Add complex media type API version reader support. Resolves #887

src/AspNet/WebApi/src/Asp.Versioning.WebApi/MediaTypeApiVersionReaderBuilder.cs

@@ -0,0 +1,123 @@
+// Copyright (c) .NET Foundation and contributors. All rights reserved.
+
+namespace Asp.Versioning;
+
+using Asp.Versioning.Routing;
+using System.Globalization;
+using System.Net.Http.Headers;
+using System.Web.Http.Routing;
+
+/// <content>
+/// Provides additional implementation specific to ASP.NET Web API.
+/// </content>
+public partial class MediaTypeApiVersionReaderBuilder
+{
+    /// <summary>
+    /// Adds a template used to read an API version from a media type.
+    /// </summary>
+    /// <param name="template">The template used to match the media type.</param>
+    /// <param name="parameterName">The optional name of the API version parameter in the template.
+    /// If a value is not specified, there is expected to be a single template parameter.</param>
+    /// <returns>The current <see cref="MediaTypeApiVersionReaderBuilder"/>.</returns>
+    /// <remarks>The template syntax is the same used by route templates; however, constraints are not supported.</remarks>
+#pragma warning disable CA1716 // Identifiers should not match keywords
+    public virtual MediaTypeApiVersionReaderBuilder Template( string template, string? parameterName = default )
+#pragma warning restore CA1716 // Identifiers should not match keywords
+    {
+        if ( string.IsNullOrEmpty( template ) )
+        {
+            throw new ArgumentNullException( nameof( template ) );
+        }
+
+        if ( string.IsNullOrEmpty( parameterName ) )
+        {
+            var parser = new RouteParser();
+            var parsedRoute = parser.Parse( template );
+            var parameters = from content in parsedRoute.PathSegments.OfType<IPathContentSegment>()
+                             from parameter in content.Subsegments.OfType<IPathParameterSubsegment>()
+                             select parameter;
+
+            if ( parameters.Count() > 1 )
+            {
+                var message = string.Format( CultureInfo.CurrentCulture, CommonSR.InvalidMediaTypeTemplate, template );
+                throw new ArgumentException( message, nameof( template ) );
+            }
+        }
+
+        var route = new HttpRoute( template );
+
+        AddReader( mediaTypes => ReadMediaTypePattern( mediaTypes, route, parameterName ) );
+
+        return this;
+    }
+
+    private static IReadOnlyList<string> ReadMediaTypePattern(
+        IReadOnlyList<MediaTypeHeaderValue> mediaTypes,
+        HttpRoute route,
+        string? parameterName )
+    {
+        var assumeOneParameter = string.IsNullOrEmpty( parameterName );
+        var version = default( string );
+        var versions = default( List<string> );
+        using var request = new HttpRequestMessage();
+
+        for ( var i = 0; i < mediaTypes.Count; i++ )
+        {
+            var mediaType = mediaTypes[i].MediaType;
+            request.RequestUri = new Uri( "http://localhost/" + mediaType );
+            var data = route.GetRouteData( string.Empty, request );
+
+            if ( data == null )
+            {
+                continue;
+            }
+
+            var values = data.Values;
+
+            if ( values.Count == 0 )
+            {
+                continue;
+            }
+
+            object datum;
+
+            if ( assumeOneParameter )
+            {
+                datum = values.Values.First();
+            }
+            else if ( !values.TryGetValue( parameterName, out datum ) )
+            {
+                continue;
+            }
+
+            if ( datum is not string value || string.IsNullOrEmpty( value ) )
+            {
+                continue;
+            }
+
+            if ( version == null )
+            {
+                version = value;
+            }
+            else if ( versions == null )
+            {
+                versions = new( capacity: mediaTypes.Count - i + 1 )
+                {
+                    version,
+                    value,
+                };
+            }
+            else
+            {
+                versions.Add( value );
+            }
+        }
+
+        if ( version is null )
+        {
+            return Array.Empty<string>();
+        }
+
+        return versions is null ? new[] { version } : versions.ToArray();
+    }
+}