Provide method to describe API versions for Minimal APIs.Relates to #812

Author: commonsensesoftware

src/AspNetCore/WebApi/src/Asp.Versioning.Mvc.ApiExplorer/IEndpointRouteBuilderExtensions.cs

@@ -0,0 +1,44 @@
+// Copyright (c) .NET Foundation and contributors. All rights reserved.
+
+namespace Microsoft.AspNetCore.Builder;
+
+using Asp.Versioning;
+using Asp.Versioning.ApiExplorer;
+using Microsoft.AspNetCore.Routing;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Options;
+
+/// <summary>
+/// Provides extension methods for <see cref="IEndpointRouteBuilder"/>.
+/// </summary>
+[CLSCompliant( false )]
+public static class IEndpointRouteBuilderExtensions
+{
+    /// <summary>
+    /// Returns a read-only list of API version descriptions.
+    /// </summary>
+    /// <param name="endpoints">The <see cref="IEndpointRouteBuilder">endpoints</see> to build the
+    /// API version descriptions from.</param>
+    /// <returns>A new <see cref="IReadOnlyList{T}">read-only list</see> of<see cref="ApiVersionDescription">API version descriptions</see>.</returns>
+    public static IReadOnlyList<ApiVersionDescription> DescribeApiVersions( this IEndpointRouteBuilder endpoints )
+    {
+        if ( endpoints == null )
+        {
+            throw new ArgumentNullException( nameof( endpoints ) );
+        }
+
+        // this should be produced by IApiVersionDescriptionProvider via di; however, for minimal apis, the
+        // endpoints in the registered EndpointDataSource may not have been built yet. this is important
+        // for the api explorer extensions (ex: openapi). the following is the same setup that would occur
+        // through via di, but the IEndpointRouteBuilder is expected to be the WebApplication used during
+        // setup. unfortunately, the behavior cannot simply be changed by replacing IApiVersionDescriptionProvider
+        // in the container for minimal apis, but that is not a common scenario. all the types and pieces
+        // necessary to change this behavior is still possible outside of this method, but it's on the developer
+        var source = new CompositeEndpointDataSource( endpoints.DataSources );
+        var policyManager = endpoints.ServiceProvider.GetRequiredService<ISunsetPolicyManager>();
+        var options = endpoints.ServiceProvider.GetRequiredService<IOptions<ApiExplorerOptions>>();
+        var provider = new DefaultApiVersionDescriptionProvider( source, policyManager, options );
+
+        return provider.ApiVersionDescriptions;
+    }
+}