Perl Tutorials - Herong's Tutorial Examples - v6.01, by Dr. Herong Yang
GameServer.pl - XML Communication Server Example
This section provides a tutorial example on how write an XML communication server program to accept client connections, send and receive XML messages.
In the following example, I wrote a simple client and server based game application. It's a simple game, in which the server accepts new client connections, and holds a number for the client to guess.
The information is exchanged between the client and server in plain XML format, and delivered with plain TCP communication protocol.
Here is the server program, GameServer.pl:
#- GameServer.pl
#- Copyright (c) HerongYang.com. All Rights Reserved.
#
use Socket;
use XML::Simple;
$xs = new XML::Simple(keeproot => 1, forcearray => 1);
$gameID = 0;
$number = 0;
$response = "<s><i>0</i><m>hello</m></s>";
&runServer;
exit;
sub runServer {
open(LOG,">> GameServer.log");
select(LOG); $|=1;
open(STDERR, ">&LOG") || die "Die: Setting STDERR to log file";
open(REC,">> GameServer.rec");
select(REC); $|=1;
socket(SOCK,PF_INET,SOCK_STREAM,'tcp');
bind(SOCK, pack_sockaddr_in("8080", INADDR_ANY));
listen(SOCK, 1); # can only take one client at a time
print LOG localtime().": Listening to port 8080\n";
for (;;) {
$cAddress = accept(NEWSOCK,SOCK) || die "Error: Accepting: $!";
($cPort, $cHost) = unpack_sockaddr_in($cAddress);
$cHostName = inet_ntoa($cHost);
print LOG localtime().": Connected with $cHostName at $cPort\n";
open(STDIN, "+<&NEWSOCK") || die "Die: Setting socket STDIN";
open(STDOUT, "+>&NEWSOCK") || die "Die: Setting socket STDOUT";
select(STDOUT); $|=1;
&serve;
close(STDIN);
close(STDOUT);
}
}
sub serve {
my ($tag,$fin,$msg);
while (<STDIN>) {
/<(\w+)>/ && ($tag=$1) unless $tag;
/<\/$tag>/ && ($fin=$tag) if $tag;
$msg = $msg.$_;
last if $fin;
}
print REC "$msg\n";
my $ref = $xs->XMLin($msg);
if (exists($ref->{c}->[0]->{i})) {
my $gid = $ref->{c}->[0]->{i}->[0];
my $num = $ref->{c}->[0]->{n}->[0];
if ($gid == $gameID) {
$msg = &oldGame($gid,$num);
} else {
$msg = &invalidGame($gid,$num);
}
} else {
$msg = &newGame;
}
print STDOUT $msg;
print REC "$msg\n";
}
sub oldGame {
my ($gid,$num) = @_;
my $ref = $xs->XMLin($response);
my $msg;
if ($num == $number) {
$msg = "Congratulations!\n"
."I have another number between 0 and 99 for you to guess.";
$gameID++;
$number = rand(100);
} elsif ($num > $number) {
$msg = "Your guess is too high.\n Please make another guess.";
} else {
$msg = "Your guess is too low.\n Please make another guess.";
}
$ref->{s}->[0]->{i}->[0] = $gameID;
$ref->{s}->[0]->{m}->[0] = $msg;
return $xs->XMLout($ref);
}
sub newGame {
$gameID++;
$number = rand(100);
my $ref = $xs->XMLin($response);
$ref->{s}->[0]->{m}->[0] = "Welcome to Game Server!\n"
."I have a number between 0 and 99 for you to guess.";
$ref->{s}->[0]->{i}->[0] = $gameID;
return $xs->XMLout($ref);
}
sub invalidGame {
my ($sid,$num) = @_;
my $ref = $xs->XMLin($response);
$ref->{s}->[0]->{m}->[0] = "Sorry. Your game ID doesn't exist.";
return $xs->XMLout($ref);
}
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>
Table of Contents
Data Types: Values and Variables
Expressions, Operations and Simple Statements
Name Spaces and Perl Module Files
Hard References - Addresses of Memory Objects
Objects (or References) and Classes (or Packages)
Typeglob and Importing Identifiers from Other Packages
String Built-in Functions and Performance
File Handles and Data Input/Output
Open Directories and Read File Names
File System Functions and Operations
Socket Communication Over the Internet
XML::Simple Module - XML Parser and Generator
XML Messages over Socket Connections
►GameServer.pl - XML Communication Server Example
GameClient.pl - XML Communication Client Example
SOAP::Lite - SOAP Server-Client Communication Module
Perl Programs as IIS Server CGI Scripts
CGI (Common Gateway Interface)
XML-RPC - Remote Procedure Call with XML and HTTP
RPC::XML - Perl Implementation of XML-RPC
Integrating Perl with Apache Web Server
CGI.pm Module for Building Web Pages
LWP::UserAgent and Web Site Testing
Converting Perl Script to Executable Binary