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1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * The ASF licenses this file to You under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  You may obtain a copy of the License at
8    *
9    *      http://www.apache.org/licenses/LICENSE-2.0
10   *
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   * See the License for the specific language governing permissions and
15   * limitations under the License.
16   */
17  
18  package org.apache.commons.net.telnet;
19  
20  /**
21   * The TelnetCommand class cannot be instantiated and only serves as a storehouse for telnet command constants.
22   *
23   * @see org.apache.commons.net.telnet.Telnet
24   * @see org.apache.commons.net.telnet.TelnetClient
25   */
26  
27  public final class TelnetCommand {
28      /** The maximum value a command code can have. This value is 255. */
29      public static final int MAX_COMMAND_VALUE = 255;
30  
31      /** Interpret As Command code. Value is 255 according to RFC 854. */
32      public static final int IAC = 255;
33  
34      /** Don't use option code. Value is 254 according to RFC 854. */
35      public static final int DONT = 254;
36  
37      /** Request to use option code. Value is 253 according to RFC 854. */
38      public static final int DO = 253;
39  
40      /** Refuse to use option code. Value is 252 according to RFC 854. */
41      public static final int WONT = 252;
42  
43      /** Agree to use option code. Value is 251 according to RFC 854. */
44      public static final int WILL = 251;
45  
46      /** Start subnegotiation code. Value is 250 according to RFC 854. */
47      public static final int SB = 250;
48  
49      /** Go Ahead code. Value is 249 according to RFC 854. */
50      public static final int GA = 249;
51  
52      /** Erase Line code. Value is 248 according to RFC 854. */
53      public static final int EL = 248;
54  
55      /** Erase Character code. Value is 247 according to RFC 854. */
56      public static final int EC = 247;
57  
58      /** Are You There code. Value is 246 according to RFC 854. */
59      public static final int AYT = 246;
60  
61      /** Abort Output code. Value is 245 according to RFC 854. */
62      public static final int AO = 245;
63  
64      /** Interrupt Process code. Value is 244 according to RFC 854. */
65      public static final int IP = 244;
66  
67      /** Break code. Value is 243 according to RFC 854. */
68      public static final int BREAK = 243;
69  
70      /** Data mark code. Value is 242 according to RFC 854. */
71      public static final int DM = 242;
72  
73      /** No Operation code. Value is 241 according to RFC 854. */
74      public static final int NOP = 241;
75  
76      /** End subnegotiation code. Value is 240 according to RFC 854. */
77      public static final int SE = 240;
78  
79      /** End of record code. Value is 239. */
80      public static final int EOR = 239;
81  
82      /** Abort code. Value is 238. */
83      public static final int ABORT = 238;
84  
85      /** Suspend process code. Value is 237. */
86      public static final int SUSP = 237;
87  
88      /** End of file code. Value is 236. */
89      public static final int EOF = 236;
90  
91      /** Synchronize code. Value is 242. */
92      public static final int SYNCH = 242;
93  
94      /** String representations of commands. */
95      private static final String[] commandString = { "IAC", "DONT", "DO", "WONT", "WILL", "SB", "GA", "EL", "EC", "AYT", "AO", "IP", "BRK", "DMARK", "NOP", "SE",
96              "EOR", "ABORT", "SUSP", "EOF" };
97  
98      private static final int FIRST_COMMAND = IAC;
99      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 }