IO Ping Tutorial (Spritely Goblins)

6.5.1 IO Ping Tutorial

This tutorial builds up a simple echo server and client using Goblins’ IO objects. The general way the server works is it has an initial ^ping-server object which sets up a socket to bind to an IP and port, it then listens for new connections and for each new connection spawns a ^server-client. The ^server-client reads a line on the socket and writes what it read back to the socket.

Similarly, for the client, there is a ^echo-client; this takes an IP and port to connect to and spawns a socket. Its behavior is that it takes a message which it writes to the socket and then hands back a promise to the line it reads back from the socket.

The original ping server in the Fibers manual can be found here: https://github.com/wingo/fibers/wiki/Manual#41-ping).

The server:

(use-modules (rnrs bytevectors)
             (ice-9 textual-ports)
             (ice-9 rdelim)
             (ice-9 match)
             (goblins)
             (goblins actor-lib io)
             (goblins actor-lib methods)
             (fibers conditions))

(define (create-non-blocking-socket)
  "Returns a socket configured for non-blocking interaction"
  (let ((sock (socket PF_INET SOCK_STREAM 0)))
    (fcntl sock F_SETFL (logior O_NONBLOCK (fcntl sock F_GETFL)))
    sock))

(define (setup-socket-to-listen! sock address port)
  "Sets up the socket to listen to given ADDRESS and PORT"
  (setsockopt sock SOL_SOCKET SO_REUSEADDR 1)
  (fcntl sock F_SETFD FD_CLOEXEC)
  (bind sock AF_INET (inet-pton AF_INET address) port)
  (listen sock 1024)
  (sigaction SIGPIPE SIG_IGN))

(define (^ping-server _bcom)
  (define sock
    (spawn ^io (create-non-blocking-socket)
           #:init
           (lambda (port)
             ;; This blocks so we want to do it in the #:init
             ;; code as that happens inside the ^io event loop.
             (setup-socket-to-listen! port "127.0.0.1" 11211))
           #:cleanup
           (lambda (port)
             (close port))))

  (define (socket-loop)
    "Accept a new connection and spawn a ^client-server for it"
    (on (<- sock (lambda (port)
                   (accept port SOCK_NONBLOCK)))
        (lambda (client-sock-pair)
          (match client-sock-pair
            [(client-sock . addr)
             (spawn ^server-client client-sock)]))
        #:finally socket-loop))

  ;; Kick off the socket loop
  (socket-loop)

  (methods
   [(shutdown)
    ($ sock 'halt)]))

(define (^server-client _bcom port)
  (define sock
    (spawn ^read-write-io port
           #:init (lambda (port)
                    (setvbuf port 'block 1024)
                    ;; Disable Nagle's algorithm. We buffer ourselves.
                    (setsockopt port IPPROTO_TCP TCP_NODELAY 1))
           #:cleanup (lambda (port)
                       (close port))))
  (define (read-and-reply-loop)
    (on (<- sock 'read read-line)
        (lambda (line)
          (match line
            [(? eof-object?) ($ sock 'halt)]
            [other
             (<-np sock 'write
                   (lambda (port)
                     (put-string port other)
                     (put-char port #\newline)
                     (force-output port)))
             (read-and-reply-loop)]))))

  ;; Kick off loop
  (read-and-reply-loop)
  (methods
   [(shutdown)
    ($ sock 'halt)]))

;; Setup a vat and spawn the server
(define server-vat
  (spawn-vat #:name "server-vat"))
(with-vat server-vat
  (spawn ^ping-server))

The Client:

;; Same as above:
(define (create-non-blocking-socket)
  "Returns a socket configured for non-blocking interaction"
  (let ((sock (socket PF_INET SOCK_STREAM 0)))
    (fcntl sock F_SETFL (logior O_NONBLOCK (fcntl sock F_GETFL)))
    sock))

(define (setup-socket-to-connect! sock addr port)
  (let ((connection-info (car (getaddrinfo addr (number->string port)))))
    ;; Disable Nagle's algorithm.  We buffer ourselves.
    (setsockopt sock IPPROTO_TCP TCP_NODELAY 1)
    (setvbuf sock 'block 1024)
    (connect sock (addrinfo:addr connection-info))))

(define (^echo-client _bcom to-address to-port)
  (define sock
    (spawn ^read-write-io (create-non-blocking-socket)
           #:init
           (lambda (port)
             (setup-socket-to-connect! port to-address to-port))
           #:cleanup
           (lambda (port)
             (close port))))

  (lambda (msg)
    ($ sock 'write
       (lambda (port)
         (put-string port msg)
         (put-char port #\newline)
         (force-output port)))
    (<- sock 'read get-line)))

(define client-vat
  (spawn-vat #:name "client-vat"))
(define echo-client
  (with-vat client-vat
    (spawn ^echo-client "127.0.0.1" 11211)))

Finally, lets try this:

,enter-vat client-vat
goblins[1]> (define reply-vow
              (<- echo-client "Hello world!"))
goblins[1]> ,vat-resolve reply-vow
"Hello world!"