gallery3d/exif/ExifParser.java

/*
 * Copyright (C) 2012 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.exif;

import android.util.Log;

import java.io.IOException;
import java.io.InputStream;
import java.nio.ByteOrder;
import java.nio.charset.Charset;
import java.util.Map.Entry;
import java.util.TreeMap;

/**
 * This class provides a low-level EXIF parsing API. Given a JPEG format
 * InputStream, the caller can request which IFD's to read via
 * {@link #parse(InputStream, int)} with given options.
 * <p>
 * Below is an example of getting EXIF data from IFD 0 and EXIF IFD using the
 * parser.
 *
 * <pre>
 * void parse() {
 *     ExifParser parser = ExifParser.parse(mImageInputStream,
 *             ExifParser.OPTION_IFD_0 | ExifParser.OPTIONS_IFD_EXIF);
 *     int event = parser.next();
 *     while (event != ExifParser.EVENT_END) {
 *         switch (event) {
 *             case ExifParser.EVENT_START_OF_IFD:
 *                 break;
 *             case ExifParser.EVENT_NEW_TAG:
 *                 ExifTag tag = parser.getTag();
 *                 if (!tag.hasValue()) {
 *                     parser.registerForTagValue(tag);
 *                 } else {
 *                     processTag(tag);
 *                 }
 *                 break;
 *             case ExifParser.EVENT_VALUE_OF_REGISTERED_TAG:
 *                 tag = parser.getTag();
 *                 if (tag.getDataType() != ExifTag.TYPE_UNDEFINED) {
 *                     processTag(tag);
 *                 }
 *                 break;
 *         }
 *         event = parser.next();
 *     }
 * }
 *
 * void processTag(ExifTag tag) {
 *     // process the tag as you like.
 * }
 * </pre>
 */
class ExifParser {
    private static final boolean LOGV = false;
    private static final String TAG = "ExifParser";
    /**
     * When the parser reaches a new IFD area. Call {@link #getCurrentIfd()} to
     * know which IFD we are in.
     */
    public static final int EVENT_START_OF_IFD = 0;
    /**
     * When the parser reaches a new tag. Call {@link #getTag()}to get the
     * corresponding tag.
     */
    public static final int EVENT_NEW_TAG = 1;
    /**
     * When the parser reaches the value area of tag that is registered by
     * {@link #registerForTagValue(ExifTag)} previously. Call {@link #getTag()}
     * to get the corresponding tag.
     */
    public static final int EVENT_VALUE_OF_REGISTERED_TAG = 2;

    /**
     * When the parser reaches the compressed image area.
     */
    public static final int EVENT_COMPRESSED_IMAGE = 3;
    /**
     * When the parser reaches the uncompressed image strip. Call
     * {@link #getStripIndex()} to get the index of the strip.
     *
     * @see #getStripIndex()
     * @see #getStripCount()
     */
    public static final int EVENT_UNCOMPRESSED_STRIP = 4;
    /**
     * When there is nothing more to parse.
     */
    public static final int EVENT_END = 5;

    /**
     * Option bit to request to parse IFD0.
     */
    public static final int OPTION_IFD_0 = 1 << 0;
    /**
     * Option bit to request to parse IFD1.
     */
    public static final int OPTION_IFD_1 = 1 << 1;
    /**
     * Option bit to request to parse Exif-IFD.
     */
    public static final int OPTION_IFD_EXIF = 1 << 2;
    /**
     * Option bit to request to parse GPS-IFD.
     */
    public static final int OPTION_IFD_GPS = 1 << 3;
    /**
     * Option bit to request to parse Interoperability-IFD.
     */
    public static final int OPTION_IFD_INTEROPERABILITY = 1 << 4;
    /**
     * Option bit to request to parse thumbnail.
     */
    public static final int OPTION_THUMBNAIL = 1 << 5;

    protected static final int EXIF_HEADER = 0x45786966; // EXIF header "Exif"
    protected static final short EXIF_HEADER_TAIL = (short) 0x0000; // EXIF header in APP1

    // TIFF header
    protected static final short LITTLE_ENDIAN_TAG = (short) 0x4949; // "II"
    protected static final short BIG_ENDIAN_TAG = (short) 0x4d4d; // "MM"
    protected static final short TIFF_HEADER_TAIL = 0x002A;

    protected static final int TAG_SIZE = 12;
    protected static final int OFFSET_SIZE = 2;

    private static final Charset US_ASCII = Charset.forName("US-ASCII");

    protected static final int DEFAULT_IFD0_OFFSET = 8;

    private final CountedDataInputStream mTiffStream;
    private final int mOptions;
    private int mIfdStartOffset = 0;
    private int mNumOfTagInIfd = 0;
    private int mIfdType;
    private ExifTag mTag;
    private ImageEvent mImageEvent;
    private int mStripCount;
    private ExifTag mStripSizeTag;
    private ExifTag mJpegSizeTag;
    private boolean mNeedToParseOffsetsInCurrentIfd;
    private boolean mContainExifData = false;
    private int mApp1End;
    private int mOffsetToApp1EndFromSOF = 0;
    private byte[] mDataAboveIfd0;
    private int mIfd0Position;
    private int mTiffStartPosition;
    private final ExifInterface mInterface;

    private static final short TAG_EXIF_IFD = ExifInterface
            .getTrueTagKey(ExifInterface.TAG_EXIF_IFD);
    private static final short TAG_GPS_IFD = ExifInterface.getTrueTagKey(ExifInterface.TAG_GPS_IFD);
    private static final short TAG_INTEROPERABILITY_IFD = ExifInterface
            .getTrueTagKey(ExifInterface.TAG_INTEROPERABILITY_IFD);
    private static final short TAG_JPEG_INTERCHANGE_FORMAT = ExifInterface
            .getTrueTagKey(ExifInterface.TAG_JPEG_INTERCHANGE_FORMAT);
    private static final short TAG_JPEG_INTERCHANGE_FORMAT_LENGTH = ExifInterface
            .getTrueTagKey(ExifInterface.TAG_JPEG_INTERCHANGE_FORMAT_LENGTH);
    private static final short TAG_STRIP_OFFSETS = ExifInterface
            .getTrueTagKey(ExifInterface.TAG_STRIP_OFFSETS);
    private static final short TAG_STRIP_BYTE_COUNTS = ExifInterface
            .getTrueTagKey(ExifInterface.TAG_STRIP_BYTE_COUNTS);

    private final TreeMap<Integer, Object> mCorrespondingEvent = new TreeMap<Integer, Object>();

    private boolean isIfdRequested(int ifdType) {
        switch (ifdType) {
            case IfdId.TYPE_IFD_0:
                return (mOptions & OPTION_IFD_0) != 0;
            case IfdId.TYPE_IFD_1:
                return (mOptions & OPTION_IFD_1) != 0;
            case IfdId.TYPE_IFD_EXIF:
                return (mOptions & OPTION_IFD_EXIF) != 0;
            case IfdId.TYPE_IFD_GPS:
                return (mOptions & OPTION_IFD_GPS) != 0;
            case IfdId.TYPE_IFD_INTEROPERABILITY:
                return (mOptions & OPTION_IFD_INTEROPERABILITY) != 0;
        }
        return false;
    }

    private boolean isThumbnailRequested() {
        return (mOptions & OPTION_THUMBNAIL) != 0;
    }

    private ExifParser(InputStream inputStream, int options, ExifInterface iRef)
            throws IOException, ExifInvalidFormatException {
        if (inputStream == null) {
            throw new IOException("Null argument inputStream to ExifParser");
        }
        if (LOGV) {
            Log.v(TAG, "Reading exif...");
        }
        mInterface = iRef;
        mContainExifData = seekTiffData(inputStream);
        mTiffStream = new CountedDataInputStream(inputStream);
        mOptions = options;
        if (!mContainExifData) {
            return;
        }

        parseTiffHeader();
        long offset = mTiffStream.readUnsignedInt();
        if (offset > Integer.MAX_VALUE) {
            throw new ExifInvalidFormatException("Invalid offset " + offset);
        }
        mIfd0Position = (int) offset;
        mIfdType = IfdId.TYPE_IFD_0;
        if (isIfdRequested(IfdId.TYPE_IFD_0) || needToParseOffsetsInCurrentIfd()) {
            registerIfd(IfdId.TYPE_IFD_0, offset);
            if (offset != DEFAULT_IFD0_OFFSET) {
                mDataAboveIfd0 = new byte[(int) offset - DEFAULT_IFD0_OFFSET];
                read(mDataAboveIfd0);
            }
        }
    }

    /**
     * Parses the the given InputStream with the given options
     *
     * @exception IOException
     * @exception ExifInvalidFormatException
     */
    protected static ExifParser parse(InputStream inputStream, int options, ExifInterface iRef)
            throws IOException, ExifInvalidFormatException {
        return new ExifParser(inputStream, options, iRef);
    }

    /**
     * Parses the the given InputStream with default options; that is, every IFD
     * and thumbnaill will be parsed.
     *
     * @exception IOException
     * @exception ExifInvalidFormatException
     * @see #parse(InputStream, int)
     */
    protected static ExifParser parse(InputStream inputStream, ExifInterface iRef)
            throws IOException, ExifInvalidFormatException {
        return new ExifParser(inputStream, OPTION_IFD_0 | OPTION_IFD_1
                | OPTION_IFD_EXIF | OPTION_IFD_GPS | OPTION_IFD_INTEROPERABILITY
                | OPTION_THUMBNAIL, iRef);
    }

    /**
     * Moves the parser forward and returns the next parsing event
     *
     * @exception IOException
     * @exception ExifInvalidFormatException
     * @see #EVENT_START_OF_IFD
     * @see #EVENT_NEW_TAG
     * @see #EVENT_VALUE_OF_REGISTERED_TAG
     * @see #EVENT_COMPRESSED_IMAGE
     * @see #EVENT_UNCOMPRESSED_STRIP
     * @see #EVENT_END
     */
    protected int next() throws IOException, ExifInvalidFormatException {
        if (!mContainExifData) {
            return EVENT_END;
        }
        int offset = mTiffStream.getReadByteCount();
        int endOfTags = mIfdStartOffset + OFFSET_SIZE + TAG_SIZE * mNumOfTagInIfd;
        if (offset < endOfTags) {
            mTag = readTag();
            if (mTag == null) {
                return next();
            }
            if (mNeedToParseOffsetsInCurrentIfd) {
                checkOffsetOrImageTag(mTag);
            }
            return EVENT_NEW_TAG;
        } else if (offset == endOfTags) {
            // There is a link to ifd1 at the end of ifd0
            if (mIfdType == IfdId.TYPE_IFD_0) {
                long ifdOffset = readUnsignedLong();
                if (isIfdRequested(IfdId.TYPE_IFD_1) || isThumbnailRequested()) {
                    if (ifdOffset != 0) {
                        registerIfd(IfdId.TYPE_IFD_1, ifdOffset);
                    }
                }
            } else {
                int offsetSize = 4;
                // Some camera models use invalid length of the offset
                if (mCorrespondingEvent.size() > 0) {
                    offsetSize = mCorrespondingEvent.firstEntry().getKey() -
                            mTiffStream.getReadByteCount();
                }
                if (offsetSize < 4) {
                    Log.w(TAG, "Invalid size of link to next IFD: " + offsetSize);
                } else {
                    long ifdOffset = readUnsignedLong();
                    if (ifdOffset != 0) {
                        Log.w(TAG, "Invalid link to next IFD: " + ifdOffset);
                    }
                }
            }
        }
        while (mCorrespondingEvent.size() != 0) {
            Entry<Integer, Object> entry = mCorrespondingEvent.pollFirstEntry();
            Object event = entry.getValue();
            try {
                skipTo(entry.getKey());
            } catch (IOException e) {
                Log.w(TAG, "Failed to skip to data at: " + entry.getKey() +
                        " for " + event.getClass().getName() + ", the file may be broken.");
                continue;
            }
            if (event instanceof IfdEvent) {
                mIfdType = ((IfdEvent) event).ifd;
                mNumOfTagInIfd = mTiffStream.readUnsignedShort();
                mIfdStartOffset = entry.getKey();

                if (mNumOfTagInIfd * TAG_SIZE + mIfdStartOffset + OFFSET_SIZE > mApp1End) {
                    Log.w(TAG, "Invalid size of IFD " + mIfdType);
                    return EVENT_END;
                }

                mNeedToParseOffsetsInCurrentIfd = needToParseOffsetsInCurrentIfd();
                if (((IfdEvent) event).isRequested) {
                    return EVENT_START_OF_IFD;
                } else {
                    skipRemainingTagsInCurrentIfd();
                }
            } else if (event instanceof ImageEvent) {
                mImageEvent = (ImageEvent) event;
                return mImageEvent.type;
            } else {
                ExifTagEvent tagEvent = (ExifTagEvent) event;
                mTag = tagEvent.tag;
                if (mTag.getDataType() != ExifTag.TYPE_UNDEFINED) {
                    readFullTagValue(mTag);
                    checkOffsetOrImageTag(mTag);
                }
                if (tagEvent.isRequested) {
                    return EVENT_VALUE_OF_REGISTERED_TAG;
                }
            }
        }
        return EVENT_END;
    }

    /**
     * Skips the tags area of current IFD, if the parser is not in the tag area,
     * nothing will happen.
     *
     * @throws IOException
     * @throws ExifInvalidFormatException
     */
    protected void skipRemainingTagsInCurrentIfd() throws IOException, ExifInvalidFormatException {
        int endOfTags = mIfdStartOffset + OFFSET_SIZE + TAG_SIZE * mNumOfTagInIfd;
        int offset = mTiffStream.getReadByteCount();
        if (offset > endOfTags) {
            return;
        }
        if (mNeedToParseOffsetsInCurrentIfd) {
            while (offset < endOfTags) {
                mTag = readTag();
                offset += TAG_SIZE;
                if (mTag == null) {
                    continue;
                }
                checkOffsetOrImageTag(mTag);
            }
        } else {
            skipTo(endOfTags);
        }
        long ifdOffset = readUnsignedLong();
        // For ifd0, there is a link to ifd1 in the end of all tags
        if (mIfdType == IfdId.TYPE_IFD_0
                && (isIfdRequested(IfdId.TYPE_IFD_1) || isThumbnailRequested())) {
            if (ifdOffset > 0) {
                registerIfd(IfdId.TYPE_IFD_1, ifdOffset);
            }
        }
    }

    private boolean needToParseOffsetsInCurrentIfd() {
        switch (mIfdType) {
            case IfdId.TYPE_IFD_0:
                return isIfdRequested(IfdId.TYPE_IFD_EXIF) || isIfdRequested(IfdId.TYPE_IFD_GPS)
                        || isIfdRequested(IfdId.TYPE_IFD_INTEROPERABILITY)
                        || isIfdRequested(IfdId.TYPE_IFD_1);
            case IfdId.TYPE_IFD_1:
                return isThumbnailRequested();
            case IfdId.TYPE_IFD_EXIF:
                // The offset to interoperability IFD is located in Exif IFD
                return isIfdRequested(IfdId.TYPE_IFD_INTEROPERABILITY);
            default:
                return false;
        }
    }

    /**
     * If {@link #next()} return {@link #EVENT_NEW_TAG} or
     * {@link #EVENT_VALUE_OF_REGISTERED_TAG}, call this function to get the
     * corresponding tag.
     * <p>
     * For {@link #EVENT_NEW_TAG}, the tag may not contain the value if the size
     * of the value is greater than 4 bytes. One should call
     * {@link ExifTag#hasValue()} to check if the tag contains value. If there
     * is no value,call {@link #registerForTagValue(ExifTag)} to have the parser
     * emit {@link #EVENT_VALUE_OF_REGISTERED_TAG} when it reaches the area
     * pointed by the offset.
     * <p>
     * When {@link #EVENT_VALUE_OF_REGISTERED_TAG} is emitted, the value of the
     * tag will have already been read except for tags of undefined type. For
     * tags of undefined type, call one of the read methods to get the value.
     *
     * @see #registerForTagValue(ExifTag)
     * @see #read(byte[])
     * @see #read(byte[], int, int)
     * @see #readLong()
     * @see #readRational()
     * @see #readString(int)
     * @see #readString(int, Charset)
     */
    protected ExifTag getTag() {
        return mTag;
    }

    /**
     * Gets number of tags in the current IFD area.
     */
    protected int getTagCountInCurrentIfd() {
        return mNumOfTagInIfd;
    }

    /**
     * Gets the ID of current IFD.
     *
     * @see IfdId#TYPE_IFD_0
     * @see IfdId#TYPE_IFD_1
     * @see IfdId#TYPE_IFD_GPS
     * @see IfdId#TYPE_IFD_INTEROPERABILITY
     * @see IfdId#TYPE_IFD_EXIF
     */
    protected int getCurrentIfd() {
        return mIfdType;
    }

    /**
     * When receiving {@link #EVENT_UNCOMPRESSED_STRIP}, call this function to
     * get the index of this strip.
     *
     * @see #getStripCount()
     */
    protected int getStripIndex() {
        return mImageEvent.stripIndex;
    }

    /**
     * When receiving {@link #EVENT_UNCOMPRESSED_STRIP}, call this function to
     * get the number of strip data.
     *
     * @see #getStripIndex()
     */
    protected int getStripCount() {
        return mStripCount;
    }

    /**
     * When receiving {@link #EVENT_UNCOMPRESSED_STRIP}, call this function to
     * get the strip size.
     */
    protected int getStripSize() {
        if (mStripSizeTag == null)
            return 0;
        return (int) mStripSizeTag.getValueAt(0);
    }

    /**
     * When receiving {@link #EVENT_COMPRESSED_IMAGE}, call this function to get
     * the image data size.
     */
    protected int getCompressedImageSize() {
        if (mJpegSizeTag == null) {
            return 0;
        }
        return (int) mJpegSizeTag.getValueAt(0);
    }

    private void skipTo(int offset) throws IOException {
        mTiffStream.skipTo(offset);
        while (!mCorrespondingEvent.isEmpty() && mCorrespondingEvent.firstKey() < offset) {
            mCorrespondingEvent.pollFirstEntry();
        }
    }

    /**
     * When getting {@link #EVENT_NEW_TAG} in the tag area of IFD, the tag may
     * not contain the value if the size of the value is greater than 4 bytes.
     * When the value is not available here, call this method so that the parser
     * will emit {@link #EVENT_VALUE_OF_REGISTERED_TAG} when it reaches the area
     * where the value is located.
     *
     * @see #EVENT_VALUE_OF_REGISTERED_TAG
     */
    protected void registerForTagValue(ExifTag tag) {
        if (tag.getOffset() >= mTiffStream.getReadByteCount()) {
            mCorrespondingEvent.put(tag.getOffset(), new ExifTagEvent(tag, true));
        }
    }

    private void registerIfd(int ifdType, long offset) {
        // Cast unsigned int to int since the offset is always smaller
        // than the size of APP1 (65536)
        mCorrespondingEvent.put((int) offset, new IfdEvent(ifdType, isIfdRequested(ifdType)));
    }

    private void registerCompressedImage(long offset) {
        mCorrespondingEvent.put((int) offset, new ImageEvent(EVENT_COMPRESSED_IMAGE));
    }

    private void registerUncompressedStrip(int stripIndex, long offset) {
        mCorrespondingEvent.put((int) offset, new ImageEvent(EVENT_UNCOMPRESSED_STRIP
                , stripIndex));
    }

    private ExifTag readTag() throws IOException, ExifInvalidFormatException {
        short tagId = mTiffStream.readShort();
        short dataFormat = mTiffStream.readShort();
        long numOfComp = mTiffStream.readUnsignedInt();
        if (numOfComp > Integer.MAX_VALUE) {
            throw new ExifInvalidFormatException(
                    "Number of component is larger then Integer.MAX_VALUE");
        }
        // Some invalid image file contains invalid data type. Ignore those tags
        if (!ExifTag.isValidType(dataFormat)) {
            Log.w(TAG, String.format("Tag %04x: Invalid data type %d", tagId, dataFormat));
            mTiffStream.skip(4);
            return null;
        }
        // TODO: handle numOfComp overflow
        ExifTag tag = new ExifTag(tagId, dataFormat, (int) numOfComp, mIfdType,
                ((int) numOfComp) != ExifTag.SIZE_UNDEFINED);
        int dataSize = tag.getDataSize();
        if (dataSize > 4) {
            long offset = mTiffStream.readUnsignedInt();
            if (offset > Integer.MAX_VALUE) {
                throw new ExifInvalidFormatException(
                        "offset is larger then Integer.MAX_VALUE");
            }
            // Some invalid images put some undefined data before IFD0.
            // Read the data here.
            if ((offset < mIfd0Position) && (dataFormat == ExifTag.TYPE_UNDEFINED)) {
                byte[] buf = new byte[(int) numOfComp];
                System.arraycopy(mDataAboveIfd0, (int) offset - DEFAULT_IFD0_OFFSET,
                        buf, 0, (int) numOfComp);
                tag.setValue(buf);
            } else {
                tag.setOffset((int) offset);
            }
        } else {
            boolean defCount = tag.hasDefinedCount();
            // Set defined count to 0 so we can add \0 to non-terminated strings
            tag.setHasDefinedCount(false);
            // Read value
            readFullTagValue(tag);
            tag.setHasDefinedCount(defCount);
            mTiffStream.skip(4 - dataSize);
            // Set the offset to the position of value.
            tag.setOffset(mTiffStream.getReadByteCount() - 4);
        }
        return tag;
    }

    /**
     * Check the tag, if the tag is one of the offset tag that points to the IFD
     * or image the caller is interested in, register the IFD or image.
     */
    private void checkOffsetOrImageTag(ExifTag tag) {
        // Some invalid formattd image contains tag with 0 size.
        if (tag.getComponentCount() == 0) {
            return;
        }
        short tid = tag.getTagId();
        int ifd = tag.getIfd();
        if (tid == TAG_EXIF_IFD && checkAllowed(ifd, ExifInterface.TAG_EXIF_IFD)) {
            if (isIfdRequested(IfdId.TYPE_IFD_EXIF)
                    || isIfdRequested(IfdId.TYPE_IFD_INTEROPERABILITY)) {
                registerIfd(IfdId.TYPE_IFD_EXIF, tag.getValueAt(0));
            }
        } else if (tid == TAG_GPS_IFD && checkAllowed(ifd, ExifInterface.TAG_GPS_IFD)) {
            if (isIfdRequested(IfdId.TYPE_IFD_GPS)) {
                registerIfd(IfdId.TYPE_IFD_GPS, tag.getValueAt(0));
            }
        } else if (tid == TAG_INTEROPERABILITY_IFD
                && checkAllowed(ifd, ExifInterface.TAG_INTEROPERABILITY_IFD)) {
            if (isIfdRequested(IfdId.TYPE_IFD_INTEROPERABILITY)) {
                registerIfd(IfdId.TYPE_IFD_INTEROPERABILITY, tag.getValueAt(0));
            }
        } else if (tid == TAG_JPEG_INTERCHANGE_FORMAT
                && checkAllowed(ifd, ExifInterface.TAG_JPEG_INTERCHANGE_FORMAT)) {
            if (isThumbnailRequested()) {
                registerCompressedImage(tag.getValueAt(0));
            }
        } else if (tid == TAG_JPEG_INTERCHANGE_FORMAT_LENGTH
                && checkAllowed(ifd, ExifInterface.TAG_JPEG_INTERCHANGE_FORMAT_LENGTH)) {
            if (isThumbnailRequested()) {
                mJpegSizeTag = tag;
            }
        } else if (tid == TAG_STRIP_OFFSETS && checkAllowed(ifd, ExifInterface.TAG_STRIP_OFFSETS)) {
            if (isThumbnailRequested()) {
                if (tag.hasValue()) {
                    for (int i = 0; i < tag.getComponentCount(); i++) {
                        registerUncompressedStrip(i, tag.getValueAt(i));
                    }
                } else {
                    mCorrespondingEvent.put(tag.getOffset(), new ExifTagEvent(tag, false));
                }
            }
        } else if (tid == TAG_STRIP_BYTE_COUNTS
                && checkAllowed(ifd, ExifInterface.TAG_STRIP_BYTE_COUNTS)
                &&isThumbnailRequested() && tag.hasValue()) {
            mStripSizeTag = tag;
        }
    }

    private boolean checkAllowed(int ifd, int tagId) {
        int info = mInterface.getTagInfo().get(tagId);
        if (info == ExifInterface.DEFINITION_NULL) {
            return false;
        }
        return ExifInterface.isIfdAllowed(info, ifd);
    }

    protected void readFullTagValue(ExifTag tag) throws IOException {
        // Some invalid images contains tags with wrong size, check it here
        short type = tag.getDataType();
        if (type == ExifTag.TYPE_ASCII || type == ExifTag.TYPE_UNDEFINED ||
                type == ExifTag.TYPE_UNSIGNED_BYTE) {
            int size = tag.getComponentCount();
            if (mCorrespondingEvent.size() > 0) {
                if (mCorrespondingEvent.firstEntry().getKey() < mTiffStream.getReadByteCount()
                        + size) {
                    Object event = mCorrespondingEvent.firstEntry().getValue();
                    if (event instanceof ImageEvent) {
                        // Tag value overlaps thumbnail, ignore thumbnail.
                        Log.w(TAG, "Thumbnail overlaps value for tag: \n" + tag.toString());
                        Entry<Integer, Object> entry = mCorrespondingEvent.pollFirstEntry();
                        Log.w(TAG, "Invalid thumbnail offset: " + entry.getKey());
                    } else {
                        // Tag value overlaps another tag, shorten count
                        if (event instanceof IfdEvent) {
                            Log.w(TAG, "Ifd " + ((IfdEvent) event).ifd
                                    + " overlaps value for tag: \n" + tag.toString());
                        } else if (event instanceof ExifTagEvent) {
                            Log.w(TAG, "Tag value for tag: \n"
                                    + ((ExifTagEvent) event).tag.toString()
                                    + " overlaps value for tag: \n" + tag.toString());
                        }
                        size = mCorrespondingEvent.firstEntry().getKey()
                                - mTiffStream.getReadByteCount();
                        Log.w(TAG, "Invalid size of tag: \n" + tag.toString()
                                + " setting count to: " + size);
                        tag.forceSetComponentCount(size);
                    }
                }
            }
        }
        switch (tag.getDataType()) {
            case ExifTag.TYPE_UNSIGNED_BYTE:
            case ExifTag.TYPE_UNDEFINED: {
                byte buf[] = new byte[tag.getComponentCount()];
                read(buf);
                tag.setValue(buf);
            }
                break;
            case ExifTag.TYPE_ASCII:
                tag.setValue(readString(tag.getComponentCount()));
                break;
            case ExifTag.TYPE_UNSIGNED_LONG: {
                long value[] = new long[tag.getComponentCount()];
                for (int i = 0, n = value.length; i < n; i++) {
                    value[i] = readUnsignedLong();
                }
                tag.setValue(value);
            }
                break;
            case ExifTag.TYPE_UNSIGNED_RATIONAL: {
                Rational value[] = new Rational[tag.getComponentCount()];
                for (int i = 0, n = value.length; i < n; i++) {
                    value[i] = readUnsignedRational();
                }
                tag.setValue(value);
            }
                break;
            case ExifTag.TYPE_UNSIGNED_SHORT: {
                int value[] = new int[tag.getComponentCount()];
                for (int i = 0, n = value.length; i < n; i++) {
                    value[i] = readUnsignedShort();
                }
                tag.setValue(value);
            }
                break;
            case ExifTag.TYPE_LONG: {
                int value[] = new int[tag.getComponentCount()];
                for (int i = 0, n = value.length; i < n; i++) {
                    value[i] = readLong();
                }
                tag.setValue(value);
            }
                break;
            case ExifTag.TYPE_RATIONAL: {
                Rational value[] = new Rational[tag.getComponentCount()];
                for (int i = 0, n = value.length; i < n; i++) {
                    value[i] = readRational();
                }
                tag.setValue(value);
            }
                break;
        }
        if (LOGV) {
            Log.v(TAG, "\n" + tag.toString());
        }
    }

    private void parseTiffHeader() throws IOException,
            ExifInvalidFormatException {
        short byteOrder = mTiffStream.readShort();
        if (LITTLE_ENDIAN_TAG == byteOrder) {
            mTiffStream.setByteOrder(ByteOrder.LITTLE_ENDIAN);
        } else if (BIG_ENDIAN_TAG == byteOrder) {
            mTiffStream.setByteOrder(ByteOrder.BIG_ENDIAN);
        } else {
            throw new ExifInvalidFormatException("Invalid TIFF header");
        }

        if (mTiffStream.readShort() != TIFF_HEADER_TAIL) {
            throw new ExifInvalidFormatException("Invalid TIFF header");
        }
    }

    private boolean seekTiffData(InputStream inputStream) throws IOException,
            ExifInvalidFormatException {
        CountedDataInputStream dataStream = new CountedDataInputStream(inputStream);
        if (dataStream.readShort() != JpegHeader.SOI) {
            throw new ExifInvalidFormatException("Invalid JPEG format");
        }

        short marker = dataStream.readShort();
        while (marker != JpegHeader.EOI
                && !JpegHeader.isSofMarker(marker)) {
            int length = dataStream.readUnsignedShort();
            // Some invalid formatted image contains multiple APP1,
            // try to find the one with Exif data.
            if (marker == JpegHeader.APP1) {
                int header = 0;
                short headerTail = 0;
                if (length >= 8) {
                    header = dataStream.readInt();
                    headerTail = dataStream.readShort();
                    length -= 6;
                    if (header == EXIF_HEADER && headerTail == EXIF_HEADER_TAIL) {
                        mTiffStartPosition = dataStream.getReadByteCount();
                        mApp1End = length;
                        mOffsetToApp1EndFromSOF = mTiffStartPosition + mApp1End;
                        return true;
                    }
                }
            }
            if (length < 2 || (length - 2) != dataStream.skip(length - 2)) {
                Log.w(TAG, "Invalid JPEG format.");
                return false;
            }
            marker = dataStream.readShort();
        }
        return false;
    }

    protected int getOffsetToExifEndFromSOF() {
        return mOffsetToApp1EndFromSOF;
    }

    protected int getTiffStartPosition() {
        return mTiffStartPosition;
    }

    /**
     * Reads bytes from the InputStream.
     */
    protected int read(byte[] buffer, int offset, int length) throws IOException {
        return mTiffStream.read(buffer, offset, length);
    }

    /**
     * Equivalent to read(buffer, 0, buffer.length).
     */
    protected int read(byte[] buffer) throws IOException {
        return mTiffStream.read(buffer);
    }

    /**
     * Reads a String from the InputStream with US-ASCII charset. The parser
     * will read n bytes and convert it to ascii string. This is used for
     * reading values of type {@link ExifTag#TYPE_ASCII}.
     */
    protected String readString(int n) throws IOException {
        return readString(n, US_ASCII);
    }

    /**
     * Reads a String from the InputStream with the given charset. The parser
     * will read n bytes and convert it to string. This is used for reading
     * values of type {@link ExifTag#TYPE_ASCII}.
     */
    protected String readString(int n, Charset charset) throws IOException {
        if (n > 0) {
            return mTiffStream.readString(n, charset);
        } else {
            return "";
        }
    }

    /**
     * Reads value of type {@link ExifTag#TYPE_UNSIGNED_SHORT} from the
     * InputStream.
     */
    protected int readUnsignedShort() throws IOException {
        return mTiffStream.readShort() & 0xffff;
    }

    /**
     * Reads value of type {@link ExifTag#TYPE_UNSIGNED_LONG} from the
     * InputStream.
     */
    protected long readUnsignedLong() throws IOException {
        return readLong() & 0xffffffffL;
    }

    /**
     * Reads value of type {@link ExifTag#TYPE_UNSIGNED_RATIONAL} from the
     * InputStream.
     */
    protected Rational readUnsignedRational() throws IOException {
        long nomi = readUnsignedLong();
        long denomi = readUnsignedLong();
        return new Rational(nomi, denomi);
    }

    /**
     * Reads value of type {@link ExifTag#TYPE_LONG} from the InputStream.
     */
    protected int readLong() throws IOException {
        return mTiffStream.readInt();
    }

    /**
     * Reads value of type {@link ExifTag#TYPE_RATIONAL} from the InputStream.
     */
    protected Rational readRational() throws IOException {
        int nomi = readLong();
        int denomi = readLong();
        return new Rational(nomi, denomi);
    }

    private static class ImageEvent {
        int stripIndex;
        int type;

        ImageEvent(int type) {
            this.stripIndex = 0;
            this.type = type;
        }

        ImageEvent(int type, int stripIndex) {
            this.type = type;
            this.stripIndex = stripIndex;
        }
    }

    private static class IfdEvent {
        int ifd;
        boolean isRequested;

        IfdEvent(int ifd, boolean isInterestedIfd) {
            this.ifd = ifd;
            this.isRequested = isInterestedIfd;
        }
    }

    private static class ExifTagEvent {
        ExifTag tag;
        boolean isRequested;

        ExifTagEvent(ExifTag tag, boolean isRequireByUser) {
            this.tag = tag;
            this.isRequested = isRequireByUser;
        }
    }

    /**
     * Gets the byte order of the current InputStream.
     */
    protected ByteOrder getByteOrder() {
        return mTiffStream.getByteOrder();
    }
}