Log4JXmlEventLayout - Added support for configuration of Parameters

src/NLog/LayoutRenderers/Log4JXmlEventLayoutRenderer.cs

@@ -370,15 +370,20 @@ private static void AppendException(LogEventInfo logEvent, XmlWriter xtw)
 
         private void AppendParameters(LogEventInfo logEvent, XmlWriter xtw)
         {
-            if (Parameters.Count > 0)
+            for (int i = 0; i < Parameters?.Count; ++i)
             {
-                foreach (NLogViewerParameterInfo parameter in Parameters)
-                {
-                    xtw.WriteStartElement("log4j", "data", dummyNamespace);
-                    xtw.WriteAttributeSafeString("name", parameter.Name);
-                    xtw.WriteAttributeSafeString("value", parameter.Layout.Render(logEvent));
-                    xtw.WriteEndElement();
-                }
+                var parameter = Parameters[i];
+                if (string.IsNullOrEmpty(parameter?.Name))
+                    continue;
+
+                var parameterValue = parameter.Layout?.Render(logEvent) ?? string.Empty;
+                if (!parameter.IncludeEmptyValue && string.IsNullOrEmpty(parameterValue))
+                    continue;
+
+                xtw.WriteStartElement("log4j", "data", dummyNamespace);
+                xtw.WriteAttributeSafeString("name", parameter.Name);
+                xtw.WriteAttributeSafeString("value", parameterValue);
+                xtw.WriteEndElement();
             }
         }
 

src/NLog/Layouts/JsonAttribute.cs

@@ -41,6 +41,7 @@ namespace NLog.Layouts
     [NLogConfigurationItem]
     [ThreadAgnostic]
     [ThreadSafe]
+    [AppDomainFixedOutput]
     public class JsonAttribute
     {
         /// <summary>

src/NLog/Layouts/Log4JXmlEventLayout.cs

@@ -33,9 +33,11 @@
 
 namespace NLog.Layouts
 {
+    using System.Collections.Generic;
     using System.Text;
     using NLog.Config;
     using NLog.LayoutRenderers;
+    using NLog.Targets;
 
     /// <summary>
     /// A specialized layout that renders Log4j-compatible XML events.
@@ -55,12 +57,22 @@ public class Log4JXmlEventLayout : Layout, IIncludeContext
         public Log4JXmlEventLayout()
         {
             Renderer = new Log4JXmlEventLayoutRenderer();
+            Parameters = new List<NLogViewerParameterInfo>();
+            Renderer.Parameters = Parameters;
         }
 
         /// <summary>
         /// Gets the <see cref="Log4JXmlEventLayoutRenderer"/> instance that renders log events.
         /// </summary>
-        public Log4JXmlEventLayoutRenderer Renderer { get; private set; }
+        public Log4JXmlEventLayoutRenderer Renderer { get; }
+
+        /// <summary>
+        /// Gets the collection of parameters. Each parameter contains a mapping
+        /// between NLog layout and a named parameter.
+        /// </summary>
+        /// <docgen category='Payload Options' order='10' />
+        [ArrayParameter(typeof(NLogViewerParameterInfo), "parameter")]
+        public IList<NLogViewerParameterInfo> Parameters { get => Renderer.Parameters; set => Renderer.Parameters = value;  }
 
         /// <summary>
         /// Gets or sets a value indicating whether to include contents of the <see cref="MappedDiagnosticsContext"/> dictionary.

src/NLog/Targets/NLogViewerParameterInfo.cs

@@ -40,6 +40,9 @@ namespace NLog.Targets
     /// Represents a parameter to a NLogViewer target.
     /// </summary>
     [NLogConfigurationItem]
+    [ThreadAgnostic]
+    [ThreadSafe]
+    [AppDomainFixedOutput]
     public class NLogViewerParameterInfo
     {
         /// <summary>
@@ -62,5 +65,11 @@ public NLogViewerParameterInfo()
         /// <docgen category='Parameter Options' order='10' />
         [RequiredParameter]
         public Layout Layout { get; set; }
+
+        /// <summary>
+        /// Gets or sets whether an attribute with empty value should be included in the output
+        /// </summary>
+        /// <docgen category='Parameter Options' order='100' />
+        public bool IncludeEmptyValue { get; set; } = true;
     }
 }

tests/NLog.UnitTests/LayoutRenderers/Log4JXmlTests.cs

@@ -31,19 +31,20 @@
 // THE POSSIBILITY OF SUCH DAMAGE.
 // 
 
-using System.Collections.Generic;
-using NLog.Config;
-
 namespace NLog.UnitTests.LayoutRenderers
 {
-    using System.Threading;
-    using System.Diagnostics;
     using System;
-    using System.Xml;
-    using System.Reflection;
+    using System.Collections.Generic;
+    using System.Diagnostics;
     using System.IO;
-    using Xunit;
+    using System.Reflection;
+    using System.Threading;
+    using System.Xml;
+    using NLog.Config;
     using NLog.Internal;
+    using NLog.Layouts;
+    using NLog.Targets;
+    using Xunit;
 
     public class Log4JXmlTests : NLogTestBase
     {
@@ -53,8 +54,8 @@ public void Log4JXmlTest()
             LogManager.Configuration = XmlLoggingConfiguration.CreateFromXmlString(@"
             <nlog throwExceptions='true'>
                 <targets>
-        <target name='debug' type='Debug' layout='${log4jxmlevent:includeCallSite=true:includeSourceInfo=true:includeNdlc=true:includeMdc=true:IncludeNdc=true:includeMdlc=true:IncludeAllProperties=true:ndcItemSeparator=\:\::includenlogdata=true:loggerName=${logger}}' />
-       </targets>
+                    <target name='debug' type='Debug' layout='${log4jxmlevent:includeCallSite=true:includeSourceInfo=true:includeNdlc=true:includeMdc=true:IncludeNdc=true:includeMdlc=true:IncludeAllProperties=true:ndcItemSeparator=\:\::includenlogdata=true:loggerName=${logger}}' />
+                </targets>
                 <rules>
                     <logger name='*' minlevel='Debug' writeTo='debug' />
                 </rules>
@@ -235,6 +236,35 @@ public void Log4JXmlTest()
             }
         }
 
+        [Fact]
+        void Log4JXmlEventLayoutParameterTest()
+        {
+            var log4jLayout = new Log4JXmlEventLayout()
+            {
+                Parameters =
+                {
+                    new NLogViewerParameterInfo
+                    {
+                        Name = "mt",
+                        Layout = "${message:raw=true}",
+                    }
+                },
+            };
+            log4jLayout.Renderer.AppInfo = "MyApp";
+            var logEventInfo = new LogEventInfo
+            {
+                LoggerName = "MyLOgger",
+                TimeStamp = new DateTime(2010, 01, 01, 12, 34, 56, DateTimeKind.Utc),
+                Level = LogLevel.Info,
+                Message = "hello, {0}",
+                Parameters = new[] { "world" },
+            };
+
+            var threadid = Environment.CurrentManagedThreadId;
+            var machinename = Environment.MachineName;
+            Assert.Equal($"<log4j:event logger=\"MyLOgger\" level=\"INFO\" timestamp=\"1262349296000\" thread=\"{threadid}\"><log4j:message>hello, world</log4j:message><log4j:properties><log4j:data name=\"mt\" value=\"hello, {{0}}\" /><log4j:data name=\"log4japp\" value=\"MyApp\" /><log4j:data name=\"log4jmachinename\" value=\"{machinename}\" /></log4j:properties></log4j:event>", log4jLayout.Render(logEventInfo)); 
+        }
+
         [Fact]
         void BadXmlValueTest()
         {