Bad state: Cannot add event while adding a stream

[MCSQNXA]

I tried to run the code in a web project, but encountered the error 'Bad state: Cannot add event while adding a stream'

import 'dart:async';
import 'dart:convert' as convert;

import 'package:file_picker/file_picker.dart';
import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;

void main() {
runApp(const MyApp());
}

class MyApp extends StatelessWidget {
const MyApp({super.key});

@OverRide
Widget build(BuildContext context) {
return MaterialApp(
home: TextButton(onPressed: () => doS(), child: Text('data')),
);
}
}

Future doS() async {
try {
FilePickerResult? result = await FilePicker.platform.pickFiles(
type: FileType.custom,
allowedExtensions: ["txt", "zip"],
withData: false,
withReadStream: true,
);

if (result == null) {
  return;
}

final req = http.StreamedRequest(
  'POST',
  Uri.parse('http://127.0.0.1/upload'),
);
req.contentLength = result.files[0].size;
req.sink.addStream(result.files[0].readStream!);

unawaited(req.sink.close());

final rsp = await req.send();

if (rsp.statusCode == 200) {
  debugPrint(convert.utf8.decode(await rsp.stream.toBytes()));
}

} catch (e) {
debugPrint(e.toString());
}
}

[brianquinlan]

I think that the problem is that you are not awaiting addStream i.e.

- req.sink.addStream(result.files[0].readStream!);
+ await req.sink.addStream(result.files[0].readStream!);

Please reopen the issue if that doesn't solve the problem.

[MCSQNXA]

Thank you for your reply, but addStream will continue to block and cannot continue running until the HTTP function is sent

[MCSQNXA]

I think that the problem is that you are not awaiting addStream i.e.

• req.sink.addStream(result.files[0].readStream!);

• await req.sink.addStream(result.files[0].readStream!);
  Please reopen the issue if that doesn't solve the problem.

Thank you for your reply, but addStream will continue to block and cannot continue running until the HTTP function is sent

[brianquinlan]

Then maybe you want to do (untested):

- req.sink.addStream(result.files[0].readStream!);
- unawaited(req.sink.close());
+ unawaited(req.sink.addStream(result.files[0].readStream!)).then((_) => req.sink.close()));

[MCSQNXA]

Then maybe you want to do (untested):

• req.sink.addStream(result.files[0].readStream!);
• unawaited(req.sink.close());

• unawaited(req.sink.addStream(result.files[0].readStream!)).then((_) => req.sink.close()));

I tried, but it's still a bad state: Cannot add event while adding a stream

[brianquinlan]

Could you post your exact code and the exact stacktrace that you get?

[MCSQNXA]

Could you post your exact code and the exact stacktrace that you get?

import 'dart:async';
import 'dart:convert' as convert;

import 'package:file_picker/file_picker.dart';
import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;

void main() {
runApp(const MyApp());
}

class MyApp extends StatelessWidget {
const MyApp({super.key});

@OverRide
Widget build(BuildContext context) {
return MaterialApp(
home: TextButton(onPressed: () => doS(), child: Text('data')),
);
}
}

Future doS() async {
try {
FilePickerResult? result = await FilePicker.platform.pickFiles(
type: FileType.custom,
allowedExtensions: ["txt", "zip"],
withData: false,
withReadStream: true,
);

if (result == null) {
  return;
}

final req = http.StreamedRequest(
  'POST',
  Uri.parse('http://127.0.0.1/upload'),
);
req.contentLength = result.files[0].size;

await req.sink.addStream(result.files[0].readStream!);

unawaited(req.sink.close());

final rsp = await req.send();

if (rsp.statusCode == 200) {
  debugPrint(convert.utf8.decode(await rsp.stream.toBytes()));
}

} catch (e) {
debugPrint(e.toString());
}
}

Launching lib\main.dart on Chrome in debug mode...
Waiting for connection from debug service on Chrome...
This app is linked to the debug service: ws://127.0.0.1:49778/3NwK13chmcM=/ws
Debug service listening on ws://127.0.0.1:49778/3NwK13chmcM=/ws
Debug service listening on ws://127.0.0.1:49778/3NwK13chmcM=/ws
Bad state: Cannot add event while adding a stream

PS S:\SecludedClient\frontend> flutter doctor
Doctor summary (to see all details, run flutter doctor -v):
[✓] Flutter (Channel stable, 3.29.2, on Microsoft Windows [版本 10.0.26100.3915], locale zh-CN)
[✓] Windows Version (11 专业版 64-bit, 24H2, 2009)
[✓] Android toolchain - develop for Android devices (Android SDK version 35.0.1)
[✓] Chrome - develop for the web
[✓] Visual Studio - develop Windows apps (Visual Studio Enterprise 2022 17.12.5)
[!] Android Studio (not installed)
[✓] IntelliJ IDEA Ultimate Edition (version 2025.1)
[✓] VS Code (version 1.99.3)
[✓] Connected device (4 available)
[!] Network resources
✗ A network error occurred while checking "https://maven.google.com/": 信号灯超时时间已到

✗ A network error occurred while checking "https://github.com/": 远程计算机拒绝网络连接。

! Doctor found issues in 2 categories.

This is my diagnosis, and I think it should be fine because other HTTP functions in this library can run normally

[MCSQNXA]

Could you post your exact code and the exact stacktrace that you get?

versions:

http: ^1.3.0
file_picker: ^10.1.2

[brianquinlan]

You didn't modify your code to match my suggestion.

[MCSQNXA]

You didn't modify your code to match my suggestion.

Thank you, I have resolved it and need to modify it to

req.sink.addStream(file.readStream!).then((_) => req.sink.close());