propagate trace for http requests

dart/lib/src/http_client/tracing_client.dart

@@ -46,15 +46,28 @@ class TracingClient extends BaseClient {
 
     StreamedResponse? response;
     try {
-      if (span != null) {
-        if (containsTargetOrMatchesRegExp(
-            _hub.options.tracePropagationTargets, request.url.toString())) {
-          addSentryTraceHeader(span, request.headers);
-          addBaggageHeader(
+      if (containsTargetOrMatchesRegExp(
+          _hub.options.tracePropagationTargets, request.url.toString())) {
+        if (span != null) {
+          addSentryTraceHeaderFromSpan(span, request.headers);
+          addBaggageHeaderFromSpan(
             span,
             request.headers,
             logger: _hub.options.logger,
           );
+        } else {
+          final scope = _hub.scope;
+          final propagationContext = scope.propagationContext;
+
+          final traceHeader = SentryTraceHeader(
+              propagationContext.traceId, propagationContext.spanId);
+          addSentryTraceheader(traceHeader, request.headers);
+
+          final baggage = propagationContext.baggage;
+          if (baggage != null) {
+            final baggageHeader = SentryBaggageHeader.fromBaggage(baggage);
+            addBaggageHeader(baggageHeader, request.headers, logger: _hub.options.logger);
+          }
         }
       }
 

dart/lib/src/hub.dart

@@ -66,6 +66,9 @@ class Hub {
   /// Last event id recorded by the Hub
   SentryId get lastEventId => _lastEventId;
 
+  @internal
+  Scope get scope => _peek().scope;
+
   /// Captures the event.
   Future<SentryId> captureEvent(
     SentryEvent event, {

dart/lib/src/utils/tracing_utils.dart

@@ -1,17 +1,31 @@
 import '../../sentry.dart';
 
-void addSentryTraceHeader(ISentrySpan span, Map<String, dynamic> headers) {
+void addSentryTraceHeaderFromSpan(ISentrySpan span, Map<String, dynamic> headers) {
   final traceHeader = span.toSentryTrace();
   headers[traceHeader.name] = traceHeader.value;
 }
 
+void addSentryTraceheader(SentryTraceHeader traceHeader, Map<String, dynamic> headers) {
+  headers[traceHeader.name] = traceHeader.value;
+}
+
+void addBaggageHeaderFromSpan(
+    ISentrySpan span,
+    Map<String, dynamic> headers, {
+      SentryLogger? logger,
+    }) {
+  final baggage = span.toBaggageHeader();
+  if (baggage != null) {
+    addBaggageHeader(baggage, headers, logger: logger);
+  }
+}
+
+
 void addBaggageHeader(
-  ISentrySpan span,
+  SentryBaggageHeader baggage,
   Map<String, dynamic> headers, {
   SentryLogger? logger,
 }) {
-  final baggage = span.toBaggageHeader();
-  if (baggage != null) {
     final currentValue = headers[baggage.name] as String? ?? '';
 
     final currentBaggage = SentryBaggage.fromHeader(
@@ -36,7 +50,6 @@ void addBaggageHeader(
     final newBaggage = SentryBaggage(mergedBaggage, logger: logger);
 
     headers[baggage.name] = newBaggage.toHeaderString();
-  }
 }
 
 bool containsTargetOrMatchesRegExp(