Add GetMessageTemplateProperties option

src/Serilog.AspNetCore/AspNetCore/RequestLoggingMiddleware.cs

@@ -18,6 +18,7 @@
 using Serilog.Extensions.Hosting;
 using Serilog.Parsing;
 using System;
+using System.Collections.Generic;
 using System.Diagnostics;
 using System.Linq;
 using System.Threading.Tasks;
@@ -32,6 +33,7 @@ class RequestLoggingMiddleware
         readonly MessageTemplate _messageTemplate;
         readonly Action<IDiagnosticContext, HttpContext> _enrichDiagnosticContext;
         readonly Func<HttpContext, double, Exception, LogEventLevel> _getLevel;
+        readonly Func<HttpContext, string, double, int, IEnumerable<LogEventProperty>> _getMessageTemplateProperties;
         readonly ILogger _logger;
         readonly bool _includeQueryInRequestPath;
         static readonly LogEventProperty[] NoProperties = new LogEventProperty[0];
@@ -47,6 +49,7 @@ public RequestLoggingMiddleware(RequestDelegate next, DiagnosticContext diagnost
             _messageTemplate = new MessageTemplateParser().Parse(options.MessageTemplate);
             _logger = options.Logger?.ForContext<RequestLoggingMiddleware>();
             _includeQueryInRequestPath = options.IncludeQueryInRequestPath;
+            _getMessageTemplateProperties = options.GetMessageTemplateProperties;
         }
 
         // ReSharper disable once UnusedMember.Global
@@ -90,13 +93,7 @@ bool LogCompletion(HttpContext httpContext, DiagnosticContextCollector collector
                 collectedProperties = NoProperties;
 
             // Last-in (correctly) wins...
-            var properties = collectedProperties.Concat(new[]
-            {
-                new LogEventProperty("RequestMethod", new ScalarValue(httpContext.Request.Method)),
-                new LogEventProperty("RequestPath", new ScalarValue(GetPath(httpContext, _includeQueryInRequestPath))),
-                new LogEventProperty("StatusCode", new ScalarValue(statusCode)),
-                new LogEventProperty("Elapsed", new ScalarValue(elapsedMs))
-            });
+            var properties = collectedProperties.Concat(_getMessageTemplateProperties(httpContext, GetPath(httpContext, _includeQueryInRequestPath), elapsedMs, statusCode));
 
             var evt = new LogEvent(DateTimeOffset.Now, level, ex ?? collectedException, _messageTemplate, properties);
             logger.Write(evt);
@@ -123,7 +120,7 @@ static string GetPath(HttpContext httpContext, bool includeQueryInRequestPath)
             {
                 requestPath = httpContext.Request.Path.ToString();
             }
-            
+
             return requestPath;
         }
     }

src/Serilog.AspNetCore/AspNetCore/RequestLoggingOptions.cs

@@ -15,6 +15,7 @@
 using Microsoft.AspNetCore.Http;
 using Serilog.Events;
 using System;
+using System.Collections.Generic;
 
 // ReSharper disable UnusedAutoPropertyAccessor.Global
 
@@ -34,6 +35,15 @@ static LogEventLevel DefaultGetLevel(HttpContext ctx, double _, Exception ex) =>
                 : ctx.Response.StatusCode > 499
                     ? LogEventLevel.Error
                     : LogEventLevel.Information;
+
+        IEnumerable<LogEventProperty> DefaultGetMessageTemplateProperties(HttpContext httpContext, string requestPath, double elapsedMs, int statusCode) =>
+            new[]
+            {
+                new LogEventProperty("RequestMethod", new ScalarValue(httpContext.Request.Method)),
+                new LogEventProperty("RequestPath", new ScalarValue(requestPath)),
+                new LogEventProperty("StatusCode", new ScalarValue(statusCode)),
+                new LogEventProperty("Elapsed", new ScalarValue(elapsedMs))
+            };
 
         /// <summary>
         /// Gets or sets the message template. The default value is
@@ -74,13 +84,19 @@ static LogEventLevel DefaultGetLevel(HttpContext ctx, double _, Exception ex) =>
         /// </summary>
         public bool IncludeQueryInRequestPath { get; set; }
 
+        /// <summary>
+        /// A function to specify the values of the MessageTemplateProperties.
+        /// </summary>
+        public Func<HttpContext, string, double, int, IEnumerable<LogEventProperty>> GetMessageTemplateProperties { get; set; }
+
         /// <summary>
         /// Constructor
         /// </summary>
         public RequestLoggingOptions()
         {
             GetLevel = DefaultGetLevel;
             MessageTemplate = DefaultRequestCompletionMessageTemplate;
+            GetMessageTemplateProperties = DefaultGetMessageTemplateProperties;
         }
     }
 }

test/Serilog.AspNetCore.Tests/SerilogWebHostBuilderExtensionsTests.cs

@@ -12,6 +12,8 @@
 using Microsoft.AspNetCore.Http;
 using Serilog.Filters;
 using Serilog.AspNetCore.Tests.Support;
+using Serilog.Events;
+using System.Net.Http;
 
 // Newer frameworks provide IHostBuilder
 #pragma warning disable CS0618
@@ -66,6 +68,34 @@ public async Task RequestLoggingMiddlewareShouldEnrich()
             Assert.True(completionEvent.Properties.ContainsKey("Elapsed"));
         }
 
+        [Fact]
+        public async Task RequestLoggingMiddlewareShouldEnrichWithCustomisedProperties()
+        {
+            var (sink, web) = Setup(options =>
+            {
+                options.MessageTemplate = "HTTP {RequestMethod} responded {Status} in {ElapsedMilliseconds:0.0000} ms";
+                options.GetMessageTemplateProperties = (ctx, path, elapsedMs, status) =>
+                    new[]
+                    {
+                            new LogEventProperty("RequestMethod", new ScalarValue(ctx.Request.Method)),
+                            new LogEventProperty("Status", new ScalarValue(status)),
+                            new LogEventProperty("ElapsedMilliseconds", new ScalarValue(elapsedMs))
+                    };
+            });
+
+            await web.CreateClient().GetAsync("/resource");
+
+            Assert.NotEmpty(sink.Writes);
+
+            var completionEvent = sink.Writes.First(logEvent => Matching.FromSource<RequestLoggingMiddleware>()(logEvent));
+
+            Assert.Equal("string", completionEvent.Properties["SomeString"].LiteralValue());
+            Assert.Equal(200, completionEvent.Properties["Status"].LiteralValue());
+            Assert.Equal("GET", completionEvent.Properties["RequestMethod"].LiteralValue());
+            Assert.True(completionEvent.Properties.ContainsKey("ElapsedMilliseconds"));
+            Assert.False(completionEvent.Properties.ContainsKey("Elapsed"));
+        }
+
         [Fact]
         public async Task RequestLoggingMiddlewareShouldEnrichWithCollectedExceptionIfNoUnhandledException()
         {