How to get the address after jump in php

For PHP developers, obtaining the jump address may be a very common problem, such as needing to obtain the real jump address in the crawler program. In this article, we will explore how to get the redirected address using PHP.

HTTP redirection

In the HTTP protocol, redirection means that when the client (such as a website browser) requests the server (such as a website server), the server returns a redirection response, telling The client needs to resend the request to another address. This process is called HTTP redirection.

There are many ways to implement HTTP redirection, the most common of which is to use HTTP status codes 302 (Found) and 303 (See Other). When the server returns these status codes, the client automatically performs a redirection and jumps to the new URL address.

Get the redirected address

In PHP, we can use curl and header functions to get the redirected address. The following is a sample code for using curl to obtain the redirected address:

function getRedirectUrl($url){
    $ch = curl_init();
    curl_setopt($ch, CURLOPT_URL, $url);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
    curl_setopt($ch, CURLOPT_FOLLOWLOCATION, true);
    curl_setopt($ch, CURLOPT_AUTOREFERER, true);
    $redirectUrl = curl_getinfo($ch, CURLINFO_EFFECTIVE_URL);
    curl_close($ch);
    return $redirectUrl;
}

This function accepts a URL as a parameter and returns the new address after redirection of this URL. For this function, we need to pay attention to the following points:

1. The curl_setopt function is used to set some parameters of the curl request, such as url, return data type, whether to follow the jump, etc.;
2. CURLOPT_RETURNTRANSFER instructs curl to return the obtained data as a string instead of outputting it directly;
3. CURLOPT_FOLLOWLOCATION instructs curl to automatically jump to the redirect address when encountering an HTTP 3xx response;
4. CURLOPT_AUTOREFERER instructs curl When automatically jumping, set the Referer field of the HTTP request header to the address before the jump.

In addition to using curl, we can also use the header function to obtain the redirected address, as shown below:

function getRedirectUrl($url){
    $redirectUrl = null;
    $headers = get_headers($url, true);
    if (isset($headers['Location'])) {
        $redirectUrl = $headers['Location'];
    } else if(isset($headers['location'])) {
        $redirectUrl = $headers['location'];
    }
    return $redirectUrl;
}

This function calls the get_headers function to obtain the $url specification The response header information of the URL. If the response header contains the Location or location field, it can be considered that the request has been redirected and the redirection address will be returned. It should be noted that using the header function can only support redirection with an HTTP response status code of 302 or 303, and cannot support other status codes.

Summary

In this article, we introduced how to use PHP to get the address after HTTP redirection. For situations where we need to track the redirected address in the program, we can use the curl or header function to obtain the Location field in the HTTP response header to obtain the redirected URL address.

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