/**
 * @license
 * Copyright Google Inc. All Rights Reserved.
 *
 * Use of this source code is governed by an MIT-style license that can be
 * found in the LICENSE file at https://angular.io/license
 */
/**
 * Immutable set of Http headers, with lazy parsing.
 *
 * @publicApi
 */
export declare class HttpHeaders {
    /**
     * Internal map of lowercase header names to values.
     */
    private headers;
    /**
     * Internal map of lowercased header names to the normalized
     * form of the name (the form seen first).
     */
    private normalizedNames;
    /**
     * Complete the lazy initialization of this object (needed before reading).
     */
    private lazyInit;
    /**
     * Queued updates to be materialized the next initialization.
     */
    private lazyUpdate;
    constructor(headers?: string | {
        [name: string]: string | string[];
    });
    /**
     * Checks for existence of header by given name.
     */
    has(name: string): boolean;
    /**
     * Returns first header that matches given name.
     */
    get(name: string): string | null;
    /**
     * Returns the names of the headers
     */
    keys(): string[];
    /**
     * Returns list of header values for a given name.
     */
    getAll(name: string): string[] | null;
    append(name: string, value: string | string[]): HttpHeaders;
    set(name: string, value: string | string[]): HttpHeaders;
    delete(name: string, value?: string | string[]): HttpHeaders;
    private maybeSetNormalizedName;
    private init;
    private copyFrom;
    private clone;
    private applyUpdate;
}