Add a diagnostic source event that fires when a route is matched

src/Http/Routing/src/EndpointRoutingMiddleware.cs

@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
+using System.Diagnostics;
 using System.Runtime.CompilerServices;
 using System.Threading;
 using System.Threading.Tasks;
@@ -13,9 +14,12 @@ namespace Microsoft.AspNetCore.Routing
 {
     internal sealed class EndpointRoutingMiddleware
     {
+        private const string DiagnosticsRouteMatchedKey = "Microsoft.AspNetCore.Routing.RouteMatched";
+
         private readonly MatcherFactory _matcherFactory;
         private readonly ILogger _logger;
         private readonly EndpointDataSource _endpointDataSource;
+        private readonly DiagnosticListener _diagnosticListener;
         private readonly RequestDelegate _next;
 
         private Task<Matcher> _initializationTask;
@@ -24,6 +28,7 @@ public EndpointRoutingMiddleware(
             MatcherFactory matcherFactory,
             ILogger<EndpointRoutingMiddleware> logger,
             IEndpointRouteBuilder endpointRouteBuilder,
+            DiagnosticListener diagnosticListener,
             RequestDelegate next)
         {
             if (matcherFactory == null)
@@ -48,6 +53,7 @@ public EndpointRoutingMiddleware(
 
             _matcherFactory = matcherFactory;
             _logger = logger;
+            _diagnosticListener = diagnosticListener;
             _next = next;
 
             _endpointDataSource = new CompositeEndpointDataSource(endpointRouteBuilder.DataSources);
@@ -106,6 +112,13 @@ private Task SetRoutingAndContinue(HttpContext httpContext)
             }
             else
             {
+                // Raise an event if the route matched
+                if (_diagnosticListener.IsEnabled() && _diagnosticListener.IsEnabled(DiagnosticsRouteMatchedKey))
+                {
+                    // We're just going to send the HttpContext since it has all of the relevant information
+                    _diagnosticListener.Write(DiagnosticsRouteMatchedKey, httpContext);
+                }
+
                 Log.MatchSuccess(_logger, endpoint);
             }
 

src/Http/Routing/test/UnitTests/EndpointRoutingMiddlewareTest.cs

@@ -2,6 +2,8 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
+using System.Collections.Generic;
+using System.Diagnostics;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Builder;
 using Microsoft.AspNetCore.Http;
@@ -57,16 +59,26 @@ public async Task Invoke_OnCall_WritesToConfiguredLogger()
         {
             // Arrange
             var expectedMessage = "Request matched endpoint 'Test endpoint'";
+            bool eventFired = true;
 
             var sink = new TestSink(
                 TestSink.EnableWithTypeName<EndpointRoutingMiddleware>,
                 TestSink.EnableWithTypeName<EndpointRoutingMiddleware>);
             var loggerFactory = new TestLoggerFactory(sink, enabled: true);
+            var listener = new DiagnosticListener("TestListener");
+
+            listener.Subscribe(new DelegateObserver(pair =>
+            {
+                eventFired = true;
+
+                Assert.Equal("Microsoft.AspNetCore.Routing.RouteMatched", pair.Key);
+                Assert.IsAssignableFrom<HttpContext>(pair.Value);
+            }));
 
             var httpContext = CreateHttpContext();
 
             var logger = new Logger<EndpointRoutingMiddleware>(loggerFactory);
-            var middleware = CreateMiddleware(logger);
+            var middleware = CreateMiddleware(logger, listener: listener);
 
             // Act
             await middleware.Invoke(httpContext);
@@ -75,6 +87,7 @@ public async Task Invoke_OnCall_WritesToConfiguredLogger()
             Assert.Empty(sink.Scopes);
             var write = Assert.Single(sink.Writes);
             Assert.Equal(expectedMessage, write.State?.ToString());
+            Assert.True(eventFired);
         }
 
         [Fact]
@@ -159,19 +172,46 @@ private HttpContext CreateHttpContext()
         private EndpointRoutingMiddleware CreateMiddleware(
             Logger<EndpointRoutingMiddleware> logger = null,
             MatcherFactory matcherFactory = null,
+            DiagnosticListener listener = null,
             RequestDelegate next = null)
         {
             next ??= c => Task.CompletedTask;
             logger ??= new Logger<EndpointRoutingMiddleware>(NullLoggerFactory.Instance);
             matcherFactory ??= new TestMatcherFactory(true);
+            listener ??= new DiagnosticListener("Microsoft.AspNet");
 
             var middleware = new EndpointRoutingMiddleware(
                 matcherFactory,
                 logger,
                 new DefaultEndpointRouteBuilder(Mock.Of<IApplicationBuilder>()),
+                listener,
                 next);
 
             return middleware;
         }
+
+        private class DelegateObserver : IObserver<KeyValuePair<string, object>>
+        {
+            private readonly Action<KeyValuePair<string, object>> _onNext;
+
+            public DelegateObserver(Action<KeyValuePair<string,object>> onNext)
+            {
+                _onNext = onNext;
+            }
+            public void OnCompleted()
+            {
+
+            }
+
+            public void OnError(Exception error)
+            {
+
+            }
+
+            public void OnNext(KeyValuePair<string, object> value)
+            {
+                _onNext(value);
+            }
+        }
     }
 }