Merge branch '2.1.x' into 2.2.x

Closes gh-21052

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/embedded/jetty/JettyWebServer.java

@@ -148,7 +148,7 @@ public void start() throws WebServerException {
 					}
 					catch (IOException ex) {
 						if (connector instanceof NetworkConnector && findBindException(ex) != null) {
-							throw new PortInUseException(((NetworkConnector) connector).getPort());
+							throw new PortInUseException(((NetworkConnector) connector).getPort(), ex);
 						}
 						throw ex;
 					}

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/embedded/netty/NettyWebServer.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2019 the original author or authors.
+ * Copyright 2012-2020 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.
@@ -21,6 +21,7 @@
 import java.util.List;
 import java.util.function.Predicate;
 
+import io.netty.channel.unix.Errors.NativeIoException;
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
 import reactor.netty.ChannelBindException;
@@ -47,7 +48,12 @@
  */
 public class NettyWebServer implements WebServer {
 
-	private static final Predicate<HttpServerRequest> ALWAYS = (r) -> true;
+	/**
+	 * Permission denied error code from {@code errno.h}.
+	 */
+	private static final int ERROR_NO_EACCES = -13;
+
+	private static final Predicate<HttpServerRequest> ALWAYS = (request) -> true;
 
 	private static final Log logger = LogFactory.getLog(NettyWebServer.class);
 
@@ -81,8 +87,8 @@ public void start() throws WebServerException {
 			}
 			catch (Exception ex) {
 				ChannelBindException bindException = findBindException(ex);
-				if (bindException != null) {
-					throw new PortInUseException(bindException.localPort());
+				if (bindException != null && !isPermissionDenied(bindException.getCause())) {
+					throw new PortInUseException(bindException.localPort(), ex);
 				}
 				throw new WebServerException("Unable to start Netty", ex);
 			}
@@ -91,6 +97,17 @@ public void start() throws WebServerException {
 		}
 	}
 
+	private boolean isPermissionDenied(Throwable bindExceptionCause) {
+		try {
+			if (bindExceptionCause instanceof NativeIoException) {
+				return ((NativeIoException) bindExceptionCause).expectedErr() == ERROR_NO_EACCES;
+			}
+		}
+		catch (Throwable ex) {
+		}
+		return false;
+	}
+
 	private DisposableServer startHttpServer() {
 		HttpServer server = this.httpServer;
 		if (this.routeProviders.isEmpty()) {

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/embedded/undertow/UndertowServletWebServer.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2019 the original author or authors.
+ * Copyright 2012-2020 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.
@@ -151,7 +151,7 @@ public void start() throws WebServerException {
 						List<Port> actualPorts = getActualPorts();
 						failedPorts.removeAll(actualPorts);
 						if (failedPorts.size() == 1) {
-							throw new PortInUseException(failedPorts.iterator().next().getNumber());
+							throw new PortInUseException(failedPorts.iterator().next().getNumber(), ex);
 						}
 					}
 					throw new WebServerException("Unable to start embedded Undertow", ex);

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/embedded/undertow/UndertowWebServer.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2019 the original author or authors.
+ * Copyright 2012-2020 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.
@@ -109,7 +109,7 @@ public void start() throws WebServerException {
 						List<UndertowWebServer.Port> actualPorts = getActualPorts();
 						failedPorts.removeAll(actualPorts);
 						if (failedPorts.size() == 1) {
-							throw new PortInUseException(failedPorts.iterator().next().getNumber());
+							throw new PortInUseException(failedPorts.iterator().next().getNumber(), ex);
 						}
 					}
 					throw new WebServerException("Unable to start embedded Undertow", ex);

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/server/PortInUseException.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2019 the original author or authors.
+ * Copyright 2012-2020 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.
@@ -32,7 +32,16 @@ public class PortInUseException extends WebServerException {
 	 * @param port the port that was in use
 	 */
 	public PortInUseException(int port) {
-		super("Port " + port + " is already in use", null);
+		this(port, null);
+	}
+
+	/**
+	 * Creates a new port in use exception for the given {@code port}.
+	 * @param port the port that was in use
+	 * @param cause the cause of the exception
+	 */
+	public PortInUseException(int port, Throwable cause) {
+		super("Port " + port + " is already in use", cause);
 		this.port = port;
 	}
 

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/web/embedded/netty/NettyReactiveWebServerFactoryTests.java

@@ -62,7 +62,7 @@ void exceptionIsThrownWhenPortIsAlreadyInUse() {
 		this.webServer.start();
 		factory.setPort(this.webServer.getPort());
 		assertThatExceptionOfType(PortInUseException.class).isThrownBy(factory.getWebServer(new EchoHandler())::start)
-				.satisfies(this::portMatchesRequirement);
+				.satisfies(this::portMatchesRequirement).withCauseInstanceOf(Throwable.class);
 	}
 
 	private void portMatchesRequirement(PortInUseException exception) {