如何在PHP中读取任何请求标头

<?php
// 获取所有请求标头
$headers = getallheaders();

// 打印所有请求标头
foreach ($headers as $name => $value) {
    echo $name . ': ' . $value . '<br>';
}
?>

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