Add NLog instrumentation for OpenTelemetry .NET Auto-Instrumentation

Directory.Packages.props

@@ -6,6 +6,8 @@
     <PackageVersion Include="DotNet.ReproducibleBuilds" Version="1.2.25" />
     <PackageVersion Include="log4net" Version="3.1.0" />
     <PackageVersion Include="MinVer" Version="6.0.0" />
+    <PackageVersion Include="NLog" Version="5.3.2" />
+    <PackageVersion Include="NLog.Extensions.Logging" Version="5.3.11" />
     <PackageVersion Include="OpenTelemetry" Version="1.12.0" />
     <PackageVersion Include="OpenTelemetry.Api" Version="1.12.0" />
     <PackageVersion Include="OpenTelemetry.Exporter.Console" Version="1.12.0" />

src/OpenTelemetry.AutoInstrumentation/.publicApi/net462/PublicAPI.Unshipped.txt

@@ -1,3 +1,4 @@
+OpenTelemetry.AutoInstrumentation.Instrumentations.NLog.Bridge.Integrations.TargetCollectionIntegration
 OpenTelemetry.AutoInstrumentation.Instrumentations.RabbitMqLegacy.Integrations.AsyncDefaultBasicConsumerIntegration
 OpenTelemetry.AutoInstrumentation.Instrumentations.RabbitMqLegacy.Integrations.DefaultBasicConsumerIntegration
 OpenTelemetry.AutoInstrumentation.Instrumentations.RabbitMqLegacy.Integrations.ModelBaseBasicGetIntegration

src/OpenTelemetry.AutoInstrumentation/.publicApi/net8.0/PublicAPI.Unshipped.txt

@@ -1,3 +1,4 @@
+OpenTelemetry.AutoInstrumentation.Instrumentations.NLog.Bridge.Integrations.TargetCollectionIntegration
 OpenTelemetry.AutoInstrumentation.Instrumentations.RabbitMqLegacy.Integrations.AsyncDefaultBasicConsumerIntegration
 OpenTelemetry.AutoInstrumentation.Instrumentations.RabbitMqLegacy.Integrations.DefaultBasicConsumerIntegration
 OpenTelemetry.AutoInstrumentation.Instrumentations.RabbitMqLegacy.Integrations.ModelBaseBasicGetIntegration

src/OpenTelemetry.AutoInstrumentation/Configurations/ConfigurationKeys.cs

@@ -223,6 +223,12 @@ public static class Logs
         /// </summary>
         public const string EnableLog4NetBridge = "OTEL_DOTNET_AUTO_LOGS_ENABLE_LOG4NET_BRIDGE";
 
+        /// <summary>
+        /// Configuration key for whether or not experimental NLog bridge
+        /// should be enabled.
+        /// </summary>
+        public const string EnableNLogBridge = "OTEL_DOTNET_AUTO_LOGS_ENABLE_NLOG_BRIDGE";
+
         /// <summary>
         /// Configuration key for disabling all log instrumentations.
         /// </summary>

src/OpenTelemetry.AutoInstrumentation/Configurations/LogInstrumentation.cs

@@ -17,4 +17,9 @@ internal enum LogInstrumentation
     /// Log4Net instrumentation.
     /// </summary>
     Log4Net = 1,
+
+    /// <summary>
+    /// NLog instrumentation.
+    /// </summary>
+    NLog = 2,
 }

src/OpenTelemetry.AutoInstrumentation/Configurations/LogSettings.cs

@@ -33,6 +33,11 @@ internal class LogSettings : Settings
     /// </summary>
     public bool EnableLog4NetBridge { get; private set; }
 
+    /// <summary>
+    /// Gets a value indicating whether the experimental NLog bridge is enabled.
+    /// </summary>
+    public bool EnableNLogBridge { get; private set; }
+
     /// <summary>
     /// Gets the list of enabled instrumentations.
     /// </summary>
@@ -54,6 +59,7 @@ protected override void OnLoad(Configuration configuration)
 
         IncludeFormattedMessage = configuration.GetBool(ConfigurationKeys.Logs.IncludeFormattedMessage) ?? false;
         EnableLog4NetBridge = configuration.GetBool(ConfigurationKeys.Logs.EnableLog4NetBridge) ?? false;
+        EnableNLogBridge = configuration.GetBool(ConfigurationKeys.Logs.EnableNLogBridge) ?? false;
 
         var instrumentationEnabledByDefault =
             configuration.GetBool(ConfigurationKeys.Logs.LogsInstrumentationEnabled) ??

src/OpenTelemetry.AutoInstrumentation/Generated/net8.0/SourceGenerators/SourceGenerators.InstrumentationDefinitionsGenerator/InstrumentationDefinitions.g.cs

@@ -17,7 +17,7 @@ internal static partial class InstrumentationDefinitions
 {
     private static NativeCallTargetDefinition[] GetDefinitionsArray()
     {
-        var nativeCallTargetDefinitions = new List<NativeCallTargetDefinition>(39);
+        var nativeCallTargetDefinitions = new List<NativeCallTargetDefinition>(40);
         // Traces
         var tracerSettings = Instrumentation.TracerSettings.Value;
         if (tracerSettings.TracesEnabled)
@@ -104,6 +104,12 @@ private static NativeCallTargetDefinition[] GetDefinitionsArray()
             {
                 nativeCallTargetDefinitions.Add(new("Microsoft.Extensions.Logging", "Microsoft.Extensions.Logging.LoggingBuilder", ".ctor", ["System.Void", "Microsoft.Extensions.DependencyInjection.IServiceCollection"], 9, 0, 0, 9, 65535, 65535, AssemblyFullName, "OpenTelemetry.AutoInstrumentation.Instrumentations.Logger.LoggingBuilderIntegration"));
             }
+
+            // NLog
+            if (logSettings.EnabledInstrumentations.Contains(LogInstrumentation.NLog))
+            {
+                nativeCallTargetDefinitions.Add(new("NLog", "NLog.Config.LoggingConfiguration", "GetConfiguredNamedTargets", ["NLog.Targets.Target[]"], 4, 0, 0, 6, 65535, 65535, AssemblyFullName, "OpenTelemetry.AutoInstrumentation.Instrumentations.NLog.Bridge.Integrations.TargetCollectionIntegration"));
+            }
         }
 
         // Metrics

src/OpenTelemetry.AutoInstrumentation/Instrumentations/NLog/Bridge/Integrations/TargetCollectionIntegration.cs

@@ -0,0 +1,77 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+using OpenTelemetry.AutoInstrumentation.CallTarget;
+using OpenTelemetry.AutoInstrumentation.Logging;
+#if NET
+using OpenTelemetry.AutoInstrumentation.Logger;
+#endif
+
+namespace OpenTelemetry.AutoInstrumentation.Instrumentations.NLog.Bridge.Integrations;
+
+/// <summary>
+/// NLog Target Collection integration.
+/// This integration hooks into NLog's target collection methods to automatically
+/// inject the OpenTelemetry target when the NLog bridge is enabled.
+///
+/// The integration targets NLog's LoggingConfiguration.GetConfiguredNamedTargets method
+/// which is called when NLog retrieves the list of configured targets.
+/// </summary>
+[InstrumentMethod(
+assemblyName: "NLog",
+typeName: "NLog.Config.LoggingConfiguration",
+methodName: "GetConfiguredNamedTargets",
+returnTypeName: "NLog.Targets.Target[]",
+parameterTypeNames: new string[0],
+minimumVersion: "4.0.0",
+maximumVersion: "6.*.*",
+integrationName: "NLog",
+type: InstrumentationType.Log)]
+public static class TargetCollectionIntegration
+{
+#if NET
+    private static readonly IOtelLogger Logger = OtelLogging.GetLogger();
+    private static int _warningLogged;
+#endif
+
+    /// <summary>
+    /// Intercepts the completion of NLog's GetConfiguredNamedTargets method.
+    /// This method is called after NLog has retrieved its configured targets,
+    /// allowing us to inject the OpenTelemetry target into the collection.
+    /// </summary>
+    /// <typeparam name="TTarget">The type of the target being returned.</typeparam>
+    /// <typeparam name="TReturn">The type of the return value (target array).</typeparam>
+    /// <param name="instance">The LoggingConfiguration instance.</param>
+    /// <param name="returnValue">The array of configured targets returned by NLog.</param>
+    /// <param name="exception">Any exception that occurred during the method execution.</param>
+    /// <param name="state">The call target state.</param>
+    /// <returns>A CallTargetReturn containing the modified target array with the OpenTelemetry target injected.</returns>
+    internal static CallTargetReturn<TReturn> OnMethodEnd<TTarget, TReturn>(TTarget instance, TReturn returnValue, Exception exception, in CallTargetState state)
+    {
+#if NET
+        // Check if ILogger bridge has been initialized and warn if so
+        // This prevents conflicts between different logging bridges
+        if (LoggerInitializer.IsInitializedAtLeastOnce)
+        {
+            if (Interlocked.Exchange(ref _warningLogged, 1) != default)
+            {
+                return new CallTargetReturn<TReturn>(returnValue);
+            }
+
+            Logger.Warning("Disabling addition of NLog bridge due to ILogger bridge initialization.");
+            return new CallTargetReturn<TReturn>(returnValue);
+        }
+#endif
+
+        // Only inject the target if the NLog bridge is enabled and we have a valid target array
+        if (Instrumentation.LogSettings.Value.EnableNLogBridge && returnValue is Array targetsArray)
+        {
+            // Use the target initializer to inject the OpenTelemetry target
+            var modifiedTargets = OpenTelemetryTargetInitializer<TReturn>.Initialize(targetsArray);
+            return new CallTargetReturn<TReturn>(modifiedTargets);
+        }
+
+        // Return the original targets if injection is not enabled or not applicable
+        return new CallTargetReturn<TReturn>(returnValue);
+    }
+}