XML in Client and Server Communication

Part:   1  2  

(Continued from previous part...)

The game ID concept is used to identify if an incoming XML message is for continuing an existing game or starting a new game. When the server receives a client message for the first time, it will assign a new game ID, and return the game ID to the client. The client program must use this game ID in the subsequent messages to continue the same game.

The server is not written to serve multiple clients simultaneously.

Let's run GameServer.pl in command window, and let it listen to port 8080 for any client program connection.

Now in another command window, we can run the telnet command to test the server, "telnet localhost 8080". Then enter the following XML message to the telnet program. Remember telnet will not echo your input on the screen, so you have to type in the message "blindly".

<c><m>Hi there!</m></c>

You will get the following message from the server displayed on the telnet window

<s>
     <m>Welcome to Game Server!
          I have a number between 0 and 99 for you to guess
.</m>
       <i>2</i>
               </s>

XML with Socket Communication Example - GameClient.pl

Now let's see a real client program, GameClient.pl:

#- GameClient.pl
#- Copyright (c) 1999 by Dr. Herong Yang
#
   use Socket;
   use XML::Simple;
   &init;
   $ref = $xs->XMLin("game_1.xml");
   $ref = &send($ref);
   $gid = $ref->{s}->[0]->{i}->[0];
   $ref = $xs->XMLin("game_2.xml");
   $ref->{c}->[0]->{i}->[0] = $gid;
   $ref->{c}->[0]->{n}->[0] = "39";
   $ref = &send($ref);
   $ref = $xs->XMLin("game_2.xml");
   $ref->{c}->[0]->{i}->[0] = "-1";
   $ref->{c}->[0]->{n}->[0] = "29";
   $ref = &send($ref);
   exit;
sub init {
   open(LOG,">> GameClient.log");
   select(LOG); $|=1;
   open(STDERR, ">&LOG") || die "Die: Setting STDERR to log file";
   open(REC,">> GameClient.rec");
   select(REC); $|=1;
   $xs = new XML::Simple(keeproot => 1, forcearray => 1, 
      searchpath => ".");
   $host = "localhost";
   $port = "8080";
}
sub send {
   my ($ref) = @_;
   socket(SOCK,PF_INET,SOCK_STREAM,'tcp');
#   bind(SOCK, pack_sockaddr_in("1024", INADDR_ANY)); # no need to bind
   $sAddress = pack_sockaddr_in($port,inet_aton($host));
   connect(SOCK, $sAddress) || die "Die: Connecting to $host $port";
   open(STDIN, "+<&SOCK") || die "Die: Setting STDIN to socket";
   open(STDOUT, "+>&SOCK") || die "Die: Setting STDOUT to socket";
   select(STDOUT); $|=1;
   my $xml = $xs->XMLout($ref);
   print STDOUT $xml;
   print REC "$xml\n";
   my ($tag,$fin,$msg);
   while (<STDIN>) {
      /<(\w+)>/ && ($tag=$1) unless $tag;
      /<\/$tag>/ && ($fin=$tag) if $tag;
      $msg = $msg.$_;
      last if $fin;
   }
   print REC "$msg\n";
   close(STDIN);
   close(STDOUT);
   return $xs->XMLin($msg);
}

This client program is also simple. It reads some XML message files prepared a game, and send them over to the server one at a time. There are two XML message files:

1. game_1.xml:

<c><m>Hello</m></c>

2. game_2.xml:

<c><i>0</i><n>0</n></c>

If you run the client program, you should get the following in the GameClient.rec recording file:

a<c>
  <m>Hello</m>
</c>

<s>
  <m>Welcome to Game Server!
I have a number between 0 and 99 for you to guess.</m>
  <i>1</i>
</s>

<c>
  <n>39</n>
  <i>1</i>
</c>

<s>
  <m>Your guess is too high.
 Please make another quess.</m>
  <i>1</i>
</s>

<c>
  <n>29</n>
  <i>-1</i>
</c>

<s>
  <m>Sorry. Your game ID doesn't exist.</m>
  <i>0</i>
</s>

This clearly shows you a simple conversation between the client and server with XML messages.

Part:   1  2