In this article, let us discuss how to write Perl socket programming using the inbuilt socket modules in Perl.
Perl socket modules provides an object interface that makes it easier to create and use TCP / UPD sockets.
本文讨论使用Perl内建的socket模块来实现Perl socket编程

This article covers the following topics:
本文的主题如下:
. Perl example code for TCP client and server             (Perl实现TCP客户端和服务端)
. Perl example code for UDP client and server             (Perl实现UDP客户端和服务端)
. Read and write descriptor list using Select(IO::Select) (使用select来读写描述符列表)


CPAN module IO::Socket::INET is used to perform socket operations such as 
— creating, binding, connecting, listening and closing the socket.
IO::Select module is used for obtaining the descriptors that are ready for read/write operations.
IO::Socket::INET用来执行socket操作,如创建，绑定，连接，监听，和关闭socket;
IO::Select模块用来获得可读/写操作的描述符;

Perl TCP Client and Server
TCP is a connection oriented networking protocol. 
In this example, let us review the Perl code-snippet that will explaining us the simple client and server communication.


Perl TCP Server Operation
Perl TCP 服务端操作
The socket operation such as socket creation, binding and listening to the socket is performed by the IO::Socket::INET module.

The Perl code given below does the following:
. Create the Socket                           (创建socket)
. Bind the socket to an address and port      (绑定socket的地址和端口)
. Listen to the socket at the port address    (监听端口)
. Accept the client connections               (接受连接)
. Perform read/write operation on the socket. (执行读写操作)


#!/usr/bin/perl
#tcpserver.pl

use IO::Socket::INET;

# flush after every write
$| = 1;


my ($socket,$client_socket);
my ($peeraddress,$peerport);


# creating object interface of IO::Socket::INET modules which internally does
# socket creation, binding and listening at the specified port address.
$socket = new IO::Socket::INET (
    LocalHost => '127.0.0.1',
    LocalPort => '5000',
    Proto => 'tcp',
    Listen => 5,
    Reuse => 1
) or die "ERROR in Socket Creation : $!\n”;


print "SERVER Waiting for client connection on port 5000";


while(1)
{
  # waiting for new client connection.
  $client_socket = $socket->accept();


  # get the host and port number of newly connected client.
  $peer_address = $client_socket->peerhost();
  $peer_port = $client_socket->peerport();


  print “Accepted New Client Connection From : $peeraddress, $peerport\n ”;


  # write operation on the newly accepted client.
  $data = “DATA from Server”;
  print $client_socket “$data\n”;


  # we can also send the data through IO::Socket::INET module,
  # $client_socket->send($data);


  # read operation on the newly accepted client
  $data = <$client_socket>;


  # we can also read from socket through recv()  in IO::Socket::INET
  # $client_socket->recv($data,1024);
  print “Received from Client : $data\n”;
}


$socket->close();


Also, refer to our earlier Perl debugger article to learn how to debug your perl code.

Perl TCP Client Operation
Perl TCP 客户端操作
The Perl code given below does the following:
. Create the socket.                                 (创建socket) 
. Connect to the remote machine at a specific port.  (连接服务端的端口)
. Perform read/write operation on the socket.        (执行读/写操作)


#!/usr/bin/perl
#tcpclient.pl


use IO::Socket::INET;


# flush after every write
$| = 1;


my ($socket,$client_socket);


# creating object interface of IO::Socket::INET modules which internally creates
# socket, binds and connects to the TCP server running on the specific port.
$socket = new IO::Socket::INET (
    PeerHost => '127.0.0.1',
    PeerPort => '5000',
    Proto => 'tcp',
) or die "ERROR in Socket Creation : $!\n”;


print “TCP Connection Success.\n”;


# read the socket data sent by server.
$data = <$socket>;


# we can also read from socket through recv()  in IO::Socket::INET
# $socket->recv($data,1024);
print “Received from Server : $data\n”;


# write on the socket to server.
$data = “DATA from Client”;
print $socket “$data\n”;


# we can also send the data through IO::Socket::INET module,
# $socket->send($data);


sleep (10);
$socket->close();

Note: You can use Vim editor as a Perl IDE using the perl-support.vim Plugin.

Perl UDP Server
Perl UDP 服务端
The Perl code given below does the following:
. Create the socket.                     (创建socket) 
. Bind the socket to the specific port.  (绑定端口)


#!/usr/bin/perl
#udpserver.pl


use IO::Socket::INET;


# flush after every write
$| = 1;


my ($socket,$received_data);
my ($peeraddress,$peerport);


#  we call IO::Socket::INET->new() to create the UDP Socket and bound
# to specific port number mentioned in LocalPort and there is no need to provide
# LocalAddr explicitly as in TCPServer.
$socket = new IO::Socket::INET (
    LocalPort => '5000',
    Proto => 'udp',
) or die "ERROR in Socket Creation : $!\n”;


while(1)
{
  # read operation on the socket
  $socket->recv($recieved_data,1024);


  #get the peerhost and peerport at which the recent data received.
  $peer_address = $socket->peerhost();
  $peer_port = $socket->peerport();
  print "\n($peer_address , $peer_port) said : $recieved_data";


  #send the data to the client at which the read/write operations done recently.
  $data = “data from server\n”;
  print $socket “$data”;
}


$socket->close();


Perl UDP Client
Perl UDP 客户端
The Perl code given below does the following:
. Create the UDP client.                          (创建socket) 
. Connect to the specific UDP server.             (连接到指定UDP服务端)
. Perform write and read operation on the socket. (执行读/写操作)


#!/usr/bin/perl
#udpclient.pl


use IO::Socket::INET;


# flush after every write
$| = 1;


my ($socket,$data);


# We call IO::Socket::INET->new() to create the UDP Socket
# and bind with the PeerAddr.
$socket = new IO::Socket::INET (
    PeerAddr   => '127.0.0.1:5000',
    Proto        => 'udp'
) or die "ERROR in Socket Creation : $!\n”;


#send operation
$data = “data from client”;
$socket->send($data);


#read operation
$data = <$socket>;
print “Data received from socket : $data\n ”;


sleep(10);
$socket->close();


Also, refer to our earlier article to understand Perl Array Reference.


IO::Select Module – Get to know the list of ready descriptors
IO::Select Module – 获得准备好的描述符


IO::Select module provides following two major functions:
. can_read() returns the available read descriptors   (返回可读的描述符) 
. can_write() returns the available write descriptors (返回可写的描述符)


To understand the usage of IO::Select, we are going to use this module in the tcpserver code.

Step 1 : Create the IO::Socket object interface
创建 IO::Socket对象接口

The following code-snippet creates the object interface of IO::Socket::INET modules 
which internally creates a socket, binds and listens to a specified port address.

$socket = new IO::Socket::INET (
    LocalHost => '127.0.0.1',
    LocalPort => '5000',
    Proto => 'tcp',
    Listen => 5,
    Reuse => 1
) or die "ERROR in Socket Creation : $!\n";

$select = IO::Select->new($socket) or die "IO::Select $!";


Step 2 : Add descriptors to Select objects
将描述符添加到Select对象

The following code-snippet adds the descriptor to the list of select objects to get the descriptors ready.

@ready_clients = $select->can_read(0);
foreach my $fh (@ready_clients)  {
  print $fh "";
  if($fh == $socket) {
    my $new = $socket->accept();
    $select->add($new);
  }
}

Step 3: Get descriptors which are ready to read
获得可读的描述符

Following Perl code-snippets gets the list of descriptor that are ready to read.

@ready_clients = $select->can_read(0);
foreach my $fh (@ready_clients)  {
  if($fh != $socket)  {
    chomp($data=<$socket>);
    print $data,"\n";
  }
}


In the same way, we can do for the write operation on the socket.

Step 4: Remove Client Socket Descriptor from Select list
将客户端socket描述符从select列表中删除

When the connection is closed, you can remove the client socket descriptor for the select list as shown below.
当连接关闭后，需要将socket描述符从select列表中删除


SIGPIPE signal gets generated when we try to send/receive data on the socket that is closed by the remote machine.  So, we can assign the signal handler for SIGPIPE signal, which should remove of descriptor from the select list as shown below. 在使用socket进行数据的发送/接收中，当远端机器关闭socket连接时，将会发送SIGIPE信号. 因此，我们可以在收到SIGIPE信号时，将描述符从select 列表中删除 # $current_client is the global variable which has the recent file descriptor # on which the send/receive operation is tried. ### Handle the PIPE $SIG{PIPE} =  sub {   ####If we receieved SIGPIPE signal then call Disconnect this client function   print "Received SIGPIPE , removing a client..\n";   unless(defined $current_client){     print "No clients to remove!\n";   }else{     $Select->remove($current_client);     $current_client->close;   }   #print Dumper $Self->Select->handles;   print "Total connected clients =>".(($Select->count)-1)."<\n"; };