src/main/java/org/apache/commons/net/time/TimeUDPClient.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.commons.net.time;

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.InetAddress;
import java.util.Date;

import org.apache.commons.net.DatagramSocketClient;

/**
 * The TimeUDPClient class is a UDP implementation of a client for the
 * Time protocol described in RFC 868.  To use the class, merely
 * open a local datagram socket with
 * {@link org.apache.commons.net.DatagramSocketClient#open  open }
 * and call {@link #getTime  getTime } or
 * {@link #getTime  getDate } to retrieve the time. Then call
 * {@link org.apache.commons.net.DatagramSocketClient#close  close }
 * to close the connection properly.  Unlike
 * {@link org.apache.commons.net.time.TimeTCPClient},
 * successive calls to {@link #getTime  getTime } or
 * {@link #getDate  getDate } are permitted
 * without re-establishing a connection.  That is because UDP is a
 * connectionless protocol and the Time protocol is stateless.
 *
 *
 * @see TimeTCPClient
 */

public final class TimeUDPClient extends DatagramSocketClient
{
    /** The default time port.  It is set to 37 according to RFC 868. */
    public static final int DEFAULT_PORT = 37;

    /**
     * The number of seconds between 00:00 1 January 1900 and
     * 00:00 1 January 1970.  This value can be useful for converting
     * time values to other formats.
     */
    public static final long SECONDS_1900_TO_1970 = 2208988800L;

    private final byte[] dummyData = new byte[1];
    private final byte[] timeData = new byte[4];

    /** Same as <code> getTime(host, DEFAULT_PORT); </code>
     * @param host the time server
     * @return the date
     * @throws IOException on error
     */
    public Date getDate(final InetAddress host) throws IOException
    {
        return new Date((getTime(host, DEFAULT_PORT) - SECONDS_1900_TO_1970) * 1000L);
    }

    /**
     * Retrieves the time from the server and returns a Java Date
     * containing the time converted to the local time zone.
     *
     * @param host The address of the server.
     * @param port The port of the service.
     * @return A Date value containing the time retrieved from the server
     *     converted to the local time zone.
     * @throws IOException  If an error occurs while fetching the time.
     */
    public Date getDate(final InetAddress host, final int port) throws IOException
    {
        return new Date((getTime(host, port) - SECONDS_1900_TO_1970) * 1000L);
    }


    /** Same as <code> getTime(host, DEFAULT_PORT); </code>
     * @param host the time server
     * @return the time returned from the server
     * @throws IOException on error
     */
    public long getTime(final InetAddress host) throws IOException
    {
        return getTime(host, DEFAULT_PORT);
    }


    /**
     * Retrieves the time from the specified server and port and
     * returns it. The time is the number of seconds since
     * 00:00 (midnight) 1 January 1900 GMT, as specified by RFC 868.
     * This method reads the raw 32-bit big-endian
     * unsigned integer from the server, converts it to a Java long, and
     * returns the value.
     *
     * @param host The address of the server.
     * @param port The port of the service.
     * @return The time value retrieved from the server.
     * @throws IOException If an error occurs while retrieving the time.
     */
    public long getTime(final InetAddress host, final int port) throws IOException
    {
        long time;
        final DatagramPacket sendPacket;
        final DatagramPacket receivePacket;

        sendPacket = new DatagramPacket(dummyData, dummyData.length, host, port);
        receivePacket = new DatagramPacket(timeData, timeData.length);

        _socket_.send(sendPacket);
        _socket_.receive(receivePacket);

        time = 0L;
        time |= (((timeData[0] & 0xff) << 24) & 0xffffffffL);
        time |= (((timeData[1] & 0xff) << 16) & 0xffffffffL);
        time |= (((timeData[2] & 0xff) << 8) & 0xffffffffL);
        time |= ((timeData[3] & 0xff) & 0xffffffffL);

        return time;
    }

}