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How to fix the error: Socket_recv cannot read from socket 0 Operation completed successfully

I found this simple chat tutorial using WebSocket and PHP Socket: http://www.sanwebe.com/2013/05/chat-using-websocket-php-socket

It works fine, but I get the following error in my CLI:

Warning: socket_recv(); unable to read from socket [0]: The operation completed successfully

I did my research, but nothing on the Internet has a definite answer to this question. I also tried to contact the author of the blog, but he did not respond to my message for a month. I'm new to web sockets, please help.

The error occurs when the user leaves the chat room.

Here is the server script:

$host = 'localhost'; //host
$port = '9000'; //port
$null = NULL; //null var

//Create TCP/IP sream socket
$socket = socket_create(AF_INET, SOCK_STREAM, SOL_TCP);
//reuseable port
socket_set_option($socket, SOL_SOCKET, SO_REUSEADDR, 1);

//bind socket to specified host
socket_bind($socket, 0, $port);

//listen to port
socket_listen($socket);

//create & add listning socket to the list
$clients = array($socket);

//start endless loop, so that our script doesn't stop
while (true) {
    //manage multipal connections
    $changed = $clients;
    //returns the socket resources in $changed array
    socket_select($changed, $null, $null, 0, 10);

    //check for new socket
    if (in_array($socket, $changed)) {
        $socket_new = socket_accept($socket); //accpet new socket
        $clients[] = $socket_new; //add socket to client array

        $header = socket_read($socket_new, 1024); //read data sent by the socket
        perform_handshaking($header, $socket_new, $host, $port); //perform websocket handshake

        socket_getpeername($socket_new, $ip); //get ip address of connected socket
        $response = mask(json_encode(
            array(
                'type'      =>  'system', 
                'message'   =>  $ip.' connected'
            )
        )); //prepare json data

        send_message($response); //notify all users about new connection

        //make room for new socket
        $found_socket = array_search($socket, $changed);
        unset($changed[$found_socket]);

    }   


    //loop through all connected sockets
    foreach ($changed as $changed_socket) {

        //check for any incomming data
        while(socket_recv($changed_socket, $buf, 1024, 0) >= 1) {

            $received_text = unmask($buf); //unmask data
            $tst_msg = json_decode($received_text); //json decode 

            $user_name = ''; 
            $user_message = ''; 
            $user_color = '';

            if($tst_msg){
                $user_name = $tst_msg->name;
                $user_message = $tst_msg->message; //message text
                $user_color = $tst_msg->color; //color
            }

            //prepare data to be sent to client
            $response_text = mask(json_encode(
                array(
                    'type'      =>  'usermsg', 
                    'name'      =>  $user_name, 
                    'message'   =>  $user_message, 
                    'color'     =>  $user_color
                )
            ));

            send_message($response_text); //send data
            break 2; //exist this loop
        }       

        $buf = @socket_read($changed_socket, 1024, PHP_NORMAL_READ);
        if ($buf === false) { // check disconnected client

            // remove client for $clients array
            $found_socket = array_search($changed_socket, $clients);
            socket_getpeername($changed_socket, $ip);
            unset($clients[$found_socket]);

            //notify all users about disconnected connection
            $response = mask(json_encode(
                array(
                    'type'      => 'system', 
                    'message'   => $ip . ' disconnected'
                )
            ));
            send_message($response);
        }
    }

}
// close the listening socket
socket_close($sock);

function send_message($msg) {

    global $clients;
    foreach($clients as $changed_socket) {
        @socket_write($changed_socket,$msg,strlen($msg));
    }

    return true;

}


//Unmask incoming framed message
function unmask($text) {

    $length = ord($text[1]) & 127;
    if($length == 126) {
        $masks = substr($text, 4, 4);
        $data = substr($text, 8);
    }
    elseif($length == 127) {
        $masks = substr($text, 10, 4);
        $data = substr($text, 14);
    }
    else {
        $masks = substr($text, 2, 4);
        $data = substr($text, 6);
    }
    $text = "";
    for ($i = 0; $i < strlen($data); ++$i) {
        $text .= $data[$i] ^ $masks[$i%4];
    }
    return $text;
}

//Encode message for transfer to client.
function mask($text) {
    $b1 = 0x80 | (0x1 & 0x0f);
    $length = strlen($text);

    if($length <= 125)
        $header = pack('CC', $b1, $length);
    elseif($length > 125 && $length < 65536)
        $header = pack('CCn', $b1, 126, $length);
    elseif($length >= 65536)
        $header = pack('CCNN', $b1, 127, $length);
    return $header.$text;
}

//handshake new client.
function perform_handshaking($receved_header, $client_conn, $host, $port) {
    $headers = array();
    $lines = preg_split("/\r\n/", $receved_header);
    foreach($lines as $line) {
        $line = chop($line);
        if(preg_match('/\A(\S+): (.*)\z/', $line, $matches)){
            $headers[$matches[1]] = $matches[2];
        }
    }

    $secKey = $headers['Sec-WebSocket-Key'];
    $secAccept = base64_encode(pack('H*', sha1($secKey . '258EAFA5-E914-47DA-95CA-C5AB0DC85B11')));
    //hand shaking header
    $upgrade  = "HTTP/1.1 101 Web Socket Protocol Handshake\r\n" .
    "Upgrade: websocket\r\n" .
    "Connection: Upgrade\r\n" .
    "WebSocket-Origin: $host\r\n" .
    "WebSocket-Location: ws://$host:$port/demo/shout.php\r\n".
    "Sec-WebSocket-Accept:$secAccept\r\n\r\n";
    socket_write($client_conn,$upgrade,strlen($upgrade));
}

Here is the client script:

<!DOCTYPE html>
<html>
<head>
<meta charset='UTF-8' />
<style type="text/css">
<!--
.chat_wrapper {
    width: 500px;
    margin-right: auto;
    margin-left: auto;
    background: #CCCCCC;
    border: 1px solid #999999;
    padding: 10px;
    font: 12px 'lucida grande',tahoma,verdana,arial,sans-serif;
}
.chat_wrapper .message_box {
    background: #FFFFFF;
    height: 150px;
    overflow: auto;
    padding: 10px;
    border: 1px solid #999999;
}
.chat_wrapper .panel input{
    padding: 2px 2px 2px 5px;
}
.system_msg{color: #BDBDBD;font-style: italic;}
.user_name{font-weight:bold;}
.user_message{color: #88B6E0;}
-->
</style>
</head>
<body>  
<?php 
$colours = array('007AFF','FF7000','FF7000','15E25F','CFC700','CFC700','CF1100','CF00BE','F00');
$user_colour = array_rand($colours);
?>

<script src="//ajax.googleapis.com/ajax/libs/jquery/2.0.0/jquery.min.js"></script>

<script language="javascript" type="text/javascript">  
$(document).ready(function(){
    //create a new WebSocket object.
    var wsUri = "ws://localhost:9000/websockets/server.php";    
    websocket = new WebSocket(wsUri); 

    websocket.onopen = function(ev) { // connection is open 
        $('#message_box').append("<div class=\"system_msg\">Connected!</div>"); //notify user
    }

    $('#send-btn').click(function(){ //use clicks message send button   
        var mymessage = $('#message').val(); //get message text
        var myname = $('#name').val(); //get user name

        if(myname == ""){ //empty name?
            alert("Enter your Name please!");
            return;
        }
        if(mymessage == ""){ //emtpy message?
            alert("Enter Some message Please!");
            return;
        }

        //prepare json data
        var msg = {
            message: mymessage,
            name: myname,
            color : '<?php echo $colours[$user_colour]; ?>'
        };
        //convert and send data to server
        websocket.send(JSON.stringify(msg));
    });

    //#### Message received from server?
    websocket.onmessage = function(ev) {

        var msg = JSON.parse(ev.data); //PHP sends Json data
        var type = msg.type; //message type
        var umsg = msg.message; //message text
        var uname = msg.name; //user name
        var ucolor = msg.color; //color

        if(type == 'usermsg' && uname){
            $('#message_box').append("<div><span class=\"user_name\" style=\"color:#"+ucolor+"\">"+uname+"</span> : <span class=\"user_message\">"+umsg+"</span></div>");       
        }

        if(type == 'system'){
            $('#message_box').append("<div class=\"system_msg\">"+umsg+"</div>");       
        }

        $('#message').val(''); //reset text
    };

    websocket.onerror = function(ev){
        $('#message_box').append("<div class=\"system_error\">Error Occurred - "+ev.data+"</div>");
    };
    websocket.onclose = function(ev){
        $('#message_box').append("<div class=\"system_msg\">Connection Closed</div>");
    };

});
</script>
<div class="chat_wrapper">
<div class="message_box" id="message_box"></div>
<div class="panel">
<input type="text" name="name" id="name" placeholder="Your Name" maxlength="10" style="width:20%"  />
<input type="text" name="message" id="message" placeholder="Message" maxlength="80" style="width:60%" />
<button id="send-btn">Send</button>
</div>
</div>

</body>
</html>
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