/**
 * Validates and normalizes a backend URL.
 *
 * @param backendURL - The URL to validate (absolute or relative)
 * @returns An object with isAbsolute flag and the normalized URL
 * @throws {Error} If the URL format is invalid
 *
 * @example
 * ```ts
 * validateBackendURL('https://api.example.com/');
 * // Returns: { isAbsolute: true, normalizedURL: 'https://api.example.com' }
 *
 * validateBackendURL('/api/consent/');
 * // Returns: { isAbsolute: false, normalizedURL: '/api/consent' }
 * ```
 *
 * @public
 */
export declare function validateBackendURL(backendURL: string): {
    isAbsolute: boolean;
    normalizedURL: string;
};
/**
 * Normalizes a backend URL, resolving relative URLs using request headers.
 *
 * @remarks
 * For absolute URLs, returns the URL as-is (with trailing slash trimmed).
 * For relative URLs, attempts to construct the full URL using:
 * 1. x-forwarded-proto + x-forwarded-host/host headers
 * 2. Referer header as fallback
 *
 * @param backendURL - The backend URL (absolute or relative)
 * @param headersList - The Headers object from the incoming request
 * @returns The normalized absolute URL, or null if it cannot be determined
 *
 * @example
 * ```ts
 * import { normalizeBackendURL } from '@c15t/react/server';
 *
 * // Absolute URL - returns as-is
 * normalizeBackendURL('https://api.example.com/', headers);
 * // Returns: 'https://api.example.com'
 *
 * // Relative URL - resolved from headers
 * normalizeBackendURL('/api/consent', headers);
 * // Returns: 'https://example.com/api/consent' (based on headers)
 * ```
 *
 * @public
 */
export declare function normalizeBackendURL(backendURL: string, headersList: Headers): string | null;