Convert StructureValue into IDictionary<string,object> when possible

Changed the way the fallback `ToString()` is applied so that array/dictionary/structure elements still have their essential structure when transmitted, even if their elements are not scalar (`ToRawValue()` scalarizes them).

src/Microsoft.Diagnostics.EventFlow.Inputs.Serilog/SerilogInput.cs

@@ -106,7 +106,7 @@ private EventData ToEventData(LogEvent logEvent)
             return eventData;
         }
 
-        private object ToRawValue(LogEventPropertyValue logEventValue)
+        private static object ToRawValue(LogEventPropertyValue logEventValue)
         {
             // Special-case a few types of LogEventPropertyValue that allow us to maintain better type fidelity.
             // For everything else take the default string rendering as the data.
@@ -119,20 +119,40 @@ private object ToRawValue(LogEventPropertyValue logEventValue)
             SequenceValue sequenceValue = logEventValue as SequenceValue;
             if (sequenceValue != null)
             {
-                object[] arrayResult = sequenceValue.Elements.OfType<ScalarValue>().Select(e => e.Value).ToArray();
+                object[] arrayResult = sequenceValue.Elements.Select(e => ToRawScalar(e)).ToArray();
                 if (arrayResult.Length == sequenceValue.Elements.Count)
                 {
                     // All values extracted successfully, it is a flat array of scalars
                     return arrayResult;
                 }
             }
 
+            StructureValue structureValue = logEventValue as StructureValue;
+            if (structureValue != null)
+            {
+                IDictionary<string, object> structureResult = new Dictionary<string, object>(structureValue.Properties.Count);
+                foreach (var property in structureValue.Properties)
+                {
+                    structureResult[property.Name] = ToRawScalar(property.Value);
+                }
+
+                if (structureResult.Count == structureValue.Properties.Count)
+                {
+                    if (structureValue.TypeTag != null)
+                    {
+                        structureResult["$type"] = structureValue.TypeTag;
+                    }
+
+                    return structureResult;
+                }
+            }
+
             DictionaryValue dictionaryValue = logEventValue as DictionaryValue;
             if (dictionaryValue != null)
             {
                 IDictionary<string, object> dictionaryResult = dictionaryValue.Elements
-                    .Where(kvPair => kvPair.Key.Value is string && kvPair.Value is ScalarValue)
-                    .ToDictionary(kvPair => (string)kvPair.Key.Value, kvPair => ((ScalarValue)kvPair.Value).Value);
+                    .Where(kvPair => kvPair.Key.Value is string)
+                    .ToDictionary(kvPair => (string)kvPair.Key.Value, kvPair => ToRawScalar(kvPair.Value));
                 if (dictionaryResult.Count == dictionaryValue.Elements.Count)
                 {
                     return dictionaryResult;
@@ -142,5 +162,16 @@ private object ToRawValue(LogEventPropertyValue logEventValue)
             // Fall back to string rendering of the value
             return logEventValue.ToString();
         }
+
+        private static object ToRawScalar(LogEventPropertyValue value)
+        {
+            ScalarValue scalarValue = value as ScalarValue;
+            if (scalarValue != null)
+            {
+                return scalarValue.Value;
+            }
+
+            return value.ToString();
+        }
     }
 }

test/Microsoft.Diagnostics.EventFlow.Inputs.Tests/SerilogInputTests.cs

@@ -8,6 +8,7 @@
 using Moq;
 using Serilog;
 using Xunit;
+using System.Collections.Generic;
 
 namespace Microsoft.Diagnostics.EventFlow.Inputs.Tests
 {
@@ -146,5 +147,25 @@ public void HandlesDuplicatePropertyNames()
                     Times.Exactly(2));
             }
         }
+
+        [Fact]
+        public void RepresentsStructuresAsRawDictionaries()
+        {
+            var healthReporterMock = new Mock<IHealthReporter>();
+            var observer = new Mock<IObserver<EventData>>();
+            using (var serilogInput = new SerilogInput(healthReporterMock.Object))
+            using (serilogInput.Subscribe(observer.Object))
+            {
+                var logger = new LoggerConfiguration().WriteTo.Observers(events => events.Subscribe(serilogInput)).CreateLogger();
+
+                var structure = new { A = "alpha", B = "bravo" };
+                logger.Information("Here is {@AStructure}", structure);
+
+                observer.Verify(s => s.OnNext(It.Is<EventData>(data =>
+                    ((IDictionary<string, object>)data.Payload["AStructure"])["A"].Equals("alpha") &&
+                    ((IDictionary<string, object>)data.Payload["AStructure"])["B"].Equals("bravo")
+                )));
+            }
+        }
     }
 }