PHP fsockopen函数说明：

Open Internet or Unix domain socket connection（打开套接字链接）

Initiates a socket connection to the resource specified by target .

fsockopen() returns a file pointer which may be used together with the other file functions (such as fgets() , fgetss() , fwrite() , fclose() , and feof() ).就是返回一个文件句柄

开启PHP fsockopen这个函数

PHP fsockopen需要 PHP.ini 中 allow_url_fopen 选项开启

例子如下：

$fp = fsockopen("www.example.com", 80, $errno, $errstr, 30);
if (!$fp) {
echo "$errstr ($errno)<br/>\n";
} else {
$out = "GET / HTTP/1.1\r\n";
$out .= "Host: www.example.com\r\n";
$out .= "Connection: Close\r\n\r\n";
fwrite($fp, $out);
while (!feof($fp)) {
echo fgets($fp, 128);
}
fclose($fp);
}

处理下载问题时，所用到的方法

function downloadFile($file) {
$host = '********';

$out = "GET $file HTTP/1.0\r\n";
$out .= "Host: $host\r\n";
$out .= "Connection: Close\r\n\r\n";

$fp = fsockopen($host, 80);
fwrite($fp, $out);

$headers = array();
$body = '';
$filenameExt = '';
$isBody = false;
while(true) {
$line = fgets($fp);
if (false === $line) {
break;
}
if ($line == "\r\n") {
$isBody = true;
continue;
}

if ($isBody) {
$body .= $line;
echo strlen($body) . " ... \r";
} else {
if (strpos($line, 'filename')) {
preg_match('!filename="(.+?)\.([\w]+)"!', $line, $filename);
$filenameExt = $filename[2];
}
$headers[] = trim($line);
}
}
fclose($fp);

return array('fileExt' => $filenameExt, 'headers' => $headers, 'body' => $body);
}