signalr_client

A Flutter SignalR Client for ASP.NET Core.
ASP.NET Core SignalR is an open-source library that simplifies adding real-time web functionality to apps. Real-time web functionality enables server-side code to push content to clients instantly.

Tested with ASP.NET Core 3.1 & ASP .NET Core 6

The client is able to invoke server side hub functions (including streaming functions) and to receive method invocations issued by the server. It also supports the auto-reconnect feature.

The client supports the following transport protocols:

• WebSocket
• Service Side Events
• Long Polling

The client supports the following hub protocols:

• Json
• MessagePack

Examples

• Chat client/server - A simple client/server chat application.
• Integration test app - To see how a client calls various types of hub functions.

Getting Started

Add signalr_netcore to your pubspec.yaml dependencies:

...
dependencies:
  flutter:
    sdk: flutter

  signalr_netcore:
...

Important Note: if you are experiencing issues (for example not receiving message callback) with the latest version, please give a try to older version as signalr_netcore: 0.1.7+2-nullsafety.3 but bear in mind that this version does not support auto reconnect functionalities and need to be handled manually.

Usage

Let's demo some basic usages:

1. Create a hub connection:

// Import the library.
import 'package:signalr_netcore/signalr_client.dart';

// The location of the SignalR Server.
final serverUrl = "192.168.10.50:51001";
// Creates the connection by using the HubConnectionBuilder.
final hubConnection = HubConnectionBuilder().withUrl(serverUrl).build();
// When the connection is closed, print out a message to the console.
final hubConnection.onclose( (error) => print("Connection Closed"));

Logging is supported via the dart logging package:

// Import theses libraries.
import 'package:logging/logging.dart';
import 'package:signalr_netcore/signalr_client.dart';

// Configer the logging
Logger.root.level = Level.ALL;
// Writes the log messages to the console
Logger.root.onRecord.listen((LogRecord rec) {
  print('${rec.level.name}: ${rec.time}: ${rec.message}');
});

// If you want only to log out the message for the higer level hub protocol:
final hubProtLogger = Logger("SignalR - hub");
// If youn want to also to log out transport messages:
final transportProtLogger = Logger("SignalR - transport");

// The location of the SignalR Server.
final serverUrl = "192.168.10.50:51001";
final connectionOptions = HttpConnectionOptions
final httpOptions = new HttpConnectionOptions(logger: transportProtLogger);
//final httpOptions = new HttpConnectionOptions(logger: transportProtLogger, transport: HttpTransportType.WebSockets); // default transport type.
//final httpOptions = new HttpConnectionOptions(logger: transportProtLogger, transport: HttpTransportType.ServerSentEvents);
//final httpOptions = new HttpConnectionOptions(logger: transportProtLogger, transport: HttpTransportType.LongPolling);

// If you need to authorize the Hub connection than provide a an async callback function that returns 
// the token string (see AccessTokenFactory typdef) and assigned it to the accessTokenFactory parameter:
// final httpOptions = new HttpConnectionOptions( .... accessTokenFactory: () async => await getAccessToken() ); 

// Creates the connection by using the HubConnectionBuilder.
final hubConnection = HubConnectionBuilder().withUrl(serverUrl, options: httpOptions).configureLogging(hubProtLogger).build();
// When the connection is closed, print out a message to the console.
final hubConnection.onclose( (error) => print("Connection Closed"));

2. Connect to a Hub:

Calling following method starts handshaking and connects the client to SignalR server

await hubConnection.start();

3. Calling a Hub function:

Assuming there is this hub function:

public string MethodOneSimpleParameterSimpleReturnValue(string p1)
{
  Console.WriteLine($"'MethodOneSimpleParameterSimpleReturnValue' invoked. Parameter value: '{p1}");
  return p1;
}

The client can invoke the function by using:

  final result = await hubConnection.invoke("MethodOneSimpleParameterSimpleReturnValue", args: <Object>["ParameterValue"]);
  logger.log(LogLevel.Information, "Result: '$result");

4. Calling a client function:

Assuming the server calls a function "aClientProvidedFunction":

  await Clients.Caller.SendAsync("aClientProvidedFunction", null);

The Client provides the function like this:

  
  hubConnection.on("aClientProvidedFunction", _handleAClientProvidedFunction);

  // To unregister the function use:
  // a) to unregister a specific implementation:
  // hubConnection.off("aClientProvidedFunction", method: _handleServerInvokeMethodNoParametersNoReturnValue);
  // b) to unregister all implementations:
  // hubConnection.off("aClientProvidedFunction");
  ...
  void _handleAClientProvidedFunction(List<Object> parameters) {
    logger.log(LogLevel.Information, "Server invoked the method");
  }

5. Using Msgpack for serialization

The Hub should be configured to use the msgpack protocol in both the client and server

Client

import 'package:signalr_netcore/msgpack_hub_protocol.dart';
_hubConnection = HubConnectionBuilder()
          .withUrl(_serverUrl, options: httpOptions)
          /* Configure the Hub with msgpack protocol */
          .withHubProtocol(MessagePackHubProtocol())
          .withAutomaticReconnect()
          .configureLogging(logger)
          .build();

Server

Add the following packge to your ASP NET core project Microsoft.AspNetCore.SignalR.Protocols.MessagePack

public void ConfigureServices(IServiceCollection services)
        {
            // Configure the hub to use msgpack protocol
            services.AddSignalR().AddMessagePackProtocol();

        }

A note about the parameter types

All function parameters and return values are serialized/deserialized into/from JSON by using the dart:convert package (json.endcode/json.decode). Make sure that you:

• use only simple parameter types

or

• use objects that implements toJson() since that method is used by the dart:convert package to serialize an object.

Flutter Json 101:

• flutter.io
• json.encode
• json.decode

MSGPACK

All function parameters and return values are serialized/deserialized into/from Msgpack by using the msgpack_dart package. Make sure that you:

• use only simple parameter types or
• Convert your classes to maps using Json encode/decode and then pass it to msgpack or
• Serialize the message into bytes using msgpack_dart using custom encoders and decoders before passing it to signalr

Msgpack - It's like JSON but fast and small.

How to expose a MessageHeaders object so the client can send default headers

Code Example:

final defaultHeaders = MessageHeaders();
defaultHeaders.setHeaderValue("HEADER_MOCK_1", "HEADER_VALUE_1");
defaultHeaders.setHeaderValue("HEADER_MOCK_2", "HEADER_VALUE_2");

final httpConnectionOptions = new HttpConnectionOptions(
          httpClient: WebSupportingHttpClient(logger,
              httpClientCreateCallback: _httpClientCreateCallback),
          accessTokenFactory: () => Future.value('JWT_TOKEN'),
          logger: logger,
          logMessageContent: true,
          headers: defaultHeaders);

final _hubConnection = HubConnectionBuilder()
          .withUrl(_serverUrl, options: httpConnectionOptions)
          .withAutomaticReconnect(retryDelays: [2000, 5000, 10000, 20000, null])
          .configureLogging(logger)
          .build();

Http Request Log:

I/flutter ( 5248): Starting connection with transfer format 'TransferFormat.Text'.
I/flutter ( 5248): Sending negotiation request: https://localhost:5000/negotiate?negotiateVersion=1
I/flutter ( 5248): HTTP send: url 'https://localhost:5000/negotiate?negotiateVersion=1', method: 'POST' content: '' content length = '0' 
headers: '{ content-type: text/plain;charset=UTF-8 }, { HEADER_MOCK_1: HEADER_VALUE_1 }, { X-Requested-With: FlutterHttpClient }, { HEADER_MOCK_2: HEADER_VALUE_2 }, { Authorization: Bearer JWT_TOKEN }'