AutofacAppBuilderExtensions.cs

// This software is part of the Autofac IoC container
// Copyright © 2014 Autofac Contributors
// https://autofac.org
//
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using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Globalization;
using System.Linq;
using System.Threading;
using Autofac;
using Autofac.Core;
using Autofac.Core.Lifetime;
using Autofac.Integration.Owin;
using Autofac.Integration.Owin.Properties;
using Microsoft.Owin;

namespace Owin
{
    /// <summary>
    /// Extension methods for configuring Autofac within the OWIN pipeline.
    /// </summary>
    [EditorBrowsable(EditorBrowsableState.Never)]
    public static class AutofacAppBuilderExtensions
    {
        /// <summary>
        /// Unique key used to indicate the middleware for injecting the request lifetime scope has been registered with the application.
        /// </summary>
        private static readonly string InjectorRegisteredKey = "AutofacLifetimeScopeInjectorRegistered:" + Constants.AutofacMiddlewareBoundary;

        /// <summary>
        /// Registers a callback to dispose an Autofac <see cref="ILifetimeScope"/>
        /// when the OWIN <c>host.OnAppDisposing</c> event is triggered. This is a
        /// convenience method that will dispose an Autofac container or child scope
        /// when an OWIN application is shutting down.
        /// </summary>
        /// <param name="app">The application builder.</param>
        /// <param name="lifetimeScope">The Autofac lifetime scope that should be disposed.</param>
        /// <returns>The application builder.</returns>
        /// <exception cref="System.ArgumentNullException">
        /// Thrown if <paramref name="app" /> or <paramref name="lifetimeScope" /> is <see langword="null" />.
        /// </exception>
        public static IAppBuilder DisposeScopeOnAppDisposing(this IAppBuilder app, ILifetimeScope lifetimeScope)
        {
            if (app == null)
            {
                throw new ArgumentNullException(nameof(app));
            }

            if (lifetimeScope == null)
            {
                throw new ArgumentNullException(nameof(lifetimeScope));
            }

            var context = new OwinContext(app.Properties);
            var token = context.Get<CancellationToken>("host.OnAppDisposing");

            if (token.CanBeCanceled)
            {
                token.Register(lifetimeScope.Dispose);
            }

            return app;
        }

        /// <summary>
        /// Determines if the Autofac lifetime scope injector middleware is
        /// registered with the application pipeline.
        /// </summary>
        /// <param name="app">The application builder.</param>
        /// <returns>
        /// <see langword="true"/> if the Autofac lifetime scope injector has been registered
        /// with the <paramref name="app"/>; <see langword="false"/> if not.
        /// </returns>
        /// <exception cref="System.ArgumentNullException">
        /// Thrown if <paramref name="app"/> is <see langword="null"/>.
        /// </exception>
        /// <remarks>
        /// <para>
        /// This method is useful when composing an application where you may
        /// accidentally register more than one Autofac lifetime scope injector
        /// with the pipeline - for example, accidentally calling both
        /// <see cref="UseAutofacMiddleware(IAppBuilder, ILifetimeScope)"/>
        /// and <see cref="UseAutofacLifetimeScopeInjector(IAppBuilder, ILifetimeScope)"/>
        /// on the same <see cref="IAppBuilder"/>. This allows you to check
        /// an <see cref="IAppBuilder"/> and only add Autofac to the pipeline
        /// if it hasn't already been registered.
        /// </para>
        /// </remarks>
        public static bool IsAutofacLifetimeScopeInjectorRegistered(this IAppBuilder app)
        {
            if (app == null)
            {
                throw new ArgumentNullException(nameof(app));
            }

            return app.Properties.ContainsKey(InjectorRegisteredKey);
        }

        /// <summary>
        /// Adds middleware to inject a request-scoped Autofac lifetime scope into the OWIN pipeline.
        /// </summary>
        /// <param name="app">The application builder.</param>
        /// <param name="container">The root Autofac application lifetime scope/container.</param>
        /// <returns>The application builder.</returns>
        /// <exception cref="System.ArgumentNullException">
        /// Thrown if <paramref name="app"/> or <paramref name="container"/> is <see langword="null"/>.
        /// </exception>
        /// <remarks>
        /// <para>
        /// This extension is used when separating the notions of injecting the
        /// lifetime scope and adding middleware to the pipeline from the container.
        /// </para>
        /// <para>
        /// Since middleware registration order matters, generally you want the
        /// Autofac request lifetime scope registered early in the pipeline, but
        /// you may not want the middleware registered with Autofac added to the
        /// pipeline until later.
        /// </para>
        /// <para>
        /// This method gets used in conjunction with <see cref="UseMiddlewareFromContainer{T}(IAppBuilder)"/>.
        /// Do not use this with <see cref="UseAutofacMiddleware(IAppBuilder, ILifetimeScope)"/>
        /// or you'll get unexpected results!
        /// </para>
        /// </remarks>
        /// <example>
        /// <code lang="C#">
        /// app
        ///   .UseAutofacLifetimeScopeInjector(container)
        ///   .UseBasicAuthentication()
        ///   .Use((c, next) =&gt;
        ///   {
        ///     //authorization
        ///     return next();
        ///   })
        ///   .UseMiddlewareFromContainer&lt;PathRewriter&gt;()
        ///   .UseSendFileFallback()
        ///   .UseStaticFiles();
        /// </code>
        /// </example>
        /// <seealso cref="UseMiddlewareFromContainer{T}(IAppBuilder)"/>
        public static IAppBuilder UseAutofacLifetimeScopeInjector(this IAppBuilder app, ILifetimeScope container)
        {
            if (app == null)
            {
                throw new ArgumentNullException(nameof(app));
            }

            if (container == null)
            {
                throw new ArgumentNullException(nameof(container));
            }

            return app.RegisterAutofacLifetimeScopeInjector(container);
        }

        /// <summary>
        /// Adds middleware to inject an externally-defined Autofac lifetime scope into the OWIN pipeline.
        /// </summary>
        /// <param name="app">The application builder.</param>
        /// <param name="scopeProvider">The delegate to get the scope (either from passed OWIN context or anywhere else).</param>
        /// <returns>The application builder.</returns>
        /// <exception cref="System.ArgumentNullException">
        /// Thrown if <paramref name="app"/> or <paramref name="scopeProvider"/> is <see langword="null"/>.
        /// </exception>
        /// <remarks>
        /// <para>
        /// This extension is used when separating the notions of injecting the
        /// lifetime scope and adding middleware to the pipeline from the container.
        /// </para>
        /// <para>
        /// Since middleware registration order matters, generally you want the
        /// Autofac request lifetime scope registered early in the pipeline, but
        /// you may not want the middleware registered with Autofac added to the
        /// pipeline until later.
        /// </para>
        /// <para>
        /// This method won't add any disposal of passed lifetime scope;
        /// the caller is responsible for disposing it at the appropriate moment.
        /// </para>
        /// <para>
        /// This method gets used in conjunction with <see cref="UseMiddlewareFromContainer{T}(IAppBuilder)"/>.
        /// Do not use this with <see cref="UseAutofacMiddleware(IAppBuilder, ILifetimeScope)"/>
        /// or you'll get unexpected results!
        /// </para>
        /// </remarks>
        /// <example>
        /// <code lang="C#">
        /// app
        ///   .UseAutofacLifetimeScopeInjector(c => GetSomeExternallyDefinedLifetimeScope(c))
        ///   .UseBasicAuthentication()
        ///   .Use((c, next) =&gt;
        ///   {
        ///     //authorization
        ///     return next();
        ///   })
        ///   .UseMiddlewareFromContainer&lt;PathRewriter&gt;()
        ///   .UseSendFileFallback()
        ///   .UseStaticFiles();
        /// </code>
        /// </example>
        /// <seealso cref="UseMiddlewareFromContainer{T}(IAppBuilder)"/>
        public static IAppBuilder UseAutofacLifetimeScopeInjector(this IAppBuilder app, Func<IOwinContext, ILifetimeScope> scopeProvider)
        {
            if (app == null)
            {
                throw new ArgumentNullException(nameof(app));
            }

            if (scopeProvider == null)
            {
                throw new ArgumentNullException(nameof(scopeProvider));
            }

            return app.RegisterAutofacLifetimeScopeInjector(scopeProvider, false);
        }

        /// <summary>
        /// Adds middleware to both inject a request-scoped Autofac lifetime scope into the OWIN pipeline
        /// as well as add all middleware components registered with Autofac.
        /// </summary>
        /// <param name="app">The application builder.</param>
        /// <param name="container">The root Autofac application lifetime scope/container.</param>
        /// <returns>The application builder.</returns>
        /// <exception cref="System.ArgumentNullException">
        /// Thrown if <paramref name="app"/> or <paramref name="container"/> is <see langword="null"/>.
        /// </exception>
        /// <remarks>
        /// <para>
        /// This extension registers the Autofac lifetime scope and all Autofac-registered
        /// middleware into the application at the same time. This is the simplest
        /// way to integrate Autofac into OWIN but has the least control over
        /// pipeline construction.
        /// </para>
        /// <para>
        /// Do not use this with <see cref="UseAutofacLifetimeScopeInjector(IAppBuilder, ILifetimeScope)"/>
        /// or <see cref="UseMiddlewareFromContainer{T}(IAppBuilder)"/>
        /// or you'll get unexpected results!
        /// </para>
        /// </remarks>
        /// <example>
        /// <code lang="C#">
        /// app
        ///   .UseAutofacMiddleware(container)
        ///   .UseBasicAuthentication()
        ///   .Use((c, next) =&gt;
        ///   {
        ///     //authorization
        ///     return next();
        ///   })
        ///   .UseSendFileFallback()
        ///   .UseStaticFiles();
        /// </code>
        /// </example>
        public static IAppBuilder UseAutofacMiddleware(this IAppBuilder app, ILifetimeScope container)
        {
            if (app == null)
            {
                throw new ArgumentNullException(nameof(app));
            }

            if (container == null)
            {
                throw new ArgumentNullException(nameof(container));
            }

            return app
                .RegisterAutofacLifetimeScopeInjector(container)
                .UseAllMiddlewareRegisteredInContainer(container);
        }

        /// <summary>
        /// Adds a middleware to the OWIN pipeline that will be constructed using Autofac
        /// </summary>
        /// <param name="app">The application builder.</param>
        /// <returns>The application builder.</returns>
        /// <exception cref="System.ArgumentNullException">
        /// Thrown if <paramref name="app"/> is <see langword="null"/>.
        /// </exception>
        /// <remarks>
        /// <para>
        /// This extension is used when separating the notions of injecting the
        /// lifetime scope and adding middleware to the pipeline from the container.
        /// </para>
        /// <para>
        /// Since middleware registration order matters, generally you want the
        /// Autofac request lifetime scope registered early in the pipeline, but
        /// you may not want the middleware registered with Autofac added to the
        /// pipeline until later.
        /// </para>
        /// <para>
        /// This method gets used in conjunction with <see cref="UseAutofacLifetimeScopeInjector(IAppBuilder, ILifetimeScope)"/>.
        /// Do not use this with <see cref="UseAutofacMiddleware(IAppBuilder, ILifetimeScope)"/>
        /// or you'll get unexpected results!
        /// </para>
        /// </remarks>
        /// <example>
        /// <code lang="C#">
        /// app
        ///   .UseAutofacLifetimeScopeInjector(container)
        ///   .UseBasicAuthentication()
        ///   .Use((c, next) =&gt;
        ///   {
        ///     //authorization
        ///     return next();
        ///   })
        ///   .UseMiddlewareFromContainer&lt;PathRewriter&gt;()
        ///   .UseSendFileFallback()
        ///   .UseStaticFiles();
        /// </code>
        /// </example>
        /// <seealso cref="UseAutofacLifetimeScopeInjector(IAppBuilder, ILifetimeScope)"/>
        public static IAppBuilder UseMiddlewareFromContainer<T>(this IAppBuilder app)
            where T : OwinMiddleware
        {
            if (app == null)
            {
                throw new ArgumentNullException(nameof(app));
            }

            if (!app.IsAutofacLifetimeScopeInjectorRegistered())
            {
                throw new InvalidOperationException(string.Format(CultureInfo.InvariantCulture, Resources.LifetimeScopeInjectorNotFoundWhileRegisteringMiddleware, typeof(T)));
            }

            return app.Use<AutofacMiddleware<T>>();
        }

        /// <summary>
        /// Locates all explicitly registered middleware instances and generates the list of
        /// corresponding <see cref="AutofacMiddleware{T}"/> types that should be inserted
        /// into the application pipeline.
        /// </summary>
        /// <param name="container">
        /// The <see cref="IComponentContext"/> containing registrations to convert to middleware.
        /// </param>
        /// <returns>
        /// An <see cref="IEnumerable{T}"/> of <see cref="AutofacMiddleware{T}"/> wrapped around
        /// registered middleware types.
        /// </returns>
        internal static IEnumerable<Type> GenerateAllAutofacMiddleware(IComponentContext container)
        {
            return container.ComponentRegistry.Registrations.SelectMany(r => r.Services)
                .OfType<TypedService>()
                .Where(s => IsMiddlewareButNotAutofac(s.ServiceType))
                .Select(service => typeof(AutofacMiddleware<>).MakeGenericType(service.ServiceType))
                .ToArray();
        }

        /// <summary>
        /// Determines whether a type is middleware we should wrap.
        /// </summary>
        /// <param name="typeToCheck">The type to check.</param>
        /// <returns>
        /// <see langword="true" /> if the type is middleware, not abstract, and not
        /// already wrapped; otherwise <see langword="false" />.
        /// </returns>
        private static bool IsMiddlewareButNotAutofac(Type typeToCheck)
        {
            return typeToCheck.IsAssignableTo<OwinMiddleware>() &&
                !typeToCheck.IsAbstract &&
                !(typeToCheck.IsGenericType && typeToCheck.GetGenericTypeDefinition() == typeof(AutofacMiddleware<>));
        }

        private static IAppBuilder RegisterAutofacLifetimeScopeInjector(this IAppBuilder app, ILifetimeScope container)
        {
            return app
                .RegisterAutofacLifetimeScopeInjector(context =>
                    container.BeginLifetimeScope(MatchingScopeLifetimeTags.RequestLifetimeScopeTag, b => b.RegisterInstance(context).As<IOwinContext>()),
                    true);
        }

        private static IAppBuilder RegisterAutofacLifetimeScopeInjector(this IAppBuilder app, Func<IOwinContext,ILifetimeScope> scopeProvider, bool dispose)
        {
            app.Use(async (context, next) =>
            {
                if (context.GetAutofacLifetimeScope() != null)
                {
                    await next();
                    return;
                }

                var lifetimeScope = scopeProvider(context);
                try
                {
                    context.SetAutofacLifetimeScope(lifetimeScope);
                    await next();
                }
                finally
                {
                    if (dispose)
                    {
                        lifetimeScope?.Dispose();
                    }
                }
            });

            app.Properties[InjectorRegisteredKey] = true;
            return app;
        }

        private static IAppBuilder UseAllMiddlewareRegisteredInContainer(this IAppBuilder app, IComponentContext container)
        {
            var typedServices = GenerateAllAutofacMiddleware(container);
            if (!typedServices.Any())
            {
                return app;
            }

            foreach (var typedService in typedServices)
            {
                app.Use(typedService);
            }

            return app;
        }
    }
}