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Does this help
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‎src/Mvc/Mvc.Testing/src/HostFactoryResolver.cs

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// Licensed to the .NET Foundation under one or more agreements.
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// The .NET Foundation licenses this file to you under the MIT license.
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using System;
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using System.Collections.Generic;
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using System.Diagnostics;
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using System.Reflection;
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using System.Threading;
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using System.Threading.Tasks;
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#nullable enable
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namespace Microsoft.Extensions.Hosting
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{
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internal sealed class HostFactoryResolver
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{
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private const BindingFlags DeclaredOnlyLookup = BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.Static | BindingFlags.DeclaredOnly;
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public const string BuildWebHost = nameof(BuildWebHost);
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public const string CreateWebHostBuilder = nameof(CreateWebHostBuilder);
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public const string CreateHostBuilder = nameof(CreateHostBuilder);
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// The amount of time we wait for the diagnostic source events to fire
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private static readonly TimeSpan s_defaultWaitTimeout = TimeSpan.FromSeconds(5);
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public static Func<string[], TWebHost>? ResolveWebHostFactory<TWebHost>(Assembly assembly)
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{
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return ResolveFactory<TWebHost>(assembly, BuildWebHost);
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}
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public static Func<string[], TWebHostBuilder>? ResolveWebHostBuilderFactory<TWebHostBuilder>(Assembly assembly)
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{
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return ResolveFactory<TWebHostBuilder>(assembly, CreateWebHostBuilder);
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}
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public static Func<string[], THostBuilder>? ResolveHostBuilderFactory<THostBuilder>(Assembly assembly)
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{
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return ResolveFactory<THostBuilder>(assembly, CreateHostBuilder);
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}
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// This helpers encapsulates all of the complex logic required to:
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// 1. Execute the entry point of the specified assembly in a different thread.
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// 2. Wait for the diagnostic source events to fire
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// 3. Give the caller a chance to execute logic to mutate the IHostBuilder
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// 4. Resolve the instance of the applications's IHost
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// 5. Allow the caller to determine if the entry point has completed
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public static Func<string[], object>? ResolveHostFactory(Assembly assembly,
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TimeSpan? waitTimeout = null,
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bool stopApplication = true,
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Action<object>? configureHostBuilder = null,
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Action<Exception?>? entrypointCompleted = null)
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{
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if (assembly.EntryPoint is null)
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{
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return null;
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}
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try
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{
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// Attempt to load hosting and check the version to make sure the events
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// even have a chance of firing (they were added in .NET >= 6)
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var hostingAssembly = Assembly.Load("Microsoft.Extensions.Hosting");
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if (hostingAssembly.GetName().Version is Version version && version.Major < 6)
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{
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return null;
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}
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// We're using a version >= 6 so the events can fire. If they don't fire
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// then it's because the application isn't using the hosting APIs
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}
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catch
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{
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// There was an error loading the extensions assembly, return null.
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return null;
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}
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return args => new HostingListener(args, assembly.EntryPoint, waitTimeout ?? s_defaultWaitTimeout, stopApplication, configureHostBuilder, entrypointCompleted).CreateHost();
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}
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private static Func<string[], T>? ResolveFactory<T>(Assembly assembly, string name)
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{
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var programType = assembly?.EntryPoint?.DeclaringType;
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if (programType == null)
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{
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return null;
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}
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var factory = programType.GetMethod(name, DeclaredOnlyLookup);
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if (!IsFactory<T>(factory))
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{
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return null;
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}
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return args => (T)factory!.Invoke(null, new object[] { args })!;
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}
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// TReturn Factory(string[] args);
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private static bool IsFactory<TReturn>(MethodInfo? factory)
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{
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return factory != null
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&& typeof(TReturn).IsAssignableFrom(factory.ReturnType)
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&& factory.GetParameters().Length == 1
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&& typeof(string[]).Equals(factory.GetParameters()[0].ParameterType);
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}
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// Used by EF tooling without any Hosting references. Looses some return type safety checks.
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public static Func<string[], IServiceProvider?>? ResolveServiceProviderFactory(Assembly assembly, TimeSpan? waitTimeout = null)
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{
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// Prefer the older patterns by default for back compat.
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var webHostFactory = ResolveWebHostFactory<object>(assembly);
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if (webHostFactory != null)
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{
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return args =>
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{
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var webHost = webHostFactory(args);
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return GetServiceProvider(webHost);
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};
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}
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var webHostBuilderFactory = ResolveWebHostBuilderFactory<object>(assembly);
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if (webHostBuilderFactory != null)
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{
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return args =>
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{
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var webHostBuilder = webHostBuilderFactory(args);
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var webHost = Build(webHostBuilder);
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return GetServiceProvider(webHost);
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};
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}
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var hostBuilderFactory = ResolveHostBuilderFactory<object>(assembly);
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if (hostBuilderFactory != null)
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{
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return args =>
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{
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var hostBuilder = hostBuilderFactory(args);
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var host = Build(hostBuilder);
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return GetServiceProvider(host);
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};
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}
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var hostFactory = ResolveHostFactory(assembly, waitTimeout: waitTimeout);
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if (hostFactory != null)
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{
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return args =>
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{
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var host = hostFactory(args);
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return GetServiceProvider(host);
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};
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}
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return null;
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}
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private static object? Build(object builder)
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{
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var buildMethod = builder.GetType().GetMethod("Build");
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return buildMethod?.Invoke(builder, Array.Empty<object>());
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}
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private static IServiceProvider? GetServiceProvider(object? host)
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{
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if (host == null)
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{
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return null;
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}
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var hostType = host.GetType();
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var servicesProperty = hostType.GetProperty("Services", DeclaredOnlyLookup);
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return (IServiceProvider?)servicesProperty?.GetValue(host);
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}
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private sealed class HostingListener : IObserver<DiagnosticListener>, IObserver<KeyValuePair<string, object?>>
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{
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private readonly string[] _args;
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private readonly MethodInfo _entryPoint;
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private readonly TimeSpan _waitTimeout;
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private readonly bool _stopApplication;
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private readonly TaskCompletionSource<object> _hostTcs = new();
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private IDisposable? _disposable;
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private Action<object>? _configure;
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private Action<Exception?>? _entrypointCompleted;
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private static readonly AsyncLocal<HostingListener> _currentListener = new();
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public HostingListener(string[] args, MethodInfo entryPoint, TimeSpan waitTimeout, bool stopApplication, Action<object>? configure, Action<Exception?>? entrypointCompleted)
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{
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_args = args;
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_entryPoint = entryPoint;
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_waitTimeout = waitTimeout;
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_stopApplication = stopApplication;
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_configure = configure;
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_entrypointCompleted = entrypointCompleted;
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}
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public object CreateHost()
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{
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using var subscription = DiagnosticListener.AllListeners.Subscribe(this);
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// Kick off the entry point on a new thread so we don't block the current one
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// in case we need to timeout the execution
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var thread = new Thread(() =>
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{
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Exception? exception = null;
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try
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{
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// Set the async local to the instance of the HostingListener so we can filter events that
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// aren't scoped to this execution of the entry point.
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_currentListener.Value = this;
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var parameters = _entryPoint.GetParameters();
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if (parameters.Length == 0)
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{
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_entryPoint.Invoke(null, Array.Empty<object>());
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}
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else
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{
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_entryPoint.Invoke(null, new object[] { _args });
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}
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// Try to set an exception if the entry point returns gracefully, this will force
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// build to throw
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_hostTcs.TrySetException(new InvalidOperationException("Unable to build IHost"));
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}
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catch (TargetInvocationException tie) when (tie.InnerException is StopTheHostException)
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{
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// The host was stopped by our own logic
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}
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catch (TargetInvocationException tie)
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{
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exception = tie.InnerException ?? tie;
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// Another exception happened, propagate that to the caller
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_hostTcs.TrySetException(exception);
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}
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catch (Exception ex)
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{
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exception = ex;
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// Another exception happened, propagate that to the caller
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_hostTcs.TrySetException(ex);
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}
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finally
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{
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// Signal that the entry point is completed
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_entrypointCompleted?.Invoke(exception);
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}
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})
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{
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// Make sure this doesn't hang the process
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IsBackground = true
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};
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// Start the thread
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thread.Start();
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try
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{
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// Wait before throwing an exception
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if (!_hostTcs.Task.Wait(_waitTimeout))
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{
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throw new InvalidOperationException("Unable to build IHost");
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}
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}
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catch (AggregateException) when (_hostTcs.Task.IsCompleted)
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{
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// Lets this propagate out of the call to GetAwaiter().GetResult()
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}
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Debug.Assert(_hostTcs.Task.IsCompleted);
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return _hostTcs.Task.GetAwaiter().GetResult();
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}
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public void OnCompleted()
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{
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_disposable?.Dispose();
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}
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public void OnError(Exception error)
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{
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}
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public void OnNext(DiagnosticListener value)
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{
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if (_currentListener.Value != this)
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{
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// Ignore events that aren't for this listener
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return;
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}
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if (value.Name == "Microsoft.Extensions.Hosting")
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{
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_disposable = value.Subscribe(this);
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}
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}
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public void OnNext(KeyValuePair<string, object?> value)
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{
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if (_currentListener.Value != this)
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{
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// Ignore events that aren't for this listener
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return;
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}
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if (value.Key == "HostBuilding")
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{
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_configure?.Invoke(value.Value!);
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}
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if (value.Key == "HostBuilt")
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{
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_hostTcs.TrySetResult(value.Value!);
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if (_stopApplication)
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{
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// Stop the host from running further
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throw new StopTheHostException();
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}
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}
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}
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private sealed class StopTheHostException : Exception
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{
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}
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}
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}
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}

‎src/Mvc/Mvc.Testing/src/Microsoft.AspNetCore.Mvc.Testing.csproj

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<Reference Include="Microsoft.AspNetCore.Mvc.Core" />
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<Reference Include="Microsoft.Extensions.DependencyModel" />
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<Reference Include="Microsoft.Extensions.Hosting" />
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<Reference Include="Microsoft.Extensions.HostFactoryResolver.Sources" />
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<!-- <Reference Include="Microsoft.Extensions.HostFactoryResolver.Sources" /> -->
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</ItemGroup>
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<ItemGroup>

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