Emulating a Web server - PHP

Emulating the behavior of a real Web server with low-level sockets is a quite easy process to perform. In this case, I’m not going to use real HTTP commands like GET or POST requests, since it’d be rather pointless (probably you have a production-level Web server already installed on your computer), so instead I’ll create an “always-on” TCP server, which will be capable of fetching a specific (X)HTML file, according to the request made by a client.

At the end of this interaction, the contents of this file will be displayed to the user, in this way emulating the interactive process between a real Web server and the corresponding HTTP user agent.

Having explained how the Web server will work, here is the PHP class that precisely implements this application. Please, have a look at the code listed below:

// define 'WebServer' class
class WebServer {
    var $docDir;
    var $host;
    var $port;
    var $socket;
    var $comSocket;
    function WebServer($host='127.0.0.1',$port='12345',$docDir='defaultDir'){
        $this->docDir=$docDir;
        $this->host=$host;
        $this->port=$port;
        $this->createSocket();
        $this->readUserInput();
    }
    function createSocket(){
        set_time_limit(0);
        // create low level socket
        if(!$this->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($this->socket,$this->host,$this->port)){
            trigger_error('Error binding socket to TCP
port',E_USER_ERROR);
        }
        // begin listening connections
        if(!socket_listen($this->socket)){
            trigger_error('Error listening socket
connections',E_USER_ERROR);
        }
        // create communication socket
        if(!$this->comSocket=socket_accept($this->socket)){
            trigger_error('Error creating communication
socket',E_USER_ERROR);
        }
        // display welcome message
        $message='Welcome to the Console Web Server! Please type
below the file name you want to fetch...'."\r\n";
        socket_write($this->comSocket,$message,strlen($message));
    }
    // read user input
    function readUserInput(){
        // start a loop and continue reading user input
        do{
            // delay loop execution
            sleep(10);
            // read socket input
            $socketInput=socket_read($this->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 
                    $socketOutput=$this->fetchFile
($socketInput)."\r\n";
                    // write data back to socket server
                    socket_write($this-
>comSocket,$socketOutput,strlen($socketOutput));
                }
                else{
                    // if 'STOP' command was entered close
communication socket & terminate all the connections
                    socket_close($this->comSocket);
                    break;
                }
            }
        }
        while(true);
        // close global socket
        socket_close($this->socket);
    }
    // fetch (X)HTML file
    function fetchFile($socketInput){
        $path='C:\\php\cli\\'.$this->docDir.'\\'.trim
($socketInput);
        if(!file_exists($path)){
            return 'File not found on this server. Please try
again';
        }
        return file_get_contents($path);
    }
}

As you can see, the above class, which I have amazingly called “WebServer,” implements a basic Web server by using some of the PHP socket-related functions you saw in previous tutorials. Its constructor takes up three arguments: the host to which a connection is established, the TCP port used by the server and the client in conjunction, and finally the physical directory where the server will fetch all the requested files.

In order to create a low-level socket and read/write data streams, the class additionally exposes the “createSocket()” method, which also calls the private “readUserInput()” method, handy for reading the name of the file being fetched. Finally, the “fetchFile()” method is tasked with retrieving the contents of the file specified by the client.

Before I proceed further, I’d like to clarify one important point: notice that the “fetchFile()” method uses the predefined “C:\php\cli” path, in order to fetch all the requested files. In this case, the server will be run on a Windows system, but if you’re working with Linux or some other operating system, you may want to change this directory and fetch files from another location.

Having addressed the topic mentioned before, it’s time to put this Web server to work. Please click on the link below to see an example that shows how the server will retrieve files requested by a Telnet client.