Since I already showed you how to use a procedural script for creating a multi-request TCP server, I'll now list different versions of the same application, just in case you want to work with a reusable function or, specifically in the object-based area, with a PHP class. Here are the respective definitions for both approaches:

/*
/**************************************************************
/ 'createSocketServer()' function
/**************************************************************
*/
function createSocketServer($host='127.0.0.1',$port=12345){
    set_time_limit(0);
    // create low level socket
    if(!$socket=socket_create(AF_INET,SOCK_STREAM,0)){
        trigger_error('Error creating new socket',E_USER_ERROR);
    }
    // tie up socket to TCP port
    if(!socket_bind($socket,$host,$port)){
        trigger_error('Error binding socket to TCP
port',E_USER_ERROR);
    }
    // begin listening connections
    if(!socket_listen($socket)){
        trigger_error('Error listening socket
connections',E_USER_ERROR);
    }
    // create communication socket
    if(!$comSocket=socket_accept($socket)){
        trigger_error('Error creating communication
socket',E_USER_ERROR);
    }
    $message='This is a simple TCP/IP server created with PHP
sockets!'."rn";
    socket_write($comSocket,$message,strlen($message));
    // start a loop and continue reading user input
    do{
        // delay loop execution
        sleep(10);
        // read socket input
        $socketInput=socket_read($comSocket,1024);
        if(trim($socketInput)!=''){     
            // if user did not entered the 'STOP" command
continue reading data
            if(trim($socketInput)!='STOP'){
                // convert to uppercase socket input 
                $socketOutput='The string you entered was
'.$socketInput."rn";
                // write data back to socket server
                socket_write($comSocket,$socketOutput,strlen
($socketOutput));
                echo 'The string you entered is '.$socketOutput;
            }
            else{
                // if 'STOP' command was entered close
communication socket & terminate all the connections
                socket_close($comSocket);
                break;
            }
        }
    }
    while(true);
    // close global socket
    socket_close($socket);
}

/*
/*************************************************************
/  'SocketServer()' class
/*************************************************************
*/
class SocketServer{
    var $host;
    var $port;
    var $delay=10;
    var $message="This is a simple TCP/IP server created with PHP
sockets!rn";
    function SocketServer($host='127.0.0.1',$port=12345){
        if(!is_int($port)||$port<1||$port>65535){
            trigger_error('Invalid port number',E_USER_ERROR);
        }
        $this->host=$host;
        $this->port=$port;
        $this->connect();
    }
    function connect(){
        set_time_limit(0);
        // create low level socket
        if(!$socket=socket_create(AF_INET,SOCK_STREAM,0)){
            trigger_error('Error creating new
socket',E_USER_ERROR);
        }
        // tie up socket to TCP port
        if(!socket_bind($socket,$this->host,$this->port)){
            trigger_error('Error binding socket to TCP
port',E_USER_ERROR);
        }
        // begin listening connections
        if(!socket_listen($socket)){
            trigger_error('Error listening socket
connections',E_USER_ERROR);
        }
        // create communication socket
        if(!$comSocket=socket_accept($socket)){
            trigger_error('Error creating communication
socket',E_USER_ERROR);
        }
        socket_write($comSocket,$this->message,strlen($this-
>message));
        // start a loop and continue reading user input
        do{
            // delay loop execution
            sleep($this->delay);
            // read socket input
            $socketInput=socket_read($comSocket,1024);
            if(trim($socketInput)!=''){ 
                // if user did not entered the 'STOP" command
continue reading data
                if(trim($socketInput)!='STOP'){
                    $socketOutput='The string you entered was
'.$socketInput."rn";
                    // write data back to socket server
                    socket_write($comSocket,$socketOutput,strlen
($socketOutput));
                    echo 'The string you entered is
'.$socketOutput;
                }
                else{
                    // if 'STOP' command was entered close
communication socket & terminate all the connections
                    socket_close($comSocket);
                    break;
                }
            }
        }
        while(true);
        // close global socket
        socket_close($socket);
    }
}

In the first case, if you're going to use the "createSocketServer()" function, this one can be used like this:

// call 'createSocketServer()" function
createSocketServer();

Or, in case you prefer to work with an object-oriented approach, the "SocketServer" class can be utilized as follows:

// instantiate 'SocketServer' object
$sock=&new SocketServer();

To wrap up

That's all for the moment. In this second part of the series, I've shown you how to build an extensible TCP server that handles multiple incoming requests, using the PHP socket-related functions that you learned in the first tutorial. But, do you think that's all? Nope; in the last article, I'll demonstrate how to implement a Web server on your own machine, by utilizing a few low-level sockets. You don't have any excuses to miss it!