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8  * particular file as subject to the "Classpath" exception as provided
9  * by Oracle in the LICENSE file that accompanied this code.
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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).
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17  * You should have received a copy of the GNU General Public License version
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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 {@literal <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 
TelnetOutputStream(OutputStream fd, boolean binary)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      */
setStickyCRLF(boolean on)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      */
write(int c)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      */
write(byte bytes[], int off, int length)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 }
141