CircularDependencyDetectorMiddleware.cs

// This software is part of the Autofac IoC container
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using System;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using System.Runtime.CompilerServices;
using Autofac.Core.Resolving.Pipeline;

namespace Autofac.Core.Resolving.Middleware
{
    /// <summary>
    /// Common stage. Added to the start of all component pipelines.
    /// </summary>
    internal class CircularDependencyDetectorMiddleware : IResolveMiddleware
    {
        /// <summary>
        /// Defines the default max resolve depth.
        /// </summary>
        public const int DefaultMaxResolveDepth = 50;

        /// <summary>
        /// Gets the default instance of <see cref="CircularDependencyDetectorMiddleware"/>.
        /// </summary>
        public static CircularDependencyDetectorMiddleware Default { get; } = new CircularDependencyDetectorMiddleware(DefaultMaxResolveDepth);

        private readonly int _maxResolveDepth;

        /// <summary>
        /// Initializes a new instance of the <see cref="CircularDependencyDetectorMiddleware"/> class.
        /// </summary>
        /// <param name="maxResolveDepth">The max resolve depth.</param>
        public CircularDependencyDetectorMiddleware(int maxResolveDepth)
        {
            _maxResolveDepth = maxResolveDepth;
        }

        /// <inheritdoc/>
        public PipelinePhase Phase => PipelinePhase.ResolveRequestStart;

        /// <inheritdoc/>
        public void Execute(ResolveRequestContextBase context, Action<ResolveRequestContextBase> next)
        {
            var activationDepth = context.Operation.RequestDepth;

            if (activationDepth > _maxResolveDepth)
            {
#if NETSTANDARD2_1
                // In .NET Standard 2.1 we will try and keep going until we run out of stack space.
                if (!RuntimeHelpers.TryEnsureSufficientExecutionStack())
                {
                    throw new DependencyResolutionException(string.Format(CultureInfo.CurrentCulture, CircularDependencyDetectorMessages.MaxDepthExceeded, context.Service));
                }
#else
                // Pre .NET Standard 2.1 we just end at 50.
                throw new DependencyResolutionException(string.Format(CultureInfo.CurrentCulture, CircularDependencyDetectorMessages.MaxDepthExceeded, context.Service));
#endif
            }

            var requestStack = context.Operation.RequestStack;

            // The first one is the current resolve request.
            // Do our circular dependency check.
            if (activationDepth > 1)
            {
                var registration = context.Registration;

                foreach (var requestEntry in requestStack)
                {
                    if (requestEntry.Registration == registration)
                    {
                        throw new DependencyResolutionException(string.Format(
                            CultureInfo.CurrentCulture,
                            CircularDependencyDetectorMessages.CircularDependency,
                            CreateDependencyGraphTo(registration, requestStack)));
                    }
                }
            }

            requestStack.Push(context);

            try
            {
                // Circular dependency check is done, move to the next stage.
                next(context);
            }
            finally
            {
                requestStack.Pop();
            }
        }

        /// <inheritdoc/>
        public override string ToString() => nameof(CircularDependencyDetectorMiddleware);

        private static string CreateDependencyGraphTo(IComponentRegistration registration, IEnumerable<ResolveRequestContextBase> requestStack)
        {
            if (registration == null) throw new ArgumentNullException(nameof(registration));
            if (requestStack == null) throw new ArgumentNullException(nameof(requestStack));

            var dependencyGraph = Display(registration);

            return requestStack.Select(a => a.Registration)
                .Aggregate(dependencyGraph, (current, requestor) => Display(requestor) + " -> " + current);
        }

        private static string Display(IComponentRegistration registration)
        {
            return registration.Activator.DisplayName();
        }
    }
}