socket_recv()

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

从已连接的socket接收数据

说明

socket_recv(resource $socket,string &$buf,int $len,int $flags): int

函数socket_recv()从$socket中接受长度为$len字节的数据，并保存在$buf中。socket_recv()用于从已连接的socket中接收数据。除此之外，可以设定一个或多个 flags 来控制函数的具体行为。

$buf以引用形式传递，因此必须是一个以声明的有效的变量。从$socket中接收到的数据将会保存在$buf中。

参数

$socket

参数$socket必须是一个由socket_create()创建的socket资源。

$buf

从socket中获取的数据将被保存在由$buf制定的变量中。如果有错误发生，如链接被重置，数据不可用等等，$buf将被设为NULL。

$len

长度最多为$len字节的数据将被接收。

$flags

$flags的值可以为下列任意flag的组合。使用按位或运算符(|)来组合不同的flag。

可用的$flags值

Flag	描述
MSG_OOB	处理超出边界的数据
MSG_PEEK	从接受队列的起始位置接收数据，但不将他们从接受队列中移除。
MSG_WAITALL	在接收到至少$len字节的数据之前，造成一个阻塞，并暂停脚本运行（block）。但是，如果接收到中断信号，或远程服务器断开连接，该函数将返回少于$len字节的数据。
MSG_DONTWAIT	如果制定了该flag，函数将不会造成阻塞，即使在全局设置中指定了阻塞设置。

返回值

socket_recv()返回一个数字，表示接收到的字节数。如果发生了错误，则返回FALSE错误码可使用socket_last_error()接收。也可使用函数socket_strerror()来取得关于错误的文字描述。

范例

socket_recv()范例

该范例简单地使用socket_recv()重写了范例中的第一个例子。

<?php
error_reporting(E_ALL);
echo "<h2>TCP/IP Connection</h2>\n";
/* Get the port for the WWW service. */
$service_port = getservbyname('www', 'tcp');
/* Get the IP address for the target host. */
$address = gethostbyname('www.example.com');
/* Create a TCP/IP socket. */
$socket = socket_create(AF_INET, SOCK_STREAM, SOL_TCP);
if ($socket === false) {
    echo "socket_create() failed: reason: " . socket_strerror(socket_last_error()) . "\n";
} else {
    echo "OK.\n";
}
echo "Attempting to connect to '$address' on port '$service_port'...";
$result = socket_connect($socket, $address, $service_port);
if ($result === false) {
    echo "socket_connect() failed.\nReason: ($result) " . socket_strerror(socket_last_error($socket)) . "\n";
} else {
    echo "OK.\n";
}
$in = "HEAD / HTTP/1.1\r\n";
$in .= "Host: www.example.com\r\n";
$in .= "Connection: Close\r\n\r\n";
$out = '';
echo "Sending HTTP HEAD request...";
socket_write($socket, $in, strlen($in));
echo "OK.\n";
echo "Reading response:\n\n";
$buf = 'This is my buffer.';
if (false !== ($bytes = socket_recv($socket, $buf, 2048, MSG_WAITALL))) {
    echo "Read $bytes bytes from socket_recv(). Closing socket...";
} else {
    echo "socket_recv() failed; reason: " . socket_strerror(socket_last_error($socket)) . "\n";
}
socket_close($socket);
echo $buf . "\n";
echo "OK.\n\n";
?>

The above example will produce something like:

<h2>TCP/IP Connection</h2>
OK.
Attempting to connect to '208.77.188.166' on port '80'...OK.
Sending HTTP HEAD request...OK.
Reading response:
Read 123 bytes from socket_recv(). Closing socket...HTTP/1.1 200 OK
Date: Mon, 14 Sep 2009 08:56:36 GMT
Server: Apache/2.2.3 (Red Hat)
Last-Modified: Tue, 15 Nov 2005 13:24:10 GMT
ETag: "b80f4-1b6-80bfd280"
Accept-Ranges: bytes
Content-Length: 438
Connection: close
Content-Type: text/html; charset=UTF-8
OK.

I've used socket_select and socket_recv with a while loop and found myself in trouble when remote side closed connection. The code below produced infinite loop and socket_select returned immediately (which lead to high cpu time consumption).
<?
socket_set_nonblock($my_socket);
$streams = array($my_socket/*, ... */);
$lastAccess = time();
while (socket_select($streams, $write = NULL, $except = NULL, SLEEP_TIME_SECONDS, SLEEP_TIME_MILLISECONDS) !== FALSE) {
  if (in_array($my_socket, $streams)) {
    while (@socket_recv($my_socket, $data, 8192, 0)) {
      echo $data;
    }
    $lastAccess = time();
  } else {
    if (time() $lastAccess > LAST_ACCESS_TIMEOUT) {
      break;
    }
  }
  // ...
  $streams = array($my_socket/*, ... */);
}
?>
The solution was simple, but quite hard to find because socket_recv is not documented. socket_recv returns FALSE if there is no data and 0 if the socket is widowed (disconnected by remote side). So I had just to check return value of socket_recv. The problem now sounds stupid, but I've spend some time to find it out.
I hope this will save some of somebody's hair ;)

Workaround for the missing MSG_DONTWAIT flag according to the bug report page:
<?php if(!defined('MSG_DONTWAIT')) define('MSG_DONTWAIT', 0x40); ?>

<?php
$er = error_reporting(0);
$bytes  = socket_recv($socket,$buffer,1,MSG_WAITALL);
error_reporting($er);
// MEGA BUG HERE
// this statuses are wrong and swapped, closed socket must be with "FALSE"
// but in fact he swap the values:
// http://php.net/manual/en/function.socket-recv.php
// 
if($bytes===false){ // no data available, socket not closed
  echo 'WS_READ_ERR1: '.socket_strerror(socket_last_error($socket)).PHP_EOL;
  // print when no data available:
  // WS_READ_ERR1: Resource temporarily unavailable
  continue;
}else if($bytes===0){ // socket closed
  echo 'WS_READ_ERR2: '.socket_strerror(socket_last_error($socket)).PHP_EOL;
  // print when socket closed:
  // WS_READ_ERR2: Success
  $process->close();
}
?>

In PHP version 5.* there is a bug: MSG_DONTWAIT flag is not defined (see https://bugs.php.net/bug.php?id=48326)

It looks like that mysterious flags are just the recv(2) flags passed to your OS syscall and nothing more...
ext/sockets/sockets.c:PHP_FUNCTION(socket_recv)
...
    if ((retval = recv(php_sock->bsd_socket, recv_buf, len, flags)) < 1) {
        efree(recv_buf);
...
for linux you can type `man 2 recv' and you will see complete description of thouse flags.
Sergey S. Kosrtyliov <rathamahata@rathamahata.net>
http://www.rathamahata.net/

in case you want to empty/unset $buffer, but failing to do so, try using 0 as flag.
PHP_NORMAL_READ and PHP_BINARY_READ respectively hold 1 and 2 as value.

It seems like the flags are just passed to the underlying recv() function of your OS, hence there no MSG_DONTWAIT flag on Windows and you should not define it yourself in that case, it just won't work.

My last post was incorrect. The int flag set to 2 apparently reset the file position pointer so what I was reading was the first record repeatedly. 
My workaroud ended up being the following:
for($ct=1; $ct<=$numrecs; $ct++) {
  $rec = "";
  $nr=socket_recv($fp,$rec,76,0);
    
  //grab the extra bytes.
  $terminator = "";
  while ($terminator != ".") {
    $nr=socket_recv($fp,$terminator,1,0);
  }
  
   $custarray[]=substr($rec,0,76);     
}
Martin K.

I'm glad that Bastion left the above post about the mysterious int flag. He just helped to fix a problem that I've spent six hours on. Here's my code:
for($ct=1; $ct<=$numrecs; $ct++) {
   $rec = "";
   $nr=socket_recv($fp,$rec,77,0);
   print "Rec # $ct -->";
     print "$rec";
     print "<br>";
   }
The code is pretty simple, it just loops through all my records and prints them out. All records are 77 bytes and all end with a period. The first 36 records print perfectly then at 37 things go bad. The records start to get offset. The last few characters of the 37th record end up printing on the 38th record. The data on the sending side was perfect, so I knew that the problem was with socked_recv.
After reading the above post I tried changing the int flag. Changing the flag to 2 worked:
$nr=socket_recv($fp,$rec,77,2);
Now everything lines up perfectly. I had always left int flag as 0 since it's undocumented. 
Martin K.

Usage example for MSG_PEEK: this function tells if the socket has data available to be read, but preserving it to be read at a future moment.
<?php
// Workaround for the missing define
if(!defined('MSG_DONTWAIT')) define('MSG_DONTWAIT', 0x40);
// Function to check if there is data available in the socket
function SocketHasData($socket) {
  // Based on the following fact:
  // $result=0 -> disconnected, $result=false -> no data
  $data = ''; // We need a buffer, but we won't use it
  // MSG_PEEK means to preserve data in the queue, so it can
  // actually be read afterwards
  $result = socket_recv($socket, $data, 1, MSG_PEEK | MSG_DONTWAIT );
  if ($result === false) return false; // If no data, returns false
  return true; // Otherwise returns true
}
?>

To read from socket both on linux and windows OS having flash as a client I use function bellow. $length is the size of a chunk, not the max length to read. It will continue reading until EOL char occures or client disconnects (or in case of error), so it works for bigger packets as well.
   function read($descriptor, $length = 1024) {
      $this->method = "read";
      if(!$client){
        echo("No valid socket descriptor !\n");
        return false;
      }
      $read ='';
    while(($flag=socket_recv($descriptor, $buf, $length,0))>0){
       $asc=ord(substr($buf, -1));
      if ($asc==0) {
        $read.=substr($buf,0,-1);
        break;
      }else{
        $read.=$buf;
      }
    }
      if ($flag<0){
      //error
      return false;
    }elseif ($flag==0){
      //Client disconnected
      return false;
    }else{
       return $read;
    }
   }

socket_recv()
returns FALSE if client returned no data
returns 0 (zero) if client disconnected
also (asuming case socket_select() "gave" us a "changed" socket):
if 
socket_recv() returned FALSE 
and no bytes were received 
then
client "crashed" (call it disconnected).
else if
socket_recv() returned 0 (zero) 
and no bytes were received 
then
client "normaly" disconnected.
Im pretty sure -- 99.99%.
Example:
<?php
function receive($socket)
{
  // !
  // on all following cases we assume that
  // socket_select() returned the current socket as "changed"
  // !
  $timeout = 3; // set your timeout
  /* important */
  $socket_recv_return_values['no_data_received'] = false;
  $socket_recv_return_values['client_disconnected'] = 0;
  $start = time();
  $received_data = null;
  $received_bytes = null;
  socket_set_nonblock($socket);
  socket_clear_error();
  while(
    ($t_out=((time() $start) >= $timeout)) === false
    and ($read=@socket_recv($socket, $buf, 4096, 0)) >= 1
  ){
    $received_data = (isset($received_data)) ? $received_data . $buf : $buf;
    $received_bytes = (isset($received_bytes)) ? $received_bytes + $read : $read;
  }
  $last_error = socket_last_error($socket);
  socket_set_block($socket);
  if($t_out === true){
    throw new Exception(
      'timeout after ' . ((!$received_bytes) ? 0 : $received_bytes) . ' bytes',
      0 // your eCode here
    );
  }
  elseif($last_error !== false and $last_error !== 0){
    throw new Exception(
      socket_strerror($last_error),
      $last_error
    );
  }
  else{
    if($read === $socket_recv_return_values['no_data_received']){
      // client returned NO DATA
      // but we were in a loop and could have got some data before:
      if($received_bytes < 1){
        // client is connected but sent NO DATA ?
        // no:
        // in this case the client must be "crashed" because -
        // it is not possible to "send no data" (zero bytes)
        // socket_select() now returns this socket as "changed" "forever"
        throw new Exception(
          'client crashed',
          0 // your eCode here
        );
      }else{
        // client returned DATA
        return $received_data;
      }
    }
    elseif($read === $socket_recv_return_values['client_disconnected']){
      // client disconnected
      if($received_bytes < 1){
        // client disconnected before/without sending any bytes
        throw new Exception(
          'client disconnected',
          0 // your eCode here
        );
      }
      else{
        // *this value* ^= $socket_recv_return_values['client_disconnected']
        //
        // client disconnected AFTER sending data (we were in a loop!)
        // socket_select() will return this socket "forever" as "changed" and -
        // socket_recv() will return *this value* "forever".
        // we will be "back" again "very soon" to see:
        // socket_recv() returns *this value* AND no bytes received
        // which results in disconnect-exception above
        return $received_data;
      }
    }
  }
}
?>