flutter 网络 : How to Upload a Large File?

Question

有没有办法将大文件上传到服务器？

我将 MultipartRequest 与 MultipartFile 一起使用，例如:

  List<int> fileBytes) async {
  var request = new http.MultipartRequest("POST", Uri.parse(url));
  request.files.add(http.MultipartFile.fromBytes(
    'file',
    fileBytes,
    contentType: MediaType('application', 'octet-stream'),
    filename: fileName));
  request.headers.addAll(headers);
  var streamedResponse = await request.send();
  return await http.Response.fromStream(streamedResponse);

并像这样读取文件:

    html.InputElement uploadInput = html.FileUploadInputElement();
    uploadInput.multiple = false;
    uploadInput.draggable = true;
    uploadInput.click();

    uploadInput.onChange.listen((e) {
      final files = uploadInput.files;
      final file = files[0];

      final reader = new html.FileReader();

      reader.onLoadEnd.listen((e) {
        setState(() {
          _bytesData =
              Base64Decoder().convert(reader.result.toString().split(",").last);
          _selectedFile = _bytesData;
        });
      });

      reader.readAsDataUrl(file);
    });

对于大约 30 MB 的文件是可以的，但对于超过 30 MB 的文件，我会得到 错误代码:内存不足。

我做错了什么吗？我在某处看到了

MultipartFile.fromBytes will give you some issues on bigger files, as the browser will limit your memory consumption.

我认为他的解决方案是:

There’s a fromStream constructor. Usually, for bigger files, I just use HttpRequest, and put the File object in a FormData instance.

我使用了 MultipartFile 和 MultipartFile.fromString 并且两次(对于 150 MB 文件)都再次发生。我该如何使用这个解决方案？或者对于超过 500 MB 的文件有更好的方法吗？

更新

使用 Worker 添加了一个答案。这不是一个很好的解决方案，但我认为这可能会对某人有所帮助。

Answer 1

目前，我使用这种方法解决了这个问题:

导入:

import 'package:universal_html/html.dart' as html;

flutter 部分:

class Upload extends StatefulWidget {
  @override
  _UploadState createState() => _UploadState();
}

class _UploadState extends State<Upload> {
  html.Worker myWorker;
  html.File file;

  _uploadFile() async {
    String _uri = "/upload";

    myWorker.postMessage({"file": file, "uri": _uri});
  }

  _selectFile() {
    html.InputElement uploadInput = html.FileUploadInputElement();
    uploadInput.multiple = false;
    uploadInput.click();

    uploadInput.onChange.listen((e) {
      file = uploadInput.files.first;
    });
  }

  @override
  void initState() {
    myWorker = new html.Worker('upload_worker.js');
    myWorker.onMessage.listen((e) {
      setState(() {
        //progressbar,...
      });
    });

    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return Column(
      children: [
        RaisedButton(
          onPressed: _selectFile(),
          child: Text("Select File"),
        ),
        RaisedButton(
          onPressed: _uploadFile(),
          child: Text("Upload"),
        ),
      ],
    );
  }
}

Javascript 部分:

在 web 文件夹中(在 index.html 旁边)，创建文件“upload_worker.js”。

self.addEventListener('message', async (event) => {
    var file = event.data.file;
    var url = event.data.uri;
    uploadFile(file, url);
});

function uploadFile(file, url) {
    var xhr = new XMLHttpRequest();
    var formdata = new FormData();
    var uploadPercent;

    formdata.append('file', file);

    xhr.upload.addEventListener('progress', function (e) {
        //Use this if you want to have a progress bar
        if (e.lengthComputable) {
            uploadPercent = Math.floor((e.loaded / e.total) * 100);
            postMessage(uploadPercent);
        }
    }, false);
    xhr.onreadystatechange = function () {
        if (xhr.readyState == XMLHttpRequest.DONE) {
            postMessage("done");
        }
    }
    xhr.onerror = function () {
        // only triggers if the request couldn't be made at all
        postMessage("Request failed");
    };

    xhr.open('POST', url, true);

    xhr.send(formdata);
}