src/main/java/org/apache/commons/net/time/TimeTCPClient.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
 *
 *      https://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.DataInputStream;
import java.io.IOException;
import java.util.Date;

import org.apache.commons.net.SocketClient;

/**
 * The TimeTCPClient class is a TCP implementation of a client for the Time protocol described in RFC 868. To use the class, merely establish a connection with
 * {@link org.apache.commons.net.SocketClient#connect connect} and call either {@link #getTime getTime()} or {@link #getDate getDate()} to retrieve the time,
 * then call {@link org.apache.commons.net.SocketClient#disconnect disconnect} to close the connection properly.
 *
 *
 * @see TimeUDPClient
 */

public final class TimeTCPClient extends SocketClient {
    /** 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;

    /**
     * The default TimeTCPClient constructor. It merely sets the default port to {@code DEFAULT_PORT}.
     */
    public TimeTCPClient() {
        setDefaultPort(DEFAULT_PORT);
    }

    /**
     * Gets the time from the server and returns a Java Date containing the time converted to the local time zone.
     * <p>
     * The server will have closed the connection at this point, so you should call {@link org.apache.commons.net.SocketClient#disconnect disconnect} after
     * calling this method. To retrieve another time, you must initiate another connection with {@link org.apache.commons.net.SocketClient#connect connect}
     * before calling {@code getDate()} again.
     * </p>
     *
     * @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() throws IOException {
        return new Date((getTime() - SECONDS_1900_TO_1970) * 1000L);
    }

    /**
     * Gets the time from the server 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.
     * <p>
     * The server will have closed the connection at this point, so you should call {@link org.apache.commons.net.SocketClient#disconnect disconnect} after
     * calling this method. To retrieve another time, you must initiate another connection with {@link org.apache.commons.net.SocketClient#connect connect}
     * before calling {@code getTime()} again.
     * </p>
     *
     * @return The time value retrieved from the server.
     * @throws IOException If an error occurs while fetching the time.
     */
    public long getTime() throws IOException {
        final DataInputStream input;
        input = new DataInputStream(_input_);
        return input.readInt() & 0xffffffffL;
    }

}