socket_select

(PHP 4 >= 4.1.0, PHP 5, PHP 7)

socket_select — Runs the select() system call on the given arrays of sockets with a specified timeout

Description

int socket_select ( array &$read , array &$write , array &$except , int $tv_sec [, int $tv_usec = 0 ] )

socket_select() accepts arrays of sockets and waits for them to change status. Those coming with BSD sockets background will recognize that those socket resource arrays are in fact the so-called file descriptor sets. Three independent arrays of socket resources are watched.

Parameters

read: The sockets listed in the read array will be watched to see if characters become available for reading (more precisely, to see if a read will not block - in particular, a socket resource is also ready on end-of-file, in which case a socket_read() will return a zero length string).
write: The sockets listed in the write array will be watched to see if a write will not block.
except: The sockets listed in the except array will be watched for exceptions.
tv_sec: The tv_sec and tv_usec together form the timeout parameter. The timeout is an upper bound on the amount of time elapsed before socket_select() return. tv_sec may be zero , causing socket_select() to return immediately. This is useful for polling. If tv_sec is NULL (no timeout), socket_select() can block indefinitely.
tv_usec

Warning

On exit, the arrays are modified to indicate which socket resource actually changed status.

You do not need to pass every array to socket_select(). You can leave it out and use an empty array or NULL instead. Also do not forget that those arrays are passed by reference and will be modified after socket_select() returns.

Note:
Due a limitation in the current Zend Engine it is not possible to pass a constant modifier like NULL directly as a parameter to a function which expects this parameter to be passed by reference. Instead use a temporary variable or an expression with the leftmost member being a temporary variable:

Example #1 Using NULL with socket_select()

<?php $e = NULL; socket_select($r, $w, $e, 0); ?>

Return Values

On success socket_select() returns the number of socket resources contained in the modified arrays, which may be zero if the timeout expires before anything interesting happens. On error FALSE is returned. The error code can be retrieved with socket_last_error().

Note:
Be sure to use the === operator when checking for an error. Since the socket_select() may return 0 the comparison with == would evaluate to TRUE:

Example #2 Understanding socket_select()'s result

<?php $e = NULL; if (false === socket_select($r, $w, $e, 0)) { echo "socket_select() failed, reason: " . socket_strerror(socket_last_error()) . "\n"; } ?>

Examples

Example #3 socket_select() example


<?php
/* Prepare the read array */
$read   = array($socket1, $socket2);
$write  = NULL;
$except = NULL;
$num_changed_sockets = socket_select($read, $write, $except, 0);

if ($num_changed_sockets === false) {
    /* Error handling */
} else if ($num_changed_sockets > 0) {
    /* At least at one of the sockets something interesting happened */
}
?>

Notes

Note:
Be aware that some socket implementations need to be handled very carefully. A few basic rules:

You should always try to use socket_select() without timeout. Your program should have nothing to do if there is no data available. Code that depends on timeouts is not usually portable and difficult to debug.

No socket resource must be added to any set if you do not intend to check its result after the socket_select() call, and respond appropriately. After socket_select() returns, all socket resources in all arrays must be checked. Any socket resource that is available for writing must be written to, and any socket resource available for reading must be read from.

If you read/write to a socket returns in the arrays be aware that they do not necessarily read/write the full amount of data you have requested. Be prepared to even only be able to read/write a single byte.

It's common to most socket implementations that the only exception caught with the except array is out-of-bound data received on a socket.

User Contributed Notes

vardhan ( at ) rogers ( dot ) com

10 years ago


A simple PHP script using socket_select() to manage multiple connections.
connect using "telnet localhost 9050". it broadcasts your messages that you send through telnet to other users connected to the server -- sort of like a chat script

#!/usr/local/bin/php
<?php

    $port = 9050;
    
    // create a streaming socket, of type TCP/IP
    $sock = socket_create(AF_INET, SOCK_STREAM, SOL_TCP);
    
    // set the option to reuse the port
    socket_set_option($sock, SOL_SOCKET, SO_REUSEADDR, 1);
    
    // "bind" the socket to the address to "localhost", on port $port
    // so this means that all connections on this port are now our resposibility to send/recv data, disconnect, etc..
    socket_bind($sock, 0, $port);
    
    // start listen for connections
    socket_listen($sock);

    // create a list of all the clients that will be connected to us..
    // add the listening socket to this list
    $clients = array($sock);
    
    while (true) {
        // create a copy, so $clients doesn't get modified by socket_select()
        $read = $clients;
        
        // get a list of all the clients that have data to be read from
        // if there are no clients with data, go to next iteration
        if (socket_select($read, $write = NULL, $except = NULL, 0) < 1)
            continue;
        
        // check if there is a client trying to connect
        if (in_array($sock, $read)) {
            // accept the client, and add him to the $clients array
            $clients[] = $newsock = socket_accept($sock);
            
            // send the client a welcome message
            socket_write($newsock, "no noobs, but ill make an exception :)\n".
            "There are ".(count($clients) - 1)." client(s) connected to the server\n");
            
            socket_getpeername($newsock, $ip);
            echo "New client connected: {$ip}\n";
            
            // remove the listening socket from the clients-with-data array
            $key = array_search($sock, $read);
            unset($read[$key]);
        }
        
        // loop through all the clients that have data to read from
        foreach ($read as $read_sock) {
            // read until newline or 1024 bytes
            // socket_read while show errors when the client is disconnected, so silence the error messages
            $data = @socket_read($read_sock, 1024, PHP_NORMAL_READ);
            
            // check if the client is disconnected
            if ($data === false) {
                // remove client for $clients array
                $key = array_search($read_sock, $clients);
                unset($clients[$key]);
                echo "client disconnected.\n";
                // continue to the next client to read from, if any
                continue;
            }
            
            // trim off the trailing/beginning white spaces
            $data = trim($data);
            
            // check if there is any data after trimming off the spaces
            if (!empty($data)) {
            
                // send this to all the clients in the $clients array (except the first one, which is a listening socket)
                foreach ($clients as $send_sock) {
                
                    // if its the listening sock or the client that we got the message from, go to the next one in the list
                    if ($send_sock == $sock || $send_sock == $read_sock)
                        continue;
                    
                    // write the message to the client -- add a newline character to the end of the message
                    socket_write($send_sock, $data."\n");
                    
                } // end of broadcast foreach
                
            }
            
        } // end of reading foreach
    }

    // close the listening socket
    socket_close($sock);
?>

John

5 years ago


The way the document describes socket_select()'s handling of sockets polled for read is rather obscure.

It says that it checks to see if reading would not "block," but the overall description of socket_select() says it checks for a change in blocking status. Unfortunately, these are in conflict.

If a socket already has data in the buffer, calling socket_select() on that socket would never return (assuming null timeout), and would block forever. :-( This is because the blocking status wouldn't change. It simply stays "non-blocking"

It is important to remember NOT to select() on a socket which may already have data available.

An example...
<?php
//... $socket is already here...
$done = false;
$n = 0;
do{
    $tmp = 0;
    $r = $w = $e = array();
    $r = array($socket);
    socket_select($r,$w,$e,null);
    $n = socket_recv($socket, $tmp, 1024, 0);

    //$done = true; //Something determines that we are done reading...
}while(!$done);
?>
This MAY NOT work... socket_select() is always being called... but we may have data in the input buffer.

We need to ensure that the last time we read, nothing was read... (empty buffer)
<?php
//... $socket is already here...
$done = false;
$n = 0;
do{
    $tmp = 0;
    $r = $w = $e = array();
    $r = array($socket);
    if($n === 0) socket_select($r,$w,$e,null);
    $n = socket_recv($socket, $tmp, 1024, 0);

    //$done = true; //Something determines that we are done reading...
}while(!$done);
?>

Viorel

3 years ago


Probably you will want to use 

// get a list of all the clients that have data to be read from
// if there are no clients with data, go to next iteration
        if (socket_select($read, $write = NULL, $except = NULL, NULL) < 1)
            continue;
            
instead  
        if (socket_select($read, $write = NULL, $except = NULL, 0) < 1)
            continue;
which will hang your CPU to 100% (return immediate if nothing to be done)

antti r

4 months ago


as of 12/2015 and php 5.3.3, the socket_select() maximum sockets is still 1024 and not risable by process file limits (bash ulimit -n). PHP new compilation is required to raise the limits. Or one might rather choose forking or multiple binaries.

magemerlin at list dot ru

6 years ago


If you using a Flash client - you should know some specific features:

1) when client connects to the server - it is sending to you "<policy-file-request/>"."\0" string. Server should answer an XML policy file, then disconnect from this client. Code is something like 

if ('<policy-file-request/>'==substr($data, 0, 22))
                {
                    echo "policy requset.\n";
                    flush();ob_flush();
                    $msg = '<'.'?xml version="1.0"?>
<!DOCTYPE cross-domain-policy SYSTEM "http://www.macromedia.com/xml/dtds/cross-domain-policy.dtd">
<cross-domain-policy>
<allow-access-from domain="*" to-ports="*" />
</cross-domain-policy>'."\0";
                    echo "Say to client (crossdomain.xml) ... ";
                    flush();ob_flush();
                    socket_write($read_sock, $msg, strlen($msg));
                    echo "OK\n";
                    flush();ob_flush();
                    
                    echo "Closing ... ";
                    flush();ob_flush();
                    socket_close($read_sock);
                    echo "OK\n";
                    flush();ob_flush();
                }
                else
                {
// here is normal IO operations with client
}

2) every output to client should be ended with "\0" (if using XMLSocket in Flash client) - otherwise flash will not generate onData event

Russian examples is there - http://www.flasher.ru/forum/showpost.php?p=901346&postcount=7

qartis at gmail dot com

8 years ago


In regards to the code posted by vardhan ( at ) rogers ( dot ) com, it appears that on the following line:
        if (socket_select($read, $write = NULL, $except = NULL, 0) < 1)
the timeout parameter is accidentally set to 0, rather than NULL. This means that the select call will return immediately rather than blocking indefinitely.

Change the socket_select line to the following for great success:
        if (socket_select($read, $write = NULL, $except = NULL, NULL) < 1)

simon dot riget at gmail dot com

2 years ago


A verry simple HTTP webserver written in PHP
Run it in the shell with php <name of file> and test in in the browser with <server address>:8080/test

<?php
  // Reduce the amount of warnings displayed
  error_reporting(E_ALL ^ E_NOTICE);

  // Set up socket for listening 
  $host_socket = socket_create(AF_INET, SOCK_STREAM, SOL_TCP);
  if(!$host_socket) die("Failed to start event server. socket_create: ". socket_strerror(socket_last_error())."\n");

  // set the option to reuse the port
  if(! socket_set_option($host_socket, SOL_SOCKET, SO_REUSEADDR, 1) )
    die("Failed to start event server. socket_set_option: ". socket_strerror(socket_last_error())."\n");

  // bind host socket to localhost or 0.0.0.0 on port 8080
  if(! socket_bind($host_socket,"0.0.0.0",8080) )
    die("Failed to start event server. socket_bind: ". socket_strerror(socket_last_error())."\n");

  // start listening for connections
  if(! socket_listen($host_socket,10) )
    die("Failed to start event server. socket_listen: ".socket_strerror(socket_last_error())."\n");

  while (true) {
    // Make list of sockets to listen for changes in, including host
    $read = array($host_socket);
         
    // get a list of all the clients that have data to be read from
    $ready=@socket_select($read, $write = NULL, $except = NULL,0);
    if ($ready=== false)
      die("Failed to listen for clients: ". socket_strerror(socket_last_error()));

    // a client request service
    elseif($ready>0){
      // accept new client
      $newsocket = socket_accept($host_socket);

      // Read from socket
      $input = socket_read($newsocket, 1024);
      if($input){
        unset($client_header);
        // Read headers; Split into safe lines
        $line=explode("\n",preg_replace('/[^A-Za-z0-9\-+\n :;=%*?.,\/_]/','',substr($input,0,2000)));
        // Split request line into its parts
        list($client_header["method"],$client_header["url"],$client_header["protocol"])=explode(" ",$line[0]);
        // Remove the request line again.
        unset($line[0]);
        // Make key=value array of headers
        foreach($line as $l){
          list($key,$val)=explode(": ",$l);
          if($key) $client_header[strtolower($key)]=$val;
        }
        // Get IP of client
        socket_getpeername($newsocket, $client_header['ip']);

        // Decode url
        $client_header+=(array)parse_url($client_header['url']);
        parse_str($client_header['query'],$client_header['arg']);

        print_r($client_header);

        // Serve file
        if(strpos($client_header['path'],".html") && file_exists(__DIR__.$client_header['path'])){
          echo "Sending a HTML page to client\n";
          socket_write($newsocket,"$client_header[protocol] 200 OK\r\n");    
          socket_write($newsocket,"Content-type: text/html; charset=utf-8\r\n\r\n");
          socket_write($newsocket,file_get_contents(__DIR__.$client_header['path'])."\r\n\r\n");
          socket_close($newsocket);
        }elseif($client_header['path']=="/test"){
          echo "Sending test HTML page to client\n";
          socket_write($newsocket,"<!DOCTYPE HTML><html><head><html><body><h1>Its working!</h1>Have fun\r\n");
          socket_write($newsocket,"<pre>Request header: ". print_r($client_header,true) . "</pre>\r\n");
          socket_write($newsocket,"</body></html>\r\n\r\n");
          socket_close($newsocket);
        }else{
          echo "$client_header[protocol] 404 Not Found\r\n";
          socket_write($newsocket,"$client_header[protocol] 404 Not Found\r\n\r\n");   
          socket_close($newsocket);
        }
      }
    }
  }
  socket_close($host_socket);
?>

Whosawhatsis at that google email thingy

10 years ago


Another solution to the problem of keys not being preserved is to have an additional array for looking up sockets that uses their resource identifiers as keys. This can be obtained using array_flip() in some cases, but is particularly useful if each socket is associated with an object. In this case, you can make the object's constructor add a pointer to itself to the lookup array with its socket resource identifier as a key and use the following code to execute a read method for the object associated with each socket returned by socket_select():

<?php
socket_select($reads, $writes, $excepts, 0);

foreach ($sockets as $socket) {
    $lookuparray[$socket]->read();
}
?>

jean at briskula dot si

5 years ago


As it was already said, some clients need \0 character to end transmission, for example Flash's XMLSocket.

You should also be prepared to read less data than you have requested. 

Here is an example of a socket buffer - it's an array which has socket resources for keys and an array of a timestamp and recieved data as values.

I find that the best practice for sending data is trailing it with a new line and zero character (\n\0), because you will probably have different types of clients which behave differently for reading data from sockets. Some need a \n to fire an event, some need \0.

For recieving data, sometimes you will get splitted data - this can hapen because the buffer is full (in my example 8192 bytes) or it just gets broken during transmission in lower levels.

Sometimes you can read two messages at once, but they have a zero character in between, so you can just use preg_split() to split the messages. The second message may not be complete, so you add it to your buffer.

<?php
    const message_delimiter = "\n\0";

    /*
     * Clear socket buffers older than 1 hour
     */
    function clear_buffer() {
        foreach($this->buffer as $key=>$val) {
            if(time() - $val['ts'] > 3600) {
                unset($this->buffer[$key]);
            }
        }
    }

    /*
     * Add data to a buffer
     */
    function buffer_add($sock,$data) {
        if(!isset($this->buffer[$sock])) {
            $this->buffer[$sock]['data'] = '';
        }

        $this->buffer[$sock]['data'] .= $data;
        $this->buffer[$sock]['ts'] = time();
    }

    function buffer_get($sock) {
        // split buffer by the end of string
        $lines = preg_split('/\0/',$this->buffer[$sock]['data']);

        // reset buffer to the last line of input
        // if the buffer was sent completely, the last line of input should be
        // an empty string
        $this->buffer[$sock]['data'] = trim($lines[count($lines)-1]);

        if(!empty($this->buffer[$sock]['data'])) {
            debug("buffer is not empty for $sock, len: ".strlen($this->buffer[$sock]['data']));
        }

        // remove the last line of input (incomplete data)
        // parse any complete data
        unset($lines[count($lines)-1]);

        // return only the fully sent data
        return $lines;
    }

    function read(&$sock,$len=8192,$flag=MSG_DONTWAIT) {
        $lines = array();

        $this->clear_buffer();

        $bytes_read = @socket_recv($sock,$read_data,$len,$flag);

        if ($bytes_read === false || $bytes_read == 0) {
            return false;
        } else {
            debug("recv: $read_data");
            $this->buffer_add($sock,$read_data);
            return $this->buffer_get($sock);
        }
    }

    /*
     * Write to a socket
     * add a newline and null character at the end
     * some clients don't read until new line is recieved
     *
     * try to send the rest of the data if it gets truncated
     */
    function write(&$sock,$msg) {
        $msg = $msg.self::message_delimiter;
        $length = strlen($msg);
        while(true) {
            $sent = @socket_write($sock,$msg,$length);
            if($sent <= 0) {
                return false;
            }
            if($sent < $length) {
                $msg = substr($msg, $sent);
                $length -= $sent;
                debug("Message truncated: Resending: $msg");
            } else {
                return true;
            }
        }
        return false;
    }
?>

eidberger at jakota dot de

7 years ago


Just noticed that you have to loop socket_select () when using UDP to get all queued packets:



<?php

while (socket_select ($aRead, $aWrite, $aExcept, 1) > 0) {

    foreach ($aReadUdp as $oSocket) {

        $this->clientReadUdp ($oSocket);

    }

}

?>



That's important because every call of socket_select () on UDP brings you only one result. But there could be 10.000 results queued and if your turnarround time is to slow (server busy, other sleeps etc.), you'll never progress all results in near realtime.

danny at dansheps dot com

7 years ago


Just to add to this.  Since the information contained in the notes is somewhat old.   It appears keys are being preserved now.

So, if you rely on knowing which keys need to be worked with and were like me and thought that it didnot preserve.  Well it does.

Anonymous

9 years ago


If you want to use a simple fractional value for timeout:

<?php
socket_select(..., floor($timeout), ceil($timeout*1000000));
?>

ludvig dot ericson at gmail dot com

10 years ago


Regarding the comment below, No, it does not, it's a system call and I believe it's rather hard to preserve keys.

Additionally, socket_select should be used like it was a user-inputted array, that you don't know what you sent in to.

<?php
$reads = $clients;
$reads[] = $server;

socket_select($reads);

foreach ($reads as $read) {
    /* do some stuff */
}
?>

crimson at NOSPAMtechnologist dot com

10 years ago


Note that the resulting arrays do NOT maintain keys (PHP 4.3.2) after being run through this function:

Before:
Array
(
    [Client_Socket] => Resource id #6
    [Server_Socket] => Resource id #9
)

After:
Array
(
    [0] => Resource id #6
    [1] => Resource id #9
)

It would have been nice to have the keys stay to figure out which stream you need to receive from, but you'll have to use some fancy foreach loop to figure out which sockets to check.

drenintell

11 years ago


The continuation of my my previous post on 28-Apr-2005 10:19 at
http://ca3.php.net/manual/en/function.socket-select.php

Here it is: (Link is broken into 2 parts)

'http://gtkphp.org/php_socket_select_hangs
_explanation_and_solution.html'

Richard Neill

11 years ago


It is probably a bad idea to watch an array of sockets for input with socket_select, and then socket_read() using PHP_NORMAL_READ.

Although this seems desirable, you can end up with a permanently blocked program, if someone sends you malformed input which is missing a trailing \n \r. Guess how I found that out.

calimero dot NOSPAM at NOSPAM dot creatixnet dot com

13 years ago


Please note that the timeout parameter has important side-effects on the CPU usage of your script.

Setting the timeout to 0 will make your CPU looping without any time to have some rest and handle other running processes on your system, causing the system load to increase heavily while your script is running.

Personnaly, I use a value of 15 ms for this parameter. this ensures a good listening frequency while letting your system load clear.

Example :
$read = array($ListeningSocket);
$num_changed_sockets = socket_select($read, $write = NULL, $except = NULL, 0, 10);

Hope this helps.

julian dot haupt at gmx dot de

13 years ago


hello,

i just made a class which acts similiar to Perl's IO::Select in order to make socket selecting very easy



your script should look something like that:



<?php

$server = new Server;

$client = new Client;



for (;;) {

  foreach ($select->can_read(0) as $socket) {



    if ($socket == $client->socket) {

      // New Client Socket

      $select->add(socket_accept($client->socket));

    }

    else {

      //there's something to read on $socket

    }

  }

}

?>



you should of course implement some routines to detect broken sockets and remove them from the select object.



you can also do output buffering and check in the main-loop for sockets that are ready to write



<?php

class select {

  var $sockets;



  function select($sockets) {



    $this->sockets = array();



    foreach ($sockets as $socket) {

      $this->add($socket);

    }

  }



  function add($add_socket) {

    array_push($this->sockets,$add_socket);

  }



  function remove($remove_socket) {

    $sockets = array();



    foreach ($this->sockets as $socket) {

      if($remove_socket != $socket)

        $sockets[] = $socket;

    }



    $this->sockets = $sockets;

  }



  function can_read($timeout) {

    $read = $this->sockets;

    socket_select($read,$write = NULL,$except = NULL,$timeout);

    return $read;

  }



  function can_write($timeout) {

    $write = $this->sockets;

    socket_select($read = NULL,$write,$except = NULL,$timeout);

    return $write;

  }

}

?>

daveb at optusnet dot com dot au

13 years ago


If you haven't done any network programming before, PHP's socket_select() might appear a bit strange to you. I've written a simple php "partyline" script to demonstrate the multi-socket use of select'ing at http://dave.dapond.com/socketselect.php.txt

Aaron (aaron at acephalo dot us)

6 years ago


socket_select() can also serve as a more granular sleep():



<?php

  # half-second sleep

  $undef = array();

  socket_select($undef, $undef, $undef, 0, "500000");

?>

socket_select

Description

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