ConfigureWebHostBuilder.cs

// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System.Diagnostics.CodeAnalysis;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Hosting.Infrastructure;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;

namespace Microsoft.AspNetCore.Builder;

/// <summary>
/// A non-buildable <see cref="IWebHostBuilder"/> for <see cref="WebApplicationBuilder"/>.
/// Use <see cref="WebApplicationBuilder.Build"/> to build the <see cref="WebApplicationBuilder"/>.
/// </summary>
public sealed class ConfigureWebHostBuilder : IWebHostBuilder, ISupportsStartup
{
    private readonly IWebHostEnvironment _environment;
    private readonly ConfigurationManager _configuration;
    private readonly IServiceCollection _services;
    private readonly WebHostBuilderContext _context;

    internal ConfigureWebHostBuilder(WebHostBuilderContext webHostBuilderContext, ConfigurationManager configuration, IServiceCollection services)
    {
        _configuration = configuration;
        _environment = webHostBuilderContext.HostingEnvironment;
        _services = services;
        _context = webHostBuilderContext;
    }

    IWebHost IWebHostBuilder.Build()
    {
        throw new NotSupportedException($"Call {nameof(WebApplicationBuilder)}.{nameof(WebApplicationBuilder.Build)}() instead.");
    }

    /// <inheritdoc />
    public IWebHostBuilder ConfigureAppConfiguration(Action<WebHostBuilderContext, IConfigurationBuilder> configureDelegate)
    {
        var previousContentRoot = HostingPathResolver.ResolvePath(_context.HostingEnvironment.ContentRootPath);
        var previousContentRootConfig = _configuration[WebHostDefaults.ContentRootKey];
        var previousWebRoot = HostingPathResolver.ResolvePath(_context.HostingEnvironment.WebRootPath, previousContentRoot);
        var previousWebRootConfig = _configuration[WebHostDefaults.WebRootKey];
        var previousApplication = _configuration[WebHostDefaults.ApplicationKey];
        var previousEnvironment = _configuration[WebHostDefaults.EnvironmentKey];
        var previousHostingStartupAssemblies = _configuration[WebHostDefaults.HostingStartupAssembliesKey];
        var previousHostingStartupAssembliesExclude = _configuration[WebHostDefaults.HostingStartupExcludeAssembliesKey];

        // Run these immediately so that they are observable by the imperative code
        configureDelegate(_context, _configuration);

        if (!string.Equals(previousWebRootConfig, _configuration[WebHostDefaults.WebRootKey], StringComparison.OrdinalIgnoreCase)
            && !string.Equals(HostingPathResolver.ResolvePath(previousWebRoot, previousContentRoot), HostingPathResolver.ResolvePath(_configuration[WebHostDefaults.WebRootKey], previousContentRoot), StringComparison.OrdinalIgnoreCase))
        {
            // Diasllow changing the web root for consistency with other types.
            throw new NotSupportedException($"The web root changed from \"{HostingPathResolver.ResolvePath(previousWebRoot, previousContentRoot)}\" to \"{HostingPathResolver.ResolvePath(_configuration[WebHostDefaults.WebRootKey], previousContentRoot)}\". Changing the host configuration using WebApplicationBuilder.WebHost is not supported. Use WebApplication.CreateBuilder(WebApplicationOptions) instead.");
        }
        else if (!string.Equals(previousApplication, _configuration[WebHostDefaults.ApplicationKey], StringComparison.OrdinalIgnoreCase))
        {
            // Disallow changing any host configuration
            throw new NotSupportedException($"The application name changed from \"{previousApplication}\" to \"{_configuration[WebHostDefaults.ApplicationKey]}\". Changing the host configuration using WebApplicationBuilder.WebHost is not supported. Use WebApplication.CreateBuilder(WebApplicationOptions) instead.");
        }
        else if (!string.Equals(previousContentRootConfig, _configuration[WebHostDefaults.ContentRootKey], StringComparison.OrdinalIgnoreCase)
            && !string.Equals(previousContentRoot, HostingPathResolver.ResolvePath(_configuration[WebHostDefaults.ContentRootKey]), StringComparison.OrdinalIgnoreCase))
        {
            // Disallow changing any host configuration
            throw new NotSupportedException($"The content root changed from \"{previousContentRoot}\" to \"{HostingPathResolver.ResolvePath(_configuration[WebHostDefaults.ContentRootKey])}\". Changing the host configuration using WebApplicationBuilder.WebHost is not supported. Use WebApplication.CreateBuilder(WebApplicationOptions) instead.");
        }
        else if (!string.Equals(previousEnvironment, _configuration[WebHostDefaults.EnvironmentKey], StringComparison.OrdinalIgnoreCase))
        {
            // Disallow changing any host configuration
            throw new NotSupportedException($"The environment changed from \"{previousEnvironment}\" to \"{_configuration[WebHostDefaults.EnvironmentKey]}\". Changing the host configuration using WebApplicationBuilder.WebHost is not supported. Use WebApplication.CreateBuilder(WebApplicationOptions) instead.");
        }
        else if (!string.Equals(previousHostingStartupAssemblies, _configuration[WebHostDefaults.HostingStartupAssembliesKey], StringComparison.OrdinalIgnoreCase))
        {
            // Disallow changing any host configuration
            throw new NotSupportedException($"The hosting startup assemblies changed from \"{previousHostingStartupAssemblies}\" to \"{_configuration[WebHostDefaults.HostingStartupAssembliesKey]}\". Changing the host configuration using WebApplicationBuilder.WebHost is not supported. Use WebApplication.CreateBuilder(WebApplicationOptions) instead.");
        }
        else if (!string.Equals(previousHostingStartupAssembliesExclude, _configuration[WebHostDefaults.HostingStartupExcludeAssembliesKey], StringComparison.OrdinalIgnoreCase))
        {
            // Disallow changing any host configuration
            throw new NotSupportedException($"The hosting startup assemblies exclude list changed from \"{previousHostingStartupAssembliesExclude}\" to \"{_configuration[WebHostDefaults.HostingStartupExcludeAssembliesKey]}\". Changing the host configuration using WebApplicationBuilder.WebHost is not supported. Use WebApplication.CreateBuilder(WebApplicationOptions) instead.");
        }

        return this;
    }

    /// <inheritdoc />
    public IWebHostBuilder ConfigureServices(Action<WebHostBuilderContext, IServiceCollection> configureServices)
    {
        // Run these immediately so that they are observable by the imperative code
        configureServices(_context, _services);
        return this;
    }

    /// <inheritdoc />
    public IWebHostBuilder ConfigureServices(Action<IServiceCollection> configureServices)
    {
        return ConfigureServices((WebHostBuilderContext context, IServiceCollection services) => configureServices(services));
    }

    /// <inheritdoc />
    public string? GetSetting(string key)
    {
        return _configuration[key];
    }

    /// <inheritdoc />
    public IWebHostBuilder UseSetting(string key, string? value)
    {
        // All properties on IWebHostEnvironment are non-nullable.
        if (value is null)
        {
            return this;
        }

        var previousContentRoot = HostingPathResolver.ResolvePath(_context.HostingEnvironment.ContentRootPath);
        var previousWebRoot = HostingPathResolver.ResolvePath(_context.HostingEnvironment.WebRootPath);
        var previousApplication = _configuration[WebHostDefaults.ApplicationKey];
        var previousEnvironment = _configuration[WebHostDefaults.EnvironmentKey];
        var previousHostingStartupAssemblies = _configuration[WebHostDefaults.HostingStartupAssembliesKey];
        var previousHostingStartupAssembliesExclude = _configuration[WebHostDefaults.HostingStartupExcludeAssembliesKey];

        if (string.Equals(key, WebHostDefaults.WebRootKey, StringComparison.OrdinalIgnoreCase) &&
                !string.Equals(HostingPathResolver.ResolvePath(previousWebRoot, previousContentRoot), HostingPathResolver.ResolvePath(value, previousContentRoot), StringComparison.OrdinalIgnoreCase))
        {
            // Disallow changing any host configuration
            throw new NotSupportedException($"The web root changed from \"{HostingPathResolver.ResolvePath(previousWebRoot, previousContentRoot)}\" to \"{HostingPathResolver.ResolvePath(value, previousContentRoot)}\". Changing the host configuration using WebApplicationBuilder.WebHost is not supported. Use WebApplication.CreateBuilder(WebApplicationOptions) instead.");
        }
        else if (string.Equals(key, WebHostDefaults.ApplicationKey, StringComparison.OrdinalIgnoreCase) &&
                !string.Equals(previousApplication, value, StringComparison.OrdinalIgnoreCase))
        {
            // Disallow changing any host configuration
            throw new NotSupportedException($"The application name changed from \"{previousApplication}\" to \"{value}\". Changing the host configuration using WebApplicationBuilder.WebHost is not supported. Use WebApplication.CreateBuilder(WebApplicationOptions) instead.");
        }
        else if (string.Equals(key, WebHostDefaults.ContentRootKey, StringComparison.OrdinalIgnoreCase) &&
                !string.Equals(previousContentRoot, HostingPathResolver.ResolvePath(value), StringComparison.OrdinalIgnoreCase))
        {
            // Disallow changing any host configuration
            throw new NotSupportedException($"The content root changed from \"{previousContentRoot}\" to \"{HostingPathResolver.ResolvePath(value)}\". Changing the host configuration using WebApplicationBuilder.WebHost is not supported. Use WebApplication.CreateBuilder(WebApplicationOptions) instead.");
        }
        else if (string.Equals(key, WebHostDefaults.EnvironmentKey, StringComparison.OrdinalIgnoreCase) &&
                !string.Equals(previousEnvironment, value, StringComparison.OrdinalIgnoreCase))
        {
            // Disallow changing any host configuration
            throw new NotSupportedException($"The environment changed from \"{previousEnvironment}\" to \"{value}\". Changing the host configuration using WebApplicationBuilder.WebHost is not supported. Use WebApplication.CreateBuilder(WebApplicationOptions) instead.");
        }
        else if (string.Equals(key, WebHostDefaults.HostingStartupAssembliesKey, StringComparison.OrdinalIgnoreCase) &&
                !string.Equals(previousHostingStartupAssemblies, value, StringComparison.OrdinalIgnoreCase))
        {
            // Disallow changing any host configuration
            throw new NotSupportedException($"The hosting startup assemblies changed from \"{previousHostingStartupAssemblies}\" to \"{value}\". Changing the host configuration using WebApplicationBuilder.WebHost is not supported. Use WebApplication.CreateBuilder(WebApplicationOptions) instead.");
        }
        else if (string.Equals(key, WebHostDefaults.HostingStartupExcludeAssembliesKey, StringComparison.OrdinalIgnoreCase) &&
                !string.Equals(previousHostingStartupAssembliesExclude, value, StringComparison.OrdinalIgnoreCase))
        {
            // Disallow changing any host configuration
            throw new NotSupportedException($"The hosting startup assemblies exclude list changed from \"{previousHostingStartupAssembliesExclude}\" to \"{value}\". Changing the host configuration using WebApplicationBuilder.WebHost is not supported. Use WebApplication.CreateBuilder(WebApplicationOptions) instead.");
        }

        // Set the configuration value after we've validated the key
        _configuration[key] = value;

        return this;
    }

    IWebHostBuilder ISupportsStartup.Configure(Action<IApplicationBuilder> configure)
    {
        throw new NotSupportedException("Configure() is not supported by WebApplicationBuilder.WebHost. Use the WebApplication returned by WebApplicationBuilder.Build() instead.");
    }

    IWebHostBuilder ISupportsStartup.Configure(Action<WebHostBuilderContext, IApplicationBuilder> configure)
    {
        throw new NotSupportedException("Configure() is not supported by WebApplicationBuilder.WebHost. Use the WebApplication returned by WebApplicationBuilder.Build() instead.");
    }

    IWebHostBuilder ISupportsStartup.UseStartup([DynamicallyAccessedMembers(StartupLinkerOptions.Accessibility)] Type startupType)
    {
        throw new NotSupportedException("UseStartup() is not supported by WebApplicationBuilder.WebHost. Use the WebApplication returned by WebApplicationBuilder.Build() instead.");
    }

    IWebHostBuilder ISupportsStartup.UseStartup<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicMethods)] TStartup>(Func<WebHostBuilderContext, TStartup> startupFactory)
    {
        throw new NotSupportedException("UseStartup() is not supported by WebApplicationBuilder.WebHost. Use the WebApplication returned by WebApplicationBuilder.Build() instead.");
    }
}