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 storehouse for telnet command constants.
022 *
023 * @see org.apache.commons.net.telnet.Telnet
024 * @see org.apache.commons.net.telnet.TelnetClient
025 */
026
027public final class TelnetCommand {
028    /** The maximum value a command code can have. This value is 255. */
029    public static final int MAX_COMMAND_VALUE = 255;
030
031    /** Interpret As Command code. Value is 255 according to RFC 854. */
032    public static final int IAC = 255;
033
034    /** Don't use option code. Value is 254 according to RFC 854. */
035    public static final int DONT = 254;
036
037    /** Request to use option code. Value is 253 according to RFC 854. */
038    public static final int DO = 253;
039
040    /** Refuse to use option code. Value is 252 according to RFC 854. */
041    public static final int WONT = 252;
042
043    /** Agree to use option code. Value is 251 according to RFC 854. */
044    public static final int WILL = 251;
045
046    /** Start subnegotiation code. Value is 250 according to RFC 854. */
047    public static final int SB = 250;
048
049    /** Go Ahead code. Value is 249 according to RFC 854. */
050    public static final int GA = 249;
051
052    /** Erase Line code. Value is 248 according to RFC 854. */
053    public static final int EL = 248;
054
055    /** Erase Character code. Value is 247 according to RFC 854. */
056    public static final int EC = 247;
057
058    /** Are You There code. Value is 246 according to RFC 854. */
059    public static final int AYT = 246;
060
061    /** Abort Output code. Value is 245 according to RFC 854. */
062    public static final int AO = 245;
063
064    /** Interrupt Process code. Value is 244 according to RFC 854. */
065    public static final int IP = 244;
066
067    /** Break code. Value is 243 according to RFC 854. */
068    public static final int BREAK = 243;
069
070    /** Data mark code. Value is 242 according to RFC 854. */
071    public static final int DM = 242;
072
073    /** No Operation code. Value is 241 according to RFC 854. */
074    public static final int NOP = 241;
075
076    /** End subnegotiation code. Value is 240 according to RFC 854. */
077    public static final int SE = 240;
078
079    /** End of record code. Value is 239. */
080    public static final int EOR = 239;
081
082    /** Abort code. Value is 238. */
083    public static final int ABORT = 238;
084
085    /** Suspend process code. Value is 237. */
086    public static final int SUSP = 237;
087
088    /** End of file code. Value is 236. */
089    public static final int EOF = 236;
090
091    /** Synchronize code. Value is 242. */
092    public static final int SYNCH = 242;
093
094    /** String representations of commands. */
095    private static final String[] commandString = { "IAC", "DONT", "DO", "WONT", "WILL", "SB", "GA", "EL", "EC", "AYT", "AO", "IP", "BRK", "DMARK", "NOP", "SE",
096            "EOR", "ABORT", "SUSP", "EOF" };
097
098    private static final int FIRST_COMMAND = IAC;
099    private static final int LAST_COMMAND = EOF;
100
101    /**
102     * Returns the string representation of the telnet protocol command corresponding to the given command code.
103     *
104     * @param code The command code of the telnet protocol command.
105     * @return The string representation of the telnet protocol command.
106     */
107    public static String getCommand(final int code) {
108        return commandString[FIRST_COMMAND - code];
109    }
110
111    /**
112     * Determines if a given command code is valid. Returns true if valid, false if not.
113     *
114     * @param code The command code to test.
115     * @return True if the command code is valid, false if not.
116     **/
117    public static boolean isValidCommand(final int code) {
118        return code <= FIRST_COMMAND && code >= LAST_COMMAND;
119    }
120
121    /** Cannot be instantiated. */
122    private TelnetCommand() {
123    }
124}