Tutorial Addendum on Perl - Allotment B - Atrium Advice

listen() - Sets a atrium handle to accept approach with the defined chain admeasurement of

    

incoming affiliation requests. This action is alone acclimated by the server application.

    

For example:

    

    
   $queueSize = 5;

    
   listen(SOCK, $queueSize);

    

accept() - Waits for admission affiliation requests on the defined atrium handle,

    

accepts the first affiliation request, creates a new atrium handle, one end apprenticed to the aforementioned

    

local abode as the defined atrium handle, the additional end apprenticed to the remote

    

address accustomed in the affiliation request, and allotment the abolish address.

    

If no error, the new atrium handle is accessible for data transmission.

    

This action is alone acclimated by the server application.

    

For example:

    

    
   $address = accept(NEWSOCK,SOCK);

    

connect() - Sends a advice appeal to a limited abode that represents a anchorage

    

on a limited system. If the limited arrangement accustomed the request, the defined socket

    

handle will be apprenticed to the limited address. If no error, the defined atrium handle

    

is accessible for data transmission. This action is alone acclimated by the applicant application.

    

For example:

    

    
   $domain = 2; # Internet domain

    
   $host = pack( C4 , 216,109,118,67); # www.yahoo.com = 216.109.118.67

    
   $port = 80; 

    
   $address = pack( S n a4 x8 , $domain, $port, $host);

    
   connect(SOCK, $address);

    

The afterward diagram shows the accomplish complex in establishing an Internet

    

socket advice hotlink using the congenital functions:

    

    
       Applicant Arrangement            Server System

    
       Internet Abode #a      Internet Abode #b

    
Step   Accessible Anchorage #p        Accessible Anchorage #q

    

 

    
1                               socket(SOCK,2,1,6);

    
2                               bind(SOCK,#b+#q);

    
3                               listen(SOCK,5);

    
4                               accept(NEWSOCK,SOCK);

    
5      Socket(SOCK,2,1,6);      (waiting)

    
6      bind(SOCK,#a+#p);        (waiting)

    
7      connect(SOCK,#b+#q);     (receiving request)

    
8      (estalishing the link)   (establishing the link)

    
9      (SOCK is ready)          (NEWSOCK is ready)

    

ReverseEchoer.pl - A Simple Atrium Server Application

    

The afterward program alleged ReverseEchoer.pl is a simple atrium server application,

    

which listens for a affiliation request. Already connected, it

    

reads what curve of argument from the applicant application, reverses the argument lines,

    

and echoes aback to the limited application:

    

 

    
#- ReverseEchoer.pl

    
#- Absorb (c) 1999 by Dr.  Yang

    
#

    
   $domain = 2; # Internet domain

    
   $type = 1; # Sequenced, reliable, two-way connection, byte streams

    
   $proto = 6; # Manual Ascendancy Agreement (TCP)

    
   socket(SOCK,$domain,$type,$proto);

    
   $host = pack( C4 , 0,0,0,0); # Bounded wildcard host id: 0.0.0.0

    
   $port = 8888;

    
   $address = pack( S n a4 x8 , $domain, $port, $host);

    
   bind(SOCK, $address);

    
   $queueSize = 5; # Chain up to 5 connections

    
   listen(SOCK, $queueSize);

    
   book STDOUT "Server host: ",join( . ,unpack( C4 , $host)),"

";

    
   book STDOUT "Server port: $port

";

    
   $cAddress = accept(NEWSOCK,SOCK);

    
   ($cDomain, $cPort, $cHost) = unpack( S n a4 x8 , $cAddress);

    
   book STDOUT "Client host: ",join( . ,unpack( C4 , $cHost)),"

";

    
   book STDOUT "Client port: $cPort

";

    
   select(NEWSOCK); $| = 1; select(STDOUT);

    
   book NEWSOCK "Welcome to About-face Answer Server.

";

    
   while ($m=<NEWSOCK>) {

    
      $m =~ s/

|

//g;

    
      endure if ($m eq ".");

    
      $m = reverse($m);

    
      book NEWSOCK "$m

";

    
   }

    
   close(NEWSOCK);

    
   exit;

    

Note that:

    

    
• The atrium is apprenticed to the bounded arrangement with the wildcard host abode 0.0.0.0,
  
      

  which represents any IP abode on the bounded host system.
  
      



    
• Setting $| to 1 is to about-face on auto even to the absence book handle. In adjustment to
  
      

  turn on auto even to NEWSOCK, I accept to use select() action to about-face absence file
  
      

  handles.
  
      



    
• If a argument band accustomed alone contains a individual appearance . ,
  
      

  the advice hotlink will be concluded by the close() call.
  
      



    

Run ReverseEchoer.pl, you will get the afterward achievement on the animate window:

    

 

    
Server host: 0.0.0.0

    
Server port: 8888

    

This tells us that the program is accessible to acquire appeal at abode 0.0.0.0

    

and anchorage 8888.

    

To analysis ReverseEchoer.pl, we can use an absolute applicant program alleged telnet

    

to admit the advice appeal and allocution to ReverseEchoer.pl. Accessible addition

    

command window and blazon in the afterward command:

    

 

    
telnet localhost 8888

    

Immediately, you will see added achievement on the animate window of ReverseEchoer:

    

 

    
Client host: 127.0.0.1

    
Client port: 1032

    

This tells us that the server atrium accustomed a affiliation request, and

    

a advice hotlink has be accustomed with the applicant application,

    

which is the telnet program active on the aforementioned machine. The applicant host, 127.0.0.1,

    

is the accepted IP abode for "localhost". The applicant port, 1032, was

    

picked up by the telnet program.