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    socket_select

    (PHP 4 >= 4.1.0, PHP 5, PHP 7, PHP 8)

    socket_select — 与えられたソケットの配列に対し、指定した有効時間で select() システムコールを実行する

    説明

    socket_select(
        ?array &$read,
        ?array &$write,
        ?array &$except,
        ?int $seconds,
        int $microseconds = 0
    ): int|false

    socket_select() はソケットの配列を受け取り、 それらの状態が変化するまで待ちます。BSD のソケットについての知識がある方なら、 これらのソケットの配列が、いわゆるファイル記述子セットであることがご理解いただけるでしょう。 3 つの独立した配列でソケットを監視します。

    パラメータ

    read

    配列 read に挙げられたソケットでは、 文字が読み込み可能になっているかどうか（厳密に言うと、読み込みが ブロックされていないかどうか - 実際には、ソケット記述子はファイルの 終端でも有効です。そのような場合、socket_read() は長さゼロの文字列を返します）を監視します。

    write

    配列 write に挙げられたソケットでは、 書き込みがブロックされていないかどうかを監視します。

    except

    配列 except に挙げられたソケットでは、 例外を監視します。

    seconds

    seconds および microseconds は、ともにタイムアウトを指定するパラメータです。 タイムアウトは、socket_select() が結果を返すまでの経過時間の最大値です。 seconds はゼロにすることも可能で、そうすると socket_select() は結果をすぐに返します。 これはポーリングをする際に有用です。seconds に null（タイムアウトしない）を指定すると、 socket_select() は無期限にブロックします。

    microseconds

    警告

    終了時に配列は書き換えられ、 どのソケットの状態が変わったのかがわかるようになります。

    socket_select() のすべての配列を設定する必要はありません。 使用しないものについては空の配列や null をかわりに指定しておくことが可能です。 また、これらの配列は参照渡し であり、 socket_select() をコールした後でその中身が書き換えられていることに注意しましょう。

    注意:

    現状の Zend Engine の制限により、関数の参照渡しパラメータに null のような定数値を直接渡すことができません。一時的な変数を使用するか、 あるいは一番左に一時変数を使用する式を使用してください。

    例1 socket_select() での null の使用

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

    戻り値

    成功した場合は、socket_select() は配列内で 変化のあったソケットの数を返します。もし何かがおこる前に タイムアウト時間が経過した場合は、ゼロを返すことになります。 エラー時には false が返されます。エラーコードは socket_last_error() で取得可能です。

    注意:

    エラーかどうかを調べる際には、必ず === 演算子を 使用するようにしましょう。socket_select() は 0 を返す場合もあり、このような場合に == を用いて比較すると、エラーと判定されてしまいます。

    例2 socket_select() の返す結果を知る

    <?php
    $e     = NULL;
    if (    false === socket_select($r, $w, $e, 0)) {
    echo     "socket_select() は失敗しました。原因: " .
    socket_strerror(socket_last_error()) . "\n";
    }
    ?>

    例

    例3 socket_select() の例

    <?php
    /* 読み込み用の配列を準備する */
    $read = array($socket1, $socket2);
    $write = NULL;
    $except = NULL;
    $num_changed_sockets = socket_select($read, $write, $except, 0);

    if (    $num_changed_sockets === false) {
    /* エラー処理 */
    } else if ($num_changed_sockets > 0) {
    /* すくなくともひとつのソケットで、何らかの出来事が起こっています */
    }
    ?>

    注意

    注意:

    ソケットの実装によっては、取り扱いに注意すべきものがあることを知っておいてください。 基本的なルールは以下のとおりです。

    • 基本的に socket_select() のタイムアウトは 指定しないように心がけましょう。もしデータがなかった場合に、 プログラム側でそれを判定できなくなってしまいます。タイムアウトに 依存しているコードは移植性が悪く、デバッグが困難です。
    • socket_select() のコール後に値をチェックして 適切に処理するつもりがないソケットは、決して配列に追加してはいけません。 socket_select() から値が返ってきたあとは、 配列内のすべてのソケットをチェックする必要があります。 すべての書き込み用ソケットは書き込める必要がありますし、 またすべての読み込み用ソケットは読み込める必要があります。
    • 配列で返されたソケットに対して読み込み/書き込みをする場合には、 指定したデータを必ずしもすべて読み込み/書き込みするとは限らないことを 知っておいてください。たった 1 バイトしか読み込み/書き込みが できなかった場合にも対処できるよう準備しておきましょう。
    • ほとんどのソケット実装で、except でキャッチできる 例外はただひとつ、すなわちソケットが受け取ったデータが帯域外で あったということだけです。

    参考

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    User Contributed Notes 22 notes

    up
    49
    vardhan ( at ) rogers ( dot ) com
    19 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);
    ?>
    up
    8
    malcolm.murphy
    8 years ago
    This was mentioned by [Viorel] above but I think it warrants being repeated...

    The example provided by [vardhan ( at ) rogers ( dot ) com], while otherwise exceptional, uses the value int(0) for $tv_sec which will cause the iteration to loop as fast as possible, consequently using up any available CPU time.

    *** Ideally, $tv_sec should always be set to NULL ***, especially if you are using socket_select in a loop. If you must temporarily stop listening for events to perform another task, then the timeout should be as high as possible to reduce CPU strain (another note suggested preventing 100% CPU usage by setting a low $tv_usec value, which only makes the problem slightly less worse but does not solve it).

    Setting the timeout to an explicit null value is basically the same as setting it to infinite. The script will only execute the while loop once every time there is an event.
    up
    2
    Richard Neill
    20 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.
    up
    1
    jean at briskula dot si
    13 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;
    }
    ?>
    up
    1
    danny at dansheps dot com
    16 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.
    up
    2
    calimero dot NOSPAM at NOSPAM dot creatixnet dot com
    21 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.
    up
    2
    antti r
    9 years 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.
    up
    2
    John
    14 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);
    ?>
    up
    2
    Viorel
    11 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)
    up
    0
    simon dot riget at gmail dot com
    11 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);
    ?>
    up
    0
    magemerlin at list dot ru
    14 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
    up
    0
    eidberger at jakota dot de
    15 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.
    up
    0