Flutter大文件实现分块上传和断点续传

最近在搞flutter的大文件上传功能，记录一下断点续传的视线
1.将文件进行分块，我们和后台约定的是3M每块

static const int partSize = 1024 * 1024 * 3; //3m每块

///上传文件 后台要记录从第几块开始传，也就是currentPart
Future<bool> _uploadZip(String path) async {
    File file = File(path);
    String fileName = FileUtil.getBaseName(file.path);
    int fileSize = file.lengthSync(); //文件总大小
    int totalPart = (fileSize * 1.0 / partSize).ceil(); //分块总数 向上取整
    int currentPart = currentPart; //当前要传第几块 由后台记录返回的
   
   //开启循环上传每一块
    while (currentPart < totalPart) {
      bool isOK = await _uploadPart(file, currentPart, totalPart, fileSize, fileName);
      if (!isOK) {
        invokeStateListener(ProgressState.error, null);
        return false;
      }
      //更新进度
      invokeProgressListeners((currentPart + 1) * 1.0 / totalPart);
      currentPart++;
    }
    //所有分快上传成功
    invokeStateListener(ProgressState.complete, null);
    return true;
  }

2.将每一个分块上传到后台，并记录上传是否成功

Future<bool> _uploadPart(File file, int currentPart, int totalPart, int fileSize, String fileName) async {
    //开始读文件的位置     
    int start = currentPart * partSize; 
    //读取文件的长度 注意不要让长度超过总长度
    var length = (start + partSize > fileSize) ? (fileSize - start) : partSize; 

    RandomAccessFile raf = file.openSync(mode: FileMode.read);
    raf.setPositionSync(start);
    Uint8List data = raf.readSync(length);//从文件总长度中截取出要上传的长度

    Map<String, dynamic> map = {};
    map['total'] = totalPart; //总块数
    map['currentPart'] = currentPart; //当前上传到第几块
    map['part'] = MultipartFile.fromBytes(data, filename:'随便设置文件名');//当前快的数据 

    Map<String, dynamic>? response = await 真正的上传函数
    //自定义逻辑 失败的话返回false
 
    return true;
  }