PHP套接字服务器，检查客户端是否还活着

Question

I have a php server listening for 1 c# client.

When a connection is established, it is kept alive until client sends the command "quit" which kills the PHP server.

But when the c# client disconnects without the "quit" command (ie : clicking the close (x) button in the windows form) the server just keep listening, and can't receive any other connection from that client.

Is there a way to check from the server side (PHP) if connection is still alive with client?

My php server code is based on example1 of: http://php.net/manual/en/sockets.examples.php

If someone is interested in reproducing the bug/error behavior, paste code from example1 : http://php.net/manual/en/sockets.examples.php , connect by telnet from a remote client in lan, unplug client wire... php server will hang around forever, no new connection is accepted.

Answer 1

In your loop, you need to check the return value of socket_read() . If it returns FALSE, then there was a read error (which can be caused by the remote host closing the connection). The example code in the link you provided covers this case.

If you need to gracefully handle certain error states, you can always check the socket error code using socket_last_error() -- this note decribes the possible codes.

Edit:

When using putty for telnet, if i close with X button, connecion is closed properly in PHP, but if i unplug the ethernet wire of the putty machine, PHP server just hangs around.

The reason that the connection is closed when killing PuTTY is that PuTTY closes its open connection(s) when exiting. This causes socket_read() to return with an error code (I believe ECONNRESET ). If you pull the network cable, it doesn't have a chance to do that.

Depending on how your network is configured, the TCP connection should eventually fail. You can attempt to control the timeout by setting SO_RCVTIMEO with socket_set_option() , but this doesn't always work on all platforms (I'm looking at you, WinSock) .

Alternatively, you can roll your own polling loop using socket_select() with a reasonable timeout. If none of the connected sockets have data to send after your timeout, then kill the server.

Answer 2

The following code will show the state of connection.

  $address='example.com';
    $port = '9065';
    if (isset($port) && ($socket=socket_create(AF_INET, SOCK_STREAM, SOL_TCP))
     && (socket_connect($socket, $address, $port)))  {
    $text="Connection successful on IP $address, port $port";
    socket_close($socket);
    }
    else  {
    $text='Unable to connect<pre>'.socket_strerror(socket_last_error()).'</pre>';
    }
    echo $text;

Answer 3

I did this by checking if the socket_select() $read array includes the connection in question but socket_read() data is empty (twice).

It seems that socket_select() adds disconnected clients to the $read array and socket_read() gives an empty string '' when trying to read the disconnected client's data.

Answer 4

As Michael Dodd says, using socket_select() can have all sockets that have received data plus those they have closed. Also you can have all those that their buffer can accept data for transmission, and / or those that have raised some exception. Do have this info, a (separate) copy of sockets array must be placed in 2nd and / 3d parameter of function. (if not needed, this function must have $null as a variable equal to null, not just null)

The following example shows how to read data and test sockets if they are still open. I am using this code for sockets that have been created by socket_accept() on a listening socket, and it is working without problems. Instead of using socket_recv, socket_read can be used.

//all sockets created have been inserted to an array $socketArray
//get a copy of the sockets array
$tempArray = $socketArray;
//this command will remove from $tempArray all sockets that have no data and are alive, with a timeout of 0 sec, 100 msec
socket_select($tempArray, $null, $null, 0, 100);
if (count($tempArray)) {
    //if we have some sockets in the array
    foreach($tempArray as $socket) {
        //read some data
        $count = socket_recv($socket, $socketData, 1024, 0);
        if ($count) {
            //your code to do what you want with $socketData
        } else {
            //find socket position in initial socket array
            $index = array_search($socket, $socketArray);
            //if found, remove it from array and close the socket
            if ($index !== false) {
                array_splice($socketArray, $index, 1);
                socket_close($socket);
            }
        }
    }
}