1 /*
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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
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15  * accompanied this code).
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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 read 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 TelnetInputStream extends FilterInputStream {
73     /** If stickyCRLF is true, then we're a machine, like an IBM PC,
74         where a Newline is a CR followed by LF.  On UNIX, this is false
75         because Newline is represented with just a LF character. */
76     boolean         stickyCRLF = false;
77     boolean         seenCR = false;
78 
79     public boolean  binaryMode = false;
80 
TelnetInputStream(InputStream fd, boolean binary)81     public TelnetInputStream(InputStream fd, boolean binary) {
82         super(fd);
83         binaryMode = binary;
84     }
85 
setStickyCRLF(boolean on)86     public void setStickyCRLF(boolean on) {
87         stickyCRLF = on;
88     }
89 
read()90     public int read() throws IOException {
91         if (binaryMode)
92             return super.read();
93 
94         int c;
95 
96         /* If last time we determined we saw a CRLF pair, and we're
97            not turning that into just a Newline (that is, we're
98            stickyCRLF), then return the LF part of that sticky
99            pair now. */
100 
101         if (seenCR) {
102             seenCR = false;
103             return '\n';
104         }
105 
106         if ((c = super.read()) == '\r') {    /* CR */
107             switch (c = super.read()) {
108             default:
109             case -1:                        /* this is an error */
110                 throw new TelnetProtocolException("misplaced CR in input");
111 
112             case 0:                         /* NUL - treat CR as CR */
113                 return '\r';
114 
115             case '\n':                      /* CRLF - treat as NL */
116                 if (stickyCRLF) {
117                     seenCR = true;
118                     return '\r';
119                 } else {
120                     return '\n';
121                 }
122             }
123         }
124         return c;
125     }
126 
127     /** read into a byte array */
read(byte bytes[])128     public int read(byte bytes[]) throws IOException {
129         return read(bytes, 0, bytes.length);
130     }
131 
132     /**
133      * Read into a byte array at offset <i>off</i> for length <i>length</i>
134      * bytes.
135      */
read(byte bytes[], int off, int length)136     public int read(byte bytes[], int off, int length) throws IOException {
137         if (binaryMode)
138             return super.read(bytes, off, length);
139 
140         int c;
141         int offStart = off;
142 
143         while (--length >= 0) {
144             c = read();
145             if (c == -1)
146                 break;
147             bytes[off++] = (byte)c;
148         }
149         return (off > offStart) ? off - offStart : -1;
150     }
151 }
152