Class for making responses on legacy servers slightly less painful

Responder.php

<?php

class Responder
{
    /**
     * @param int $statusCode
     * @param array $headers
     * @param string|callable $body
     */
    public function respond($statusCode, $headers = null, $body = "")
    {
        $reasonPhraseLookup = array(
            100 => "Continue",
            101 => "Switching Protocols",
            102 => "Processing",
            200 => "OK",
            201 => "Created",
            202 => "Accepted",
            203 => "Non-Authoritative Information",
            204 => "No Content",
            205 => "Reset Content",
            206 => "Partial Content",
            207 => "Multi-Status",
            208 => "Already Reported",
            226 => "IM Used",
            300 => "Multiple Choices",
            301 => "Moved Permanently",
            302 => "Found",
            303 => "See Other",
            304 => "Not Modified",
            305 => "Use Proxy",
            307 => "Temporary Redirect",
            308 => "Permanent Redirect",
            400 => "Bad Request",
            401 => "Unauthorized",
            402 => "Payment Required",
            403 => "Forbidden",
            404 => "Not Found",
            405 => "Method Not Allowed",
            406 => "Not Acceptable",
            407 => "Proxy Authentication Required",
            408 => "Request Timeout",
            409 => "Conflict",
            410 => "Gone",
            411 => "Length Required",
            412 => "Precondition Failed",
            413 => "Payload Too Large",
            414 => "URI Too Long",
            415 => "Unsupported Media Type",
            416 => "Range Not Satisfiable",
            417 => "Expectation Failed",
            421 => "Misdirected Request",
            422 => "Unprocessable Entity",
            423 => "Locked",
            424 => "Failed Dependency",
            426 => "Upgrade Required",
            428 => "Precondition Required",
            429 => "Too Many Requests",
            431 => "Request Header Fields Too Large",
            500 => "Internal Server Error",
            501 => "Not Implemented",
            502 => "Bad Gateway",
            503 => "Service Unavailable",
            504 => "Gateway Timeout",
            505 => "HTTP Version Not Supported",
            506 => "Variant Also Negotiates",
            507 => "Insufficient Storage",
            508 => "Loop Detected",
            510 => "Not Extended",
            511 => "Network Authentication Required"
        );

        $reasonPhrase = "";
        if (isset($reasonPhraseLookup[$statusCode])) {
            $reasonPhrase = $reasonPhraseLookup[$statusCode];
        }

        // Status Line
        header("HTTP/1.1 $statusCode $reasonPhrase");

        // Headers
        if (!is_array($headers)) {
            $headers = array();
        }
        foreach ($headers as $name => $values) {
            if (is_array($values)) {
                foreach ($values as $value) {
                    header("$name: $value", false);
                }
            } else {
                header("$name: $values", false);
            }
        }

        // Body
        if (is_callable($body)) {
            $body();
        } else {
            print (string) $body;
        }
        exit;
    }
}