【Flutter通信】不用插件使用SSE协议

import 'dart:async';
import 'dart:convert';
import 'package:http/http.dart' as http;
 
class ServerSentEventsClient {
  static const _defaultHeaders = {
    'Accept': 'text/event-stream',
    'Cache-Control': 'no-cache',
  };
 
  final String url;
  final Map<String, String>? headers;
  final Duration? timeout;
  final void Function(String event, String data)? onEvent;
  final void Function(Object error, StackTrace? stackTrace)? onError;
  final void Function()? onDone;
 
  late http.Client _httpClient;
  late StreamSubscription<String> _subscription;
 
  ServerSentEventsClient(
    this.url, {
    this.headers,
    this.timeout,
    this.onEvent,
    this.onError,
    this.onDone,
  }) {
    _httpClient = http.Client();
    _start();
  }
 
  void _start() async {
    final response = await _httpClient.get(
      Uri.parse(url),
      headers: {..._defaultHeaders, ...?headers},
    );
 
    if (response.statusCode == 200) {
      final stream = response.stream
        .transform(utf8.decoder)
        .expand((chunk) sync* {
          final parts = chunk.toString().split('\n');
          for (var part in parts) {
            if (part.isNotEmpty) {
              yield part;
            }
          }
        })
        .where((line) => line.isNotEmpty)
        .map((line) {
          final parts = line.split(':');
          return MapEntry(
            parts[0].trim(),
            parts.length > 1 ? parts.sublist(1).join(':').trim() : null,
          );
        });
 
      _subscription = stream.listen((event) {
        final data = <String, String?>{};
        if (event['data'] != null) {
          final map = jsonDecode(event['data']);
          map.forEach((key, value) {
            data[key] = value?.toString();
          });
        }
 
        onEvent?.call(event['event'] ?? '', jsonEncode(data));
      }, onError: (error, stackTrace) {
        onError?.call(error, stackTrace);
      }, onDone: () {
        onDone?.call();
      });
    } else {
      // Handle error response
    }
  }
 
  void dispose() {
    _subscription.cancel();
    _httpClient.close();
  }
}
 
// 使用方法
void main() {
  final client = ServerSentEventsClient(
    'https://example.com/stream',
    onEvent: (event, data) {
      print('Event: $event, Data: $data');
    },
    onError: (error, stackTrace) {
      print('Error: $error');
    },
    onDone: () {
      print('Stream is done.');