Use HttpClient via IHttpClientFactory in a .NET Core console app without implementing IHostedService

If you're looking for the F# version, go here.

Not that there's anything wrong with IHostedService, but sometimes you just want a plain old console app without having to implement another interface just so that you can inject and use IHttpClientFactory.

By using the new HostApplicationBuilder pattern (encapsulated in the ConsoleHost class), there is much less ceremony involved with setting up the Generic Host HostBuilder so that you can inject IHttpClientFactory into your classes. Beyond that, you merely create an IServiceScope to make everything work:

using var serviceScope = host.Services.CreateScope();
var services = serviceScope.ServiceProvider;

try
{
    var testSvc = services.GetRequiredService<TestService>();
    var html = await testSvc.GetMicrosoftAsync();

    Console.WriteLine($"Web page: {new string(html.Take(1000).ToArray())}");
}
catch (Exception ex)
{
    Log.Error(ex, "Unhandled exception");
}

This code creates an IServiceScope in main, and then uses that to get our registered TestService class, which returns the HTML of https://www.microsoft.com as a string. We then display the first 1,000 characters.

The TestService class looks like this:

using System.Net.Http;
using System.Threading.Tasks;

namespace HttpClientTestNotHostedService
{
    public class TestService
    {
        private readonly HttpClient _httpClient;

        public TestService(IHttpClientFactory httpClientFactory)
        {
            _httpClient = httpClientFactory.CreateClient();
        }

        public async Task<string> GetMicrosoftAsync()
        {
            using (var requestMsg = new HttpRequestMessage(HttpMethod.Get, "https://www.microsoft.com"))
            {
                using (var responseMsg = await _httpClient.SendAsync(requestMsg))
                {
                    return await responseMsg.Content.ReadAsStringAsync();
                }
            }
        }
    }
}

And now you can use all of the newfangled IHttpClientFactory goodness in a (mostly) plain old console app!