php – 什么阻止fsockopen？

function _recaptcha_http_post($host,$path,$data,$port = 80) {

 $req = _recaptcha_qsencode ($data);

 $HTTP_Request  = "POST $path HTTP/1.0\r\n";
 $HTTP_Request .= "Host: $host\r\n";
 $HTTP_Request .= "Content-Type: application/x-www-form-urlencoded;\r\n";
 $HTTP_Request .= "Content-Length: " . strlen($req) . "\r\n";
 $HTTP_Request .= "User-Agent: reCAPTCHA/PHP\r\n";
 $HTTP_Request .= "\r\n";
 $HTTP_Request .= $req;

 $response = "";
 if( false == ( $fs = @fsockopen($host,$port,$errno,$errstr,10) ) ) {
  die ("Could not open socket");
 }

 fwrite($fs,$HTTP_Request);

 while ( !feof($fs) )
  $response .= fgets($fs,1160); // One TCP-IP packet
 fclose($fs);
 $response = explode("\r\n\r\n",$response,2);
 return $response;
}

至：

function _recaptcha_http_post($host,$port = 80) {
 $req = _recaptcha_qsencode ($data);
 $request = curl_init("http://".$host.$path);

 curl_setopt($request,CURLOPT_USERAGENT,"reCAPTCHA/PHP");
 curl_setopt($request,CURLOPT_POST,true);
 curl_setopt($request,CURLOPT_POSTFIELDS,$req);
 curl_setopt($request,CURLOPT_RETURNTRANSFER,true);

 $response = curl_exec($request);
 return $response;
}

基本上,我有兴趣找出为什么curl工作,而fsockopen失败“无法打开套接字”.谢谢.

此外：启用了套接字支持.