Disable Jetty's default Server header

Following the upgrade to Tomcat 8.5, Jetty became the only container
that sends a Server header by default. This commit updates the factory
for Jetty to disable the default Server header bringing it into line
with Tomcat and Undertow.

All three containers continue to support server.server-header which
can be used to configure a custom server header.

Closes spring-projectsgh-4730

spring-boot/src/main/java/org/springframework/boot/context/embedded/jetty/JettyEmbeddedServletContainerFactory.java

@@ -891,6 +891,13 @@ public AbstractConnector createConnector(Server server, InetSocketAddress addres
 			ServerConnector connector = new ServerConnector(server, acceptors, selectors);
 			connector.setHost(address.getHostName());
 			connector.setPort(address.getPort());
+			for (ConnectionFactory connectionFactory : connector
+					.getConnectionFactories()) {
+				if (connectionFactory instanceof HttpConfiguration.ConnectionFactory) {
+					((HttpConfiguration.ConnectionFactory) connectionFactory)
+							.getHttpConfiguration().setSendServerVersion(false);
+				}
+			}
 			return connector;
 		}
 
@@ -912,8 +919,16 @@ public Server createServer(ThreadPool threadPool) {
 						.findMethod(Server.class, "setThreadPool", ThreadPool.class)
 						.invoke(server, threadPool);
 			}
-			catch (Exception e) {
-				throw new RuntimeException("Failed to configure Jetty 8 ThreadPool", e);
+			catch (Exception ex) {
+				throw new RuntimeException("Failed to configure Jetty 8 ThreadPool", ex);
+			}
+			try {
+				ReflectionUtils
+						.findMethod(Server.class, "setSendServerVersion", boolean.class)
+						.invoke(server, false);
+			}
+			catch (Exception ex) {
+				throw new RuntimeException("Failed to disable Server header", ex);
 			}
 			return server;
 		}

spring-boot/src/test/java/org/springframework/boot/context/embedded/AbstractEmbeddedServletContainerFactoryTests.java

@@ -813,6 +813,16 @@ public void customServerHeader() throws Exception {
 		assertThat(response.getHeaders().getFirst("server")).isEqualTo("MyServer");
 	}
 
+	@Test
+	public void serverHeaderIsDisabledByDefault() throws Exception {
+		AbstractEmbeddedServletContainerFactory factory = getFactory();
+		this.container = factory
+				.getEmbeddedServletContainer(exampleServletRegistration());
+		this.container.start();
+		ClientHttpResponse response = getClientResponse(getLocalUrl("/hello"));
+		assertThat(response.getHeaders().getFirst("server")).isNull();
+	}
+
 	@Test
 	public void portClashOfPrimaryConnectorResultsInPortInUseException()
 			throws IOException {