Program.cs

// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.

using System;
using Microsoft.AspNetCore;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.HostFiltering;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Options;

namespace CreateDefaultBuilderOfTApp
{
    public class Program
    {
        static void Main(string[] args)
        {
            string responseMessage = null;

            WebHost.CreateDefaultBuilder(new[] { "--cliKey", "cliValue" })
                .ConfigureServices((context, service) => responseMessage = responseMessage ?? GetResponseMessage(context))
                .ConfigureKestrel(options => options
                    .Configure(options.ConfigurationLoader.Configuration)
                    .Endpoint("HTTP", endpointOptions =>
                    {
                        if (responseMessage == null
                            && !string.Equals("KestrelEndPointSettingValue", endpointOptions.ConfigSection["KestrelEndPointSettingName"]))
                        {
                            responseMessage = "Default Kestrel configuration not read.";
                        }
                    }))
                .Configure(app => app.Run(context =>
                {
                    // Verify allowed hosts were loaded
                    var hostFilteringOptions = app.ApplicationServices.GetRequiredService<IOptions<HostFilteringOptions>>();
                    var hosts = string.Join(',', hostFilteringOptions.Value.AllowedHosts);
                    if (responseMessage == null && !string.Equals("example.com,127.0.0.1", hosts, StringComparison.Ordinal))
                    {
                        responseMessage = "AllowedHosts not loaded into Options.";
                    }

                    var hostingEnvironment = app.ApplicationServices.GetRequiredService<IHostingEnvironment>();
                    return context.Response.WriteAsync(responseMessage ?? hostingEnvironment.ApplicationName);
                }))
                .Build()
                .Run();
        }

        private static string GetResponseMessage(WebHostBuilderContext context)
        {
            // Verify ContentRootPath set
            var contentRoot = Environment.GetEnvironmentVariable("ASPNETCORE_CONTENTROOT");
            if (!string.Equals(contentRoot, context.HostingEnvironment.ContentRootPath, StringComparison.Ordinal))
            {
                return $"ContentRootPath incorrect. Expected: {contentRoot} Actual: {context.HostingEnvironment.ContentRootPath}";
            }

            // Verify appsettings.json loaded
            if (!string.Equals("settingsValue", context.Configuration["settingsKey"], StringComparison.Ordinal))
            {
                return $"appsettings.json not loaded into Configuration.";
            }

            // Verify appsettings.environment.json loaded
            if (!string.Equals("devSettingsValue", context.Configuration["devSettingsKey"], StringComparison.Ordinal))
            {
                return $"appsettings.{context.HostingEnvironment.EnvironmentName}.json not loaded into Configuration.";
            }

            // TODO: Verify UserSecrets loaded

            // Verify environment variables loaded
            if (!string.Equals("envValue", context.Configuration["envKey"], StringComparison.Ordinal))
            {
                return $"Environment variables not loaded into Configuration.";
            }

            // Verify command line arguments loaded
            if (!string.Equals("cliValue", context.Configuration["cliKey"], StringComparison.Ordinal))
            {
                return $"Command line arguments not loaded into Configuration.";
            }

            // TODO: Verify AddConsole called
            // TODO: Verify AddDebug called
            // TODO: Verify UseIISIntegration called

            return null;
        }
    }
}