Refactor GuidGenerator to work around ILRepack of System.Diagnostics.…

…DiagnosticSource

src/Agent/NewRelic/Agent/Core/Utilities/GuidGenerator.cs

@@ -2,9 +2,8 @@
 // SPDX-License-Identifier: Apache-2.0
 
 using NewRelic.Agent.Extensions.Logging;
+using NewRelic.Reflection;
 using System;
-using System.Diagnostics;
-using System.IO;
 using System.Security.Cryptography;
 using System.Threading;
 
@@ -31,25 +30,16 @@ public static string GenerateNewRelicGuid()
 
         public static string GenerateNewRelicTraceId()
         {
-            try
+            var retVal = _traceGeneratorFunc();
+            if (retVal == null)
             {
-                return _traceGeneratorFunc();
-            }
-            catch (Exception ex)
-            {
-                // If the app does not reference System.Diagnostics.DiagnosticSource then Activity.Current will not be available.
-                // A FileNotFoundException occurs when System.Diagnostics.DiagnosticSource is unavailble.
-
-                if (!(ex is FileNotFoundException))
-                {
-                    Log.Warn(ex, "Unexpected exception type when attempting to generate a trace ID from Activity.Current");
-                }
-
                 // Fall back to using our standard method of generating traceIds.
                 Log.Info($"Trace IDs will be generated using the standard generator");
                 Interlocked.Exchange(ref _traceGeneratorFunc, GenerateTraceId);
                 return _traceGeneratorFunc();
             }
+
+            return retVal;
         }
 
         private static string GenerateTraceId()
@@ -63,12 +53,42 @@ private static string GenerateTraceId()
 
         private static string GetTraceIdFromCurrentActivity()
         {
-            if (Activity.Current != default && Activity.Current.IdFormat == ActivityIdFormat.W3C)
-            {
-                return Activity.Current.TraceId.ToString();
-            }
+            // because we ILRepack System.Diagnostics.DiagnosticSource, we have to look for the app's reference to it (if there is one)
+            // and use reflection to get the trace id from the current activity
+
+            // get list of loaded assemblies
+            var assemblies = AppDomain.CurrentDomain.GetAssemblies();
+            // find System.Diagnostics.DiagnosticSource
+            var diagnosticSourceAssembly = Array.Find(assemblies, a => a.FullName.StartsWith("System.Diagnostics.DiagnosticSource"));
+            if (diagnosticSourceAssembly == null) // customer app didn't reference the assembly
+                return null;
+
+            // find the Activity class
+            var activityType = diagnosticSourceAssembly.GetType("System.Diagnostics.Activity");
+
+            var fieldReadAccessor = VisibilityBypasser.Instance.GenerateFieldReadAccessor<object>(activityType, "s_current");
+            if (fieldReadAccessor == null)
+                return null;
+
+            var current = fieldReadAccessor(null);
+            // get the Value property
+            var valuePropertyAccessor = VisibilityBypasser.Instance.GeneratePropertyAccessor<object>(current.GetType(), "Value");
+            if (valuePropertyAccessor == null)
+                return null;
+            var value = valuePropertyAccessor(current);
+
+            // get IdFormat property
+            var idFormatGetter = VisibilityBypasser.Instance.GeneratePropertyAccessor<object>(value.GetType(), "IdFormat");
+            var idFormat = idFormatGetter(value);
+            if (idFormat == null || Enum.GetName(idFormat.GetType(), idFormat) != "W3C") // make sure it's in W3C trace id format
+                return null;
 
-            return GenerateTraceId();
+            // get TraceId property
+            var traceIdGetter = VisibilityBypasser.Instance.GeneratePropertyAccessor<object>(value.GetType(), "TraceId");
+            if (traceIdGetter == null)
+                return null;
+
+            return traceIdGetter(value).ToString();
         }
     }
 }