Distributed programming

Distributed programming
You are encouraged to solve this task according to the task description, using any language you may know.

Given two computers on a network, send messages between them. The protocol used may be language-specific or not, and should be suitable for general distributed programming.

D

Socket

Works with: Tango

Server

<lang d>module distributedserver ; import tango.net.ServerSocket, tango.text.convert.Integer,

      tango.text.Util, tango.io.Stdout ;

void main() {

 auto Ip = new InternetAddress("localhost", 12345) ;    
 auto server = new ServerSocket(Ip) ;
 auto socket = server.accept ;     
 auto buffer = new char[socket.bufferSize] ;

 bool quit = false ;
 
 while(!quit) {
   bool error = false ;    
   
   try {
     auto len = socket.input.read(buffer) ;
     auto cmd = (len > 0) ? delimit(buffer[0..len], " ") : [""] ;              
     Stdout(cmd).newline.flush ;
     switch (cmd[0]) {
       case "square":
         socket.output.write(toString(toInt(cmd[1]) * toInt(cmd[1]))) ; break ;
       case"add":
         socket.output.write(toString(toInt(cmd[1]) + toInt(cmd[2]))) ; break ;
       case "quit": 
         socket.output.write("Server Shut down") ;           
         quit = true ; break ;
       default: error = true ;
     }
   } catch (Exception e) 
     error = true ;
   if(error) socket.output.write("<Error>") ;    
   if(socket) socket.close ;
   if(!quit) socket = server.accept ;     
 } 

 if(socket) socket.close ;

}</lang>

Client

<lang d>module distributedclient ; import tango.net.SocketConduit, tango.net.InternetAddress,

      tango.text.Util, tango.io.Stdout ;

void main(char[][] args) {

 if(args.length> 1) {
   try {
     auto Ip = new InternetAddress("localhost", 12345) ;    
     auto socket = new SocketConduit ;     
     socket.connect(Ip) ;
     auto buffer = new char[socket.bufferSize] ;
 
     socket.output.write(join(args[1..$]," ")) ;
     auto len = socket.input.read(buffer) ;    
     if(len > 0) Stdout(buffer[0..len]).newline ;
   
     if(socket) socket.close ;
   } catch(Exception e) 
     Stdout(e.msg).newline ;
 } else
   Stdout("usage: supply argument as,\n\tquit\n"
     "\tsquare <number>\n\tadd <number> <number>").newline ;

}</lang>

E

Protocol: Pluribus

This service cannot be used except by clients which know the URL designating it, messages are encrypted, and the client authenticates the server. However, it is vulnerable to denial-of-service by any client knowing the URL.

Server

(The protocol is symmetric; this program is the server only in that it is the one which is started first and exports an object.)

<lang e> def storage := [].diverge()

def logService {
  to log(line :String) {
    storage.push([timer.now(), line])
  }
  to search(substring :String) {
    var matches := []
    for [time, line] ? (line.startOf(substring) != -1) in storage {
      matches with= [time, line]
    }
    return matches
  }
}

introducer.onTheAir()
def sturdyRef := makeSturdyRef.temp(logService)
println(<captp>.sturdyToURI(sturdyRef))
interp.blockAtTop()</lang>

This will print the URL of the service and run it until aborted.

Client

The URL provided by the server is given as the argument to this program.

<lang e> def [uri] := interp.getArgs()

introducer.onTheAir()
def sturdyRef := <captp>.sturdyFromURI(uri)
def logService := sturdyRef.getRcvr()

logService <- log("foot")
logService <- log("shoe")

println("Searching...")
when (def result := logService <- search("foo")) -> {
  for [time, line] in result {
    println(`At $time: $line`)
  }
}</lang>

Erlang

The protocol is erlang's own

Server

srv.erl

<lang erlang> -module(srv).

-export([start/0, wait/0]).

start() ->
   net_kernel:start([srv,shortnames]),
   erlang:set_cookie(node(), rosetta),
   Pid = spawn(srv,wait,[]),
   register(srv,Pid),
   io:fwrite("~p ready~n",[node(Pid)]),
   ok.

wait() ->
   receive
       {echo, Pid, Any} ->
           io:fwrite("-> ~p from ~p~n", [Any, node(Pid)]),
           Pid ! {hello, Any},
           wait();
       Any -> io:fwrite("Error ~p~n", [Any])
   end.</lang>

Client

client.erl

<lang erlang> -module(client).

-export([start/0, wait/0]).

start() ->
   net_kernel:start([client,shortnames]),
   erlang:set_cookie(node(), rosetta),
   {ok,Srv} = init:get_argument(server),
   io:fwrite("conencting to ~p~n", [Srv]),
   {srv, list_to_atom(Srv)} ! {echo,self(), hi},
   wait(),
   ok.

wait() ->
   receive
       {hello, Any} -> io:fwrite("Received ~p~n", [Any]);
       Any -> io:fwrite("Error ~p~n", [Any])
   end.</lang>

running it (*comes later)

|erlc srv.erl
|erl -run srv start -noshell
 srv@agneyam ready
*-> hi from client@agneyam

|erlc client.erl
|erl -run client start -run init stop -noshell -server srv@agneyam
 conencting to "srv@agneyam"
 Received hi

Objective-C

Distributed Objects are natural to Objective-C, and OpenStep and derivated framework offers an easy way of using remote objects as if it were local. The client must only know the protocol the remote object support. For the rest, calling a remote object's method or local object's method is transparent.

Works with: GNUstep

Server

The server vending the object with the name DistributedAction

ActionObjectProtocol.h <lang objc>#import <Foundation/Foundation.h> // our protocol allows "sending" "strings", but we can implement // everything we could for a "local" object @protocol ActionObjectProtocol - (NSString *)sendMessage: (NSString *)msg; @end</lang>

ActionObject.h <lang objc>#import <Foundation/Foundation.h>

1. import "ActionObjectProtocol.h"

@interface ActionObject : NSObject <ActionObjectProtocol>

 // we do not have much for this example!

@end</lang>

ActionObject.m <lang objc>#import <Foundation/Foundation.h>

1. import "ActionObject.h"

@implementation ActionObject -(NSString *)sendMessage: (NSString *)msg {

 NSLog(@"client sending message %@", msg);
 return @"server answers ...";

} @end</lang>

server.m <lang objc>#import <Foundation/Foundation.h>

1. import "ActionObject.h"

int main (void) {

 NSAutoreleasePool *pool;
 ActionObject *action;
 NSConnection *connect;
 NSSocketPort *port;
 
 pool = [[NSAutoreleasePool alloc] init];
 
 action = [[ActionObject alloc] init];

 port = (NSSocketPort *)[NSSocketPort port];
 // initWithTCPPort: 1234 and other methods are not supported yet
 // by GNUstep
 connect = [NSConnection 

connectionWithReceivePort: port sendPort: port]; // or sendPort: nil

 [connect setRootObject: action];

 /* "vend" the object ActionObject as DistributedAction; on GNUstep
    the Name Server that allows the resolution of the registered name
    is bound to port 538 */
 if ([connect registerName:@"DistributedAction"

withNameServer: [NSSocketPortNameServer sharedInstance] ] == NO)

 {
   NSLog(@"can't register the server DistributedAction");
   exit(EXIT_FAILURE);
 }
 
 NSLog(@"waiting for messages...");

 [[NSRunLoop currentRunLoop] run];

 [pool release];
 return 0;

}</lang>

Client

client.m <lang objc>#import <Foundation/Foundation.h>

1. import "ActionObjectProtocol.h"

int main(void) {

 NSAutoreleasePool *pool;
 NSArray *args;
 id <ActionObjectProtocol> action;
 NSString *msg, *backmsg;

 pool = [[NSAutoreleasePool alloc] init];

 action = (id <ActionObjectProtocol>)
   [NSConnection
     rootProxyForConnectionWithRegisteredName: @"DistributedAction" 
     host: @"localhost"
     usingNameServer: [NSSocketPortNameServer sharedInstance] ];

 if (action == nil)
 {
   NSLog(@"can't connect to the server");
   exit(EXIT_FAILURE);
 }
 
 args = [[NSProcessInfo processInfo] arguments];

 if ([args count] == 1)
 {
   NSLog(@"specify a message");
   exit(EXIT_FAILURE);
 }
 
 msg = [args objectAtIndex: 1];

 // "send" (call the selector "sendMessage:" of the (remote) object
 // action) the first argument's text as msg, store the message "sent
 // back" and then show it in the log
 backmsg = [action sendMessage: msg];
 NSLog(backmsg);

 [pool release];
 return 0;

}</lang>

OCaml

Works with: JoCaml

Minimalistic distributed logger with synchronous channels using the join calculus on top of OCaml.

Server

<lang ocaml> open Printf

 let create_logger () =
   def log(text) & logs(l) =
       printf "Logged: %s\n%!" text;
       logs((text, Unix.gettimeofday ())::l) & reply to log
 
    or search(text) & logs(l) =
       logs(l) & reply List.filter (fun (line, _) -> line = text) l to search
   in
     spawn logs([]);
     (log, search)
 
 def wait() & finished() = reply to wait
 
 let register name service = Join.Ns.register Join.Ns.here name service

 let () =
   let log, search = create_logger () in
     register "log" log;
     register "search" search;
     Join.Site.listen (Unix.ADDR_INET (Join.Site.get_local_addr(), 12345));
     wait ()</lang>

Client

<lang ocaml> open Printf

 let ns_there = Join.Ns.there (Unix.ADDR_INET (Join.Site.get_local_addr(), 12345))

 let lookup name = Join.Ns.lookup ns_there name
 
 let log : string -> unit = lookup "log"
 let search : string -> (string * float) list = lookup "search"

 let find txt =
   printf "Looking for %s...\n" txt;
   List.iter (fun (line, time) ->
                printf "Found: '%s' at t = %f\n%!" (String.escaped line) time)
     (search txt)

 let () =
   log "bar";
   find "foo";
   log "foo";
   log "shoe";
   find "foo"</lang>

Python

Works with: Python version 2.4 and 2.6

XML-RPC

Protocol: XML-RPC

Server

<lang python>

1. !/usr/bin/env python
2. -*- coding: utf-8 -*-

import SimpleXMLRPCServer

class MyHandlerInstance:

   def echo(self, data):
       Method for returning data got from client
       return 'Server responded: %s' % data

   def div(self, num1, num2):
       Method for divide 2 numbers
       return num1/num2

def foo_function():

   A function (not an instance method)
   return True

HOST = "localhost" PORT = 8000

server = SimpleXMLRPCServer.SimpleXMLRPCServer((HOST, PORT))

1. register built-in system.* functions.

server.register_introspection_functions()

1. register our instance

server.register_instance(MyHandlerInstance())

1. register our function as well

server.register_function(foo_function)

try:

   # serve forever
   server.serve_forever()

except KeyboardInterrupt:

   print 'Exiting...'
   server.server_close()

</lang>

Client

<lang python>

1. !/usr/bin/env python
2. -*- coding: utf-8 -*-

import xmlrpclib

HOST = "localhost" PORT = 8000

rpc = xmlrpclib.ServerProxy("http://%s:%d" % (HOST, PORT))

1. print what functions does server support

print 'Server supports these functions:', print ' '.join(rpc.system.listMethods())

1. echo something

rpc.echo("We sent this data to server")

1. div numbers

print 'Server says: 8 / 4 is: %d' % rpc.div(8, 4)

1. control if foo_function returns True

if rpc.foo_function():

   print 'Server says: foo_function returned True'

</lang>

HTTP

Protocol: HTTP

Server

<lang python>

1. !/usr/bin/python
2. -*- coding: utf-8 -*-

import BaseHTTPServer

HOST = "localhost" PORT = 8000

1. we just want to write own class, we replace do_GET method. This could be extended, I just added basics
2. see; http://docs.python.org/lib/module-BaseHTTPServer.html

class MyHTTPHandler(BaseHTTPServer.BaseHTTPRequestHandler):

   def do_GET(self):
       # send 200 (OK) message
       self.send_response(200)
       # send header
       self.send_header("Content-type", "text/html")
       self.end_headers()

       # send context
       self.wfile.write("<html><head><title>Our Web Title</title></head>")

self.wfile.write("<body>

This is our body. You wanted to visit %s page

</body>" % self.path)

       self.wfile.write("</html>")

if __name__ == '__main__':

   server = BaseHTTPServer.HTTPServer((HOST, PORT), MyHTTPHandler)
   try:
       server.serve_forever()
   except KeyboardInterrupt:
       print 'Exiting...'
       server.server_close()

</lang>

Client

<lang python>

1. !/usr/bin/python
2. -*- coding: utf-8 -*-

import httplib

HOST = "localhost" PORT = 8000

conn = httplib.HTTPConnection(HOST, PORT) conn.request("GET", "/somefile")

response = conn.getresponse() print 'Server Status: %d' % response.status

print 'Server Message: %s' % response.read() </lang>

Socket, Plain Text

Protocol: Plain Text

Server

<lang python>

1. !/usr/bin/python
2. -*- coding: utf-8 -*-

import SocketServer

HOST = "localhost" PORT = 8000

1. our instance that will upper whatever it gets and send back to client

class UpperCaseHandler(SocketServer.StreamRequestHandler):

   def handle(self):
       print '%s connected' % self.client_address[0]
       # get what client sends
       get = self.rfile.readline()
       # write back to client
       self.wfile.write(get.upper())

if __name__ == '__main__':

   tcpserver = SocketServer.TCPServer((HOST, PORT), UpperCaseHandler)
   try:
       tcpserver.serve_forever()
   except KeyboardInterrupt:
       print 'Exiting...'
       tcpserver.server_close()

</lang>

Client

<lang python>

1. !/usr/bin/python
2. -*- coding: utf-8 -*-

import socket

HOST = "localhost" PORT = 8000

DATA = "my name is eren"

1. connect to server and send data

sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM) sock.connect((HOST, PORT)) sock.send("%s\n" % DATA)

1. get

response = sock.recv(256) sock.close()

print "We sent: %s" % DATA print 'Server responded: %s' % response </lang>

Pyro

Note: You should install Pyro (http://pyro.sourceforge.net) first and run pyro-ns binary to run code below.

Server

<lang python>

1. !/usr/bin/python
2. -*- coding: utf-8 -*-

import Pyro.core import Pyro.naming

1. create instance that will return upper case

class StringInstance(Pyro.core.ObjBase):

   def makeUpper(self, data):
       return data.upper()

class MathInstance(Pyro.core.ObjBase):

   def div(self, num1, num2):
       return num1/num2

if __name__ == '__main__':

   server = Pyro.core.Daemon()
   name_server = Pyro.naming.NameServerLocator().getNS()
   server.useNameServer(name_server)
   server.connect(StringInstance(), 'string')
   server.connect(MathInstance(), 'math')
   try:
       server.requestLoop()
   except KeyboardInterrupt:
       print 'Exiting...'
       server.shutdown()

</lang>

Client

<lang python>

1. !/usr/bin/python
2. -*- coding: utf-8 -*-

import Pyro.core

DATA = "my name is eren" NUM1 = 10 NUM2 = 5

string = Pyro.core.getProxyForURI("PYRONAME://string") math = Pyro.core.getProxyForURI("PYRONAME://math")

print 'We sent: %s' % DATA print 'Server responded: %s\n' % string.makeUpper(DATA)

print 'We sent two numbers to divide: %d and %d' % (NUM1, NUM2) print 'Server responded the result: %s' % math.div(NUM1, NUM2) </lang>

Spread

Note: You should install Spread (http://www.spread.org) and its python bindings (http://www.python.org/other/spread/)

Server

You don't need any code for server. You should start "spread" daemon by typing "spread -c /etc/spread.conf -n localhost". If you want more configuration, look at /etc/spread.conf.

After starting daemon, if you want to make sure that it is running, enter spuser -s 4803 command where 4803 is your port set in spread.conf, you will see prompt, type j user, you should see something like this message: Received REGULAR membership for group test with 3 members, where I am member 2

Client (Listener)

<lang python>

1. !/usr/bin/python
2. -*- coding: utf-8 -*-

import spread

PORT = '4803'

1. connect spread daemon

conn = spread.connect(PORT)

1. join the room

conn.join('test')

print 'Waiting for messages... If you want to stop this script, please stop spread daemon' while True:

   recv = conn.receive()
   if hasattr(recv, 'sender') and hasattr(recv, 'message'):
       print 'Sender: %s' % recv.sender
       print 'Message: %s' % recv.message

</lang>

Client (Sender)

<lang python>

1. !/usr/bin/python
2. -*- coding: utf-8 -*-

import spread

PORT = '4803'

conn = spread.connect(PORT) conn.join('test')

conn.multicast(spread.RELIABLE_MESS, 'test', 'hello, this is message sent from python') conn.disconnect() </lang>

Ruby

Uses

Library: dRuby

The "druby:" protocol uses TCP/IP sockets for communication.

Server <lang ruby> require 'drb/drb'

 # The URI for the server to connect to
 URI="druby://localhost:8787"

 class TimeServer

   def get_current_time
     return Time.now
   end

 end

 # The object that handles requests on the server
 FRONT_OBJECT = TimeServer.new

 $SAFE = 1   # disable eval() and friends

 DRb.start_service(URI, FRONT_OBJECT)
 # Wait for the drb server thread to finish before exiting.
 DRb.thread.join</lang>

Client <lang ruby> require 'drb/drb'

 # The URI to connect to
 SERVER_URI = "druby://localhost:8787"

 # Start a local DRbServer to handle callbacks.
 #
 # Not necessary for this small example, but will be required
 # as soon as we pass a non-marshallable object as an argument
 # to a dRuby call.
 DRb.start_service

 timeserver = DRbObject.new_with_uri(SERVER_URI)
 puts timeserver.get_current_time</lang>

Tcl

A rudimentary IRC Server <lang tcl>proc main {} {

   global connections
   set connections [dict create]
   socket -server handleConnection 12345
   vwait dummyVar ;# enter the event loop

}

proc handleConnection {channel clientaddr clientport} {

   global connections
   dict set connections $channel address "$clientaddr:$clientport"
   fconfigure $channel -buffering line
   fileevent $channel readable [list handleMessage $channel]

}

proc handleMessage {channel} {

   global connections
   if {[gets $channel line] == -1} {
       disconnect $channel
   } else {
       if {[string index [string trimleft $line] 0] eq "/"} {
           set words [lassign [split [string trim $line]] command]
           handleCommand $command $words $channel
       } else {
           echo $line $channel
       }
   }

}

proc disconnect {channel} {

   global connections
   dict unset connections $channel
   fileevent $channel readable ""
   close $channel

}

proc handleCommand {command words channel} {

   global connections
   switch -exact -- [string tolower $command] {
       /nick {
           dict set connections $channel nick [lindex $words 0]
       }
       /quit {
           echo bye $channel
           disconnect $channel
       }
       default {
           puts $channel "\"$command\" not implemented"
       }
   }

}

proc echo {message senderchannel} {

   global connections
   foreach channel [dict keys $connections] {
       if {$channel ne $senderchannel} {
           set time [clock format [clock seconds] -format "%T"]
           set nick [dict get $connections $channel nick]
           puts $channel [format "\[%s\] %s: %s" $time $nick $message]
       }
   }

}

main</lang> Client <lang tcl>proc main {} {

   global argv argc
   if {$argc != 2} {
       error "usage: [info script] serveraddress serverport"
   }
   connect {*}$argv
   vwait dummyVar

}

proc connect {addr port} {

   global sock
   set sock [socket $addr $port]
   fconfigure $sock -buffering line
   fileevent $sock readable getFromServer
   fileevent stdin readable sendToServer

}

proc getFromServer {} {

   global sock
   if {[gets $sock line] == -1} {
       puts "disconnected..."
       exit
   } else {
       puts $line
   }

}

proc sendToServer {} {

   global sock
   set msg [string trim [gets stdin]]
   if {[string length $msg] > 0} {
       puts $sock $msg
   }

}

main</lang>

UnixPipes

Uses netcat

server

(echo 1; echo 2; echo 3) | nc -l 1024

client

nc 192.168.0.1 1024 | wc -l