networking - 没有互联网时 Flutter 中的 gRPC 崩溃

Question

我正在使用 gRPC 开发 Flutter 应用程序，一切正常，直到我决定看看如果没有互联网连接会发生什么。

执行此操作并发出请求后，我收到以下错误:

E/flutter (26480): gRPC Error (14, Error making call: Bad state: The http/2 connection is no longer active and can therefore not be used to make new streams.)

问题是即使重新启用连接后，错误仍然存​​在。
我必须重新创建 clientChannel 吗？

const String serverUrl = 'theaddress.com';
const int serverPort = 50051;

final ClientChannel defaultClientChannel = ClientChannel(
  serverUrl,
  port: serverPort,
  options: const ChannelOptions(
    credentials: const ChannelCredentials.insecure(),
  ),
);

我只想抛出一些错误，但一旦互联网连接恢复正常工作。

Answer 1

根据@Ishaan 的建议，我使用 Connectivity 包创建了一个客户端，该客户端在 Internet 备份时重新连接。到目前为止，它似乎正在工作。

import 'dart:async';

import 'package:connectivity/connectivity.dart';
import 'package:flutter_worker_app/generated/api.pbgrpc.dart';
import 'package:grpc/grpc.dart';
import 'package:rxdart/rxdart.dart';

class ConnectiveClient extends ApiClient {

  final CallOptions _options;
  final Connectivity _connectivity;
  ClientChannel _channel;
  bool hasRecentlyFailed = false;


  ConnectiveClient(this._connectivity, this._channel, {CallOptions options})
      : _options = options ?? CallOptions(),
        super(_channel) {
    //TODO: Cancel connectivity subscription
    _connectivity.onConnectivityChanged.listen((result) {
      if (hasRecentlyFailed && result != ConnectivityResult.none) {
        _restoreChannel();
      }
    });
  }

  ///Create new channel from original channel
  _restoreChannel() {
    _channel = ClientChannel(_channel.host,
        port: _channel.port, options: _channel.options);
    hasRecentlyFailed = false;
  }

  @override
  ClientCall<Q, R> $createCall<Q, R>(
      ClientMethod<Q, R> method, Stream<Q> requests,
      {CallOptions options}) {
    //create call
    BroadcastCall<Q, R> call = createChannelCall(
      method,
      requests,
      _options.mergedWith(options),
    );
    //listen if there was an error
    call.response.listen((_) {}, onError: (Object error) async {
      //Cannot connect - we assume it's internet problem
      if (error is GrpcError && error.code == StatusCode.unavailable) {
        //check connection
        _connectivity.checkConnectivity().then((result) {
          if (result != ConnectivityResult.none) {
            _restoreChannel();
          }
        });
        hasRecentlyFailed = true;
      }
    });
    //return original call
    return call;
  }

  /// Initiates a new RPC on this connection.
  /// This is copy of [ClientChannel.createCall]
  /// The only difference is that it creates [BroadcastCall] instead of [ClientCall]
  ClientCall<Q, R> createChannelCall<Q, R>(
      ClientMethod<Q, R> method, Stream<Q> requests, CallOptions options) {
    final call = new BroadcastCall(method, requests, options);
    _channel.getConnection().then((connection) {
      if (call.isCancelled) return;
      connection.dispatchCall(call);
    }, onError: call.onConnectionError);
    return call;
  }
}

///A ClientCall that can be listened multiple times
class BroadcastCall<Q, R> extends ClientCall<Q, R> {
  ///I wanted to use super.response.asBroadcastStream(), but it didn't work.
  ///I don't know why...
  BehaviorSubject<R> subject = BehaviorSubject<R>();

  BroadcastCall(
      ClientMethod<Q, R> method, Stream<Q> requests, CallOptions options)
      : super(method, requests, options) {
    super.response.listen(
          (data) => subject.add(data),
          onError: (error) => subject.addError(error),
          onDone: () => subject.close(),
        );
  }

  @override
  Stream<R> get response => subject.stream;
}