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/*
 * Copyright 2002-2013 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
 *
 * 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 com.xiongyingqi.util;

import javax.net.ServerSocketFactory;
import java.net.DatagramSocket;
import java.net.ServerSocket;
import java.util.Random;
import java.util.SortedSet;
import java.util.TreeSet;


public abstract class SocketUtils {

    
    public static final int PORT_RANGE_MIN = 1024;

    
    public static final int PORT_RANGE_MAX = 65535;


    private static final Random random = new Random(System.currentTimeMillis());


    
    public SocketUtils() {
        /* no-op */
    }


    
    public static int findAvailableTcpPort() {
        return findAvailableTcpPort(PORT_RANGE_MIN);
    }

    
    public static int findAvailableTcpPort(int minPort) {
        return findAvailableTcpPort(minPort, PORT_RANGE_MAX);
    }

    
    public static int findAvailableTcpPort(int minPort, int maxPort) {
        return SocketType.TCP.findAvailablePort(minPort, maxPort);
    }

    
    public static SortedSet findAvailableTcpPorts(int numRequested) {
        return findAvailableTcpPorts(numRequested, PORT_RANGE_MIN, PORT_RANGE_MAX);
    }

    
    public static SortedSet findAvailableTcpPorts(int numRequested, int minPort, int maxPort) {
        return SocketType.TCP.findAvailablePorts(numRequested, minPort, maxPort);
    }

    
    public static int findAvailableUdpPort() {
        return findAvailableUdpPort(PORT_RANGE_MIN);
    }

    
    public static int findAvailableUdpPort(int minPort) {
        return findAvailableUdpPort(minPort, PORT_RANGE_MAX);
    }

    
    public static int findAvailableUdpPort(int minPort, int maxPort) {
        return SocketType.UDP.findAvailablePort(minPort, maxPort);
    }

    
    public static SortedSet findAvailableUdpPorts(int numRequested) {
        return findAvailableUdpPorts(numRequested, PORT_RANGE_MIN, PORT_RANGE_MAX);
    }

    
    public static SortedSet findAvailableUdpPorts(int numRequested, int minPort, int maxPort) {
        return SocketType.UDP.findAvailablePorts(numRequested, minPort, maxPort);
    }


    private static enum SocketType {

        TCP {
            @Override
            protected boolean isPortAvailable(int port) {
                try {
                    ServerSocket serverSocket = ServerSocketFactory.getDefault().createServerSocket(port);
                    serverSocket.close();
                    return true;
                } catch (Exception ex) {
                    return false;
                }
            }
        },

        UDP {
            @Override
            protected boolean isPortAvailable(int port) {
                try {
                    DatagramSocket socket = new DatagramSocket(port);
                    socket.close();
                    return true;
                } catch (Exception ex) {
                    return false;
                }
            }
        };

        
        protected abstract boolean isPortAvailable(int port);

        
        private int findRandomPort(int minPort, int maxPort) {
            int portRange = maxPort - minPort;
            return minPort + random.nextInt(portRange);
        }

        
        int findAvailablePort(int minPort, int maxPort) {
            Assert.isTrue(minPort > 0, "'minPort' must be greater than 0");
            Assert.isTrue(maxPort > minPort, "'maxPort' must be greater than 'minPort'");
            Assert.isTrue(maxPort <= PORT_RANGE_MAX, "'maxPort' must be less than or equal to " + PORT_RANGE_MAX);

            int portRange = maxPort - minPort;
            int candidatePort;
            int searchCounter = 0;
            do {
                if (++searchCounter > portRange) {
                    throw new IllegalStateException(String.format(
                            "Could not find an available %s port in the range [%d, %d] after %d attempts", name(), minPort,
                            maxPort, searchCounter));
                }
                candidatePort = findRandomPort(minPort, maxPort);
            } while (!isPortAvailable(candidatePort));

            return candidatePort;
        }

        
        SortedSet findAvailablePorts(int numRequested, int minPort, int maxPort) {
            Assert.isTrue(minPort > 0, "'minPort' must be greater than 0");
            Assert.isTrue(maxPort > minPort, "'maxPort' must be greater than 'minPort'");
            Assert.isTrue(maxPort <= PORT_RANGE_MAX, "'maxPort' must be less than or equal to " + PORT_RANGE_MAX);
            Assert.isTrue(numRequested > 0, "'numRequested' must be greater than 0");
            Assert.isTrue((maxPort - minPort) >= numRequested,
                    "'numRequested' must not be greater than 'maxPort' - 'minPort'");

            final SortedSet availablePorts = new TreeSet();
            int attemptCount = 0;
            while ((++attemptCount <= numRequested + 100) && (availablePorts.size() < numRequested)) {
                availablePorts.add(findAvailablePort(minPort, maxPort));
            }

            if (availablePorts.size() != numRequested) {
                throw new IllegalStateException(String.format(
                        "Could not find %d available %s ports in the range [%d, %d]", numRequested, name(), minPort,
                        maxPort));
            }

            return availablePorts;
        }
    }

}