org.eclipse.jdt.launching/launching/org/eclipse/jdt/launching/SocketUtil.java

/*******************************************************************************
 * Copyright (c) 2000, 2015 IBM Corporation and others.
 *
 * This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License 2.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/legal/epl-2.0/
 *
 * SPDX-License-Identifier: EPL-2.0
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.jdt.launching;


import java.io.IOException;
import java.net.ConnectException;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.Random;

/**
 * Utility class to find a port to debug on.
 * @noinstantiate This class is not intended to be instantiated by clients.
 * @noextend This class is not intended to be subclassed by clients.
 */
public class SocketUtil {
	private static final Random fgRandom= new Random(System.currentTimeMillis());

	/**
	 * Returns a free port number on the specified host within the given range,
	 * or -1 if none found.
	 *
	 * @param host name or IP address of host on which to find a free port
	 * @param searchFrom the port number from which to start searching
	 * @param searchTo the port number at which to stop searching
	 * @return a free port in the specified range, or -1 of none found
	 * @deprecated Use <code>findFreePort()</code> instead. It is possible that this
	 * 	 method can return a port that is already in use since the implementation does
	 *   not bind to the given port to ensure that it is free.
	 */
	@Deprecated
	public static int findUnusedLocalPort(String host, int searchFrom, int searchTo) {

		for (int i= 0; i < 10; i++) {
			int port= getRandomPort(searchFrom, searchTo);
			try (Socket s = new Socket(host, port)) {
				s.getLocalPort(); // avoid warning on s being unused
			} catch (ConnectException e) {
				return port;
			} catch (IOException e) {
			}
		}
		return -1;
	}

	private static int getRandomPort(int low, int high) {
		return (int)(fgRandom.nextFloat() * (high-low)) + low;
	}

	/**
	 * Returns a free port number on localhost, or -1 if unable to find a free port.
	 *
	 * @return a free port number on localhost, or -1 if unable to find a free port
	 * @since 3.0
	 */
	public static int findFreePort() {
		try (ServerSocket socket = new ServerSocket(0)) {
			return socket.getLocalPort();
		} catch (IOException e) {
		}
		return -1;
	}
}