fsockopen顺利后，fwrite失败

$out = "POST $path HTTP/1.0\r\n";
        $out .= "Accept: */*\r\n";
        $out .= "Accept-Language: zh-cn\r\n";
        $out .= "Content-Type: application/x-www-form-urlencoded\r\n";
        $out .= "User-Agent: $_SERVER[HTTP_USER_AGENT]\r\n";
        $out .= "Host: $host\r\n";
        $out .= "Content-Length: ".strlen($post)."\r\n";
        $out .= "Connection: Close\r\n";
        $out .= "Cache-Control: no-cache\r\n";
        $out .= "Cookie: $cookie\r\n\r\n";
        $out .= $post;


if(!$fp) {
        return '';//note $errstr : $errno \r\n
    } else {
        stream_set_blocking($fp, $block);
        stream_set_timeout($fp, $timeout);
//程序已经跑到这里，但接受POST的文件没执行到。。
        @fwrite($fp, $out);
@fclose($fp);
}