ASP.NET Core技术研究-探秘Host主机启动过程

public static IHostBuilder CreateDefaultBuilder(string[] args)
        {
            var builder = new HostBuilder();

            builder.UseContentRoot(Directory.GetCurrentDirectory());
            builder.ConfigureHostConfiguration(config =>
            {
                config.AddEnvironmentVariables(prefix: "DOTNET_");
                if (args != null)
                {
                    config.AddCommandLine(args);
                }
            });

            builder.ConfigureAppConfiguration((hostingContext, config) =>
            {
                var env = hostingContext.HostingEnvironment;

                config.AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
                      .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true, reloadOnChange: true);

                if (env.IsDevelopment() && !string.IsNullOrEmpty(env.ApplicationName))
                {
                    var appAssembly = Assembly.Load(new AssemblyName(env.ApplicationName));
                    if (appAssembly != null)
                    {
                        config.AddUserSecrets(appAssembly, optional: true);
                    }
                }

                config.AddEnvironmentVariables();

                if (args != null)
                {
                    config.AddCommandLine(args);
                }
            })
            .ConfigureLogging((hostingContext, logging) =>
            {
                var isWindows = RuntimeInformation.IsOSPlatform(OSPlatform.Windows);

                // IMPORTANT: This needs to be added *before* configuration is loaded, this lets
                // the defaults be overridden by the configuration.
                if (isWindows)
                {
                    // Default the EventLogLoggerProvider to warning or above
                    logging.AddFilter<EventLogLoggerProvider>(level => level >= LogLevel.Warning);
                }

                logging.AddConfiguration(hostingContext.Configuration.GetSection("Logging"));
                logging.AddConsole();
                logging.AddDebug();
                logging.AddEventSourceLogger();

                if (isWindows)
                {
                    // Add the EventLogLoggerProvider on windows machines
                    logging.AddEventLog();
                }
            })
            .UseDefaultServiceProvider((context, options) =>
            {
                var isDevelopment = context.HostingEnvironment.IsDevelopment();
                options.ValidateScopes = isDevelopment;
                options.ValidateOnBuild = isDevelopment;
            });

            return builder;
        }

using System;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore;

namespace Microsoft.Extensions.Hosting
{
    /// <summary>
    /// Extension methods for configuring the IWebHostBuilder.
    /// </summary>
    public static class GenericHostBuilderExtensions
    {
        /// <summary>
        /// Initializes a new instance of the <see cref="IWebHostBuilder"/> class with pre-configured defaults.
        /// </summary>
        /// <remarks>
        ///   The following defaults are applied to the <see cref="IWebHostBuilder"/>:
        ///     use Kestrel as the web server and configure it using the application‘s configuration providers,
        ///     adds the HostFiltering middleware,
        ///     adds the ForwardedHeaders middleware if ASPNETCORE_FORWARDEDHEADERS_ENABLED=true,
        ///     and enable IIS integration.
        /// </remarks>
        /// <param name="builder">The <see cref="IHostBuilder" /> instance to configure</param>
        /// <param name="configure">The configure callback</param>
        /// <returns>The <see cref="IHostBuilder"/> for chaining.</returns>
        public static IHostBuilder ConfigureWebHostDefaults(this IHostBuilder builder, Action<IWebHostBuilder> configure)
        {
            return builder.ConfigureWebHost(webHostBuilder =>
            {
                WebHost.ConfigureWebDefaults(webHostBuilder);

                configure(webHostBuilder);
            });
        }
    }
}
© 2020 GitHub, Inc.

using System;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.DependencyInjection;

namespace Microsoft.Extensions.Hosting
{
    public static class GenericHostWebHostBuilderExtensions
    {
        public static IHostBuilder ConfigureWebHost(this IHostBuilder builder, Action<IWebHostBuilder> configure)
        {
            var webhostBuilder = new GenericWebHostBuilder(builder);
            configure(webhostBuilder);
            builder.ConfigureServices((context, services) => services.AddHostedService<GenericWebHostService>());
            return builder;
        }
    }
}

 internal static void ConfigureWebDefaults(IWebHostBuilder builder)
        {
            builder.ConfigureAppConfiguration((ctx, cb) =>
            {
                if (ctx.HostingEnvironment.IsDevelopment())
                {
                    StaticWebAssetsLoader.UseStaticWebAssets(ctx.HostingEnvironment, ctx.Configuration);
                }
            });
            builder.UseKestrel((builderContext, options) =>
            {
                options.Configure(builderContext.Configuration.GetSection("Kestrel"));
            })
            .ConfigureServices((hostingContext, services) =>
            {
                // Fallback
                services.PostConfigure<HostFilteringOptions>(options =>
                {
                    if (options.AllowedHosts == null || options.AllowedHosts.Count == 0)
                    {
                        // "AllowedHosts": "localhost;127.0.0.1;[::1]"
                        var hosts = hostingContext.Configuration["AllowedHosts"]?.Split(new[] { ‘;‘ }, StringSplitOptions.RemoveEmptyEntries);
                        // Fall back to "*" to disable.
                        options.AllowedHosts = (hosts?.Length > 0 ? hosts : new[] { "*" });
                    }
                });
                // Change notification
                services.AddSingleton<IOptionsChangeTokenSource<HostFilteringOptions>>(
                            new ConfigurationChangeTokenSource<HostFilteringOptions>(hostingContext.Configuration));

                services.AddTransient<IStartupFilter, HostFilteringStartupFilter>();

                if (string.Equals("true", hostingContext.Configuration["ForwardedHeaders_Enabled"], StringComparison.OrdinalIgnoreCase))
                {
                    services.Configure<ForwardedHeadersOptions>(options =>
                    {
                        options.ForwardedHeaders = ForwardedHeaders.XForwardedFor | ForwardedHeaders.XForwardedProto;
                        // Only loopback proxies are allowed by default. Clear that restriction because forwarders are
                        // being enabled by explicit configuration.
                        options.KnownNetworks.Clear();
                        options.KnownProxies.Clear();
                    });

                    services.AddTransient<IStartupFilter, ForwardedHeadersStartupFilter>();
                }

                services.AddRouting();
            })
            .UseIIS()
            .UseIISIntegration();
        }