Load IConfigurationProviders once in WebApplicationBuilder (#37039)

Author: halter73

src/DefaultBuilder/src/ConfigurationProviderSource.cs

@@ -0,0 +1,99 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Collections;
+using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.Primitives;
+
+namespace Microsoft.AspNetCore.Builder
+{
+    internal sealed class ConfigurationProviderSource : IConfigurationSource
+    {
+        private readonly IConfigurationProvider _configurationProvider;
+
+        public ConfigurationProviderSource(IConfigurationProvider configurationProvider)
+        {
+            _configurationProvider = configurationProvider;
+        }
+
+        public IConfigurationProvider Build(IConfigurationBuilder builder)
+        {
+            return new IgnoreFirstLoadConfigurationProvider(_configurationProvider);
+        }
+
+        // These providers have already been loaded, so no need to reload initially.
+        // Otherwise, providers that cannot be reloaded like StreamConfigurationProviders will fail.
+        private sealed class IgnoreFirstLoadConfigurationProvider : IConfigurationProvider, IEnumerable<IConfigurationProvider>, IDisposable
+        {
+            private readonly IConfigurationProvider _provider;
+
+            private bool _hasIgnoredFirstLoad;
+
+            public IgnoreFirstLoadConfigurationProvider(IConfigurationProvider provider)
+            {
+                _provider = provider;
+            }
+
+            public IEnumerable<string> GetChildKeys(IEnumerable<string> earlierKeys, string parentPath)
+            {
+                return _provider.GetChildKeys(earlierKeys, parentPath);
+            }
+
+            public IChangeToken GetReloadToken()
+            {
+                return _provider.GetReloadToken();
+            }
+
+            public void Load()
+            {
+                if (!_hasIgnoredFirstLoad)
+                {
+                    _hasIgnoredFirstLoad = true;
+                    return;
+                }
+
+                _provider.Load();
+            }
+
+            public void Set(string key, string value)
+            {
+                _provider.Set(key, value);
+            }
+
+            public bool TryGet(string key, out string value)
+            {
+                return _provider.TryGet(key, out value);
+            }
+
+            // Provide access to the original IConfigurationProvider via a single-element IEnumerable to code that goes out of its way to look for it.
+            public IEnumerator<IConfigurationProvider> GetEnumerator() => GetUnwrappedEnumerable().GetEnumerator();
+
+            IEnumerator IEnumerable.GetEnumerator() => GetUnwrappedEnumerable().GetEnumerator();
+
+            public override bool Equals(object? obj)
+            {
+                return _provider.Equals(obj);
+            }
+
+            public override int GetHashCode()
+            {
+                return _provider.GetHashCode();
+            }
+
+            public override string? ToString()
+            {
+                return _provider.ToString();
+            }
+
+            public void Dispose()
+            {
+                (_provider as IDisposable)?.Dispose();
+            }
+
+            private IEnumerable<IConfigurationProvider> GetUnwrappedEnumerable()
+            {
+                yield return _provider;
+            }
+        }
+    }
+}

src/DefaultBuilder/src/TrackingChainedConfigurationSource.cs

@@ -0,0 +1,25 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using Microsoft.Extensions.Configuration;
+
+namespace Microsoft.AspNetCore.Builder
+{
+    internal sealed class TrackingChainedConfigurationSource : IConfigurationSource
+    {
+        private readonly ChainedConfigurationSource _chainedConfigurationSource = new();
+
+        public TrackingChainedConfigurationSource(ConfigurationManager configManager)
+        {
+            _chainedConfigurationSource.Configuration = configManager;
+        }
+
+        public IConfigurationProvider? BuiltProvider { get; set; }
+
+        public IConfigurationProvider Build(IConfigurationBuilder builder)
+        {
+            BuiltProvider = _chainedConfigurationSource.Build(builder);
+            return BuiltProvider;
+        }
+    }
+}

src/DefaultBuilder/src/WebApplication.cs

@@ -1,7 +1,6 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
-using System.Reflection;
 using Microsoft.AspNetCore.Hosting;
 using Microsoft.AspNetCore.Hosting.Server;
 using Microsoft.AspNetCore.Hosting.Server.Features;
@@ -20,11 +19,11 @@ namespace Microsoft.AspNetCore.Builder
     /// </summary>
     public sealed class WebApplication : IHost, IApplicationBuilder, IEndpointRouteBuilder, IAsyncDisposable
     {
+        internal const string GlobalEndpointRouteBuilderKey = "__GlobalEndpointRouteBuilder";
+
         private readonly IHost _host;
         private readonly List<EndpointDataSource> _dataSources = new();
 
-        internal static string GlobalEndpointRouteBuilderKey = "__GlobalEndpointRouteBuilder";
-
         internal WebApplication(IHost host)
         {
             _host = host;

src/DefaultBuilder/src/WebApplicationBuilder.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System.Diagnostics;
+using System.Linq;
 using Microsoft.AspNetCore.Hosting;
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.DependencyInjection;
@@ -15,11 +16,12 @@ namespace Microsoft.AspNetCore.Builder
     /// </summary>
     public sealed class WebApplicationBuilder
     {
+        private const string EndpointRouteBuilderKey = "__EndpointRouteBuilder";
+
         private readonly HostBuilder _hostBuilder = new();
         private readonly BootstrapHostBuilder _bootstrapHostBuilder;
         private readonly WebApplicationServiceCollection _services = new();
         private readonly List<KeyValuePair<string, string>> _hostConfigurationValues;
-        private const string EndpointRouteBuilderKey = "__EndpointRouteBuilder";
 
         private WebApplication? _builtApplication;
 
@@ -62,7 +64,6 @@ internal WebApplicationBuilder(WebApplicationOptions options, Action<IHostBuilde
             });
 
             // Apply the args to host configuration last since ConfigureWebHostDefaults overrides a host specific setting (the application name).
-
             _bootstrapHostBuilder.ConfigureHostConfiguration(config =>
             {
                 if (args is { Length: > 0 })
@@ -74,7 +75,6 @@ internal WebApplicationBuilder(WebApplicationOptions options, Action<IHostBuilde
                 options.ApplyHostConfiguration(config);
             });
 
-
             Configuration = new();
 
             // Collect the hosted services separately since we want those to run after the user's hosted services
@@ -100,7 +100,7 @@ internal WebApplicationBuilder(WebApplicationOptions options, Action<IHostBuilde
             Host = new ConfigureHostBuilder(hostContext, Configuration, Services);
             WebHost = new ConfigureWebHostBuilder(webHostContext, Configuration, Services);
 
-            Services.AddSingleton<IConfiguration>(Configuration);
+            Services.AddSingleton<IConfiguration>(_ => Configuration);
         }
 
         /// <summary>
@@ -148,14 +148,13 @@ public WebApplication Build()
                 builder.AddInMemoryCollection(_hostConfigurationValues);
             });
 
-            // Wire up the application configuration by copying the already built configuration providers over to final configuration builder.
-            // We wrap the existing provider in a configuration source to avoid re-bulding the already added configuration sources.
+            // Wire up the _hostBuilder's application configuration with a ChainedConfigurationSource to the ConfigurationManager.
+            // We use a "tracking" source to avoid creating a circular reference when copying providers in ConfigureServices.
+            var chainedConfigSource = new TrackingChainedConfigurationSource(Configuration);
+
             _hostBuilder.ConfigureAppConfiguration(builder =>
             {
-                foreach (var provider in ((IConfigurationRoot)Configuration).Providers)
-                {
-                    builder.Sources.Add(new ConfigurationProviderSource(provider));
-                }
+                builder.Add(chainedConfigSource);
 
                 foreach (var (key, value) in ((IConfigurationBuilder)Configuration).Properties)
                 {
@@ -173,17 +172,6 @@ public WebApplication Build()
                 // we called ConfigureWebHostDefaults on both the _deferredHostBuilder and _hostBuilder.
                 foreach (var s in _services)
                 {
-                    // Skip the configuration manager instance we added earlier
-                    // we're already going to wire it up to this new configuration source
-                    // after we've built the application. There's a chance the user manually added
-                    // this as well but we still need to remove it from the final configuration
-                    // to avoid cycles in the configuration graph
-                    if (s.ServiceType == typeof(IConfiguration) &&
-                        s.ImplementationInstance == Configuration)
-                    {
-                        continue;
-                    }
-
                     services.Add(s);
                 }
 
@@ -205,21 +193,41 @@ public WebApplication Build()
                 // Drop the reference to the existing collection and set the inner collection
                 // to the new one. This allows code that has references to the service collection to still function.
                 _services.InnerCollection = services;
+
+                var hostBuilderProviders = ((IConfigurationRoot)context.Configuration).Providers;
+
+                if (!hostBuilderProviders.Contains(chainedConfigSource.BuiltProvider))
+                {
+                    // Something removed the _hostBuilder's TrackingChainedConfigurationSource pointing back to the ConfigurationManager.
+                    // This is likely a test using WebApplicationFactory. Replicate the effect by clearing the ConfingurationManager sources.
+                    ((IConfigurationBuilder)Configuration).Sources.Clear();
+                }
+
+                // Make the ConfigurationManager match the final _hostBuilder's configuration. To do that, we add the additional providers
+                // to the inner _hostBuilders's configuration to the ConfigurationManager. We wrap the existing provider in a
+                // configuration source to avoid rebulding or reloading the already added configuration sources.
+                foreach (var provider in hostBuilderProviders)
+                {
+                    // Avoid creating a circular reference to the ConfigurationManager via the chained configuration source.
+                    if (!ReferenceEquals(provider, chainedConfigSource.BuiltProvider))
+                    {
+                        ((IConfigurationBuilder)Configuration).Add(new ConfigurationProviderSource(provider));
+                    }
+                }
             });
 
             // Run the other callbacks on the final host builder
             Host.RunDeferredCallbacks(_hostBuilder);
 
             _builtApplication = new WebApplication(_hostBuilder.Build());
 
-            // Make builder.Configuration match the final configuration. To do that
-            // we clear the sources and add the built configuration as a source
-            ((IConfigurationBuilder)Configuration).Sources.Clear();
-            Configuration.AddConfiguration(_builtApplication.Configuration);
-
             // Mark the service collection as read-only to prevent future modifications
             _services.IsReadOnly = true;
 
+            // Resolve both the _hostBuilder's Configuration and builder.Configuration to mark both as resolved within the
+            // service provider ensuring both will be properly disposed with the provider.
+            _ = _builtApplication.Services.GetService<IEnumerable<IConfiguration>>();
+
             return _builtApplication;
         }
 
@@ -300,20 +308,5 @@ public LoggingBuilder(IServiceCollection services)
 
             public IServiceCollection Services { get; }
         }
-
-        private sealed class ConfigurationProviderSource : IConfigurationSource
-        {
-            private readonly IConfigurationProvider _configurationProvider;
-
-            public ConfigurationProviderSource(IConfigurationProvider configurationProvider)
-            {
-                _configurationProvider = configurationProvider;
-            }
-
-            public IConfigurationProvider Build(IConfigurationBuilder builder)
-            {
-                return _configurationProvider;
-            }
-        }
     }
 }