How do I read any request header in PHP

Question

How should I read any header in PHP?

For example the custom header: X-Requested-With.

Answer 1

IF: you only need a single header, instead of all headers, the quickest method is:

<?php
// Replace XXXXXX_XXXX with the name of the header you need in UPPERCASE (and with '-' replaced by '_')
$headerStringValue = $_SERVER['HTTP_XXXXXX_XXXX'];

ELSE IF: you run PHP as an Apache module or, as of PHP 5.4, using FastCGI (simple method):

apache_request_headers()

<?php
$headers = apache_request_headers();

foreach ($headers as $header => $value) {
    echo "$header: $value <br />\n";
}

ELSE: In any other case, you can use (userland implementation):

<?php
function getRequestHeaders() {
    $headers = array();
    foreach($_SERVER as $key => $value) {
        if (substr($key, 0, 5) <> 'HTTP_') {
            continue;
        }
        $header = str_replace(' ', '-', ucwords(str_replace('_', ' ', strtolower(substr($key, 5)))));
        $headers[$header] = $value;
    }
    return $headers;
}

$headers = getRequestHeaders();

foreach ($headers as $header => $value) {
    echo "$header: $value <br />\n";
}

See Also:
getallheaders() - (PHP >= 5.4) cross platform edition Alias of apache_request_headers() apache_response_headers() - Fetch all HTTP response headers.
headers_list() - Fetch a list of headers to be sent.

Answer 2

You should find all HTTP headers in the $_SERVER global variable prefixed with HTTP_ uppercased and with dashes (-) replaced by underscores (_).

For instance your X-Requested-With can be found in:

$_SERVER['HTTP_X_REQUESTED_WITH']

It might be convenient to create an associative array from the $_SERVER variable. This can be done in several styles, but here's a function that outputs camelcased keys:

$headers = array();
foreach ($_SERVER as $key => $value) {
    if (strpos($key, 'HTTP_') === 0) {
        $headers[str_replace(' ', '', ucwords(str_replace('_', ' ', strtolower(substr($key, 5)))))] = $value;
    }
}

Now just use $headers['XRequestedWith'] to retrieve the desired header.

PHP manual on $_SERVER: http://php.net/manual/en/reserved.variables.server.php

Answer 3

Pass a header name to this function to get its value without using for loop. Returns null if header not found.

/**
 * @var string $headerName case insensitive header name
 *
 * @return string|null header value or null if not found
 */
function get_header($headerName)
{
    $headers = getallheaders();
    return isset($headerName) ? $headers[$headerName] : null;
}

Note: this works only with Apache server, see: http://php.net/manual/en/function.getallheaders.php

Note: this function will process and load all of the headers to the memory and it's less performant than a for loop.

Answer 4

function getCustomHeaders()
{
    $headers = array();
    foreach($_SERVER as $key => $value)
    {
        if(preg_match("/^HTTP_X_/", $key))
            $headers[$key] = $value;
    }
    return $headers;
}

I use this function to get the custom headers, if the header starts from "HTTP_X_" we push in the array :)

Answer 5

strtolower is lacking in several of the proposed solutions, RFC2616 (HTTP/1.1) defines header fields as case-insensitive entities. The whole thing, not just the value part.

So suggestions like only parsing HTTP_ entries are wrong.

Better would be like this:

if (!function_exists('getallheaders')) {
    foreach ($_SERVER as $name => $value) {
        /* RFC2616 (HTTP/1.1) defines header fields as case-insensitive entities. */
        if (strtolower(substr($name, 0, 5)) == 'http_') {
            $headers[str_replace(' ', '-', ucwords(strtolower(str_replace('_', ' ', substr($name, 5)))))] = $value;
        }
    }
    $this->request_headers = $headers;
} else {
    $this->request_headers = getallheaders();
}

Notice the subtle differences with previous suggestions. The function here also works on php-fpm (+nginx).

Answer 6

if only one key is required to retrieved, For example "Host" address is required, then we can use

apache_request_headers()['Host']

So that we can avoid loops and put it inline to the echo outputs