1/*
2 * Copyright (C) 2013 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17package com.android.ex.photo.util;
18
19import android.util.Log;
20
21import java.io.ByteArrayInputStream;
22import java.io.InputStream;
23
24public class Exif {
25    private static final String TAG = "CameraExif";
26
27    /**
28     * Returns the degrees in clockwise. Values are 0, 90, 180, or 270.
29     * @param inputStream The input stream will not be closed for you.
30     * @param byteSize Recommended parameter declaring the length of the input stream. If you
31     *                 pass in -1, we will have to read more from the input stream.
32     * @return 0, 90, 180, or 270.
33     */
34    public static int getOrientation(final InputStream inputStream, final long byteSize) {
35        if (inputStream == null) {
36            return 0;
37        }
38
39        /*
40          Looking at this algorithm, we never look ahead more than 8 bytes. As long as we call
41          advanceTo() at the end of every loop, we should never have to reallocate a larger buffer.
42
43          Also, the most we ever read backwards is 4 bytes. pack() reads backwards if the encoding
44          is in little endian format. These following two lines potentially reads 4 bytes backwards:
45
46          int tag = pack(jpeg, offset, 4, false);
47          count = pack(jpeg, offset - 2, 2, littleEndian);
48
49          To be safe, we will always advance to some index-4, so we'll need 4 more for the +8
50          look ahead, which makes it a +12 look ahead total. Use 16 just in case my analysis is off.
51
52          This means we only need to allocate a single 16 byte buffer.
53
54          Note: If you do not pass in byteSize parameter, a single large allocation will occur.
55          For a 1MB image, I see one 30KB allocation. This is due to the line containing:
56
57          has(jpeg, byteSize, offset + length - 1)
58
59          where length is a variable int (around 30KB above) read from the EXIF headers.
60
61          This is still much better than allocating a 1MB byte[] which we were doing before.
62         */
63
64        final int lookAhead = 16;
65        final int readBackwards = 4;
66        final InputStreamBuffer jpeg = new InputStreamBuffer(inputStream, lookAhead, false);
67
68        int offset = 0;
69        int length = 0;
70
71        if (has(jpeg, byteSize, 1)) {
72            // JPEG image files begin with FF D8. Only JPEG images have EXIF data.
73            final boolean possibleJpegFormat = jpeg.get(0) == (byte) 0xFF
74                    && jpeg.get(1) == (byte) 0xD8;
75            if (!possibleJpegFormat) {
76                return 0;
77            }
78        }
79
80        // ISO/IEC 10918-1:1993(E)
81        while (has(jpeg, byteSize, offset + 3) && (jpeg.get(offset++) & 0xFF) == 0xFF) {
82            final int marker = jpeg.get(offset) & 0xFF;
83
84            // Check if the marker is a padding.
85            if (marker == 0xFF) {
86                continue;
87            }
88            offset++;
89
90            // Check if the marker is SOI or TEM.
91            if (marker == 0xD8 || marker == 0x01) {
92                continue;
93            }
94            // Check if the marker is EOI or SOS.
95            if (marker == 0xD9 || marker == 0xDA) {
96                // Loop ends.
97                jpeg.advanceTo(offset - readBackwards);
98                break;
99            }
100
101            // Get the length and check if it is reasonable.
102            length = pack(jpeg, offset, 2, false);
103            if (length < 2 || !has(jpeg, byteSize, offset + length - 1)) {
104                Log.e(TAG, "Invalid length");
105                return 0;
106            }
107
108            // Break if the marker is EXIF in APP1.
109            if (marker == 0xE1 && length >= 8 &&
110                    pack(jpeg, offset + 2, 4, false) == 0x45786966 &&
111                    pack(jpeg, offset + 6, 2, false) == 0) {
112                offset += 8;
113                length -= 8;
114                // Loop ends.
115                jpeg.advanceTo(offset - readBackwards);
116                break;
117            }
118
119            // Skip other markers.
120            offset += length;
121            length = 0;
122
123            // Loop ends.
124            jpeg.advanceTo(offset - readBackwards);
125        }
126
127        // JEITA CP-3451 Exif Version 2.2
128        if (length > 8) {
129            // Identify the byte order.
130            int tag = pack(jpeg, offset, 4, false);
131            if (tag != 0x49492A00 && tag != 0x4D4D002A) {
132                Log.e(TAG, "Invalid byte order");
133                return 0;
134            }
135            final boolean littleEndian = (tag == 0x49492A00);
136
137            // Get the offset and check if it is reasonable.
138            int count = pack(jpeg, offset + 4, 4, littleEndian) + 2;
139            if (count < 10 || count > length) {
140                Log.e(TAG, "Invalid offset");
141                return 0;
142            }
143            offset += count;
144            length -= count;
145
146            // Offset has changed significantly.
147            jpeg.advanceTo(offset - readBackwards);
148
149            // Get the count and go through all the elements.
150            count = pack(jpeg, offset - 2, 2, littleEndian);
151
152            while (count-- > 0 && length >= 12) {
153                // Get the tag and check if it is orientation.
154                tag = pack(jpeg, offset, 2, littleEndian);
155                if (tag == 0x0112) {
156                    // We do not really care about type and count, do we?
157                    final int orientation = pack(jpeg, offset + 8, 2, littleEndian);
158                    switch (orientation) {
159                        case 1:
160                            return 0;
161                        case 3:
162                            return 180;
163                        case 6:
164                            return 90;
165                        case 8:
166                            return 270;
167                    }
168                    Log.i(TAG, "Unsupported orientation");
169                    return 0;
170                }
171                offset += 12;
172                length -= 12;
173
174                // Loop ends.
175                jpeg.advanceTo(offset - readBackwards);
176            }
177        }
178
179        return 0;
180    }
181
182    private static int pack(final InputStreamBuffer bytes, int offset, int length,
183            final boolean littleEndian) {
184        int step = 1;
185        if (littleEndian) {
186            offset += length - 1;
187            step = -1;
188        }
189
190        int value = 0;
191        while (length-- > 0) {
192            value = (value << 8) | (bytes.get(offset) & 0xFF);
193            offset += step;
194        }
195        return value;
196    }
197
198    private static boolean has(final InputStreamBuffer jpeg, final long byteSize, final int index) {
199        if (byteSize >= 0) {
200            return index < byteSize;
201        } else {
202            // For large values of index, this will cause the internal buffer to resize.
203            return jpeg.has(index);
204        }
205    }
206
207    @Deprecated
208    public static int getOrientation(final byte[] jpeg) {
209        return getOrientation(new ByteArrayInputStream(jpeg), jpeg.length);
210    }
211}
212