jpegrotation.ts

// Exif orientation value to css transform mapping
type Rotation = string;
const rotations: Record<number, Rotation> = {
  1: "rotate(0deg)",
  2: "rotateY(180deg)",
  3: "rotate(180deg)",
  4: "rotate(180deg) rotateY(180deg)",
  5: "rotate(270deg) rotateY(180deg)",
  6: "rotate(90deg)",
  7: "rotate(90deg) rotateY(180deg)",
  8: "rotate(270deg)",
} as const;

function _arrayBufferToBase64(buffer) {
  var binary = "";
  var bytes = new Uint8Array(buffer);
  var len = bytes.byteLength;
  for (var i = 0; i < len; ) {
    binary += String.fromCharCode(bytes[i]);
  }
  return window.btoa(binary);
}

function parseArrayBuffer(buffer: ArrayBuffer): Rotation | null {
  var idx = 0;
  var scanner = new DataView(buffer);
  if (buffer.byteLength < 2 || scanner.getUint16(idx) != 0xffd8) {
    // Not a JPEG
    return;
  }
  idx += 2;

  var value = 1; // Non-rotated is the default
  var leftToRead = scanner.byteLength - idx;
  var littleEndian = false;
  function readUint16(offset = 0, advancePointer = true): number {
    const n = scanner.getUint16(idx + offset, littleEndian);
    if (advancePointer) {
      idx += 2 + offset;
    }
    return n;
  }

  while (idx < leftToRead) {
    var uint16 = readUint16();
    idx += 2;
    switch (uint16) {
      case 0xffe1: // Start of EXIF
        // II (0x4949) Indicates Intel format - Little Endian
        // MM (0x4D4D) Indicates Motorola format - Big Endian
        littleEndian = readUint16(8, false) === 0x4949;

        var exifLength = readUint16();
        leftToRead = exifLength - idx;

        var exifLength = scanner.getUint16(idx, littleEndian);
        maxBytes = exifLength - idx;
        idx += 2;
        break;
      case 0x0112: // Orientation tag
        // Read the value, its 6 bytes further out
        // See page 102 at the following URL
        // http://www.kodak.com/global/plugins/acrobat/en/service/digCam/exifStandard2.pdf
        value = scanner.getUint16(idx + 6, false);
        maxBytes = 0; // Stop scanning
        break;
    }
  }
  if (callback) {
    callback(base64img, value);
  }
}

export async function rotation(file: Blob): Promise<?Rotation> {
  return new Promise((resolve) => {
    var fileReader = new FileReader();
    fileReader.onloadend = () => resolve(parseArrayBuffer(fileReader.result));
    fileReader.readAsArrayBuffer(file);
  });
}