Using get_client_version in CDN scenarios is easy to misjudgment of device information

gitbox 2025-05-29

In modern web applications, it is becoming increasingly common to use CDN (content distribution network) to accelerate resource loading. CDNs can increase loading speeds by cached content and distributing it to servers around the world. However, in some cases, CDNs can also cause some problems, especially when identifying client device information.

Introduction to get_client_version function

The get_client_version function is usually used to obtain the client's version information, especially in scenarios where the terminal device type or version number needs to be judged. This function generally determines the type or version of the device based on some information in the requested HTTP header or URL.

Suppose we have a PHP function as follows:

 function get_client_version() {
    // Get user agent
    $user_agent = $_SERVER['HTTP_USER_AGENT'];
    
    // Suppose we want to judge the device version based on the user agent
    if (strpos($user_agent, 'Android') !== false) {
        return 'Android Version 10';
    } elseif (strpos($user_agent, 'iPhone') !== false) {
        return 'iPhone Version 12';
    } else {
        return 'Unknown Device';
    }
}

In the above example, the get_client_version function obtains the client's User-Agent information through $_SERVER['HTTP_USER_AGENT'] , thereby making a judgment on the device type.

Why can CDN lead to misjudgment?

Under normal circumstances, the get_client_version function obtains device information through the User-Agent requested by HTTP. However, when web applications are deployed in a CDN environment, the following problems may occur, resulting in bias in device identification:

Caching issues
The CDN will cache static resources and distribute them to local servers. In some cases, the CDN caches the User-Agent information in the request header. If different terminals request the same resource, the CDN may return a cached response, and the User-Agent information of this response is inconsistent with the actual requested terminal device. As a result, the get_client_version function may misjudgment the client's device.
CDN's proxy layer
A CDN server usually acts as a proxy, forwarding the original request to the backend server. In this process, the CDN's proxy server sometimes modifys the request header, or modifys some information according to the load balancing policy, such as User-Agent . This will cause the get_client_version function to get the wrong device information.
Impact of IP address Sometimes, the CDN will determine the source of the request based on the IP address, and then determine the device type. However, since CDNs usually distribute requests to different servers, such judgments may not be accurate. Especially when the same IP address request comes from different terminals, the CDN may mistakenly consider them to be the same device, thus affecting the version determination.

How to avoid misjudgment?

To avoid misjudging terminal devices when using the get_client_version function in a CDN environment, you can consider the following methods:

Disable cache For requests to obtain device information, try to avoid CDN cache. This can be achieved by setting specific cache policies (such as disabling cache, adding cache headers, etc.). In this way, the CDN will request the backend to obtain the latest device information every time.
Check the real client request header Use header fields such as X-Forwarded-For to ensure that the original request information that is closest to the terminal is obtained, rather than the request header modified by the CDN proxy layer.
Use JavaScript to obtain device information In some cases, device information can be obtained on the client via JavaScript instead of relying on the server-side User-Agent . This can avoid interference from the CDN layer. The example code for obtaining device information through JavaScript is as follows:
```
 var deviceInfo = navigator.userAgent;
console.log(deviceInfo); // Output deviceUser-Agentinformation
```
This information is then passed back to the server to ensure that the server can correctly identify the device.
Dynamic Request For functions that require precise device information, the get_client_version function can be placed in a separate request instead of a static resource cached through the CDN. This makes the device information acquisition process more accurate and dynamic.

Conclusion

In the CDN environment, the get_client_version function may be affected by factors such as cache and proxy layer interference, resulting in misjudgment of the terminal device. To avoid this, developers can use methods such as disabling cache, ensuring the acquisition of the original request header, and using JavaScript to obtain device information to ensure the accuracy of device identification. Through these optimizations, it can better ensure the accurate acquisition of terminal equipment information and improve user experience.

get_client_version