How to Efficiently Retrieve Request Headers in PHP?

How to Handle Header Retrieval in PHP

Requirement: Reading any request header in PHP.

Single Header Solution:

When working with a single specific header rather than all headers, the most efficient method is:

// Replace XXXXXX_XXXX with the header you need, in uppercase and '-' replaced by '_'
$headerValue = $_SERVER['HTTP_XXXXXX_XXXX'];

Retrieving All Headers (Apache Module or FastCGI):

Two methods are available for retrieving all headers when using Apache or FastCGI:

1. apache_request_headers():

Returns an array with all header values.

2. Built-in Method:

foreach ($_SERVER as $key => $value) {
    if (substr($key, 0, 5) !== 'HTTP_') {
        continue;
    }
    // Process headers...
}

Retrieving All Headers (Other Platforms):

For other platforms, a userland implementation can be used:

function getRequestHeaders() {
    // ... (Implementation same as above)
}

Advanced Note:

For PHP versions 5.4 and up, the getallheaders() function may also be used as a cross-platform equivalent of apache_request_headers().

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