如何让浏览器缓存图像，用PHP？ [英] How to get the browser to cache images, with php?

问题描述

我使用php输出图库中的所有图像，并且希望已显示的图像能够被缓存浏览器，所以PHP脚本不必再输出相同的图像。我想要的是图像显示速度更快。

调用图像时，我喜欢这样：

 < img src =showImage.php？id = 601> 
  

和 showImage.php --file ：

  $ resultat = mysql_query（
 SELECT filename，id 
 FROM Media 
 WHERE id ='。$ _ GET ['id']。''
）; 
 $ data = mysql_fetch_assoc（$ resultat）; 
 
 ... 
 
 //只有当用户登录
 if（isset（$ _ SESSION ['user']））{
标题（Content-Type：image / jpeg）; 
 
 // $ data ['filename'] can be = dsSGKLMsgKkD3325J.jpg 
 echo（file_get_contents（images /\".$ data ['filename']。））; 
 
  

解决方案

在输出消息之前检查用户是否已登录，然后您不希望浏览器缓存图像。

缓存的整个目的是调用服务器一次，然后再也不会再调用它。如果浏览器缓存图像，它将不会调用服务器，脚本也不会运行。相反，即使用户不再登录，浏览器也会从缓存中提取图像并显示它。这可能是一个非常大的安全漏洞。

I'm totally new to how to cache images.

I output all images in a gallery with php, and want the images already shown, to be cached by the browser, so the php-script don't have to output the same image again. All I want is the images to show up faster.

when calling an image I do like this:

<img src="showImage.php?id=601">

and the showImage.php-file does:

$resultat = mysql_query("
    SELECT filename, id
    FROM Media 
    WHERE id = '".$_GET['id']."'
");
$data = mysql_fetch_assoc($resultat);

...

//Only if the user are logged in
if(isset($_SESSION['user'])){
    header("Content-Type: image/jpeg");

    //$data['filename'] can be = dsSGKLMsgKkD3325J.jpg
    echo(file_get_contents("images/".$data['filename']."")); 
}

解决方案

If you are using php to check if the user is logged in before outputting the message, then you don't want the browser to cache the image.

The entire point of caching is to call the server once and then never call it again. If the browser caches the image, it won't call the server and your script won't run. Instead, the browser will pull your image from cache and display it, even if the user is no longer logged in. This could potentially be a very big security hole.

这篇关于如何让浏览器缓存图像，用PHP？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！