collector/log4j-socket/src/test/java/org/apache/karaf/decanter/collector/log/socket/SocketUtils.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 org.apache.karaf.decanter.collector.log.socket;

import java.net.InetAddress;
import java.net.ServerSocket;
import java.util.Random;

import javax.net.ServerSocketFactory;

/**
 * Utility class to determine if TCP port is available on localhost.
 */
public final class SocketUtils {

    private static final Random random = new Random();
    public static final int MIN_PORT = 40000;
    public static final int MAX_PORT = 65535;

    /**
     * Returns the first available port between {@link #MIN_PORT} and
     * {@link #MAX_PORT}
     */
    public static int findAvailablePort() {
        int port;
        do {
            port = findRandomPort(MIN_PORT, MAX_PORT);

        } while (!isPortAvailable(port));
        return port;
    }

    private static boolean isPortAvailable(int port) {
        try {
            ServerSocket serverSocker = ServerSocketFactory.getDefault().createServerSocket(port, 1,
                    InetAddress.getByName("localhost"));
            serverSocker.close();
            return true;
        } catch (Exception ex) {
            return false;
        }
    }

    private static int findRandomPort(int minPort, int maxPort) {
        if (maxPort < minPort) {
            throw new IllegalArgumentException("maxPort should be >= minPort");
        }
        int portRange = maxPort - minPort + 1;
        return random.nextInt(portRange) + minPort;
    }
}