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HTTP headers carry data between web servers and browsers for communication.

Whenever we enter a URL in the address bar of our browser, it sends an HTTP request to the server; it contains a header.

In PHP use get_headers()get the headers for a given URL

get_headers()Is a PHP built-in function that is used to get the headers sent by the server in response to an HTTP request.

<?php
$URL = 'https://www.delftstack.com/';

$headers = get_headers($URL);
foreach($headers as $value) {
    echo $value;
    echo "<br>";
}
?>

The above code gets all the headers sent by the server for https://www.delftstack.com/ .

Output:

HTTP/1.0 200 OK
Age: 0
Cache-Control: max-age=2592000, private, s-maxage=0, proxy-revalidate
Content-Type: text/html; charset=UTF-8
Date: Fri, 25 Feb 2022 12:00:31 GMT
Display: pub_site_to_orig_sol
Etag: "6b7e22637c1ca646a2c1db6894a4b0f8-ssl-df-gzip"
Pagespeed: off
Response: 200
Server: nginx
Set-Cookie: ezoadgid_96282=-1; Path=/; Domain=delftstack.com; Expires=Fri, 25 Feb 2022 12:30:31 UTC
Set-Cookie: ezoref_96282=; Path=/; Domain=delftstack.com; Expires=Fri, 25 Feb 2022 14:00:31 UTC
Set-Cookie: ezoab_96282=mod1; Path=/; Domain=delftstack.com; Expires=Fri, 25 Feb 2022 14:00:31 UTC
Set-Cookie: active_template::96282=pub_site.1645790431; Path=/; Domain=delftstack.com; Expires=Sun, 27 Feb 2022 12:00:31 UTC
Set-Cookie: lp_96282=https://www.delftstack.com/; Path=/; Domain=delftstack.com; Expires=Fri, 25 Feb 2022 12:30:31 UTC
Set-Cookie: ezovuuidtime_96282=1645790431; Path=/; Domain=delftstack.com; Expires=Sun, 27 Feb 2022 12:00:31 UTC
Set-Cookie: ezovuuid_96282=23606c54-6e8e-42a1-4745-bf6c0d668d64; Path=/; Domain=delftstack.com; Expires=Fri, 25 Feb 2022 12:30:31 UTC
Set-Cookie: ezopvc_96282=1; Path=/; Domain=delftstack.com; Expires=Fri, 25 Feb 2022 12:30:31 UTC
Strict-Transport-Security: max-age=31536000
Vary: Accept-Encoding
Vary: Accept-Encoding,User-Agent
X-Ezoic-Cdn: Hit ds;mm;ba60b18a465a11ac0d2ea4d2e9f91570;2-96282-33;ec6a48c1-7683-4a48-429a-88731467543c
X-Middleton-Display: pub_site_to_orig_sol
X-Middleton-Response: 200
X-Nf-Request-Id: 01FWR6BN2347S6Y8M9PW8W70CW
X-Origin-Cache-Control: public, max-age=0, must-revalidate
X-Sol: pub_site

$_SERVERGet a single HTTP request header for your server in PHP using

Our localhost server contains $_SERVERall the header information in an array. We can get the information of a single HTTP request header by putting a specific index name.

<?php
//print_r($_SERVER);
echo $_SERVER['HTTP_HOST']."<br>";
echo $_SERVER['HTTP_USER_AGENT']."<br>";
echo $_SERVER['HTTP_CONNECTION'];
?>

The above code gets information given a single HTTP request.

Output:

localhost
Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:97.0) Gecko/20100101 Firefox/97.0
keep-alive

Use the function in PHP apache_request_headers()to get all request headers of the Apache server

The built-in function in PHP apache_request_headers()is used to get the headers of the apache module.

<?php
$apache_headers= apache_request_headers();

foreach ($apache_headers as $key => $value) {
    echo "$key => $value <br/>";
}
?>

The output will show the HTTP information for the apache module:

Host => localhost
User-Agent => Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:97.0) Gecko/20100101 Firefox/97.0
Accept => text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,*/*;q=0.8
Accept-Language => en-US,en;q=0.5
Accept-Encoding => gzip, deflate
Connection => keep-alive
Upgrade-Insecure-Requests => 1
Sec-Fetch-Dest => document
Sec-Fetch-Mode => navigate
Sec-Fetch-Site => none
Sec-Fetch-User => ?1

getallheaders()is apache_request_headersan updated version of and works in a similar way.

$_SERVERGet all HTTP request headers from the server using

$_SERVERContains a lot of information other than the HTTP request header.

<?php
function get_HTTP_request_headers() {
    $HTTP_headers = array();
    foreach($_SERVER as $key => $value) {
        if (substr($key, 0, 5) <> 'HTTP_') {
            continue;
        }
        $single_header = str_replace(' ', '-', ucwords(str_replace('_', ' ', strtolower(substr($key, 5)))));
        $HTTP_headers[$single_header] = $value;
    }
    return $HTTP_headers;
}
$headers = get_HTTP_request_headers();
foreach ($headers as $key => $value) {
    echo "$key => $value <br/>";
}
?>

The above code will $_SERVERextract the HTTP request headers from the array.

Output:

Host => localhost
User-Agent => Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:97.0) Gecko/20100101 Firefox/97.0
Accept => text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,*/*;q=0.8
Accept-Language => en-US,en;q=0.5
Accept-Encoding => gzip, deflate
Connection => keep-alive
Upgrade-Insecure-Requests => 1
Sec-Fetch-Dest => document
Sec-Fetch-Mode => navigate
Sec-Fetch-Site => none
Sec-Fetch-User => ?1