Clear API versioning feature on reentry. Fixes #749. Resolves #748

Author: commonsensesoftware

src/Microsoft.AspNetCore.Mvc.Versioning/Versioning/ActionSelectionResult.cs

@@ -11,8 +11,8 @@
     [CLSCompliant( false )]
     public class ActionSelectionResult
     {
-        readonly HashSet<ActionDescriptor> candidateActions = new HashSet<ActionDescriptor>();
-        readonly HashSet<ActionDescriptor> matchingActions = new HashSet<ActionDescriptor>();
+        HashSet<ActionDescriptor>? candidateActions;
+        HashSet<ActionDescriptor>? matchingActions;
 
         /// <summary>
         /// Gets the best action descriptor match.
@@ -21,21 +21,21 @@ public class ActionSelectionResult
         /// <remarks>This property returns the first occurrence of a single match in the earliest iteration. If
         /// no matches exist in any iteration or multiple matches exist, this property returns <c>null</c>.</remarks>
         [CLSCompliant( false )]
-        public ActionDescriptor? BestMatch => MatchingActions.FirstOrDefault();
+        public ActionDescriptor? BestMatch => matchingActions?.FirstOrDefault();
 
         /// <summary>
         /// Gets a read-only collection of candidate actions.
         /// </summary>
         /// <value>A <see cref="IReadOnlyCollection{T}">read-only collection</see> of candidate <see cref="ActionDescriptor">actions</see>.</value>
         [CLSCompliant( false )]
-        public IReadOnlyCollection<ActionDescriptor> CandidateActions => candidateActions;
+        public IReadOnlyCollection<ActionDescriptor> CandidateActions => candidateActions ??= new();
 
         /// <summary>
         /// Gets a read-only collection of matching actions.
         /// </summary>
         /// <value>A <see cref="IReadOnlyCollection{T}">read-only collection</see> of <see cref="ActionDescriptor">matching actions</see>.</value>
         [CLSCompliant( false )]
-        public IReadOnlyCollection<ActionDescriptor> MatchingActions => matchingActions;
+        public IReadOnlyCollection<ActionDescriptor> MatchingActions => matchingActions ??= new();
 
         /// <summary>
         /// Adds the specified candidate actions to the selection result.
@@ -44,7 +44,7 @@ public class ActionSelectionResult
         /// to add to the selection result.</param>
         [CLSCompliant( false )]
         public void AddCandidates( IEnumerable<ActionDescriptor> actions ) =>
-            candidateActions.AddRange( actions ?? throw new ArgumentNullException( nameof( actions ) ) );
+            ( candidateActions ??= new() ).AddRange( actions ?? throw new ArgumentNullException( nameof( actions ) ) );
 
         /// <summary>
         /// Adds the specified matching actions to the selection result.
@@ -53,6 +53,16 @@ public void AddCandidates( IEnumerable<ActionDescriptor> actions ) =>
         /// to add to the selection result.</param>
         [CLSCompliant( false )]
         public void AddMatches( IEnumerable<ActionDescriptor> matches ) =>
-            matchingActions.AddRange( matches ?? throw new ArgumentNullException( nameof( matches ) ) );
+            ( matchingActions ??= new() ).AddRange( matches ?? throw new ArgumentNullException( nameof( matches ) ) );
+
+        /// <summary>
+        /// Clears the selection result.
+        /// </summary>
+        /// <remarks>The selection result should only ever be cleared if the routing middleware will be re-executed.</remarks>
+        public void Clear()
+        {
+            candidateActions?.Clear();
+            matchingActions?.Clear();
+        }
     }
 }

src/Microsoft.AspNetCore.Mvc.Versioning/Versioning/ApiVersioningFeature.cs

@@ -13,6 +13,7 @@ public sealed class ApiVersioningFeature : IApiVersioningFeature
         readonly HttpContext context;
         string? rawApiVersion;
         ApiVersion? apiVersion;
+        ActionSelectionResult? selectionResult;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="ApiVersioningFeature"/> class.
@@ -58,6 +59,6 @@ public ApiVersion? RequestedApiVersion
         }
 
         /// <inheritdoc />
-        public ActionSelectionResult SelectionResult { get; } = new ActionSelectionResult();
+        public ActionSelectionResult SelectionResult => selectionResult ??= new();
     }
 }

src/Microsoft.AspNetCore.Mvc.Versioning/Versioning/ApiVersioningMiddleware.cs

@@ -3,13 +3,19 @@
 namespace Microsoft.AspNetCore.Mvc.Versioning
 {
     using Microsoft.AspNetCore.Http;
+    using Microsoft.Extensions.Options;
     using System.Threading.Tasks;
 
     sealed class ApiVersioningMiddleware
     {
         readonly RequestDelegate next;
+        readonly bool usingLegacyRouting;
 
-        public ApiVersioningMiddleware( RequestDelegate next ) => this.next = next;
+        public ApiVersioningMiddleware( RequestDelegate next, IOptions<MvcOptions> options )
+        {
+            this.next = next;
+            usingLegacyRouting = !options.Value.EnableEndpointRouting;
+        }
 
         public Task InvokeAsync( HttpContext context )
         {
@@ -20,6 +26,15 @@ public Task InvokeAsync( HttpContext context )
                 feature = new ApiVersioningFeature( context );
                 context.Features.Set( feature );
             }
+            else
+            {
+                feature.RouteParameter = null;
+
+                if ( usingLegacyRouting )
+                {
+                    feature.SelectionResult.Clear();
+                }
+            }
 
             return next( context );
         }