Sai.MessageHub 1.1.0

Sai.MessageHub

Simple WebSocket message handler implemented as aspnetcore middleware. All messages are sent as text, serialised as JSON in the following format: { "Type": "type", "Data": any } Clients can send messages to the server and can add handlers for message types it wants to receive. Server can do the same, plus has the ability to respond to the client that sent the message, or send a message to all clients.

There are two possible ways of utilising the message hub:

1. Minimal API Using WebApplication extension methods AddMessageReceivedHandler, AddDefaultMessageReceivedHandler, AddClientConnectedHandler, AddClientDisconnectedHandler.
2. Using IMessageHubService, such as consumed in a worker/background service. Both option can be used in the same application, if desired.

Example Usage

Program.cs

using Sai.MessageHub;

var builder = WebApplication.CreateBuilder(args);
builder.Services.AddMessageHub();
builder.Services.AddHostedService<MyWorker>(); // Example worker which sends the time to all MessageHub clients every second

var app = builder.Build();

app.UseMessageHub();

// Begin Minimal API
// -----------------
// Message handler for "counter" type. Generic type <T> relates to data type.
// Can map multiple handlers to the same type if required.
app.AddMessageReceivedHandler<int>("counter", (context, data) =>
{
    context.SendMessageToClient("counter-response", data); // echo back to sender
    context.SendMessageToAllClients("last-counter-update", DateTime.UtcNow); // send last update to all clients
});

// Optional fallback message handler for unhandled message types
app.AddDefaultMessageReceivedHandler((context, dataJson) =>
{
    throw new NotImplementedException($"Message type '{context.Type}' is not implemented.");
});

// Optional "on connect" handler
app.AddClientConnectedHandler(context => Console.WriteLine($"Connected: {context.ConnectionID}"));

// Optional "on disconnect" handler
app.AddClientDisconnectedHandler(context => Console.WriteLine($"Disconnected: {context.ConnectionID}"));

// End Minimal API
// -----------------

app.Run();

MyWorker.cs

public class MyWorker : BackgroundService
{
    private readonly ILogger<MyWorker> _logger;
    private readonly IMessageHubService _messageHubService;
    public MyWorker(ILogger<MyWorker> logger, IMessageHubService messageHubService)
    {
        _logger = logger;
        _messageHubService = messageHubService;

        _messageHubService.AddClientConnectedHandler(client =>
        {
            logger.LogInformation("Client {0} connected", client.ConnectionID);
            client.SendMessageToClient("connected", client.ConnectionID);
        });

        _messageHubService.AddClientDisconnectedHandler(connectionID =>
        {
            logger.LogInformation("Client {0} disconnected", connectionID);
        });

        _messageHubService.AddMessageReceivedHandler<int>("counter", (context, data) =>
        {
            logger.LogInformation("Counter value: {0}", data);
        });
    }

    protected override Task ExecuteAsync(CancellationToken stoppingToken)
    {
        return Task.Run(() =>
        {
            while (!stoppingToken.IsCancellationRequested)
            {
                stoppingToken.WaitHandle.WaitOne(1000);
                _messageHubService.SendMessageToAllClients("time", DateTime.UtcNow);
            }
        });
    }
}

client.js

document.addEventListener("DOMContentLoaded", async () => {
    const messageHub = new MessageHub();

    messageHub.addMessageHandler("time", data => {
        document.querySelector(".time").innerText = data;
    });

    messageHub.addMessageHandler("counter-response", data => {
        document.querySelector(".counter-response").innerText = data;
    });

    messageHub.addMessageHandler("last-counter-update", data => {
        document.querySelector(".last-counter-update").innerText = data;
    });

    try
    {
        await messageHub.connect();
            
        let counter = 0;
        setInterval(() => {
            counter++;
            messageHub.sendMessage("counter", counter);
        }, 1000);
    }
    catch(err)
    {
        alert(err);
    }

});

messageHub.js

class MessageHub {

    constructor() {
        this.websocket = null;
        this.handlers = [];
    }

    connect() {
        return this.connectUri("ws://" + window.location.host + "/");
    }

    connectUri(wsUri) {
        return new Promise((resolve, reject) => {
            this.websocket = new WebSocket(wsUri);

            this.websocket.onopen = evt => {
                resolve();
            };

            this.websocket.onclose = evt => {
                this.websocket.close();
            };

            this.websocket.onmessage = evt => {
                const message = JSON.parse(evt.data);
                this.handlers.forEach(handler => {
                    if (handler.type == message.Type) {
                        handler.delegate(message.Data);
                    }
                });
            };

            this.websocket.onerror = evt => {
                console.error(evt);
            };
        });
    }

    sendMessage(type, data) {
        this.websocket.send('{"Type":"' + type + '","Data":' + JSON.stringify(data) + '}');
    }

    addMessageHandler(type, delegate) {
        this.handlers.push({ type: type, delegate: delegate });
    }
}