POE - Persistent Object Enviroment，http://poe.perl.org

POE是用单线程实现的基于事件驱动的，可协作完成多任务的Perl模块，简单的说，就是在单线程下的状态机，在事件的循环中，有某个注册事件发生时，就调用注册的处理代码。在用Perl做网络编程时，常常需要多进程、线程、监视Socket的IO等并发操作，相关的函数和模块即fork、threads、select，另一个选择就是使用POE单线程的事件驱动来模拟并发的进程和线程，显然单线程下可以方便的共享数据。下面实现TCP端口重定向，例一使用创建子进程和IO::Select；例二采用POE实现。

===========================================================================================
eXample one：端口重定向(fork、IO::Select）
===========================================================================================
#!C:\Perl\bin\perl.exe
#A simple TCP stream forwarder
#By shanleiguang@gmail.com, 2005/10
use strict;
use warnings;

use IO::Socket;
use IO::Select;
use Getopt::Std;
use POSIX qw(:sys_wait_h strftime);

use constant FOREVER => 1;
use constant BUFSIZE => 4096;

#父进程下处理僵死子进程
sub zombie_reaper {
while(waitpid(-1, WNOHANG) > 0) {}
$SIG{CHLD} = \&zombie_reaper;
}

$SIG{CHLD} = \&zombie_reaper;

#处理参数
my %opts;
getopts('h:l:t:p:', \%opts);

print_help() and exit if(defined($opts{'h'}));
print_help() and exit if(not defined($opts{'t'}) or not defined($opts{'p'}));
print_help() and exit if($opts{'t'} !~ m/^\d+.\d+.\d+.\d+$/);
print_help() and exit if($opts{'l'} !~ m/^\d+$/);
print_help() and exit if($opts{'p'} !~ m/^\d+$/);

my $listen_port = (defined($opts{'l'})) ? $opts{'l'} : 8080;
my $target_ip = $opts{'t'};
my $target_port = $opts{'p'};

#在本地创建监听Socket
my $socket_listen = IO::Socket::INET->new(
LocalPort => $listen_port,
Proto => 'tcp',
Listen => 5,
Reuse => 1,
);

print timestamp(), ", listening on port $listen_port ...\n";

#新建两个用于Socket IO监视的IO::Select对象
my $readers = IO::Select->new();
my $writers = IO::Select->new();

$readers->add($socket_listen);

#父进程仅监视Listening Socket的accept事件
while(FOREVER) {
my @readers = $readers->can_read;

foreach my $reader (@readers) {
if($reader eq $socket_listen) {
#创建子进程处理后续的转发，父进程继续监视Listening Socket
fork and next;

my $socket_client = $socket_listen->accept();

#在子进程中，不再需要对Listening Socket进行操作
$readers->remove($socket_listen);
$socket_listen->close();

#子进程
as_server($socket_client);

exit;
}
}
}

#子进程
sub as_server {
my $socket_client = shift;

my $client_port = $socket_client->peerport();
my $client_ip = $socket_client->peerhost();

#创建到目标地址:端口的Socket连接
my $socket_forward = IO::Socket::INET->new(
PeerAddr => $target_ip,
PeerPort => $target_port
);

print timestamp(), ", $client_ip:$client_port<->$target_ip:$target_port.\n";

#监视socket_client、socket_forward的IO情况
$readers->add($socket_client);
$readers->add($socket_forward);
$writers->add($socket_client);
$writers->add($socket_forward);

my ($rbuffer_forward, $rbuffer_client) = ('', '');

while(FOREVER) {
my @readers = $readers->can_read;

foreach my $reader (@readers) {
my $rbuffer;
#当socket_client可读时，将读取的内容追加到rbuffer_client后
#假如读取失败，则退出子进程
if($reader eq $socket_client) {
exit if(not recv($reader, $rbuffer, BUFSIZE, 0));
$rbuffer_client.= $rbuffer;
}

#当socket_forward可读时，将读取的内容追加到rbuffer_forward后
#假如读取失败，则退出子进程
if($reader eq $socket_forward) {
exit if(not recv($reader, $rbuffer, BUFSIZE, 0));
$rbuffer_forward.= $rbuffer;
}
}

my @writers = $writers->can_write;

foreach my $writer (@writers) {
#当socket_client可写，且rbuffer_forward不为空时，将rbuffer_forward
#内容写入socket_client，假如写失败，则退出子进程
if($writer eq $socket_client) {
next if(not $rbuffer_forward);
exit if(not send($writer, $rbuffer_forward, 0));
$rbuffer_forward = '';
}

#当socket_forward可写，且rbuffer_client不为空时，将rbuffer_client
#内容写入socket_forward，假如写失败，则退出子进程
if($writer eq $socket_forward) {
next if(not $rbuffer_client);
exit if(not send($writer, $rbuffer_client, 0));
$rbuffer_client = '';
}
}
}
}

sub timestamp {
return strftime "[%y/%m/%d,%H:%M:%S]", localtime;
}

sub print_help {
my $filename = (split /\\/, $0)[-1];

print <<HELP

>>> $filename [-h,-l:] <-t:,-p:>
-h print help
-l listening local port, default 8080
-t target ipaddr
-p target port
By shanleiguang\@gmail.com, 2005/10

HELP
}
===========================================================================================

===========================================================================================
eXample two：端口重定向（POE）
===========================================================================================
POE结构：

Driver->Filter->Wheel->Components
|______|______|________|
|
Session
|
Kernel

Driver： 底层文件操作的抽象，在编程时不会直接用到
Filter： 底层、中层协议操作的抽象，通常不会直接用到
Wheel： 高层协议操作的抽象，经常要用到
Components：POE提供的一些拿来就能用的组件
Session： 会话抽象，会话中需要创建高层协议抽象
Kernel： POE管理会话的内核

POE对象的数据结构：

$_[HEAP]：是会话唯一的数据存储区；
$_[SESSION]：是指向会话自身的引用；
$_[KERNEL]：是指向会话管理内核的引用；
@_[ARG0..ARG9]：用于传递给各事件处理函数的参数；

还是实例最直观：
在父会话中创建一个监听用的Socket，当有客户端连接，即有accept_sucess事件发生时，
则创建一个子会话处理后续事件，并将accept获得的客户端Socket传递给子会话；子会话
创建到目标的Socket，连接过程中，如果客户端Socket中有input事件，则将客户端的input
内容缓存在一个队列中，当连接成功后，发送给到目标的那个Socket中，见下图：

+-------------------------------+
/| Socket_listen |
/ +-------------------------------+
Client<-->|Socket_client <=> Socket_server|<-->Target
+-------------------------------+
Forwarder
===========================================================================================
#!C:\Perl\bin\perl.exe
#A simple TCP stream forwarder
#By shanleiguang@gmail.com, 2005/10
use strict;
use warnings;

use Socket;
use Getopt::Std;
use POSIX qw(strftime);
use POE qw(
Wheel::SocketFactory
Wheel::ReadWrite
Filter::Stream
);

#Get Options
my %opts;
getopts('hl:t:p:', \%opts);

print_help() and exit if(defined($opts{'h'}));
print_help() and exit if(not defined($opts{'t'}) or not defined($opts{'p'}));
print_help() and exit if($opts{'t'} !~ m/^\d+.\d+.\d+.\d+$/);
print_hekp() and exit if($opts{'p'} !~ m/^\d+$/);

my $listen_port = (defined($opts{'l'})) ? $opts{'l'} : 8080;
my $target_addr = $opts{'t'};
my $target_port = $opts{'p'};

###Create Parent - 'Listen Session'###
###创建父会话用于监听客户端的连接
###会话创建的最后将进入_start状态，执行_start的handler
###accept_success即在_start的handler中创建监听Socket的Wheel中
###的SuccessEvent事件，它的handler是forwarder_create函数
###$_[ARG0]是wheel::SocketFatory的SuccessEvent传递的参数
POE::Session->create(
inline_states => {
_start => \&forwarder_server_start,
_stop => sub { print timestamp(), ", forwarder server stopped."; },

accept_success => sub { &forwarder_create($_[ARG0]); },
accept_failure => sub { delete $_[HEAP]->{server_wheel} },
},
);

$poe_kernel->run();

exit;

###Event handlers for Parent Session###
###父会话中的事件处理函数
sub forwarder_server_start {
print timestamp(), ", listening on port $listen_port and ";
print "forward to $target_addr:$target_port\n";

#在父会话的存储区创建一个监听Socket类型的Wheel
$_[HEAP]->{server_wheel} = POE::Wheel::SocketFactory->new(
BindPort => $listen_port,
SocketProtocol => 'tcp',
ListenQueue => SOMAXCONN,
Reuse => 'on',

#ARG0 of SuccessEvent
SuccessEvent => 'accept_success',
FailureEvent => 'accept_failure',
);
}

###Create Child - 'Forward Session'###
###创建子会话
sub forwarder_create {
my $socket = shift;

POE::Session->create(
inline_states => {
_start => \&forwarder_start,
_stop => sub {
print ' ' x 4, timestamp(), ', sessionId:';
print $_[SESSION]->ID, ", forwarder stop\n";
},
client_input => \&client_input,
client_error => sub {
delete $_[HEAP]->{wheel_client};
delete $_[HEAP]->{wheel_server};
},
server_connect => \&server_connect,
server_input => sub {
$_[HEAP]->{wheel_client}->put($_[ARG0])
if(exists $_[HEAP]->{wheel_client});
},
server_error => sub {
delete $_[HEAP]->{wheel_client};
delete $_[HEAP]->{wheel_server};
},
},
#Parameters to '_start' Event
args => [$socket],
);
}

##Event Handlers of Child Session##

sub forwarder_start {
my ($heap, $socket) = @_[HEAP, ARG0];

print ' ' x 4, timestamp(), ', sessionId:';
print $_[SESSION]->ID, ", forwarder start\n";

#Buffer client's input while connecting to the target
$heap->{state} = 'connecting';
$heap->{queue} = [];

#Client<-'wheel_client'->Forwarder server
$heap->{wheel_client} = POE::Wheel::ReadWrite->new(
Handle => $socket,
Driver => POE::Driver::SysRW->new(),
Filter => POE::Filter::Stream->new(),
InputEvent => 'client_input',
ErrorEvent => 'client_error',
);

#Forwarder server<-'wheel_server'->target
$heap->{wheel_server} = POE::Wheel::SocketFactory->new(
RemoteAddress => $target_addr,
RemotePort => $target_port,
SuccessEvent => 'server_connect',
FailureEvent => 'server_error',
);
}

sub server_connect {
my ($kernel, $session, $heap, $socket) = @_[KERNEL, SESSION, HEAP, ARG0];

#Replace $heap->{wheel_server}
$heap->{wheel_server} = POE::Wheel::ReadWrite->new(
Handle => $socket,
Driver => POE::Driver::SysRW->new,
Filter => POE::Filter::Stream->new,
InputEvent => 'server_input',
ErrorEvent => 'server_error',
);

$heap->{state} = 'connected';

$kernel->call($session, 'client_input', $_) foreach(@{$heap->{queue}});

$heap->{queue} = [];
}

sub client_input {
my ($heap, $input) = @_[HEAP, ARG0];

push @{$heap->{queue}}, $input and return if($heap->{state} eq 'connecting');
$heap->{wheel_server}->put($input) if(exists $heap->{wheel_server});
}

#Common subroutines
sub timestamp {
return strftime "[%H:%M:%S]", localtime;
}

sub print_help {
my $filename = (split /\\/, $0)[-1];

print <<HELP

>>> $filename [-h,-l:] <-t:,-p:>
-h print help
-l listen port
-t target ipaddress
-p target port
A simple TCP forwarder server, 2005/10
By shanleiguang\@gmail.com

HELP
}
===========================================================================================