Ensure that W3C tracing headers are always set to request.

The replaced implementation only replaced existing headers but did not set the headers if they were absent in original request.

Signed-off-by: Juergen Fickel <juergen.fickel@bosch.io>

gateway/service/src/main/java/org/eclipse/ditto/gateway/service/endpoints/directives/RequestTracingDirective.java

@@ -20,6 +20,7 @@
 import java.net.URI;
 import java.text.MessageFormat;
 import java.util.Map;
+import java.util.Set;
 import java.util.function.Supplier;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
@@ -163,32 +164,22 @@ private static HttpRequest adjustSpanContextHeadersOfRequest(
 
         // Replace W3C tracing headers of original request because from now
         // on the newly started span is the parent of all subsequent spans.
-        return originalRequest.withHeaders(originalHttpRequestHeaders(originalRequest)
-                .map(requestHeader -> {
-                    final HttpHeader result;
-                    if (isW3cTracingHeader(requestHeader)) {
-                        @Nullable final var spanContextHeaderValue = spanContextHeaders.get(requestHeader.name());
-                        if (null != spanContextHeaderValue) {
-                            result = HttpHeader.parse(requestHeader.name(), spanContextHeaderValue);
-                        } else {
-                            result = requestHeader;
-                        }
-                    } else {
-                        result = requestHeader;
-                    }
-                    return result;
-                })
-                .collect(Collectors.toList()));
-    }
-
-    private static Stream<HttpHeader> originalHttpRequestHeaders(final HttpRequest httpRequest) {
-        final var originalRequestHeaders = httpRequest.getHeaders();
-        return StreamSupport.stream(originalRequestHeaders.spliterator(), false);
+        var result = originalRequest;
+        for (final var w3cTracingHeader : getW3cTracingHeaders(spanContextHeaders)) {
+            result = result.removeHeader(w3cTracingHeader.name()).addHeader(w3cTracingHeader);
+        }
+        return result;
     }
 
-    private static boolean isW3cTracingHeader(final HttpHeader header) {
-        return header.is(DittoHeaderDefinition.W3C_TRACESTATE.getKey()) ||
-                header.is(DittoHeaderDefinition.W3C_TRACEPARENT.getKey());
+    private static Set<HttpHeader> getW3cTracingHeaders(final Map<String, String> spanContextHeaders) {
+        return Stream.of(DittoHeaderDefinition.W3C_TRACEPARENT, DittoHeaderDefinition.W3C_TRACESTATE)
+                .map(DittoHeaderDefinition::getKey)
+                .filter(spanContextHeaders::containsKey)
+                .map(w3cTracingHeaderName -> HttpHeader.parse(
+                        w3cTracingHeaderName,
+                        spanContextHeaders.get(w3cTracingHeaderName)
+                ))
+                .collect(Collectors.toSet());
     }
 
     @Nullable