Socket Communication

Part:   1  2  3   4 

(Continued from previous part...)

In the telnet window, type in the following text:

Fish, I love you and respect you very much.
But I will kill you dead before this day ends.
.

The text will be reversed and returned back from the ReverseEchoer.pl:

Welcome to Reverse Echo Server. 
.hcum yrev uoy tcepser dna uoy evol I ,hsiF
.sdne yad siht erofeb daed uoy llik lliw I tuB
.

Note that the telnet program is not displaying text you typed in. It only displays the text received from ReverseEchoer.pl program.

SocketClient.pl - A Simple Socket Client Application

Instead of using the telnet program, we can use the following program, SocketClient.pl, to communicate with ReverseEchoer.pl:

#- SocketClient.pl
#- Copyright (c) 1999 by Dr. Herong Yang
#
   $domain = 2; # Internet domain
   $type = 1; # Sequenced, reliable, two-way connection, byte streams
   $proto = 6; # Transmission Control Protocol (TCP)
   socket(SOCK,$domain,$type,$proto);
   $host = pack('C4', 127,0,0,1); # localhost = 127.0.0.1
   $port = 1024; 
   $address = pack('S n a4 x8', $domain, $port, $host);
   bind(SOCK, $address);
   print STDOUT "Client host: ",join('.',unpack('C4', $host)),"\n";
   print STDOUT "Client port: $port\n";
   $sHost = pack('C4', 127,0,0,1); # localhost = 127.0.0.1
   $sPort = 8888; 
   $sAddress = pack('S n a4 x8', $domain, $sPort, $sHost);
   connect(SOCK, $sAddress);
   print STDOUT "Server host: ",join('.',unpack('C4', $sHost)),"\n";
   print STDOUT "Server port: $sPort\n";
   select(SOCK); $| = 1; select(STDOUT);
   while ($m=<SOCK>) {
      print STDOUT $m;
      $m = <STDIN>;
      print SOCK $m;
   }
   close(SOCK);
   exit;

Note that:

• Setting $| to 1 is to turn on auto flush to the default file handle. In order to turn on auto flush to SOCK, I have to use select() function to switch default file handles.

Now, run ReverseEchoer.pl, then run SocketClient.pl in a separate command window. If you type in the same text as in the previous test, you will get the following output:

Client host: 127.0.0.1
Client port: 1024
Server host: 127.0.0.1
Server port: 8888
Welcome to Reverse Echo Server.
Fish, I love you and respect you very much.
.hcum yrev uoy tcepser dna uoy evol I ,hsiF
But I will kill you dead before this day ends.
.sdne yad siht erofeb daed uoy llik lliw I tuB
.

Network Utility Functions

getprotobyname($protoName) - Returns the protocol number of the specified protocol name in scalar context, and ($protoName,$aliases,$protoNumber) in list context.

getservbyname($serviceName,$protoName) - Returns the port number of the specified network service name and protocol name in scalar context, and ($serviceName,$aliases,$portNumber,$protoName) in list context.

getservbyport($portNumber,$protoName) - Returns the network service name of the specified port number and protocol name in scalar context, and ($serviceName,$aliases,$portNumber,$protoName) in list context.

gethostbyname($hostName) - Returns the packed IP address of the specified host name in scalar context, and ($name,$aliases,$addrtype,$length,@addrs) in list context. The host name can also be specified in IP address format.

gethostbyaddr($packedHostAddress) - Returns the host name of the specified packed IP address in scalar context, and ($name,$aliases,$addrtype,$length,@addrs) in list context.

(Continued on next part...)

Part:   1  2  3   4