socket_recvfrom()

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

Receives data from a socket whether or not it is connection-oriented

说明

The socket_recvfrom() function receives$lenbytes of data in$buffrom$nameon port$port(if the socket is not of type AF_UNIX)using$socket.socket_recvfrom() can be used to gather data from both connected and unconnected sockets. Additionally, one or more flags can be specified to modify the behaviour of the function.

The$nameand$portmust be passed by reference. If the socket is not connection-oriented,$namewill be set to the internet protocol address of the remote host or the path to the UNIX socket. If the socket is connection-oriented,$nameis NULL. Additionally, the$portwill contain the port of the remote host in the case of an unconnected AF_INET or AF_INET6 socket.

Note:此函数可安全用于二进制对象。

参数

The$socketmust be a socket resource previously created by socket_create().

The data received will be fetched to the variable specified with$buf.

Up to$lenbytes will be fetched from remote host.

The value of$flagscan be any combination of the following flags, joined with the binary OR(|)operator.

If the socket is of the type AF_UNIX type,$nameis the path to the file. Else, for unconnected sockets,$nameis the IP address of, the remote host, or NULL if the socket is connection-oriented.

This argument only applies to AF_INET and AF_INET6 sockets, and specifies the remote port from which the data is received. If the socket is connection-oriented,$portwill be NULL.

返回值

socket_recvfrom() returns the number of bytes received, or FALSE if there was an error. The actual error code can be retrieved by calling socket_last_error(). This error code may be passed to socket_strerror() to get a textual explanation of the error.

范例

socket_recvfrom() example

This example will initiate a UDP socket on port 1223 of 127.0.0.1 and print at most 12 characters received from a remote host.

参见

• socket_recv()从已连接的socket接收数据
• socket_send()Sends data to a connected socket
• socket_sendto()Sends a message to a socket, whether it is connected or not
• socket_create()创建一个套接字（通讯节点）

If you use socket_recvfrom on a UDP socket and combine it with the MSG_DONTWAIT flag, it will raise a PHP Warning if there is nothing to read. AFAIK, there is no way around that warning except suppressing it with @ (i.e. you cannot check if there is data before calling socket_recvfrom).

Pay attention! On some PHP version the MSG_DONTWAIT flag is not defined (see https://bugs.php.net/bug.php?id=48326)

MSG_DONTWAIT doesn't seem to exist in windows sockets. However socket_set_nonblock() seems to do the trick.

I'm confused about the rerturn value of socket_recvfrom(), it said -1 when failed, but when I call like this:
if (($len = @socket_recvfrom($sock, $result, 32, 0, $ip, $port)) == -1) {
  if ($this->_debug) {
    echo "socket_read() failed: " . socket_strerror(socket_last_error()) . "\n";
  }
  return false;
}
variable $len = false, when I change the buffer length from 32 to 4096, it becomes right.

DNS RELAY USING UDP SOCKETS 

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