[UNDERTOW-2654] preserve status line in proxy scenarios

Author: baranowb

core/src/test/java/io/undertow/server/handlers/PreseverStatusTestCase.java

@@ -0,0 +1,69 @@
+/*
+ * JBoss, Home of Professional Open Source.
+ * Copyright 2025 Red Hat, Inc., and individual contributors
+ * as indicated by the @author tags.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package io.undertow.server.handlers;
+
+import java.io.IOException;
+import java.util.concurrent.ExecutionException;
+
+import org.apache.http.HttpResponse;
+import org.apache.http.client.methods.HttpGet;
+import org.junit.Assert;
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+import io.undertow.server.HttpHandler;
+import io.undertow.server.HttpServerExchange;
+import io.undertow.testutils.DefaultServer;
+import io.undertow.testutils.HttpOneOnly;
+import io.undertow.testutils.TestHttpClient;
+import io.undertow.util.StatusCodes;
+
+@RunWith(DefaultServer.class)
+@HttpOneOnly // Http2 does NOT have way to transfer status: https://httpwg.org/specs/rfc7540.html#rfc.section.8.1.2.4
+             // https://www.rfc-editor.org/rfc/rfc9113.html#name-response-pseudo-header-fiel
+public class PreseverStatusTestCase {
+    private static final String CUSTOM_REASON = "Its just a flesh wound";
+
+    @Before
+    public void setup() {
+
+        DefaultServer.setRootHandler(new BlockingHandler(new HttpHandler() {
+
+            @Override
+            public void handleRequest(HttpServerExchange exchange) throws Exception {
+                exchange.setStatusCode(StatusCodes.TOO_MANY_REQUESTS);
+                exchange.setReasonPhrase(CUSTOM_REASON);
+            }}));
+    }
+
+    @Test
+    public void testWindowSliding() throws ExecutionException, InterruptedException {
+        TestHttpClient client = new TestHttpClient();
+        try {
+            HttpGet get = new HttpGet(DefaultServer.getDefaultServerURL());
+            HttpResponse result = client.execute(get);
+            Assert.assertEquals(StatusCodes.TOO_MANY_REQUESTS, result.getStatusLine().getStatusCode());
+            Assert.assertEquals(CUSTOM_REASON, result.getStatusLine().getReasonPhrase());
+        } catch (IOException e) {
+            throw new RuntimeException(e);
+        } finally {
+            client.getConnectionManager().shutdown();
+        }
+    }
+}