session-android/src/com/android/gallery3d/data/Exif.java

/*
 * Copyright (C) 2011 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.android.gallery3d.data;

import android.util.Log;

import java.io.IOException;
import java.io.InputStream;

public class Exif {
    private static final String TAG = "CameraExif";

    public static int getOrientation(InputStream is) {
        if (is == null) {
            return 0;
        }

        byte[] buf = new byte[8];
        int length = 0;

        // ISO/IEC 10918-1:1993(E)
        while (read(is, buf, 2) && (buf[0] & 0xFF) == 0xFF) {
            int marker = buf[1] & 0xFF;

            // Check if the marker is a padding.
            if (marker == 0xFF) {
                continue;
            }

            // Check if the marker is SOI or TEM.
            if (marker == 0xD8 || marker == 0x01) {
                continue;
            }
            // Check if the marker is EOI or SOS.
            if (marker == 0xD9 || marker == 0xDA) {
                return 0;
            }

            // Get the length and check if it is reasonable.
            if (!read(is, buf, 2)) {
                return 0;
            }
            length = pack(buf, 0, 2, false);
            if (length < 2) {
                Log.e(TAG, "Invalid length");
                return 0;
            }
            length -= 2;

            // Break if the marker is EXIF in APP1.
            if (marker == 0xE1 && length >= 6) {
                if (!read(is, buf, 6)) return 0;
                length -= 6;
                if (pack(buf, 0, 4, false) == 0x45786966 &&
                    pack(buf, 4, 2, false) == 0) {
                    break;
                }
            }

            // Skip other markers.
            try {
                is.skip(length);
            } catch (IOException ex) {
                return 0;
            }
            length = 0;
        }

        // JEITA CP-3451 Exif Version 2.2
        if (length > 8) {
            int offset = 0;
            byte[] jpeg = new byte[length];
            if (!read(is, jpeg, length)) {
                return 0;
            }

            // Identify the byte order.
            int tag = pack(jpeg, offset, 4, false);
            if (tag != 0x49492A00 && tag != 0x4D4D002A) {
                Log.e(TAG, "Invalid byte order");
                return 0;
            }
            boolean littleEndian = (tag == 0x49492A00);

            // Get the offset and check if it is reasonable.
            int count = pack(jpeg, offset + 4, 4, littleEndian) + 2;
            if (count < 10 || count > length) {
                Log.e(TAG, "Invalid offset");
                return 0;
            }
            offset += count;
            length -= count;

            // Get the count and go through all the elements.
            count = pack(jpeg, offset - 2, 2, littleEndian);
            while (count-- > 0 && length >= 12) {
                // Get the tag and check if it is orientation.
                tag = pack(jpeg, offset, 2, littleEndian);
                if (tag == 0x0112) {
                    // We do not really care about type and count, do we?
                    int orientation = pack(jpeg, offset + 8, 2, littleEndian);
                    switch (orientation) {
                        case 1:
                            return 0;
                        case 3:
                            return 180;
                        case 6:
                            return 90;
                        case 8:
                            return 270;
                    }
                    Log.i(TAG, "Unsupported orientation");
                    return 0;
                }
                offset += 12;
                length -= 12;
            }
        }

        Log.i(TAG, "Orientation not found");
        return 0;
    }

    private static int pack(byte[] bytes, int offset, int length,
            boolean littleEndian) {
        int step = 1;
        if (littleEndian) {
            offset += length - 1;
            step = -1;
        }

        int value = 0;
        while (length-- > 0) {
            value = (value << 8) | (bytes[offset] & 0xFF);
            offset += step;
        }
        return value;
    }

    private static boolean read(InputStream is, byte[] buf, int length) {
        try {
            int read;
            int totalRead = 0;
            while (totalRead != length) {
                if ((read = is.read(buf, totalRead, length - totalRead)) < 0) {
                  Log.w(TAG, "stream EOF'd prematurely");
                  return false;
                }
                totalRead += read;
            }
          return true;
        } catch (IOException ex) {
            return false;
        }
    }
}