socket_recvfrom
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, $except = NULL, 0) < 1)
continue;
which will hang your CPU to 100% (return immediate if nothing to be done)
socket_select
(PHP 4 >= 4.1.0, PHP 5)
socket_select — Ejecuta la llamada a select() del sistema sobre las matrices de sockets dadas con un tiempo límite especificado
Descripción
int socket_select
( array
&$read
, array &$write
, array &$except
, int $tv_sec
[, int $tv_usec = 0
] )socket_select() acepta matrices de sockets y las espera para cambiar el estado. Aquellas que vienen con un fondo de sockets BSD reconocerán que aquellas matrices de recursos socket son de hecho los también llamados conjuntos descriptores de archivos. Se observan tres matrices de recursos socket independientes.
Parámetros
-
read -
Los sockets listados en la matriz
readserán observados para ver si los caracteres están disponibles para lectura (más precisamente, para ver si una lectura no bloqueará - en particular, un recurso socket también está listo al final del archivo, en cuyo caso un socket_read() devolverá una cadena de longitud cero). -
write -
Los sockets listados en la matriz
writeserán observados para ver si una escritura no bloqueará. -
except -
Los sockets listados en la matriz
exceptserán observados para excepciones. -
tv_sec -
tv_secytv_usecforman juntos el parámetros timeout. timeout es un límite superior de la cantidad de tiempo trancurrido antes de que socket_select() devuelva.tv_secpuede ser cero, causando que socket_select() devuelva inmediatamente. Esto es útil para consultas constantes (polling). Sitv_secesNULL(sin tiempo línmite), socket_select() puede bloquear indefinidamente. -
tv_usec -
Advertencia
Al salir, las matrices son modificadas para indicar que recurso socket realmente cambió el estado.
No es necesario pasar cada matriz a
socket_select(). En su lugar, se puede omitir y
usar una matriz vacía o NULL. No olvide también que esas matrices son
pasadas por referencia y serán modificadas después de
que socket_select() devuelva.
Nota:
A causa de una limitación en el Motor Zend actual no es posible pasar una constante como
NULLdirectamente como un parámetro a una función que espera que este parámetro sea pasado por referencia. En su lugar use una variable temporal o una expresión que su miembro más a la izquierda sea una variable temporal:Ejemplo #1 Usar
NULLcon socket_select()<?php
$e = NULL;
socket_select($r, $w, $e, 0);
?>
Valores devueltos
En caso de éxtio, socket_select() devuelve el número de
recursos socket contenidos en las matrices modificadas, lo que puede ser cero si
el tiempo límite expira antes de que ocurra algo interesante. En caso de error se
devuelve FALSE. El código de error se puede recuperar con
socket_last_error().
Nota:
Asegúrese de usar el operador === cuando verifique un error. Ya que socket_select() puede devolver 0 la comparación con == será evaluada a
TRUE:Ejemplo #2 Comprender el resultado de socket_select()
<?php
$e = NULL;
if (false === socket_select($r, $w, $e, 0)) {
echo "falló socket_select(), razón: " .
socket_strerror(socket_last_error()) . "\n";
}
?>
Ejemplos
Ejemplo #3 Un ejemplo de socket_select()
<?php
/* Preparar la matriz de lectura */
$read = array($socket1, $socket2);
$write = NULL;
$except = NULL;
$núm_sockets_cambiados = socket_select($read, $write, $except, 0);
if ($núm_sockets_cambiados === false) {
/* Manejo de errores */
} else if ($núm_sockets_cambiados > 0) {
/* Ocurrió algo interesante en al menos uno de los sockets */
}
?>
Notas
Nota:
Tenga en cuenta que algunas implementaciones de sockets necesitan ser tratadas con mucho cuidado. Unas cuantas reglas básicas:
- Debería siempre intentar usar socket_select() sin tiempo límite. Su programa no debería de hacer nada si no hay información disponible. El código que depende de tiempos límite normalmente no es portable y es difícil de depurar.
- No se deben añadir recursos socket a ningún conjunto si no se pretende verificar su resultado después de la llamada a socket_select(), y responder apropiadamente. Después de que socket_select() devuelva, todos los recursos socket en todas las matrices deben ser verificados. Cualquier recurso socket que esté disponible para escritura debe ser escrito, y cualquier recurso socket disponible para lectura debe ser leído.
- Si lee/escribe en un socket devuelto en las matrices, tenga en cuenta que no necesariamente leerán/escribirán la cantidad de información que solicitó. Esté preparado para que incluso sea capaz de leer/escrir sólo un único byte.
- En la mayoría de las implementaciones de sockets es común que la única expcepción capturada con la matriz
exceptsea información fuera de banda recibida en un socket.
Ver también
- socket_read() - Lee un máximo de longitud de bytes desde un socket
- socket_write() - Escribir en un socket
- socket_last_error() - Devuelve el último error sobre un socket
- socket_strerror() - Devuelve una cadena que describe un error de socket
add a note
User Contributed Notes
socket_select - [18 notes]
Viorel ¶
2 months ago
vardhan ( at ) rogers ( dot ) com ¶
7 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);
?>
jean at briskula dot si ¶
2 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;
}
?>
John ¶
2 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(!$done);
?>
magemerlin at list dot ru ¶
3 years ago
If you using a Flash client - you should know some specific features:
1) when client connects to the server - it is sending to you "<policy-file-request/>"."\0" string. Server should answer an XML policy file, then disconnect from this client. Code is something like
if ('<policy-file-request/>'==substr($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
Aaron (aaron at acephalo dot us) ¶
3 years ago
socket_select() can also serve as a more granular sleep():
<?php
# half-second sleep
$undef = array();
socket_select($undef, $undef, $undef, 0, "500000");
?>
eidberger at jakota dot de ¶
4 years ago
Just noticed that you have to loop socket_select () when using UDP to get all queued packets:
<?php
while (socket_select ($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 ¶
4 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.
qartis at gmail dot com ¶
5 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, $except = NULL, NULL) < 1)
Anonymous ¶
6 years ago
If you want to use a simple fractional value for timeout:
<?php
socket_select(..., floor($timeout), ceil($timeout*1000000));
?>
Whosawhatsis at that google email thingy ¶
7 years ago
Another solution to the problem of keys not being preserved is to have an additional array for looking up sockets that uses their resource identifiers as keys. This can be obtained using array_flip() in some cases, but is particularly useful if each socket is associated with an object. In this case, you can make the object's constructor add a pointer to itself to the lookup array with its socket resource identifier as a key and use the following code to execute a read method for the object associated with each socket returned by socket_select():
<?php
socket_select($reads, $writes, $excepts, 0);
foreach ($sockets as $socket) {
$lookuparray[$socket]->read();
}
?>
ludvig dot ericson at gmail dot com ¶
7 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 ¶
7 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 ¶
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'
Richard Neill ¶
8 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 ¶
10 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.
daveb at optusnet dot com dot au ¶
10 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
julian dot haupt at gmx dot de ¶
10 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;
}
}
?>