cinny/src/app/utils/stripImageMetadata.ts

/* eslint-disable no-bitwise -- byte-level container parsing */
/**
 * [Gitea #109] Remove EXIF / XMP / IPTC metadata from an image WITHOUT
 * re-encoding its pixels, so phone photos stop carrying GPS coordinates,
 * device model and timestamps into the room. JPEG, PNG and WebP are handled
 * at the container level; anything else is returned untouched.
 *
 * JPEG orientation: a bare strip would un-rotate photos whose pixels are
 * stored sideways, so when the EXIF Orientation tag is not 1 a minimal EXIF
 * block carrying only that tag is written back.
 */

export type StripResult = {
  blob: Blob;
  /** Whether any metadata segment was actually removed. */
  stripped: boolean;
  /** EXIF orientation that was preserved (JPEG only), if any. */
  orientation?: number;
};

const EXIF_HEADER = [0x45, 0x78, 0x69, 0x66, 0x00, 0x00]; // "Exif\0\0"

/** Read the EXIF Orientation tag (1–8) from an APP1 payload, or undefined. */
export function readJpegOrientation(app1: Uint8Array): number | undefined {
  if (app1.length < 14) return undefined;
  for (let i = 0; i < 6; i += 1) if (app1[i] !== EXIF_HEADER[i]) return undefined;
  const tiff = 6;
  const le = app1[tiff] === 0x49 && app1[tiff + 1] === 0x49;
  const view = new DataView(app1.buffer, app1.byteOffset, app1.byteLength);
  const u16 = (o: number) => view.getUint16(o, le);
  const u32 = (o: number) => view.getUint32(o, le);
  if (u16(tiff + 2) !== 0x2a) return undefined;
  const ifd0 = tiff + u32(tiff + 4);
  if (ifd0 + 2 > app1.length) return undefined;
  const count = u16(ifd0);
  for (let i = 0; i < count; i += 1) {
    const entry = ifd0 + 2 + i * 12;
    if (entry + 12 > app1.length) return undefined;
    if (u16(entry) === 0x0112) {
      const value = u16(entry + 8);
      return value >= 1 && value <= 8 ? value : undefined;
    }
  }
  return undefined;
}

/** A minimal APP1 segment: EXIF header + TIFF + one IFD0 entry (Orientation). */
export function buildOrientationApp1(orientation: number): Uint8Array {
  // TIFF (big-endian): "MM", 0x002A, IFD offset 8; IFD0: count 1, entry, next 0.
  const tiff = new Uint8Array([
    0x4d,
    0x4d,
    0x00,
    0x2a,
    0x00,
    0x00,
    0x00,
    0x08,
    0x00,
    0x01,
    0x01,
    0x12,
    0x00,
    0x03,
    0x00,
    0x00,
    0x00,
    0x01,
    0x00,
    orientation & 0xff,
    0x00,
    0x00,
    0x00,
    0x00,
    0x00,
    0x00,
  ]);
  const payload = new Uint8Array(EXIF_HEADER.length + tiff.length);
  payload.set(EXIF_HEADER, 0);
  payload.set(tiff, EXIF_HEADER.length);
  const seg = new Uint8Array(4 + payload.length);
  seg[0] = 0xff;
  seg[1] = 0xe1;
  const len = payload.length + 2;
  seg[2] = (len >> 8) & 0xff;
  seg[3] = len & 0xff;
  seg.set(payload, 4);
  return seg;
}

/** JPEG: drop APP1 (EXIF/XMP), APP13 (IPTC), COM; keep JFIF/ICC and the image. */
export function stripJpeg(bytes: Uint8Array): {
  out: Uint8Array;
  stripped: boolean;
  orientation?: number;
} {
  if (bytes.length < 4 || bytes[0] !== 0xff || bytes[1] !== 0xd8)
    return { out: bytes, stripped: false };
  const parts: Uint8Array[] = [bytes.subarray(0, 2)];
  let pos = 2;
  let stripped = false;
  let orientation: number | undefined;
  let insertedOrientation = false;
  while (pos + 4 <= bytes.length) {
    if (bytes[pos] !== 0xff) break;
    const marker = bytes[pos + 1];
    // Start of scan: everything from here to the end is entropy-coded data.
    if (marker === 0xda) break;
    const len = (bytes[pos + 2] << 8) | bytes[pos + 3];
    const segEnd = pos + 2 + len;
    if (len < 2 || segEnd > bytes.length) break;
    const drop = marker === 0xe1 || marker === 0xed || marker === 0xfe;
    if (drop) {
      stripped = true;
      if (marker === 0xe1 && orientation === undefined) {
        orientation = readJpegOrientation(bytes.subarray(pos + 4, segEnd));
      }
    } else {
      parts.push(bytes.subarray(pos, segEnd));
    }
    pos = segEnd;
    // Put the orientation-only EXIF right after SOI/JFIF, before anything else.
    if (!insertedOrientation && orientation !== undefined && orientation !== 1 && marker !== 0xe0) {
      insertedOrientation = true;
      parts.push(buildOrientationApp1(orientation));
    }
  }
  if (!stripped) return { out: bytes, stripped: false };
  if (orientation !== undefined && orientation !== 1 && !insertedOrientation) {
    parts.push(buildOrientationApp1(orientation));
  }
  parts.push(bytes.subarray(pos));
  const total = parts.reduce((n, p) => n + p.length, 0);
  const out = new Uint8Array(total);
  let o = 0;
  parts.forEach((p) => {
    out.set(p, o);
    o += p.length;
  });
  return { out, stripped, orientation: orientation !== 1 ? orientation : undefined };
}

const PNG_SIG = [0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a];
const PNG_DROP = new Set(['eXIf', 'tEXt', 'iTXt', 'zTXt', 'tIME']);

/** PNG: drop eXIf and text chunks (XMP lives in iTXt); keep colour chunks. */
export function stripPng(bytes: Uint8Array): { out: Uint8Array; stripped: boolean } {
  if (bytes.length < 8) return { out: bytes, stripped: false };
  for (let i = 0; i < 8; i += 1)
    if (bytes[i] !== PNG_SIG[i]) return { out: bytes, stripped: false };
  const parts: Uint8Array[] = [bytes.subarray(0, 8)];
  let pos = 8;
  let stripped = false;
  while (pos + 8 <= bytes.length) {
    const len =
      ((bytes[pos] << 24) | (bytes[pos + 1] << 16) | (bytes[pos + 2] << 8) | bytes[pos + 3]) >>> 0;
    const type = String.fromCharCode(
      bytes[pos + 4],
      bytes[pos + 5],
      bytes[pos + 6],
      bytes[pos + 7],
    );
    const end = pos + 12 + len;
    if (end > bytes.length) break;
    if (PNG_DROP.has(type)) stripped = true;
    else parts.push(bytes.subarray(pos, end));
    pos = end;
  }
  if (!stripped) return { out: bytes, stripped: false };
  parts.push(bytes.subarray(pos));
  const total = parts.reduce((n, p) => n + p.length, 0);
  const out = new Uint8Array(total);
  let o = 0;
  parts.forEach((p) => {
    out.set(p, o);
    o += p.length;
  });
  return { out, stripped };
}

const fourcc = (b: Uint8Array, o: number) =>
  String.fromCharCode(b[o], b[o + 1], b[o + 2], b[o + 3]);

/** WebP: drop EXIF/XMP chunks and clear their VP8X flags; fix the RIFF size. */
export function stripWebp(bytes: Uint8Array): { out: Uint8Array; stripped: boolean } {
  if (bytes.length < 12 || fourcc(bytes, 0) !== 'RIFF' || fourcc(bytes, 8) !== 'WEBP') {
    return { out: bytes, stripped: false };
  }
  const chunks: Uint8Array[] = [];
  let pos = 12;
  let stripped = false;
  let vp8x: Uint8Array | undefined;
  while (pos + 8 <= bytes.length) {
    const id = fourcc(bytes, pos);
    const len =
      (bytes[pos + 4] | (bytes[pos + 5] << 8) | (bytes[pos + 6] << 16) | (bytes[pos + 7] << 24)) >>>
      0;
    const end = pos + 8 + len + (len % 2);
    if (pos + 8 + len > bytes.length) break;
    if (id === 'EXIF' || id === 'XMP ') stripped = true;
    else {
      const chunk = bytes.slice(pos, Math.min(end, bytes.length));
      if (id === 'VP8X') vp8x = chunk;
      chunks.push(chunk);
    }
    pos = end;
  }
  if (!stripped) return { out: bytes, stripped: false };
  // VP8X flags byte: bit 3 = EXIF, bit 2 = XMP (0x08 / 0x04).
  if (vp8x && vp8x.length >= 9) vp8x[8] &= ~0x0c;
  const body = chunks.reduce((n, c) => n + c.length, 0);
  const out = new Uint8Array(12 + body);
  out.set(bytes.subarray(0, 12), 0);
  const riffSize = 4 + body;
  out[4] = riffSize & 0xff;
  out[5] = (riffSize >> 8) & 0xff;
  out[6] = (riffSize >> 16) & 0xff;
  out[7] = (riffSize >> 24) & 0xff;
  let o = 12;
  chunks.forEach((c) => {
    out.set(c, o);
    o += c.length;
  });
  return { out, stripped };
}

export const STRIPPABLE_TYPES = ['image/jpeg', 'image/png', 'image/webp'];

export function stripImageMetadataBytes(
  bytes: Uint8Array,
  mimeType: string,
): { out: Uint8Array; stripped: boolean; orientation?: number } {
  if (mimeType === 'image/jpeg') return stripJpeg(bytes);
  if (mimeType === 'image/png') return stripPng(bytes);
  if (mimeType === 'image/webp') return stripWebp(bytes);
  return { out: bytes, stripped: false };
}

/** Strip a File/Blob; returns the same object when nothing changed or the type is unsupported. */
export async function stripImageMetadata(file: File): Promise<StripResult & { file: File }> {
  if (!STRIPPABLE_TYPES.includes(file.type)) return { blob: file, file, stripped: false };
  const bytes = new Uint8Array(await file.arrayBuffer());
  const { out, stripped, orientation } = stripImageMetadataBytes(bytes, file.type);
  if (!stripped) return { blob: file, file, stripped: false };
  const next = new File([out as BlobPart], file.name, {
    type: file.type,
    lastModified: file.lastModified,
  });
  return { blob: next, file: next, stripped: true, orientation };
}