Socket.IO-client for .NET

An elegant socket.io client for .NET, it supports socket.io server v2/v3/v4, and has implemented http polling and websocket.

Table of Contents

• Quick start
  • Options
  • Ack
  • Binary messages
  • JsonSerializer
  • Allowing Untrusted SSL Certificates
  • ClientWebSocket Options
  • Windows 7 Support
  • Xamarin
• Breaking changes
  • Breaking changes in 3.1.0
• Change log
• Sponsors

Quick start

Connect to the socket.io server, listen events and emit some data.

var client = new SocketIO("http://localhost:11000/");

client.On("hi", response =>
{
    // You can print the returned data first to decide what to do next.
    // output: ["hi client"]
    Console.WriteLine(response);

    string text = response.GetValue<string>();

    // The socket.io server code looks like this:
    // socket.emit('hi', 'hi client');
});

client.On("test", response =>
{
    // You can print the returned data first to decide what to do next.
    // output: ["ok",{"id":1,"name":"tom"}]
    Console.WriteLine(response);
    
    // Get the first data in the response
    string text = response.GetValue<string>();
    // Get the second data in the response
    var dto = response.GetValue<TestDTO>(1);

    // The socket.io server code looks like this:
    // socket.emit('hi', 'ok', { id: 1, name: 'tom'});
});

client.OnConnected += async (sender, e) =>
{
    // Emit a string
    await client.EmitAsync("hi", "socket.io");

    // Emit a string and an object
    var dto = new TestDTO { Id = 123, Name = "bob" };
    await client.EmitAsync("register", "source", dto);
};
await client.ConnectAsync();

Options

The way to override the default options is as follows:

var client = new SocketIO("http://localhost:11000/", new SocketIOOptions
{
    Query = new List<KeyValuePair<string, string>>
    {
        new KeyValuePair<string, string>("token", "abc123"),
        new KeyValuePair<string, string>("key", "value")
    }
});

Option	Default value	Description
Path	/socket.io	name of the path that is captured on the server side
Reconnection	true	whether to reconnect automatically
ReconnectionAttempts	int.MaxValue	number of reconnection attempts before giving up
ReconnectionDelay	1000	how long to initially wait before attempting a new reconnection. Affected by +/- RandomizationFactor, for example the default initial delay will be between 500 to 1500ms.
RandomizationFactor	0.5	0 <= RandomizationFactor <= 1
ConnectionTimeout	20000	connection timeout
Query	IEnumerable<KeyValuePair<string, string>>	additional query parameters that are sent when connecting a namespace (then found in socket.handshake.query object on the server-side)
EIO	V4	If your server is using socket.io server v2.x, please explicitly set it to V3
ExtraHeaders	null	Headers that will be passed for each request to the server (via xhr-polling and via websockets). These values then can be used during handshake or for special proxies.
Transport	Polling	Websocket is used by default, you can change to http polling.
AutoUpgrade	true	If websocket is available, it will be automatically upgrade to use websocket
Auth	null	Credentials that are sent when accessing a namespace
RemoteCertificateValidationCallback	null	Verifies the remote Secure Sockets Layer (SSL) certificate used for authentication.

Ack

The server executes the client's ack function

Client

await client.EmitAsync("ack", response =>
{
    // You can print the returned data first to decide what to do next.
    // output: [{"result":true,"message":"Prometheus - server"}]
    Console.WriteLine(response);
    var result = response.GetValue<BaseResult>();
}, "Prometheus");

Server

socket.on("ack", (name, fn) => {
    fn({
        result: true,
        message: `${name} - server`
    });
});

The client executes the server's ack function

Client

client.On("ack2", async response =>
{
    // You can print the returned data first to decide what to do next.
    // output: [1, 2]
    Console.WriteLine(response);
    int a = response.GetValue<int>();
    int b = response.GetValue<int>(1);
    
    await response.CallbackAsync(b, a);
});

Server

socket.emit("ack2", 1, 2, (arg1, arg2) => {
    console.log(`arg1: ${arg1}, arg2: ${arg2}`);
});

The output of the server is:

arg1: 2, arg2: 1

Binary messages

This example shows how to emit and receive binary messages, The library uses System.Text.Json to serialize and deserialize json by default.

class FileDTO
{
    [JsonPropertyName("name")]
    public string Name { get; set; }

    [JsonPropertyName("mimeType")]
    public string MimeType { get; set; }

    [JsonPropertyName("bytes")]
    public byte[] Bytes { get; set; }
}

client.OnConnected += async (sender, e) =>
{
    await client.EmitAsync("upload", new FileDTO
    {
        Name = "template.html"
        MimeType = "text/html",
        bytes = Encoding.UTF8.GetBytes("<div>test</div>")
    });
};

client.On("new files", response =>
{
    // You can print the returned data first to decide what to do next.
    // output: [{"name":"template.html","mimeType":"text/html","bytes":{"_placeholder":true,"num":0}}]
    Console.WriteLine(response);
    var result = response.GetValue<FileDTO>();
    Console.WriteLine(Encoding.UTF8.GetString(result.Bytes))
});

Serializer

The library uses System.Text.Json to serialize and deserialize json by default, If you want to change JsonSerializerOptions, you can do this:

var client = new SocketIO("http://localhost:11000/");
client.Serializer = new SystemTextJsonSerializer(new JsonSerializerOptions
{
    PropertyNameCaseInsensitive = true
});

Of course you can also use Newtonsoft.Json library, for this, you need to install SocketIO.Serializer.NewtonsoftJson dependency.

client.Serializer = new NewtonsoftJsonSerializer(new JsonSerializerSettings
{
    ContractResolver = new DefaultContractResolver
    {
        NamingStrategy = new CamelCaseNamingStrategy()
    }
});

Allowing Untrusted SSL Certificates

var io = new SocketIO("https://localhost:11404", new SocketIOOptions
{
    RemoteCertificateValidationCallback = (_, _, _, _) =>
    {
        return true;
    }
});

Windows 7 Support

The library uses System.Net.WebSockets.ClientWebSocket by default. Unfortunately, it does not support Windows 7 or Windows Server 2008 R2. You will get a PlatformNotSupportedException. To solve this problem, you need to install the SocketIOClient.Windows7 dependency and then change the implementation of ClientWebSocket.

client.ClientWebSocketProvider = () => new ClientWebSocketManaged(...);

Xamarin

The library will always try to connect to the server, and an exception will be thrown when the connection fails. The library catches some exception types, such as: TimeoutException, WebSocketException, HttpRequestException and OperationCanceledException. If it is one of them, the library will continue to try to connect to the server. If there are other exceptions, the library will stop reconnecting and throw exception to the upper layer. You need extra attention in Xamarin.

For Xamarin.Android you should add the following code:

    public partial class MainPage: ContentPage
    {
        public MainPage()
        {
            InitializeComponent();
        }

        public SocketIOClient Socket {get;}
    }

    ...

    public class MainActivity: global::Xamarin.Forms.Platform.Android.FormsAppCompatActivity
    {
        protected override void OnCreate(Bundle savedInstanceState)
        {
            ...
            var app = new App();
            var mainPage = app.MainPage as MainPage;
            mainPage.Socket.AddExpectedException(typeof(Java.Net.SocketException));
            mainPage.Socket.AddExpectedException(typeof(Java.Net.SocketTimeoutException));
            LoadApplication(app);
        }

        ...
    }

I don't know the specific exceptions of Xamarin.iOS. Welcome to create a pr and update this document. thanks :)

Change log

[3.1.0] - 2023-08-25

Added

• SocketIO.Serializer.MessagePack serializer
• SocketIO.Serializer.NewtonsoftJson serializer
• SocketIO.Serializer.SystemTextJson serializer

Removed

• SocketIOClient.Newtonsoft.Json serializer

See more

Thanks

Thank socket.io and darrachequesne for sponsoring the project on Open Collective.

We would like to thank JetBrains for supporting the project with free licenses of their fantastic tools.