How to pass logger into SignalR hub on server side in ASP.NET Core application

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I have ASP.NET Core application with React client. I have SignalR messaging between server and client.

I have the following code on server side:

Startup.cs

    ...
    public void Configure(IApplicationBuilder app, IHostingEnvironment env)
    {
        app.UseSignalR(routes =>
        {
            routes.MapHub<ChatHub>("/signalr");
        });
    }
    ...

Question: Could I pass logger to ChatHub from Startup.cs as I do it with another services like this:

Startup.cs

        private readonly ILogger _log;

        public Startup(IHostingEnvironment env, ILogger<Startup> log)
        {
            _log = log;
        }

        public void ConfigureServices(IServiceCollection services)
        {
            services.AddSingleton(new Converter(_log));
        }
signalr asp.net-core logging c#
1 Answers

Could I pass logger to ChatHub from Startup.cs as I do it with another services like this

I'm not sure why you want to pass a logger instance to ChatHub within Startup.cs. But As far as I know, you could always inject the required dependencies when you need. You don't have to manually pass a logger instance into ChatHub during startup. Typically that will be considered as a bad practice. Just declare a dependency and let DI container inject it.

services.AddSingleton(new Converter(_log));
services.AddSingleton<Converter>();   // DI will new it and inject logger for you

And also change your ChatHub constructor to accept a ILogger<ChatHub>

public class ChatHub : Hub
{
    private readonly ILogger<ChatHub> _logger;

    public ChatHub(ILogger<ChatHub> logger)
    {
        this._logger = logger;
    }

    public async Task SendMessage(string user, string message)
    {
        this._logger.LogInformation($"send message to client\r\n {user}\t{message}");
        await Clients.All.SendAsync("ReceiveMessage", user, message);
    }
}

If you do want to custom the initialization of Converter, you could make it as below:

services.AddSingleton<Converter>(sp => {
    var logger = sp.GetRequiredService<ILogger<Converter>>();
    // add more service or dependencies manually ...
    return new Converter(logger, ...);
});
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