使用EventFlux库时无法连接localhost的问题排查

我正在用Flutter前端+Golang后端实现Server-Sent Event（SSE），但Flutter端连接后端时出现连接拒绝错误，请求帮忙排查。

错误信息 #

Error connecting to EventFlux: Instance of 'EventFluxException'
I/flutter ( 9445): Exception details: ClientException with SocketException: Connection refused (OS Error: Connection refused, errno = 111), address = localhost, port = 38134, uri=http://localhost:8080/events

Flutter代码 #

import 'dart:convert';

import 'package:dio/dio.dart';
import 'package:eventflux/client.dart';
import 'package:eventflux/enum.dart';
import 'package:eventflux/eventflux.dart';
import 'package:eventflux/models/data.dart';
import 'package:eventflux/models/response.dart';
import 'package:flutter/material.dart';
import 'package:flutter_client_sse/constants/sse_request_type_enum.dart';
import 'package:flutter_client_sse/flutter_client_sse.dart';
import 'package:sse_stream/sse_stream.dart';

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

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter EventFlux Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({Key? key}) : super(key: key);

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  final EventFlux _eventFlux = EventFlux.instance;

  String _receivedData = "";
  final dio = Dio();

  @override
  void initState() {
    super.initState();
    _connectToEventFlux();
  }


  void _connectToEventFlux() {
    _eventFlux.connect(
      EventFluxConnectionType.get,
      'http://localhost:8080/events',
      onSuccessCallback: (EventFluxResponse? response) {
        response!.stream?.listen((data) {
          // Update the UI with the received data
          setState(() {
            // Assuming your data is a string, you can update it accordingly
            // For example, you can store the data in a variable to use in the UI

            _receivedData = data.toString();
          });
        });
      },
      onError: (error) {
        // Handle errors
        print('Error connecting to EventFlux: $error');
        // Print more details about the exception if available
        print('Exception details: ${error.message}');
      },
      autoReconnect: true,
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Flutter EventFlux Demo'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            // Display the received data in the UI
            Text(
              'Received Data:',
            ),
            Text(
              _receivedData,
              style: Theme.of(context).textTheme.headline4,
            ),
          ],
        ),
      ),
    );
  }

  @override
  void dispose() {
    _eventFlux.disconnect();
    super.dispose();
  }
}

排查步骤及修复方案 #

• 修正Flutter连接地址

  • Android模拟器：将http://localhost:8080/events替换为http://10.0.2.2:8080/events，模拟器的localhost指向自身，10.0.2.2是宿主机的专用别名。
  • iOS模拟器：可直接用localhost；真机需替换为电脑的局域网IP（如http://192.168.1.100:8080/events，IP通过ifconfig/ipconfig查询）。

• 确认Golang后端状态

  • 检查服务是否启动，监听端口是否为8080，且绑定地址为0.0.0.0（而非localhost，否则仅本机可访问），示例监听代码：

    http.ListenAndServe("0.0.0.0:8080", nil)
    

  • 用浏览器或curl访问http://localhost:8080/events，验证接口是否能正常建立连接并返回SSE数据。

• 检查端口与防火墙

  • 确认8080端口未被占用：Mac/Linux用lsof -i :8080，Windows用netstat -ano | findstr :8080查询。
  • 关闭电脑防火墙或添加规则允许8080端口的网络请求。

• 验证后端SSE规范

  • 确保Golang返回的响应头包含以下字段：

    w.Header().Set("Content-Type", "text/event-stream")
    w.Header().Set("Cache-Control", "no-cache")
    w.Header().Set("Connection", "keep-alive")
    

  • 保证接口不会立即关闭连接，持续发送事件数据。

内容的提问来源于stack exchange，提问作者ong ai ling