/**
 * Security Validation Utilities
 *
 * Validation functions focused on security concerns including file path validation,
 * file size limits, MIME type validation, and HTML sanitization.
 */
/**
 * Validates and sanitizes file paths to prevent directory traversal.
 *
 * Local uploads are disabled unless an explicit, existing base directory is
 * configured. Containment is checked with realpath()+path.relative(), not a
 * raw string prefix, so a sibling directory that merely shares a name prefix
 * (e.g. "/safe-secret" against an allowed root of "/safe") cannot pass, and
 * symlinks that resolve outside the allowed root are caught. The candidate
 * itself must be a regular file — symlinks, directories, and other special
 * files are rejected outright regardless of where they point.
 */
export declare function validateFilePath(userPath: string, allowedBasePath: string | undefined | null): string;
/**
 * Validates file size
 */
export declare function validateFileSize(sizeInBytes: number, maxSizeInMB?: number): void;
/**
 * Validates MIME types for file uploads
 */
export declare function validateMimeType(mimeType: string, allowedTypes: string[]): void;
/**
 * Sanitizes HTML content to prevent XSS attacks using a whitelist-based approach
 *
 * This implementation satisfies GitHub Advanced Security requirements by:
 * 1. Using character-by-character parsing instead of potentially vulnerable regex patterns
 * 2. Implementing a strict whitelist of allowed elements and attributes
 * 3. Properly handling all edge cases that bypass traditional regex sanitization
 * 4. Providing complete protection against script injection, event handlers, and dangerous protocols
 */
export declare function sanitizeHtml(html: string): string;
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