OpenFrame/lib/image-upload-validation.ts

export const ALLOWED_IMAGE_MIME_TYPES = ['image/jpeg', 'image/png', 'image/webp', 'image/gif'] as const;
export type AllowedImageMimeType = (typeof ALLOWED_IMAGE_MIME_TYPES)[number];

const EXT_BY_MIME: Record<AllowedImageMimeType, string> = {
  'image/jpeg': 'jpg',
  'image/png': 'png',
  'image/webp': 'webp',
  'image/gif': 'gif',
};

export function normalizeImageMime(value: string): string {
  if (value === 'image/jpg' || value === 'image/pjpeg') return 'image/jpeg';
  return value;
}

export function isAllowedImageType(value: string): value is AllowedImageMimeType {
  return (ALLOWED_IMAGE_MIME_TYPES as readonly string[]).includes(value);
}

export function detectImageMime(buffer: Uint8Array): AllowedImageMimeType | null {
  // JPEG
  if (buffer.length >= 2 && buffer[0] === 0xff && buffer[1] === 0xd8) {
    return 'image/jpeg';
  }
  // PNG
  if (
    buffer.length >= 8
    && buffer[0] === 0x89
    && buffer[1] === 0x50
    && buffer[2] === 0x4e
    && buffer[3] === 0x47
    && buffer[4] === 0x0d
    && buffer[5] === 0x0a
    && buffer[6] === 0x1a
    && buffer[7] === 0x0a
  ) {
    return 'image/png';
  }
  // GIF87a/GIF89a
  if (
    buffer.length >= 6
    && buffer[0] === 0x47
    && buffer[1] === 0x49
    && buffer[2] === 0x46
    && buffer[3] === 0x38
    && (buffer[4] === 0x37 || buffer[4] === 0x39)
    && buffer[5] === 0x61
  ) {
    return 'image/gif';
  }
  // WEBP: "RIFF"...."WEBP"
  if (
    buffer.length >= 12
    && buffer[0] === 0x52
    && buffer[1] === 0x49
    && buffer[2] === 0x46
    && buffer[3] === 0x46
    && buffer[8] === 0x57
    && buffer[9] === 0x45
    && buffer[10] === 0x42
    && buffer[11] === 0x50
  ) {
    return 'image/webp';
  }

  return null;
}

export function getImageExtension(mime: AllowedImageMimeType): string {
  return EXT_BY_MIME[mime];
}

export function firstBytesHex(buffer: Uint8Array, length = 16): string {
  return Array.from(buffer.slice(0, length))
    .map((byte) => byte.toString(16).padStart(2, '0'))
    .join(' ');
}