Andoird Cannot connect to SignalR running on Blazor Server

I am trying to connect to a .net 6 Core Blazor WASM core hosted using android.

String hubUrl = "http://192.168.254.173:5050/notification?parameter=1010072";
if (isReachable) {
    hubConnection = HubConnectionBuilder.create(hubUrl).build();
    if (hubConnection.getConnectionState() != HubConnectionState.CONNECTED) {
        hubConnection.start();
        hubConnection.on("MessageModelToClients", (messageModel) -> {
            Log.i("TAG", messageModel.getMessage());
        }, MessageModel.class);
        if (hubConnection.getConnectionState() == HubConnectionState.CONNECTED) {
            Log.i("TAG", "Connected");
        } else {
            Log.e("TAG", "Failed to establish connection to SignalR hub.");
        }
    }
} else {
    System.out.println("IP address is not reachable.");
}

this is my gradle,

implementation ("com.microsoft.signalr:signalr:7.0.0")

This is my Hub on the Core Hosted Blazor WASM

public class NotificationHub : Hub 
{
    ....
    
    public override async Task OnConnectedAsync()
    {
        Console.WriteLine("Connecting...");
        var userId= Context.GetHttpContext()!.Request.Query["userid"];
        var connectionId = Context.ConnectionId;
        AddUser(connectionId, userId);
        var messageModel = new MessageModel
        {
            IsPrivate = false,
            Message = $"Logged in User: {userId}",
            Recipient = string.Empty,
            Sender = SERVER_NAME
        };
        await SendConnectedUsers();
        await SendObjectToAll(messageModel);

        Console.WriteLine($"CONNECTED: {connectionId}");

        await base.OnConnectedAsync();
    }
    
    
    ...
}

In the Program.cs

builder.Services.AddSignalR();
app.UseEndpoints(endpoints =>
{
    endpoints.MapHub<NotificationHub>("/notification");
});

Can you point out what I am doing wrong?

Solution

After checking your code and setting, there are some suggestions for you to troubleshoot it.

Make sure that your Android device is not using a cellular data network because you are using a 192.168.254.173 private IP. It can work normally under the same network segment.
Make sure that the parameters are the same, and the URL of the SignalR Client should be http://192.168.254.173:5050/notification?userid=1010072.
Try setting a breakpoint in OnConnectedAsync and see if you can get into this method.

① If yes, you can debug it. Will find the problem.
② If no, please following the point 4 to enbale the Cors.

We can enable all Origin for testing. The middleware order is very important.

public class Program
{
    public static void Main(string[] args)
    {
        ...
        // allow all Origin
        builder.Services.AddCors(options => options.AddPolicy("CorsPolicy", builder =>
        {
            builder.AllowAnyMethod()
                .SetIsOriginAllowed(_ => true)
                .AllowAnyHeader()
                .AllowCredentials();
        }));
        ...
        var app = builder.Build();

        // Configure the HTTP request pipeline.
        if (!app.Environment.IsDevelopment())
        {
            app.UseExceptionHandler("/Home/Error");
            // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
            app.UseHsts();
        }

        app.UseHttpsRedirection();
        app.UseStaticFiles();

        app.UseRouting();

        // add this line
        app.UseCors("CorsPolicy");

        app.UseAuthorization();

        app.MapControllerRoute(
            name: "default",
            pattern: "{controller=Home}/{action=Index}/{id?}");

        app.Run();
    }
}