client telcmd-new-client))
+ (socket #:accessor telcmd-socket
+ #:init-value #f))
+#+END_SRC
+
+Nothing surprising about the actor definition, though we do see that
+it has a slot for a socket.
+Unsurprisingly, that will be set up in the =*init*= handler.
+
+#+BEGIN_SRC scheme
+ (define (set-port-nonblocking! port)
+ (let ((flags (fcntl port F_GETFL)))
+ (fcntl port F_SETFL (logior O_NONBLOCK flags))))
+
+ (define (setup-socket)
+ ;; our socket
+ (define s
+ (socket PF_INET SOCK_STREAM 0))
+ ;; reuse port even if busy
+ (setsockopt s SOL_SOCKET SO_REUSEADDR 1)
+ ;; connect to port 8889 on localhost
+ (bind s AF_INET INADDR_LOOPBACK 8889)
+ ;; make it nonblocking and start listening
+ (set-port-nonblocking! s)
+ (listen s 5)
+ s)
+
+ (define (telcmd-init telcmd message)
+ (set! (telcmd-socket telcmd) (setup-socket))
+ (display "Connect like: telnet localhost 8889\n")
+ (while (actor-alive? telcmd)
+ (let ((client-connection (accept (telcmd-socket telcmd))))
+ (<- (actor-id telcmd) 'new-client client-connection))))
+
+ (define (telcmd-cleanup telcmd message)
+ (display "Closing socket!\n")
+ (when (telcmd-socket telcmd)
+ (close (telcmd-socket telcmd))))
+#+END_SRC
+
+That =setup-socket= code looks pretty hard to read!
+But that's pretty standard code for setting up a socket.
+One special thing is done though... the call to
+=set-port-nonblocking!= sets flags on the socket port so that,
+you guessed it, will be a nonblocking port.
+
+This is put to immediate use in the telcmd-init method.
+This code looks suspiciously like it /should/ block... after
+all, it just keeps looping forever.
+But since 8sync is using Guile's suspendable ports code feature,
+so every time this loop hits the =accept= call, if that call
+/would have/ blocked, instead this whole procedure suspends
+to the scheduler... automatically!... allowing other code to run.
+
+So, as soon as we do accept a connection, we send a message to
+ourselves with the =new-client= action.
+But wait!
+Aren't actors only supposed to handle one message at a time?
+If the telcmd-init loop just keeps on looping and looping,
+when will the =new-client= message ever be handled?
+8sync actors only receive one message at a time, but by default if an
+actor's message handler suspends to the agenda for some reason (such
+as to send a message or on handling I/O), that actor may continue to
+accept other messages, but always in the same thread.[fn:queued-handler]
+
+We also see that we've established a =*cleanup*= handler.
+This is run any time either the actor dies, either through self
+destructing, because the hive completes its work, or because
+a signal was sent to interrupt or terminate our program.
+In our case, we politely close the socket when =<telcmd>= dies.
+
+#+BEGIN_SRC scheme
+ (define (telcmd-new-client telcmd message client-connection)
+ (define client (car client-connection))
+ (set-port-nonblocking! client)
+ (let loop ()
+ (let ((line (read-line client)))
+ (cond ((eof-object? line)
+ (close client))
+ (else
+ (telcmd-handle-line telcmd client
+ (string-trim-right line #\return))
+ (when (actor-alive? telcmd)
+ (loop)))))))
+
+ (define (telcmd-handle-line telcmd client line)
+ (match (string-split line #\space)
+ (("") #f) ; ignore empty lines
+ (("time" _ ...)
+ (display
+ (strftime "The time is: %c\n" (localtime (current-time)))
+ client))
+ (("echo" rest ...)
+ (format client "~a\n" (string-join rest " ")))
+ ;; default
+ (_ (display "Sorry, I don't know that command.\n" client))))
+#+END_SRC
+
+Okay, we have a client, so we handle it!
+And once again... we see this goes off on a loop of its own!
+(Also once again, we have to do the =set-port-nonblocking!= song and
+dance.)
+This loop also automatically suspends when it would otherwise block...
+as long as read-line has information to process, it'll keep going, but
+if it would have blocked waiting for input, then it would suspend the
+agenda.[fn:setvbuf]
+
+The actual method called whenever we have a "line" of input is pretty
+straightforward... in fact it looks an awful lot like the IRC bot
+handle-line procedure we used earlier.
+No surprises there!
+
+Now let's run it:
+
+#+BEGIN_SRC scheme
+ (let* ((hive (make-hive))
+ (telcmd (bootstrap-actor hive <telcmd>)))
+ (run-hive hive '()))
+#+END_SRC
+
+Open up another terminal... you can connect via telnet:
+
+#+BEGIN_SRC text
+$ telnet localhost 8889
+Trying 127.0.0.1...
+Connected to localhost.
+Escape character is '^]'.
+time
+The time is: Thu Jan 5 03:20:17 2017
+echo this is an echo
+this is an echo
+shmmmmmmorp
+Sorry, I don't know that command.
+#+END_SRC
+
+Horray, it works!
+Type =Ctrl+] Ctrl+d= to exit telnet.
+
+Not so bad!
+There's more that could be optimized, but we'll consider that to be
+advanced topics of discussion.
+
+So that's a pretty solid intro to how 8sync works!
+Now that you've gone through this introduction, we hope you'll have fun
+writing and hooking together your own actors.
+Since actors are so modular, it's easy to have a program that has
+multiple subystems working together.
+You could build a worker queue system that displayed a web interface
+and spat out notifications about when tasks finish to IRC, and making
+all those actors talk to each other should be a piece of cake.
+The sky's the limit!
+
+Happy hacking!
+
+[fn:setvbuf]
+ If there's a lot of data coming in and you don't want your I/O loop
+ to become too "greedy", take a look at =setvbuf=.
+
+[fn:queued-handler]
+ This is customizable: an actor can be set up to queue messages so
+ that absolutely no messages are handled until the actor completely
+ finishes handling one message.
+ Our loop couldn't look quite like this though!
projects / 8sync.git / blobdiff