socket program is able to connect to the port which is still in TIME_WAIT

Question

Hi,

1. I have written a very simple socket server.
2. It listens in post 63254.
3. First i did a socket_create, socket_bind, socket_listen so here a connection is listening.
4. Then in a loop i do the socket accpet. so here another listen.
5. the read function reads untill i input exit.
6. after that the resource id by socket_accept closes.
7. and then the main connection closes.

when i checked this process in TCPview after closing all connections i can still see the system process showing TIME_WAIT for post 63254

if i again run the socket server program it is connecting and when one full process is over all the connection is closed and the program terminated and now i can see another TIME_WAIT for the same port. but still i could connect to the same port the third time.

in stackover question answer it is said that connection cannot be done for port which is in wait state.

I opened firefox browser it opened 4 connections. when i closed it all closed and the system process showed 4 time waits for 2 minutes. all time wait stays for 2 minutes and disappears.

so what i conclude is for every connection close the time wait is occurs and cannot be avoided.

i read many posts in stack overflow flow but still wasn't sure of it.

i run the following code in command line.

My server Code

<?
error_reporting(E_ALL);
set_time_limit(0);
ob_implicit_flush(); 

$str = '';
$buff = '';

$s = socket_create(AF_INET, SOCK_STREAM, SOL_TCP);
if(!$s)die('Unable to create socket');

if(!socket_bind($s,'127.0.0.1',63254))
    die("\nTrying to Bind: ".socket_strerror(socket_last_error()));

if(!socket_listen($s,1))
    die(socket_strerror(socket_last_error()));

    while(1)
    {
        $acc = socket_accept($s);
        if(!$acc)die(socket_strerror(socket_last_error()));
//      echo "\n".gettype($acc);
        if(!$acc)die(socket_strerror(socket_last_error()));

        while(1)
        {
            $str = socket_read($acc,512);
            $buff.= $str;
            echo $str;
//          echo '::'.gettype($str);

            if($str===false)die(socket_strerror(socket_last_error()));
            if($str=="exit\r\n")break;          
        }

//      if(!socket_shutdown($acc,2))echo socket_strerror(socket_last_error());  
        socket_close($acc);     
        if(preg_match('/exit/',$buff))break;
    }
//echo "\nConnection closed by server\n";   
//if(!socket_shutdown($s,2))echo socket_strerror(socket_last_error());
socket_close($s);
?>

The client code

<?
    set_time_limit(0);
    $f = fsockopen('127.0.0.1',63254,$a,$b,10);
    if(!$f)die('cannot connect');
    echo "\nConnected: \n";
    do{
        $buff = fgets(STDIN);   
        fwrite($f,$buff);
    }while($buff!="exit\r\n");
    fclose($f);
?>

need suggestions to improve a better client server if this is not sufficient. this code is just a child's play. just trying to understand the way communication works.

Answer 1

In stackover question answer it is said that connection cannot be done for port which is in wait state.

I don't know what answer you're referring to, but you cannot bind to a port which is in TIME_WAIT state. If you are a server you can use setReuseAddress() to overcome this. If you're a client you have to wait, or use a different outbound port, or best of all don't specify an outbound port at all, let the system find one. You are a server so this doesn't apply to you.

I opened firefox browser it opened 4 connections. when i closed it all closed and the system process showed 4 time waits for 2 minutes. all time wait stays for 2 minutes and disappears.

But those are client ports. Outbound ports. At your server they were inbound ports, and there was also a listening port on the same port number. As long as there is a listening port, an inbound connnection can succeed.

so what i conclude is for every connection close the time wait is occurs and cannot be avoided.

TIME_WAIT occurs when you are the end that sends the close first. If you are the end that received the close, and closed in response, your port doesn't go into TIME_WAIT at all.