How to solve the problem that thinkphp images are not displayed across domains

Recently, I encountered some strange problems when developing projects using the ThinkPHP framework. Our project is a picture display website, but in the browser, some pictures will not be displayed, and there is no error message in the console. Through searching and experimenting, we eventually discovered that this was an issue caused by cross-domain. In this post, I’ll share our process for identifying problems and solving them.

First, let us understand what cross-domain is. Cross-domain occurs between two websites with different domain names. When the resources of one website, such as JS, CSS, Ajax, or images, request to access the resources of another website, they are blocked due to the restrictions of the same-origin policy. The same origin policy is a very important security feature. It restricts a website to only access resources with the same domain name, protocol and port as its own.

In our project, we use a third-party library to load images, and this library uses addresses with different domain names to store images. Therefore, in the browser, the image cannot be displayed properly when it crosses domain.

In order to solve this problem, we need to make some settings on the server side. The most common solution is to set up CORS (Cross-Origin Resource Sharing) on ​​the server side. CORS allows the server to specify which domain names can access the resource when responding to client requests.

In the ThinkPHP framework, we can implement CORS by adding the following code to the index.php file:

header('Access-Control-Allow-Origin:*'); //允许所有来源访问
header('Access-Control-Allow-Method:POST,GET'); //允许访问的方式

This code allows all sources to access resources, and allows POST and GET methods access.

It should be noted here that this code should be placed at the top of index.php so that all requests can use this setting.

In addition to setting up CORS, we can also use other methods to solve cross-domain problems. For example, JSONP (JSON with Padding) is a feasible method to solve cross-domain problems. By adding a script tag to the page, the data that needs to be accessed is packaged into a function, and then the returned results are received on another website.

In the ThinkPHP framework, we can use the following code to generate the JSONP method:

$callback = isset($_GET['callback']) ? $_GET['callback'] : 'callback';
$data = array('name' => 'test', 'age' => 18);
echo $callback . '(' . json_encode($data) . ')';

Here, we first check whether the callback parameter exists in the GET parameter, and if it exists, use the parameter as the function name. Then serialize the data to be returned into JSON format and add it to the callback function. Finally, when returning data, we return the function to the browser along with the data.

To summarize, cross-domain problems are usually very common problems during development. But we can solve this problem through server-side settings. In the ThinkPHP framework, we can use CORS or JSONP to solve cross-domain issues. I hope this article can help readers in need.

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