ReactorNettyRequestUpgradeStrategy uses unique builder per request

See spring-projectsgh-25315

spring-webflux/src/main/java/org/springframework/web/reactive/socket/server/upgrade/ReactorNettyRequestUpgradeStrategy.java

@@ -57,7 +57,7 @@ public class ReactorNettyRequestUpgradeStrategy implements RequestUpgradeStrateg
 	 * @since 5.2.6
 	 */
 	public ReactorNettyRequestUpgradeStrategy() {
-		this(WebsocketServerSpec.builder());
+		this(WebsocketServerSpec::builder);
 	}
 
 
@@ -83,7 +83,7 @@ public WebsocketServerSpec getWebsocketServerSpec() {
 		return buildSpec(null);
 	}
 
-	private WebsocketServerSpec buildSpec(@Nullable String subProtocol) {
+	WebsocketServerSpec buildSpec(@Nullable String subProtocol) {
 		WebsocketServerSpec.Builder builder = this.specBuilderSupplier.get();
 		if (subProtocol != null) {
 			builder.protocols(subProtocol);

spring-webflux/src/test/java/org/springframework/web/reactive/socket/server/upgrade/ReactorNettyRequestUpgradeStrategyTests.java

@@ -0,0 +1,39 @@
+/*
+ * Copyright 2002-2020 the original author or authors.
+ *
+ * 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
+ *
+ *      https://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 org.springframework.web.reactive.socket.server.upgrade;
+
+import org.junit.jupiter.api.Test;
+import reactor.netty.http.server.WebsocketServerSpec;
+
+import static org.assertj.core.api.AssertionsForClassTypes.assertThat;
+
+/**
+ * Unit tests for {@link ReactorNettyRequestUpgradeStrategy}.
+ * @author Rossen Stoyanchev
+ */
+public class ReactorNettyRequestUpgradeStrategyTests {
+
+	@Test // gh-25315
+	void defaultWebSocketSpecBuilderIsUniquePerRequest() {
+		ReactorNettyRequestUpgradeStrategy strategy = new ReactorNettyRequestUpgradeStrategy();
+		WebsocketServerSpec spec1 = strategy.buildSpec("p1");
+		WebsocketServerSpec spec2 = strategy.getWebsocketServerSpec();
+
+		assertThat(spec1.protocols()).isEqualTo("p1");
+		assertThat(spec2.protocols()).isNull();
+	}
+
+}