/**
 * Returns whether a header field contains control characters or other bytes
 * unsafe for HTTP header serialization (including CR and LF).
 *
 * @param value - Header name or value to inspect.
 */
export declare function hasUnsafeHeaderFieldChars(value: string): boolean;
/**
 * Validates a request header name and value before passing them to fetch.
 *
 * @param name - Header field name (already trimmed when supplied from buildHeaders).
 * @param value - Header field value.
 * @returns An error message when invalid, otherwise null.
 */
export declare function validateHeaderField(name: string, value: string): string | null;
/**
 * Validates a header map and returns the first validation error, if any.
 *
 * @param headers - Header map ready for fetch.
 * @returns An error message when a field is invalid, otherwise null.
 */
export declare function validateHeaders(headers: Record<string, string>): string | null;
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