Adds config flag to disable header copying in JaxRsService (helidon-io#9990)

* Adds config flag to disable header copying in JaxRsService.

Signed-off-by: Santiago Pericas-Geertsen <santiago.pericasgeertsen@oracle.com>

Author: spericas

microprofile/server/src/main/java/io/helidon/microprofile/server/JaxRsService.java

@@ -202,7 +202,12 @@ private void handle(ServerRequest req, ServerResponse res) {
     }
 
     private void doHandle(Context ctx, ServerRequest req, ServerResponse res) {
-        ServerResponseHeaders savedResponseHeaders = ServerResponseHeaders.create(res.headers());
+        // save headers in case MP request processing fails
+        ServerResponseHeaders savedResponseHeaders = null;
+        if (req.listenerContext().config().restoreResponseHeaders()) {
+            savedResponseHeaders = ServerResponseHeaders.create(res.headers());
+        }
+
         BaseUriRequestUri uris = BaseUriRequestUri.resolve(req);
         ContainerRequest requestContext = new ContainerRequest(uris.baseUri,
                                                                uris.requestUri,
@@ -252,7 +257,9 @@ private void doHandle(Context ctx, ServerRequest req, ServerResponse res) {
                 if (res instanceof RoutingResponse routing) {
                     if (routing.reset()) {
                         res.status(Status.OK_200);
-                        savedResponseHeaders.forEach(res::header);
+                        if (savedResponseHeaders != null) {
+                            savedResponseHeaders.forEach(res::header);
+                        }
                         routing.next();
                     }
                 }

tests/integration/mp-jaxrs-preserve-headers/src/main/resources/application.yaml

@@ -14,5 +14,6 @@
 # limitations under the License.
 #
 server:
+  restore-response-headers: true
   features:
     header-adjustment:

webserver/webserver/src/main/java/io/helidon/webserver/ListenerConfigBlueprint.java

@@ -408,4 +408,17 @@ default void configureSocket(ServerSocket socket) {
     @Option.Configured
     @Option.DefaultMethod("create")
     ErrorHandling errorHandling();
+
+    /**
+     * Copy and restore response headers before and after passing a request to Jersey
+     * for processing. If Jersey fails to handle the request, and the Webserver continues
+     * processing the request, it needs to make sure the original headers are restored.
+     * Turn off this flag to avoid the extra overhead of copying headers when no handler
+     * executes after Jersey returns.
+     *
+     * @return copy/restore header setting
+     */
+    @Option.Configured
+    @Option.Default("true")
+    boolean restoreResponseHeaders();
 }