Get JPEG image dimensions in Dart

getJpegDimensions.dart

// translated to Dart from a code snippet presented here:
// https://stackoverflow.com/questions/672916/how-to-get-image-height-and-width-using-java
Future<Size> getJpegDimensions(File jpegFile) async {
  final f = await jpegFile.open();
  Size dimension;
  try {
    // check for SOI marker
    if (await f.readByte() != 255 || await f.readByte() != 216) {
      throw new FormatException(
          "SOI (Start Of Image) marker 0xff 0xd8 missing");
    }

    while (await f.readByte() == 255) {
      int marker = await f.readByte();
      int len = await f.readByte() << 8 | await f.readByte();

      if (marker == 192) {
        // skip one byte
        await f.setPosition(await f.position() + 1);

        final height = await f.readByte() << 8 | await f.readByte();
        final width = await f.readByte() << 8 | await f.readByte();

        dimension = Size(width.toDouble(), height.toDouble());
        break;
      }

      // skip len - 2 bytes
      await f.setPosition(await f.position() + len - 2);
    }
  } finally {
    await f.close();
  }

  return dimension;
}