How to determine which port ASP.NET Core 2 is listening on when a dynamic port (0) was specified

Question

I've got an ASP.NET Core 2.0 app which I intend to run as a stand-alone application. The app should start up and bind to an available port. To achieve this I configure the WebHostBuilder to listen on "http://127.0.0.1:0" and to use the Kestrel server. Once the web host starts listening I want to save the url with the actual port in a file. I want to do this as early as possible, since another application will read the file to interact with my app.

How can I determine the port the web host is listening on?

score 16 · Answer 1 · answered Nov 26 '17 at 19:07

16

You can achive it in Startup class in method Configure. You can get port from ServerAddressesFeature

Here is an example of code:

public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory, ILogger<Startup> logger)
{
     var serverAddressesFeature = app.ServerFeatures.Get<IServerAddressesFeature>();

     loggerFactory.AddFile("logs/myfile-{Date}.txt", minimumLevel: LogLevel.Information, isJson: false);

     logger.LogInformation("Listening on the following addresses: " + string.Join(", ", serverAddressesFeature.Addresses));
}

answered Nov 26 '17 at 19:07

Oleg Lukash

291
2
7

7

There are 0 addresses, any ideas why? – jjxtra Jun 26 '18 at 14:50
Are you sure @jjxtra? It is enumerator so you have to do something like this: `foreach (var address in serverAddressesFeature.Addresses) Console.WriteLine(address.ToString()); ` – mojmir.novak Jul 14 '18 at 21:49
FYI, this unfortunately does not seem to pick up url prefixes when hosting via Http.Sys. – scuba88 Oct 18 '21 at 14:50
seems like you need to run the webserver first or else you'll get no addresses – Saylent May 11 '23 at 10:00

score 12 · Answer 2 · edited Sep 10 '19 at 12:46

12

You can use the Start() method instead of Run() to access IServerAddressesFeature at the right moment:

IWebHost webHost = new WebHostBuilder()
    .UseKestrel(options => 
         options.Listen(IPAddress.Loopback, 0)) // dynamic port
    .Build();

webHost.Start();

string address = webHost.ServerFeatures
    .Get<IServerAddressesFeature>()
    .Addresses
    .First();
int port = int.Parse(address.Split(':').Last());

webHost.WaitForShutdown();

edited Sep 10 '19 at 12:46

Wayne Bloss

5,370
7
50
81

answered Aug 13 '18 at 12:08

Vladimir Panchenko

1,141
2
15
25

Instead of using `Console.ReadKey()` use `webHost.WaitForShutdown()` – Preston S Apr 01 '19 at 19:13
1

You should use `int.Parse(address.Split(':').Last());` because the address could be defined as an IPv6 address – 0BLU Jul 23 '19 at 00:05
You can also use `webHost.RunAsync()` instead of `webHost.Start()` if you want to get the default messages printed in your console/output before you get the addresses. – Wayne Bloss Sep 10 '19 at 12:54

score 3 · Answer 3 · answered Aug 02 '19 at 14:03

3

I was able to do it in the StartUp.cs using the following code:

int Url = new System.Uri(Configuration["urls"]).Port;

answered Aug 02 '19 at 14:03

Lautaro Pizzagalli

31
1

This will not work if you listen on two ports (one for HTTP and another for HTTPS) – Victorio Berra Aug 21 '19 at 19:46
With .NET Core 3.1 `Configuration["urls"]` returns null in `Startup.Configure()` so this suggestion doesn't seem to work. – Manfred Mar 01 '20 at 06:51

score 3 · Answer 4 · answered Mar 21 '20 at 18:15

3

At least from .Net Core 3 you can inject IServer and get the information.

using System;
using System.Linq;
using Microsoft.AspNetCore.Hosting.Server;
using Microsoft.AspNetCore.Hosting.Server.Features;

namespace MyApp.Controllers
{
    public class ServerInfoController : Controller
    {
        public ServerInfoController (IServer server)
        {
            var addresses = server.Features.Get<IServerAddressesFeature>()?.Addresses?.ToArray();
        }
    }
}

answered Mar 21 '20 at 18:15

James Durda

625
6
12

This is an incomplete answer .. Unable to resolve service for type 'Microsoft.AspNetCore.Hosting.Server.IServer' – Gabriel Luca Dec 31 '20 at 17:01
@GabrielLuca It appears there may be issues with `IServer` not being registered if `WebHost.CreateDefaultBuilder` isn't called. `ConfigureKestrel` does not register the `IServer` but `UseKestrel` and `CreateDefaultBuilder` do. – James Durda Dec 31 '20 at 17:43
I called also called WebHost.CreateDefaultBuilder and still not working ... I'll take back my down vote because ... it's strange how M$ changes things and something this simple is hard to .. get .. I can't change my vote unless you change the answer ... it dose not allow me .. – Gabriel Luca Dec 31 '20 at 19:16
if you can make it work .. post a small sample it will help .. – Gabriel Luca Dec 31 '20 at 19:18
Using net7 with `WebApplication.CreateBuilder(args)` this is working fine. And if you need `IServer` in StartUp, you can get it with `app.Services.GetRequiredService()`. – ArgusMagnus Mar 17 '23 at 06:29

score 2 · Answer 5 · edited Oct 18 '18 at 05:17

I'm able to do it using reflection (ugh!). I've registered an IHostedService and injected IServer. The ListenOptions property on KestrelServerOptions is internal, therefore I need to get to it using reflection. When the hosted service is called I then extract the port using the following code:

var options = ((KestrelServer)server).Options;
var propertyInfo = options.GetType().GetProperty("ListenOptions", BindingFlags.Instance | BindingFlags.NonPublic);
var listenOptions = (List<ListenOptions>)propertyInfo.GetValue(options);
var ipEndPoint = listenOptions.First().IPEndPoint;
var port = ipEndPoint.Port;

How to determine which port ASP.NET Core 2 is listening on when a dynamic port (0) was specified

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