import { IncomingMessage } from 'http';
/**
 * Derives the request host from the most‐trusted available header.
 *
 * Order:
 * 1. Forwarded: host=<value> (RFC 7239, only if trustProxy)
 * 2. X-Forwarded-Host (only if trustProxy)
 * 3. Host (always)
 *
 * @param req IncomingMessage
 * @param trustProxy whether to trust proxy headers
 * @returns the host (including port if present), or null
 */
export declare function deriveHost(req: IncomingMessage, trustProxy?: boolean): string | null;