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Apache Commons Net library contains a collection of network utilities and protocol implementations. Supported protocols include: Echo, Finger, FTP, NNTP, NTP, POP3(S), SMTP(S), Telnet, Whois

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package org.apache.commons.net.ntp;
/*
 * 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.
 */


/***
 * Common NtpUtils Helper class.
 *
 */
public final class NtpUtils {

    /***
      * Returns 32-bit integer address to IPv4 address string "%d.%d.%d.%d" format.
      *
      * @param address  the 32-bit address
      * @return  the raw IP address in a string format.
      */
     public static String getHostAddress(int address)
     {
          return ((address >>> 24) & 0xFF) + "." +
                 ((address >>> 16) & 0xFF) + "." +
                 ((address >>>  8) & 0xFF) + "." +
                 ((address >>>  0) & 0xFF);
     }

    /***
     * Returns NTP packet reference identifier as IP address.
     *
     * @param packet  NTP packet
     * @return  the packet reference id (as IP address) in "%d.%d.%d.%d" format.
     */
     public static String getRefAddress(NtpV3Packet packet)
     {
         int address = (packet == null) ? 0 : packet.getReferenceId();
         return getHostAddress(address);
     }

    /***
     * Get refId as reference clock string (e.g. GPS, WWV, LCL). If string is
     * invalid (non-ASCII character) then returns empty string "".
     * For details refer to the Comprehensive
     * List of Clock Drivers.
     *
     * @param message the message to check
     * @return reference clock string if primary NTP server
     */
    public static String getReferenceClock(NtpV3Packet message) {
        if (message == null) {
            return "";
        }
        int refId = message.getReferenceId();
        if (refId == 0) {
            return "";
        }
        StringBuilder buf = new StringBuilder(4);
        // start at highest-order byte (0x4c434c00 -> LCL)
        for (int shiftBits = 24; shiftBits >= 0; shiftBits -= 8)
        {
            char c = (char) ((refId >>> shiftBits) & 0xff);
            if (c == 0) { // 0-terminated ASCII string
                break;
            }
            if (!Character.isLetterOrDigit(c)) {
                return "";
            }
            buf.append(c);
        }
        return buf.toString();
    }

    /***
     * Return human-readable name of message mode type (RFC 1305).
     *
     * @param mode the mode type
     * @return mode name
     */
    public static String getModeName(int mode)
    {
        switch (mode) {
            case NtpV3Packet.MODE_RESERVED:
                return "Reserved";
            case NtpV3Packet.MODE_SYMMETRIC_ACTIVE:
                return "Symmetric Active";
            case NtpV3Packet.MODE_SYMMETRIC_PASSIVE:
                return "Symmetric Passive";
            case NtpV3Packet.MODE_CLIENT:
                return "Client";
            case NtpV3Packet.MODE_SERVER:
                return "Server";
            case NtpV3Packet.MODE_BROADCAST:
                return "Broadcast";
            case NtpV3Packet.MODE_CONTROL_MESSAGE:
                return "Control";
            case NtpV3Packet.MODE_PRIVATE:
                return "Private";
            default:
                return "Unknown";
        }
    }

}