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I created a .NET Core web api endpoint where I can retrieve some images that I want to display in my mobile app. I tested the endpoint locally by navigating to that route and via postman and both are working fine (showing the proper response). However, when I try to hit the endpoint from mobile side, it doesn't work. I get this cryptic error: 

System.Net.Http.HttpRequestException: Network subsystem is down

Here's more of the exception info: 

System.Net.Http.HttpRequestException: Network subsystem is down ---> System.Net.Sockets.SocketException: Network subsystem is down
  at System.Net.Http.ConnectHelper.ConnectAsync (System.String host, System.Int32 port, System.Threading.CancellationToken cancellationToken) [0x000c8] in /Users/builder/jenkins/workspace/archive-mono/2019-10/android/release/external/corefx/src/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/ConnectHelper.cs:65

I'm not sure what I'm doing wrong on the mobile side. I know for postman to get it to show, I had to turn SSL certification setting off. Do I need to do something similar on the mobile side?

Here's how I'm trying to do the call to the endpoint. I'm using refit: 

    public static class FetchMediaService
    {
        public static INevarroApi apiService;
        static string baseUrl = "https://localhost:5001";

        public static async Task<List<Uri>> CallImagesEndpoint()
        {
            apiService = RestService.For<INevarroApi>(baseUrl);
            var images = await apiService.GetImages();
            return images;
        }

    }

Where: 

    public interface INevarroApi
    {
        [Get("/images")]
        Task<List<Uri>> GetImages();
    }

OnAppearing in my codebehind for one of my views: 

        protected override async void OnAppearing()
        {
            DualScreenLayoutInfo.PropertyChanged += OnFormsWindowPropertyChanged;
            DualScreenInfo.Current.PropertyChanged += OnFormsWindowPropertyChanged;
            var images = await FetchMediaService.CallImagesEndpoint(); //Where the exception is thrown 

        }

What am I doing wrong above?

I'm testing this on Android 10 (API 29) emulator on Mac OSX and backend code is running locally using Visual Studio for Mac (backend is .NET Core 3.1 web api project).

Euridice01
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    `localhost` is the Android device/emulator itself, not your PC, use the special IP address of `10.0.2.2` : https://stackoverflow.com/questions/1720346/how-to-get-the-android-emulators-ip-address – SushiHangover Feb 17 '20 at 03:41
  • @SushiHangover I tried but then I get connection refused. What now? lol – Euridice01 Feb 17 '20 at 03:42

1 Answers1

5

If you are using IISExpress try to change your debug configuration.

Change to http://localhost:[PORT] to http://127.0.0.1:[PORT]

Then you should be able to access it in android with http://10.0.2.2:[PORT]

Vs Settings

For Kestrel

Settings should be done via IHostBuilder in Program.cs as following:

public static IHostBuilder CreateHostBuilder(string[] args)
{
    return Host.CreateDefaultBuilder(args)
                .ConfigureWebHostDefaults(webBuilder =>
                {
                    // This should do it
                    webBuilder.UseUrls("http://127.0.0.1:5000");
                    webBuilder.UseStartup<Startup>();
                });
}
SerhatDev
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  • I'm not using IIS Express unfortunately. I'm on Visual Studio for Mac and I'm running .NET Core web api project. – Euridice01 Feb 17 '20 at 04:28
  • Hey, I get a connection refused exception now that I changed it. It's not working. The url I setup on the mobile side... it's just the one hitting the change above right? – Euridice01 Feb 17 '20 at 05:15
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    if you did setup kestrel to use http://127.0.0.1:5000 this then you should be able to access it from xamarin app as http://10.0.2.2:5000. Just make sure everything is properly working with kestrel. So after the change can you access WebApi on safari with http://127.0.0.1:5000 ? If not i can try to boot my mac and give it a shot – SerhatDev Feb 17 '20 at 05:19
  • Thank you so much!! That ended up working as expected. Why 10.0.2.2 though? My machine IP says 10.0.0.2 but I used the ip you mentioned and it works! – Euridice01 Feb 17 '20 at 14:21
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    @SerhatDev this is the reason for 10.0.2.2 IP: https://stackoverflow.com/questions/9808560/why-do-we-use-10-0-2-2-to-connect-to-local-web-server-instead-of-using-computer – stackunderflows Feb 17 '20 at 19:34
  • But this seems stupid its hardly deployable freindly how could you make it work – c-sharp-and-swiftui-devni Sep 19 '21 at 12:30