Tracing improvements (#311)

* Use TryGetProperty when extracting tracing metadata to prevent exception being thrown in absence thereof

* Use JsonDocument.TryParseValue

* Handle empty metadata case and dispose of JsonDocument if instantiated

* Implement short-circuit to improve performance when there are no active diagnostic listeners

Author: josephcummings

src/EventStore.Client/Common/Diagnostics/ActivitySourceExtensions.cs

@@ -32,6 +32,9 @@ public static void TraceSubscriptionEvent(
         EventStoreClientSettings settings,
         UserCredentials? userCredentials
     ) {
+	    if (source.HasNoActiveListeners())
+		    return;
+
         var parentContext = resolvedEvent.OriginalEvent.Metadata.ExtractPropagationContext();
 
         if (parentContext is null) return;
@@ -53,6 +56,9 @@ public static void TraceSubscriptionEvent(
         this ActivitySource source,
         string operationName, ActivityKind activityKind, ActivityTagsCollection? tags = null, ActivityContext? parentContext = null
     ) {
+	    if (source.HasNoActiveListeners())
+		    return null;
+	    
         (tags ??= new ActivityTagsCollection())
             .WithRequiredTag(TelemetryTags.Database.System, "eventstoredb")
             .WithRequiredTag(TelemetryTags.Database.Operation, operationName);
@@ -67,4 +73,6 @@ public static void TraceSubscriptionEvent(
             )
             ?.Start();
     }
+    
+    static bool HasNoActiveListeners(this ActivitySource source) => !source.HasListeners();
 }

src/EventStore.Client/Common/Diagnostics/EventMetadataExtensions.cs

@@ -17,19 +17,22 @@ public static ReadOnlySpan<byte> InjectTracingContext(this ReadOnlyMemory<byte>
 
 	[MethodImpl(MethodImplOptions.AggressiveInlining)]
 	public static TracingMetadata ExtractTracingMetadata(this ReadOnlyMemory<byte> eventMetadata) {
-		try {
-			using var doc = JsonDocument.Parse(eventMetadata);
+		if (eventMetadata.IsEmpty)
+			return TracingMetadata.None;
 
-			return new TracingMetadata(
-				doc.RootElement.GetProperty(TracingConstants.Metadata.TraceId).GetString(),
-				doc.RootElement.GetProperty(TracingConstants.Metadata.SpanId).GetString()
-			);
-		}
-		catch (Exception) {
+		var reader = new Utf8JsonReader(eventMetadata.Span);
+		if (!JsonDocument.TryParseValue(ref reader, out var doc))
 			return TracingMetadata.None;
+	
+		using (doc) {
+			if (!doc.RootElement.TryGetProperty(TracingConstants.Metadata.TraceId, out var traceId)
+			 || !doc.RootElement.TryGetProperty(TracingConstants.Metadata.SpanId, out var spanId))
+				return TracingMetadata.None;
+
+			return new TracingMetadata(traceId.GetString(), spanId.GetString());
 		}
 	}
-	
+
 	[MethodImpl(MethodImplOptions.AggressiveInlining)]
 	static ReadOnlySpan<byte> InjectTracingMetadata(this ReadOnlyMemory<byte> eventMetadata, TracingMetadata tracingMetadata) {
 		if (tracingMetadata == TracingMetadata.None || !tracingMetadata.IsValid)