Added Layout renderer for ASP.NET Request route parameters (#740)

* Added Layout renderer for ASP.NET Request route parameters

* Added unit tests of AspNetRequestRouteParametersRenderer

src/Shared/LayoutRenderers/AspNetRequestRouteParametersRenderer.cs

@@ -0,0 +1,87 @@
+using System.Text;
+using NLog.LayoutRenderers;
+using System.Collections.Generic;
+using System.Linq;
+#if !ASP_NET_CORE
+using System.Web.Routing;
+#else
+using Microsoft.AspNetCore.Routing;
+#endif
+
+namespace NLog.Web.LayoutRenderers
+{
+    /// <summary>
+    /// ASP.NET Request Route Parameters
+    /// </summary>
+    /// <example>
+    /// <para>Example usage of ${aspnet-request-routeparameters}:</para>
+    /// <code lang="NLog Layout Renderer">
+    /// ${aspnet-request-routeparameters:OutputFormat=Flat}
+    /// ${aspnet-request-routeparameters:OutputFormat=JsonArray}
+    /// ${aspnet-request-routeparameters:OutputFormat=JsonDictionary}
+    /// </code>
+    /// </example>
+    [LayoutRenderer("aspnet-request-routeparameters")]
+    public class AspNetRequestRouteParametersRenderer : AspNetLayoutMultiValueRendererBase
+    {
+        /// <summary>
+        /// List Route Parameter' Key to be rendered from Request.
+        /// If empty, then render all parameters
+        /// </summary>
+        public List<string> RouteParameterKeys { get; set; }
+
+        /// <summary>
+        /// Renders the specified ASP.NET Route Parameters and appends it to the specified <see cref="StringBuilder" />.
+        /// </summary>
+        /// <param name="builder"></param>
+        /// <param name="logEvent"></param>
+        protected override void DoAppend(StringBuilder builder, LogEventInfo logEvent)
+        {
+            var context = HttpContextAccessor.HttpContext;
+            if (context == null)
+            {
+                return;
+            }
+
+#if !ASP_NET_CORE
+            RouteValueDictionary routeParameters = RouteTable.Routes?.GetRouteData(context)?.Values;
+#else
+            RouteValueDictionary routeParameters = context.GetRouteData()?.Values;
+#endif
+
+            bool printAllRouteParameter = RouteParameterKeys == null || RouteParameterKeys.Count == 0;
+            List<string> routeParameterKeys = RouteParameterKeys;
+            if (routeParameters == null || routeParameters.Count == 0)
+            {
+                return;
+            }
+
+            if (printAllRouteParameter)
+            {
+                routeParameterKeys = routeParameters.Keys.ToList();
+            }
+
+            IEnumerable<KeyValuePair<string, string>> pairs = GetPairs(routeParameters, routeParameterKeys);
+            SerializePairs(pairs, builder, logEvent);
+        }
+
+        private static IEnumerable<KeyValuePair<string, string>> GetPairs(RouteValueDictionary routeParameters, List<string> routeParameterKeys)
+        {
+            foreach (string key in routeParameterKeys)
+            {
+                // This platform specific code is to prevent an unncessary .ToString call otherwise. 
+
+                if (!routeParameters.TryGetValue(key, out object objValue))
+                {
+                    continue;
+                }
+
+                string value = objValue.ToString();
+                if (!string.IsNullOrEmpty(value))
+                {
+                    yield return new KeyValuePair<string, string>(key, value);
+                }
+            }
+        }
+    }
+}

tests/Shared/LayoutRenderers/AspNetRequestRouteParametersRendererTests.cs

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+using System;
+using System.Collections.Generic;
+using NLog.Web.LayoutRenderers;
+using NLog.Web.Enums;
+using Xunit;
+using System.Collections.Specialized;
+using NSubstitute;
+#if ASP_NET_CORE
+using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Http.Features;
+using Microsoft.AspNetCore.Routing;
+#endif
+
+namespace NLog.Web.Tests.LayoutRenderers
+{
+    public class AspNetRequestRouteParametersRendererTests : LayoutRenderersTestBase<AspNetRequestRouteParametersRenderer>
+    {
+        [Fact]
+        public void NullRouteParametersRenderersEmptyString()
+        {
+            // Arrange
+            var (renderer, httpContext) = CreateWithHttpContext();
+
+            AddRoutingFeature(httpContext);
+
+            // Act
+            string result = renderer.Render(LogEventInfo.CreateNullEvent());
+
+            // Assert
+            Assert.Empty(result);
+        }
+
+#if ASP_NET_CORE
+        [Fact]
+        public void NullKeyRendersAllRouteParameters()
+        {
+            // Arrange
+            var (renderer, httpContext) = CreateWithHttpContext();
+            renderer.RouteParameterKeys = null;
+
+            SetupRouteParameters(httpContext);
+
+            // Act
+            string result = renderer.Render(LogEventInfo.CreateNullEvent());
+
+            // Assert
+            Assert.Equal("key1=value1,key2=value2", result);
+        }
+
+        [Fact]
+        public void SingleKeyRendersRouteParameter()
+        {
+            // Arrange
+            var (renderer, httpContext) = CreateWithHttpContext();
+            renderer.RouteParameterKeys = new List<string> { "key2" };
+
+            SetupRouteParameters(httpContext);
+
+            // Act
+            string result = renderer.Render(LogEventInfo.CreateNullEvent());
+
+            // Assert
+            Assert.Equal("key2=value2", result);
+        }
+
+        private void SetupRouteParameters(HttpContext httpContext)
+        {
+            var routeData = new RouteData();
+            var routingFeature = Substitute.For<IRoutingFeature>();
+            var collection = new FeatureCollection();
+            collection.Set(routingFeature);
+            httpContext.Features.Returns(collection);
+
+            routeData.Values.Add("key1", "value1");
+            routeData.Values.Add("key2", "value2");
+            routingFeature.RouteData.Returns(routeData);
+        }
+#endif
+    }
+}