标题只能通过curl在php中检索

Question

其实我有两个问题.

(1)如果我只检索标题而不是使用php和curl进行完整页面检索,那么远程服务器上使用的处理能力或带宽是否会减少？

(2)由于我认为,我可能错了,第一个问题的答案是肯定的,我试图获取最后修改日期或If-Modified-Since标题的远程文件只是为了将它与时间日期进行比较本地存储的数据,所以我可以,如果它已被更改,将其存储在本地.但是,NULL当我运行这个时,我的脚本似乎无法获取那条信息:

class last_change {

 public last_change;

 function set_last_change() {
  $curl = curl_init();
    curl_setopt($curl, CURLOPT_URL, "http://url/file.xml");
    curl_setopt($curl, CURLOPT_HEADER, true);
    curl_setopt($curl, CURLOPT_FILETIME, true);
    curl_setopt($curl, CURLOPT_NOBODY, true);
  // $header = curl_exec($curl);
  $this -> last_change = curl_getinfo($header);
  curl_close($curl);
 }

 function get_last_change() {
  return $this -> last_change['datetime']; // I have tested with Last-Modified & If-Modified-Since to no avail
 }

}

如果$header = curl_exec($curl)未启用,即使我没有请求它,也会显示标题数据,如下所示:

HTTP/1.1 200 OK
Date: Fri, 04 Sep 2009 12:15:51 GMT
Server: Apache/2.2.8 (Linux/SUSE)
Last-Modified: Thu, 03 Sep 2009 12:46:54 GMT
ETag: "198054-118c-472abc735ab80"
Accept-Ranges: bytes
Content-Length: 4492
Content-Type: text/xml

在此基础上,返回"Last-Modified".

那么,我做错了什么？

Answer 1

你正在传递$ header curl_getinfo().它应该是$curl(卷曲手柄).您可以filetime通过传递CURLINFO_FILETIME第二个参数来获得curl_getinfo().(通常filetime不可用,在这种情况下,它将被报告为-1).

但是,你的课程似乎很浪费,丢掉了许多可能有用的信息.这是另一种可能的方式:

class URIInfo 
{
    public $info;
    public $header;
    private $url;

    public function __construct($url)
    {
        $this->url = $url;
        $this->setData();
    }

    public function setData() 
    {
        $curl = curl_init();
        curl_setopt($curl, CURLOPT_URL, $this->url);
        curl_setopt($curl, CURLOPT_FILETIME, true);
        curl_setopt($curl, CURLOPT_NOBODY, true);
        curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);
        curl_setopt($curl, CURLOPT_HEADER, true);
        $this->header = curl_exec($curl);
        $this->info = curl_getinfo($curl);
        curl_close($curl);
    }

    public function getFiletime() 
    {
        return $this->info['filetime'];
    }

    // Other functions can be added to retrieve other information.
}

$uri_info = new URIInfo('http://www.codinghorror.com/blog/');
$filetime = $uri_info->getFiletime();
if ($filetime != -1) {
    echo date('Y-m-d H:i:s', $filetime);
} else {
    echo 'filetime not available';
}

是的,服务器上的负载会更轻,因为它只返回HTTP标头(毕竟,响应HEAD请求).轻微多少会有很大差异.

Answer 2

为什么要使用CURL呢？有一个PHP函数:

$headers=get_headers("http://www.amazingjokes.com/img/2014/530c9613d29bd_CountvonCount.jpg");
print_r($headers);

返回以下内容:

Array
(
    [0] => HTTP/1.1 200 OK
    [1] => Date: Tue, 11 Mar 2014 22:44:38 GMT
    [2] => Server: Apache
    [3] => Last-Modified: Tue, 25 Feb 2014 14:08:40 GMT
    [4] => ETag: "54e35e8-8873-4f33ba00673f4"
    [5] => Accept-Ranges: bytes
    [6] => Content-Length: 34931
    [7] => Connection: close
    [8] => Content-Type: image/jpeg
)

在此之后应该很容易获得内容类型.

您还可以将format = 1添加到get_headers:

$headers=get_headers("http://www.amazingjokes.com/img/2014/530c9613d29bd_CountvonCount.jpg",1);
    print_r($headers);

这将返回以下内容:

Array
(
    [0] => HTTP/1.1 200 OK
    [Date] => Tue, 11 Mar 2014 22:44:38 GMT
    [Server] => Apache
    [Last-Modified] => Tue, 25 Feb 2014 14:08:40 GMT
    [ETag] => "54e35e8-8873-4f33ba00673f4"
    [Accept-Ranges] => bytes
    [Content-Length] => 34931
    [Connection] => close
    [Content-Type] => image/jpeg
)

更多阅读(PHP.NET)

Answer 3

(1)是的.HEAD请求(在这种情况下发出)在服务器上要轻得多,因为它只返回HTTP头,而不是像标准GET请求那样的头和内容.

(2)true在调用curl_exec()返回内容之前,需要将CURLOPT_RETURNTRANSFER选项设置为,而不是打印:

curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);

这也应该让你的班级正常工作.

Answer 4

您可以设置默认流上下文：

stream_context_set_default(
    array(
        'http' => array(
            'method' => 'HEAD'
        )
    )
);

然后使用：

$headers = get_headers($url,1);

一旦 get_headers 跳过诸如登录提示或 cookie 等触发身份验证例程之类的步骤，get_headers 似乎比 cURL 更有效。

Answer 5

这是我使用CURLOPT_HEADER的实现，然后将输出字符串解析为映射：

function http_headers($url){
    $ch = curl_init();
    curl_setopt($ch, CURLOPT_URL, $url);
    curl_setopt($ch, CURLOPT_NOBODY, true);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
    curl_setopt($ch, CURLOPT_HEADER, true);

    $headers = curl_exec($ch);

    curl_close($ch);

    $data = [];
    $headers = explode(PHP_EOL, $headers);
    foreach ($headers as $row) {
        $parts = explode(':', $row);
        if (count($parts) === 2) {
            $data[trim($parts[0])] = trim($parts[1]);
        }
    }

    return $data;
};

用法示例：

$headers = http_headers('https://i.ytimg.com/vi_webp/g-dKXOlsf98/hqdefault.webp');
print_r($headers);

Array
(
    ['Content-Type'] => 'image/webp'
    ['ETag'] => '1453807629'
    ['X-Content-Type-Options'] => 'nosniff'
    ['Server'] => 'sffe'
    ['Content-Length'] => 32958
    ['X-XSS-Protection'] => '1; mode=block'
    ['Age'] => 11
    ['Cache-Control'] => 'public, max-age=7200'
)