export declare class HttpHeaders {
    /** lowercase name => values */
    private headers;
    /** Maintain a copy of header name in the form of `lowercase name => normalized name` */
    private normalizedNames;
    constructor(headers?: string | {
        [name: string]: string | number | (string | number)[];
    } | Headers);
    /**
     * Add a new value to an existing values
     * @param name
     * @param value
     * @returns
     */
    append(name: string, value: string | string[]): HttpHeaders;
    /**
     * Set a value and overwrite an existing value
     * @param name
     * @param value
     * @returns
     */
    set(name: string, value: string | string[]): HttpHeaders;
    /**
     * Deletes a value from an existing value by a given header
     * @param name
     * @returns
     */
    delete(name: string): HttpHeaders;
    /**
     * Get the first value from the given header
     * @param name
     * @returns
     */
    get(name: string): string | null;
    /**
     * Get all values by given header
     * @param name
     * @returns
     */
    getAll(name: string): string[] | null;
    /**
     * Check if the given header is present
     * @param name
     * @returns
     */
    has(name: string): boolean;
    forEach(fn: (name: string, value: string[]) => void): void;
    keys(): string[];
    private clone;
    /**
     * @param key lowercase name
     * @param normalized normalized name
     */
    private setNormalizedName;
    private addHeaderEntry;
}