    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *      http://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 * Unless required by applicable law or agreed to in writing, software
    012 * distributed under the License is distributed on an "AS IS" BASIS,
    013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 * See the License for the specific language governing permissions and
    015 * limitations under the License.
    016 */
    017
    018package org.apache.commons.net.telnet;
    019
    020/**
    021 * The TelnetCommand class cannot be instantiated and only serves as a
    022 * storehouse for telnet command constants.
    023 * @see org.apache.commons.net.telnet.Telnet
    024 * @see org.apache.commons.net.telnet.TelnetClient
    025 */
    026
    027public final class TelnetCommand
    028{
    029    /*** The maximum value a command code can have.  This value is 255. ***/
    030    public static final int MAX_COMMAND_VALUE = 255;
    031
    032    /*** Interpret As Command code.  Value is 255 according to RFC 854. ***/
    033    public static final int IAC = 255;
    034
    035    /*** Don't use option code.  Value is 254 according to RFC 854. ***/
    036    public static final int DONT = 254;
    037
    038    /*** Request to use option code.  Value is 253 according to RFC 854. ***/
    039    public static final int DO = 253;
    040
    041    /*** Refuse to use option code.  Value is 252 according to RFC 854. ***/
    042    public static final int WONT = 252;
    043
    044    /*** Agree to use option code.  Value is 251 according to RFC 854. ***/
    045    public static final int WILL = 251;
    046
    047    /*** Start subnegotiation code.  Value is 250 according to RFC 854. ***/
    048    public static final int SB = 250;
    049
    050    /*** Go Ahead code.  Value is 249 according to RFC 854. ***/
    051    public static final int GA = 249;
    052
    053    /*** Erase Line code.  Value is 248 according to RFC 854. ***/
    054    public static final int EL = 248;
    055
    056    /*** Erase Character code.  Value is 247 according to RFC 854. ***/
    057    public static final int EC = 247;
    058
    059    /*** Are You There code.  Value is 246 according to RFC 854. ***/
    060    public static final int AYT = 246;
    061
    062    /*** Abort Output code.  Value is 245 according to RFC 854. ***/
    063    public static final int AO = 245;
    064
    065    /*** Interrupt Process code.  Value is 244 according to RFC 854. ***/
    066    public static final int IP = 244;
    067
    068    /*** Break code.  Value is 243 according to RFC 854. ***/
    069    public static final int BREAK = 243;
    070
    071    /*** Data mark code.  Value is 242 according to RFC 854. ***/
    072    public static final int DM = 242;
    073
    074    /*** No Operation code.  Value is 241 according to RFC 854. ***/
    075    public static final int NOP = 241;
    076
    077    /*** End subnegotiation code.  Value is 240 according to RFC 854. ***/
    078    public static final int SE = 240;
    079
    080    /*** End of record code.  Value is 239. ***/
    081    public static final int EOR = 239;
    082
    083    /*** Abort code.  Value is 238. ***/
    084    public static final int ABORT = 238;
    085
    086    /*** Suspend process code.  Value is 237. ***/
    087    public static final int SUSP = 237;
    088
    089    /*** End of file code.  Value is 236. ***/
    090    public static final int EOF = 236;
    091
    092    /*** Synchronize code.  Value is 242. ***/
    093    public static final int SYNCH = 242;
    094
    095    /*** String representations of commands. ***/
    096    private static final String commandString[] = {
    097                "IAC", "DONT", "DO", "WONT", "WILL", "SB", "GA", "EL", "EC", "AYT",
    098                "AO", "IP", "BRK", "DMARK", "NOP", "SE", "EOR", "ABORT", "SUSP", "EOF"
    099            };
    100
    101    private static final int FIRST_COMMAND = IAC;
    102    private static final int LAST_COMMAND = EOF;
    103
    104    /***
    105     * Returns the string representation of the telnet protocol command
    106     * corresponding to the given command code.
    107     * <p>
    108     * @param code The command code of the telnet protocol command.
    109     * @return The string representation of the telnet protocol command.
    110     ***/
    111    public static String getCommand(final int code)
    112    {
    113        return commandString[FIRST_COMMAND - code];
    114    }
    115
    116    /***
    117     * Determines if a given command code is valid.  Returns true if valid,
    118     * false if not.
    119     * <p>
    120     * @param code  The command code to test.
    121     * @return True if the command code is valid, false if not.
    122     **/
    123    public static boolean isValidCommand(final int code)
    124    {
    125        return code <= FIRST_COMMAND && code >= LAST_COMMAND;
    126    }
    127
    128    // Cannot be instantiated
    129    private TelnetCommand()
    130    { }
    131}