1/* ====================================================================
2 * Copyright (c) 2006 J.T. Beetstra
3 *
4 * Permission is hereby granted, free of charge, to any person obtaining
5 * a copy of this software and associated documentation files (the
6 * "Software"), to deal in the Software without restriction, including
7 * without limitation the rights to use, copy, modify, merge, publish,
8 * distribute, sublicense, and/or sell copies of the Software, and to
9 * permit persons to whom the Software is furnished to do so, subject to
10 * the following conditions:
11 *
12 * The above copyright notice and this permission notice shall be
13 * included in all copies or substantial portions of the Software.
14 *
15 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
16 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
17 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
18 * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
19 * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
20 * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
21 * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
22 * ====================================================================
23 */
24
25package com.beetstra.jutf7;
26
27import java.nio.ByteBuffer;
28import java.nio.CharBuffer;
29import java.nio.charset.CharsetDecoder;
30import java.nio.charset.CoderResult;
31
32/**
33 * <p>
34 * The CharsetDecoder used to decode both variants of the UTF-7 charset and the
35 * modified-UTF-7 charset.
36 * </p>
37 *
38 * @author Jaap Beetstra
39 */
40class UTF7StyleCharsetDecoder extends CharsetDecoder {
41    private final Base64Util base64;
42    private final byte shift;
43    private final byte unshift;
44    private final boolean strict;
45    private boolean base64mode;
46    private int bitsRead;
47    private int tempChar;
48    private boolean justShifted;
49    private boolean justUnshifted;
50
51    UTF7StyleCharsetDecoder(UTF7StyleCharset cs, Base64Util base64, boolean strict) {
52        super(cs, 0.6f, 1.0f);
53        this.base64 = base64;
54        this.strict = strict;
55        this.shift = cs.shift();
56        this.unshift = cs.unshift();
57    }
58
59    /*
60     * (non-Javadoc)
61     * @see java.nio.charset.CharsetDecoder#decodeLoop(java.nio.ByteBuffer,
62     * java.nio.CharBuffer)
63     */
64    protected CoderResult decodeLoop(ByteBuffer in, CharBuffer out) {
65        while (in.hasRemaining()) {
66            byte b = in.get();
67            if (base64mode) {
68                if (b == unshift) {
69                    if (base64bitsWaiting())
70                        return malformed(in);
71                    if (justShifted) {
72                        if (!out.hasRemaining())
73                            return overflow(in);
74                        out.put((char)shift);
75                    } else
76                        justUnshifted = true;
77                    setUnshifted();
78                } else {
79                    if (!out.hasRemaining())
80                        return overflow(in);
81                    CoderResult result = handleBase64(in, out, b);
82                    if (result != null)
83                        return result;
84                }
85                justShifted = false;
86            } else {
87                if (b == shift) {
88                    base64mode = true;
89                    if (justUnshifted && strict)
90                        return malformed(in);
91                    justShifted = true;
92                    continue;
93                }
94                if (!out.hasRemaining())
95                    return overflow(in);
96                out.put((char)b);
97                justUnshifted = false;
98            }
99        }
100        return CoderResult.UNDERFLOW;
101    }
102
103    private CoderResult overflow(ByteBuffer in) {
104        in.position(in.position() - 1);
105        return CoderResult.OVERFLOW;
106    }
107
108    /**
109     * <p>
110     * Decodes a byte in <i>base 64 mode</i>. Will directly write a character to
111     * the output buffer if completed.
112     * </p>
113     *
114     * @param in The input buffer
115     * @param out The output buffer
116     * @param lastRead Last byte read from the input buffer
117     * @return CoderResult.malformed if a non-base 64 character was encountered
118     *         in strict mode, null otherwise
119     */
120    private CoderResult handleBase64(ByteBuffer in, CharBuffer out, byte lastRead) {
121        CoderResult result = null;
122        int sextet = base64.getSextet(lastRead);
123        if (sextet >= 0) {
124            bitsRead += 6;
125            if (bitsRead < 16) {
126                tempChar += sextet << (16 - bitsRead);
127            } else {
128                bitsRead -= 16;
129                tempChar += sextet >> (bitsRead);
130                out.put((char)tempChar);
131                tempChar = (sextet << (16 - bitsRead)) & 0xFFFF;
132            }
133        } else {
134            if (strict)
135                return malformed(in);
136            out.put((char)lastRead);
137            if (base64bitsWaiting())
138                result = malformed(in);
139            setUnshifted();
140        }
141        return result;
142    }
143
144    /*
145     * (non-Javadoc)
146     * @see java.nio.charset.CharsetDecoder#implFlush(java.nio.CharBuffer)
147     */
148    protected CoderResult implFlush(CharBuffer out) {
149        if ((base64mode && strict) || base64bitsWaiting())
150            return CoderResult.malformedForLength(1);
151        return CoderResult.UNDERFLOW;
152    }
153
154    /*
155     * (non-Javadoc)
156     * @see java.nio.charset.CharsetDecoder#implReset()
157     */
158    protected void implReset() {
159        setUnshifted();
160        justUnshifted = false;
161    }
162
163    /**
164     * <p>
165     * Resets the input buffer position to just before the last byte read, and
166     * returns a result indicating to skip the last byte.
167     * </p>
168     *
169     * @param in The input buffer
170     * @return CoderResult.malformedForLength(1);
171     */
172    private CoderResult malformed(ByteBuffer in) {
173        in.position(in.position() - 1);
174        return CoderResult.malformedForLength(1);
175    }
176
177    /**
178     * @return True if there are base64 encoded characters waiting to be written
179     */
180    private boolean base64bitsWaiting() {
181        return tempChar != 0 || bitsRead >= 6;
182    }
183
184    /**
185     * <p>
186     * Updates internal state to reflect the decoder is no longer in <i>base 64
187     * mode</i>
188     * </p>
189     */
190    private void setUnshifted() {
191        base64mode = false;
192        bitsRead = 0;
193        tempChar = 0;
194    }
195}
196