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1   /*
2    * Copyright (c) 1994, 2013, Oracle and/or its affiliates. All rights reserved.
3    * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4    *
5    * This code is free software; you can redistribute it and/or modify it
6    * under the terms of the GNU General Public License version 2 only, as
7    * published by the Free Software Foundation.  Oracle designates this
8    * particular file as subject to the "Classpath" exception as provided
9    * by Oracle in the LICENSE file that accompanied this code.
10   *
11   * This code is distributed in the hope that it will be useful, but WITHOUT
12   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
14   * version 2 for more details (a copy is included in the LICENSE file that
15   * accompanied this code).
16   *
17   * You should have received a copy of the GNU General Public License version
18   * 2 along with this work; if not, write to the Free Software Foundation,
19   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20   *
21   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22   * or visit www.oracle.com if you need additional information or have any
23   * questions.
24   */
25  
26  package sun.net;
27  
28  import java.io.*;
29  
30  /**
31   * This class provides input and output streams for telnet clients.
32   * This class overrides write to do CRLF processing as specified in
33   * RFC 854. The class assumes it is running on a system where lines
34   * are terminated with a single newline <LF> character.
35   *
36   * This is the relevant section of RFC 824 regarding CRLF processing:
37   *
38   * <pre>
39   * The sequence "CR LF", as defined, will cause the NVT to be
40   * positioned at the left margin of the next print line (as would,
41   * for example, the sequence "LF CR").  However, many systems and
42   * terminals do not treat CR and LF independently, and will have to
43   * go to some effort to simulate their effect.  (For example, some
44   * terminals do not have a CR independent of the LF, but on such
45   * terminals it may be possible to simulate a CR by backspacing.)
46   * Therefore, the sequence "CR LF" must be treated as a single "new
47   * line" character and used whenever their combined action is
48   * intended; the sequence "CR NUL" must be used where a carriage
49   * return alone is actually desired; and the CR character must be
50   * avoided in other contexts.  This rule gives assurance to systems
51   * which must decide whether to perform a "new line" function or a
52   * multiple-backspace that the TELNET stream contains a character
53   * following a CR that will allow a rational decision.
54   *
55   *    Note that "CR LF" or "CR NUL" is required in both directions
56   *    (in the default ASCII mode), to preserve the symmetry of the
57   *    NVT model.  Even though it may be known in some situations
58   *    (e.g., with remote echo and suppress go ahead options in
59   *    effect) that characters are not being sent to an actual
60   *    printer, nonetheless, for the sake of consistency, the protocol
61   *    requires that a NUL be inserted following a CR not followed by
62   *    a LF in the data stream.  The converse of this is that a NUL
63   *    received in the data stream after a CR (in the absence of
64   *    options negotiations which explicitly specify otherwise) should
65   *    be stripped out prior to applying the NVT to local character
66   *    set mapping.
67   * </pre>
68   *
69   * @author      Jonathan Payne
70   */
71  
72  public class TelnetOutputStream extends BufferedOutputStream {
73      boolean         stickyCRLF = false;
74      boolean         seenCR = false;
75  
76      public boolean  binaryMode = false;
77  
78      public TelnetOutputStream(OutputStream fd, boolean binary) {
79          super(fd);
80          binaryMode = binary;
81      }
82  
83      /**
84       * set the stickyCRLF flag. Tells whether the terminal considers CRLF as a single
85       * char.
86       *
87       * @param   on      the <code>boolean</code> to set the flag to.
88       */
89      public void setStickyCRLF(boolean on) {
90          stickyCRLF = on;
91      }
92  
93      /**
94       * Writes the int to the stream and does CR LF processing if necessary.
95       */
96      public void write(int c) throws IOException {
97          if (binaryMode) {
98              super.write(c);
99              return;
100         }
101 
102         if (seenCR) {
103             if (c != '\n')
104                 super.write(0);
105             super.write(c);
106             if (c != '\r')
107                 seenCR = false;
108         } else { // !seenCR
109             if (c == '\n') {
110                 super.write('\r');
111                 super.write('\n');
112                 return;
113             }
114             if (c == '\r') {
115                 if (stickyCRLF)
116                     seenCR = true;
117                 else {
118                     super.write('\r');
119                     c = 0;
120                 }
121             }
122             super.write(c);
123         }
124     }
125 
126     /**
127      * Write the bytes at offset <i>off</i> in buffer <i>bytes</i> for
128      * <i>length</i> bytes.
129      */
130     public void write(byte bytes[], int off, int length) throws IOException {
131         if (binaryMode) {
132             super.write(bytes, off, length);
133             return;
134         }
135 
136         while (--length >= 0) {
137             write(bytes[off++]);
138         }
139     }
140 }