处理jpg格式的元数据, 后续会继续更新

jpg-handle.dart

import 'dart:async';
import 'dart:io';

main(List<String> arguments) async {
  // final path = "timg.jpg";
  // final path = "/Users/cai/Desktop/1CD83646CA9CF1C2B0F7364B341E8580.gif";
  final path = "/Users/cai/Desktop/sxwphone.png";

  final imgFile = File(path);

  final result = await isJpg(imgFile);
  print("${imgFile.path} is jpg : $result");
}

Future<bool> isJpg(File file) async {
  if (file == null || !file.existsSync()) {
    return false;
  }

  final length = file.lengthSync();

  final completer = MyCompleter<bool>();

  void handleEnd() {
    file.openRead(length - 2, length).listen((data) {
      if (data[0] == 0xFF && data[1] == 0xD9) {
        completer.reply(true);
      } else {
        completer.reply(false);
      }
    });
  }

  void handleStart() async {
    file.openRead(0, 2).listen((data) {
      if (data[0] == 0xFF && data[1] == 0xD8) {
        handleEnd();
      } else {
        completer.reply(false);
      }
    });
  }

  handleStart();

  return completer.future;
}

class MyCompleter<T> {
  Completer<T> completer = Completer();

  MyCompleter();

  Future<T> get future => completer.future;

  void reply(T result) {
    if (!completer.isCompleted) {
      completer.complete(result);
    }
  }
}