socket_select

(PHP 4 >= 4.1.0, PHP 5)

socket_select Esegue la system call select() su un set di socket con un dato timeout

Descrizione

int socket_select ( array $lettura , array $scrittura , array $except , int $tv_sec [, int $tv_usec ] )
Avviso

Questa funzione è SPERIMENTALE. Ovvero, il comportamento di questa funzione, il nome di questa funzione, in definitiva tutto ciò che è documentato qui può cambiare nei futuri rilasci del PHP senza preavviso. Siete avvisati, l'uso di questa funzione è a vostro rischio.

La funzione socket_select() accetta un array di socket e si mette in attesa di una variazione di stato su questi. Questa, derivando come background dai socket BSD, riconoscerà che questi array di risorse socket sono in realtà dei set di descrittori di file. Saranno monitorati 3 set di socket.

I socket indicati nell'array lettura, saranno monitorati in attesa dell'arrivo di caratteri disponibili per la lettura (più precisamente, per verificare che una lettura non sia bloccata, una risorsa socket viene definita pronta anche su fine file, in questo caso la funzione socket_read() restituirà una stringa di lunghezza zero).

I socket indicati nell'array di scrittura, sarranno monitorati per verificare che una scrittura non si blocchi.

I socket indicati nell'array except saranno monitorati per rilevare delle eccezioni.

Avviso

In uscita, gli array sarrano modificati in modo da indicare quale risorsa di tipo socket ha variato il proprio stato.

Non si è obbligati a passare tutti gli array a socket_select(). Se ne possono tralasciare, al loro posto utilizzare un array vuoto oppure NULL. Inoltre non si dimentichi che gli array sono passati per riferimento e che saranno modificati all'uscita dalla funzione socket_select().

Example #1 Esempio di socket_select()

<?php
/* Preparo l'array di lettura */  
$read = array($socket1$socket2);  
  
$num_changed_sockets socket_select($read$write NULL$except NULL0);


if (
$num_changed_sockets === false) {
    
/* Gestione dell'errore */  
} else if ($num_changed_sockets 0) {
    
/* Su almeno un socket è accaduto qualcosa di interessante */  
}  
?>

Nota:

A causa delle limitazioni della versione attuale del Zend Engine, non è possibile passare direttamente una costante, ad esempio NULL, come parametro ad una funzione che si aspetti questo passato per riferimento. Si utilizzi, invece, una variabile temporanea oppura una espressione il cui membro di sinistra sia una variabile temporanea:

Example #2 Uso di NULL con socket_select()

<?php
socket_select
($r$w$e NULL0);  
?>

I parametri tv_sec ed tv_usec insieme indicano il timeout. Il timeout indica il limite superiore di tempo che deve trascorrere prima che la funzione socket_select() esca. tv_sec può essere a zero, ciò causa una uscita immediata di socket_select(). Ciò risulta utile nei casi di polling. Se tv_sec viene impostato a NULL (nessun timeout), la funzione resta in attesa per un tempo indefinito.

Se ha successo socket_select() restituisce il numero di risorse socket contenute nell'array modificato, tale valore può essere zero se scade il timeout prima che sia accaduto qualcosa. La funzione restituisce FALSE se si verifica un errore. Il codice di errore può essere recuperato tramite la funzione socket_last_error().

Nota:

Si utilizzi l'operatore === quanto si eseguono dei test per rilevare un errore. Poiché la funzione socket_select() può restituire 0 il confronto eseguito con == sarebbe valutato come TRUE:

Example #3 Comprensione dei risultati di socket_select()

<?php
if (false === socket_select($r$w$e NULL0)) {  
    echo 
"socket_select() failed, reason: " socket_strerror(socket_last_error()) . "\n";  
}  
?>

Nota:

Si presti attenzione alle implementazioni di certi socket che richiedono di essere gestiti molto attentamente. Alcune regole di base:

  • Si cerchi di utilizzare sempre socket_select() senza il timeout. Il programma non dovrebbe avere nulla da fare se non ci sono dati disponibili. Il codice basato sui timeout solitamente non è migrabile ed è difficile da testare.
  • Nei tre set, non inserire una risorsa socket di cui non si intende controllarne il risultato dopo la chiamata a socket_select(), e ne si intende rispondere in modo appropriato. Dopo la chiamata a socket_select(), occorre verificare tutti i socket in tutti gli array. Si deve scrivere su qualsiasi socket disponibile per la scrittura, e deve essere letto qualsiasi socket diponibile per la lettura.
  • Se si ha il ritorno della disponibilità di un socket, sia in lettura che in scrittura, non è detto che sia disponile per l'intero ammontare dei dati da scrivere/leggere. Occorre essere preparati a gestire il caso in cui la disponibilità sia limitata anche ad un solo byte.
  • Nella maggior parte delle implementazioni dei socket, l'unica eccezione catturata con il parametro except è l'arrivo di dati fuori banda.

Vedere anche socket_read(), socket_write(), socket_last_error() e socket_strerror().

add a note add a note

User Contributed Notes 19 notes

up
3
Viorel
1 year 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)
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7
vardhan ( at ) rogers ( dot ) com
8 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);
?>
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1
John
3 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);
?>
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1
Whosawhatsis at that google email thingy
8 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();
}
?>
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0
jean at briskula dot si
3 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;
    }
?>
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0
magemerlin at list dot ru
4 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
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0
eidberger at jakota dot de
5 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.
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0
danny at dansheps dot com
5 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.
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0
qartis at gmail dot com
6 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)
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0
Anonymous
7 years ago
If you want to use a simple fractional value for timeout:

<?php
socket_select
(..., floor($timeout), ceil($timeout*1000000));
?>
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0
ludvig dot ericson at gmail dot com
8 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 */
}
?>
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0
crimson at NOSPAMtechnologist dot com
8 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.
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0
drenintell
8 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'
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0
Richard Neill
9 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.
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0
calimero dot NOSPAM at NOSPAM dot creatixnet dot com
11 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.
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0
daveb at optusnet dot com dot au
11 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
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0
julian dot haupt at gmx dot de
11 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;
  }
}
?>
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-1
simon dot riget at gmail dot com
4 months 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);
?>
up
-1
Aaron (aaron at acephalo dot us)
4 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");
?>
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