import { type IncomingMessage } from 'node:http';
import { type WhookHeaders } from '../types/http.js';
export declare function mergeVaryHeaders(baseHeader: string | string[], addedValue: string): string;
export declare function lowerCaseHeaders<T>(object: Record<string, T>): Record<string, T>;
/**
 * Pick the first header value if exists
 * @function
 * @param  {string} name
 * The header name
 * @param  {Object} headers
 * The headers map
 * @return {string}
 * The value if defined.
 */
export declare function pickFirstHeaderValue(name: string, headers: WhookHeaders): string | undefined;
/**
 * Pick header values
 * @function
 * @param  {string} name
 * The header name
 * @param  {Object} headers
 * The headers map
 * @return {Array}
 * The values in an array.
 */
export declare function pickAllHeaderValues(name: string, headers?: WhookHeaders): string[];
export declare function castWhookHeaders(headers?: IncomingMessage['headers']): WhookHeaders;