使用套接字在PHP（服务器）和Android（客户端）之间建立连接

I have been trying the last days to send(through form(input, submit button)) and receive data through a php script to an android application. I managed to do that but I didn't liked the solution. What I did was: Created a form:

<form action="index.php" method="get">
        <strong>Please give me a shell command:</strong> <br><input type="text" name="cmd" onmouseover="this.focus(); this.select();"><br>
        <input type="submit" value="Submit">
</form>

and when submit button was clicked:

<?php
if ( isset($_GET['cmd'])  ){
    $cmd = $_GET['cmd'];
    if (empty($cmd)){
         echo 'Please fill in a command first!';
    }else{
         echo "You gave me : \"$cmd\", right?<br>";
    }

        // don't timeout! 
    set_time_limit(0); 
    // set some variables 
    //$host = $_SERVER['HTTP_HOST'];
    $host = '10.16.5.191';
    $port = 5000;

    // create socket 
    $socket = socket_create(AF_INET, SOCK_STREAM, 0) or die("Could not create socket
"); 
    // bind socket to port 
    $result = socket_bind($socket, $host, $port) or die("Could not bind to socket
"); 
    // start listening for connections 
    $result = socket_listen($socket, 3) or die("Could not set up socket listener
"); 
    // accept incoming connections 
    // spawn another socket to handle communication 
    $spawn = socket_accept($socket) or die("Could not accept incoming connection
");

    $output = $cmd;

    socket_write($spawn, $output, strlen ($output)) or die("Could not write output
"); 

    // read client input 
    $input = socket_read($spawn, 1024) or die("Could not read input
"); 
    // clean up input string 
    $input = trim($input);  

    echo "I have read :</br> $input";
}
?>

But then I realized that want to open a connection once(until socket_accept()) and send data(socket_write()) when pressing the submit button.

So I did this:

<?php

    if ( isset($_GET['cmd']) ){
        main($_GET['cmd'],$spawn);
        return;
    }else{

        // don't timeout! 
        set_time_limit(0); 
        // set some variables 
        //$host = $_SERVER['HTTP_HOST'];
        $host = '192.168.10.21';
        $port = 5000;

        // create socket 
        $socket = socket_create(AF_INET, SOCK_STREAM, 0) or die("Could not create socket
"); 
        // bind socket to port 
        $result = socket_bind($socket, $host, $port) or die("Could not bind to socket
"); 
        // start listening for connections 
        $result = socket_listen($socket, 3) or die("Could not set up socket listener
"); 
        // accept incoming connections 
        // spawn another socket to handle communication 
        $spawn = socket_accept($socket) or die("Could not accept incoming connection
"); 
        echo "spawn: $spawn</br>";


      echo '
        <form action="" method="get">
            <strong>Please give me a shell command:</strong> <br><input type="text" name="cmd" onmouseover="this.focus(); this.select();"><br>
            <input type="submit" value="Submit">
        </form>
      ';
        }
function main($cmd,$spawn){

        // 1. Checks if the form is set

        if (empty($cmd)){
            echo 'Please fill in a command first!';
        }else{
            echo "You gave me : \"$cmd\", right?<br>";
        }
        $output = $cmd;

        socket_write($spawn, $output, strlen ($output)) or die("Could not write output
"); 

        // read client input 
        $input = socket_read($spawn, 1024) or die("Could not read input
"); 
        // clean up input string 
        $input = trim($input);  

        echo "I have read :</br> $input";
}
?>

So now i make the connection and then my php script ends! And when I send something via Submit button $spawn is not known.

I tried also $_SESSION[''] but socket_write() says that $_SESSION[''] variable is integer and not resource variable.

The android code is really simple, just opening a connection(via sockets), reads and writes.

I am new in PHP coding(last 3 days learned) What should I do? Is there a better way to do it? I want the connection to be only on local network!