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1   /*
2    * Copyright (c) 1994, 1995, 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 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 <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  
81      public TelnetInputStream(InputStream fd, boolean binary) {
82          super(fd);
83          binaryMode = binary;
84      }
85  
86      public void setStickyCRLF(boolean on) {
87          stickyCRLF = on;
88      }
89  
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 */
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      */
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 }