Implementing the Telnet state machine Subscribe Pub Share

Consolidating my various blogs into one. This was originally posted on 2010/2/26

Using my scala DSL for State Machine.

Here's the definition (in-work) of the high-level telnet state machine, a little more complicated than the example above, but not much.

The picture (thanks to http://tomi.vanek.sk/index.php?page=telnet):

The state machine is:

implicit val sm = this

val sstates @ (data, cmd, app, param, neg, subneg) = ("data", "cmd", "app", "param", "neg", "subneg")
override def start = state("data")

override val transitions : Seq[Transition] =
     (data, IAC)             -> cmd ::
     (data, 0)               -> data :: // NOP - don't know why i get these after CR
     (data, 10)              -> data :: // NOP - LF ignored?
     (data, 13)              -> data + eatLine + echo ("") :: // CR
     (data, {_:Event=>true}) -> data + eatChar + echo ("") :: // remaining chars
     (cmd, IAC)              -> data ::
     (cmd, Seq(WILL, WONT, DO, DONT)) -> neg + push ::
     // TODO 3-2 should negociate stuff, i.e. reply with will/won't
     (neg, {_:Event=>last==SM(DO)})   -> data + mode(true) + pop ::
     (neg, {_:Event=>last==SM(DONT)}) -> data + mode(false) + pop ::
     (neg, AnyEvent) -> data + echo("interesting sequence...") + pop ::  // What is this?
     (cmd, SB) -> subneg ::
     (""".*""".r, CR) -> data :: // it's important to reset the thing on ENTRE
      Nil

def eatChar (sm:StateMachine, t:Transition, e:Event)
def eatLine (sm:StateMachine, t:Transition, e:Event)

Enjoy and, more importantly, have fun!

The entire code, together with the full implementation of the Telnet receiver over a plain socket is available at TelnetReceiver.scala. As a bonus, this one comes with a full implementation of a scala REPL dialog, including content assist, part of my Scripster project!

Not only that, but you can telnet right now to demo.razie.com port 4445 and play with it... "online":

$ telnet demo.razie.com 4445
Trying 162.243.37.42...
Connected to demo.razie.com.
Escape character is '^]'.
1+2
3

Cool, huh?

---

See more in: Cool Scala Subscribe You need to log in to post a comment!

---