/**
 * Getting an image into Substack.
 *
 * Substack's upload endpoint takes a data URI under `image`, not a file upload
 * and not a URL. So whichever way the caller supplies the image, it has to be
 * read into memory and encoded first.
 *
 * Two hazards worth guarding, because this is the one tool that takes an
 * arbitrary URL from a model and fetches it:
 *   - SSRF. A model can be talked into passing http://169.254.169.254/ or a
 *     localhost address, which would make this server a proxy into a private
 *     network. Private, loopback and link-local destinations are refused, and
 *     redirects are followed manually so the check applies to every hop.
 *   - Size. An unbounded download becomes an unbounded base64 string in memory
 *     and then a rejected request, so it is capped before that happens.
 */
export declare const MAX_IMAGE_BYTES: number;
export declare function detectMimeType(bytes: Buffer): string | null;
/** RFC 1918, loopback, link-local and unique-local ranges. */
export declare function isPrivateAddress(address: string): boolean;
/** Download an image and return it as a data URI, checking every redirect hop. */
export declare function fetchImageAsDataUri(url: string, userAgent: string, timeoutMs: number): Promise<{
    dataUri: string;
    mimeType: string;
    bytes: number;
}>;
/** Read a local file and return it as a data URI. */
export declare function readImageFileAsDataUri(path: string): Promise<{
    dataUri: string;
    mimeType: string;
    bytes: number;
}>;