flutter+go构建的即时通讯app，ChatCraft

由于ChatCraft是一个完整的应用程序，并且涉及到客户端和服务器端的代码，我们无法提供所有的源代码。但是，我们可以提供一个简化的例子，展示如何使用Flutter和Go构建一个简单的即时通讯系统。

服务器端 (Go):

package main
 
import (
    "net"
    "log"
    "fmt"
)
 
func main() {
    listener, err := net.Listen("tcp", "localhost:8080")
    if err != nil {
        log.Fatal(err)
    }
    defer listener.Close()
 
    fmt.Println("Listening on localhost:8080")
    for {
        conn, err := listener.Accept()
        if err != nil {
            log.Print(err)
            continue
        }
        go handleConn(conn)
    }
}
 
func handleConn(conn net.Conn) {
    defer conn.Close()
    for {
        buf := make([]byte, 512)
        n, err := conn.Read(buf)
        if err != nil {
            log.Print(err)
            return
        }
        go broadcast(buf[:n])
    }
}
 
func broadcast(msg []byte) {
    // 这里可以实现将消息发送给所有客户端的逻辑
    fmt.Println("Broadcasting message:", string(msg))
}

客户端 (Flutter):

import 'dart:convert';
import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import 'package:web_socket_channel/io.dart';
 
void main() => runApp(MyApp());
 
class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: ChatScreen(),
    );
  }
}
 
class ChatScreen extends StatefulWidget {
  @override
  _ChatScreenState createState() => _ChatScreenState();
}
 
class _ChatScreenState extends State<ChatScreen> {
  IOWebSocketChannel _channel;
 
  @override
  void initState() {
    super.initState();
    _connect();
  }
 
  @override
  void dispose() {
    _channel.sink.close();
    super.dispose();
  }
 
  void _connect() {
    // 替换为你的服务器地址
    var url = 'ws://localhost:8080';
    _channel = IOWebSocketChannel.connect(url);
    _channel.stream.listen(_handleData, onError: _handleError);
  }
 
  void _handleData(dynamic message) {
    print('Received message: $message');
  }
 
  void _handleError(Object error) {
    print('Error: $error');
  }
 
  void _sendMessage(String message) {
    _channel.sink.add(message);
  }
 
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('ChatCraft')),
      body: Padding(
        padding: const EdgeInsets.all(25.0),
        child: Column(
          children: <Widget>[
            Expanded(
              child: ListView.builder(
                reverse: true,