Streming pb, not receiving data in real-ttime

[alieddine]

I'm facing a small issue with streaming responses from an API using Dio. When I try to print the response in the console or display it in the app, the data only appears after the API completes sending everything, rather than showing updates in real-time.

i used fast api to make a streming route

`@router.post("/stream" )
async def stream():
async def generate():
for i in range(10):
await asyncio.sleep(0.5)
yield json.dumps({"response": f"This is message {i}"})

return StreamingResponse(
    generate(),
    media_type="application/x-ndjson"
)`

and this is the flutter code i tested 
`final cancelToken = CancelToken();
  final res = await dio.post<ResponseBody>(
    baseUrl + routes[route]!,
    options: Options(
      headers: {'Authorization': 'Bearer $accessToken'},
      responseType: ResponseType.stream,
      receiveDataWhenStatusError: true,
    ),
    cancelToken: cancelToken,
    data: data,
  );
  final transformer =
      StreamTransformer<String, Map<String, dynamic>>.fromHandlers(
        handleData: (String chunk, EventSink<Map<String, dynamic>> sink) {
          try {
            final lines = chunk.split('\n');

            for (final line in lines) {
              if (line.trim().isEmpty) continue;

              String jsonString = line;
              if (line.startsWith("data: ")) {
                jsonString = line.substring(6);
              }

              final jsonData = jsonDecode(jsonString);
              sink.add(jsonData);
            }
          } catch (e) {
            print('Error parsing chunk: $chunk');
            sink.addError(e);
          }
        },
      );
  final responseStream = res.data as ResponseBody;
  final stream = responseStream.stream
      .cast<List<int>>()
      .transform(utf8.decoder) 
      .transform(const LineSplitter()) 
      .transform(transformer); 
  DateTime lastPrintTime = DateTime.now();

  final subscription = stream.listen(
    (data) {
      final now = DateTime.now();
      print(
        'Received at ${now.difference(lastPrintTime).inMilliseconds}ms: ${data["response"]}',
      );
      lastPrintTime = now;
    },
    onError: (error) {
      print('Stream error: $error');
    },
    onDone: () {
      print('Stream completed');
    },
    cancelOnError: true,
  );`

and this is the console output :

I/flutter (30884): Received at 4509ms: This is message 0
I/flutter (30884): Received at 3ms: This is message 1
I/flutter (30884): Received at 1ms: This is message 2
I/flutter (30884): Received at 2ms: This is message 3
I/flutter (30884): Received at 1ms: This is message 4
I/flutter (30884): Received at 1ms: This is message 5
I/flutter (30884): Received at 1ms: This is message 6
I/flutter (30884): Received at 2ms: This is message 7
I/flutter (30884): Received at 1ms: This is message 8
I/flutter (30884): Received at 1ms: This is message 9