https://source.android.com/ 
/*
 * 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 parse(InputStream, int) with given options. 

Below is an example of getting EXIF data from IFD 0 and EXIF IFD using the
parser.

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.
}



/**
 * 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 getCurrentIfd() to know which IFD we are in. 
/**
     * 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 getTag()to get the corresponding tag. 
/**
     * 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 registerForTagValue(ExifTag) previously. Call getTag() to get the corresponding tag. 
/**
     * 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.

/**
     * 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 getStripIndex() to get the index of the strip. 
See Also:
/**
     * 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.

/**
     * When there is nothing more to parse.
     */
    public static final int EVENT_END = 5;

    
Option bit to request to parse IFD0.

/**
     * Option bit to request to parse IFD0.
     */
    public static final int OPTION_IFD_0 = 1 << 0;
    
Option bit to request to parse IFD1.

/**
     * Option bit to request to parse IFD1.
     */
    public static final int OPTION_IFD_1 = 1 << 1;
    
Option bit to request to parse Exif-IFD.

/**
     * 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.

/**
     * 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.

/**
     * Option bit to request to parse Interoperability-IFD.
     */
    public static final int OPTION_IFD_INTEROPERABILITY = 1 << 4;
    
Option bit to request to parse thumbnail.

/**
     * 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

Throws:
/**
     * 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.

Throws:
See Also:
/**
     * 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

Throws:
See Also:
/**
     * 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:
/**
     * 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 next() return EVENT_NEW_TAG or EVENT_VALUE_OF_REGISTERED_TAG, call this function to get the corresponding tag. 
 For EVENT_NEW_TAG, the tag may not contain the value if the size of the value is greater than 4 bytes. One should call ExifTag.hasValue() to check if the tag contains value. If there is no value,call registerForTagValue(ExifTag) to have the parser emit EVENT_VALUE_OF_REGISTERED_TAG when it reaches the area pointed by the offset. 
 When 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 Also:
/**
     * 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.

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

    
Gets the ID of current IFD.

See Also:
/**
     * 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 EVENT_UNCOMPRESSED_STRIP, call this function to get the index of this strip. 
See Also:
/**
     * 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 EVENT_UNCOMPRESSED_STRIP, call this function to get the number of strip data. 
See Also:
/**
     * 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 EVENT_UNCOMPRESSED_STRIP, call this function to get the strip size. 
/**
     * 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 EVENT_COMPRESSED_IMAGE, call this function to get the image data size. 
/**
     * 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 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 EVENT_VALUE_OF_REGISTERED_TAG when it reaches the area where the value is located. 
See Also:
/**
     * 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.

/**
     * 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++) {
                        if (tag.getDataType() == ExifTag.TYPE_UNSIGNED_SHORT) {
                            registerUncompressedStrip(i, tag.getValueAt(i));
                        } else {
                            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.

/**
     * 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).

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

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

    
Reads value of type ExifTag.TYPE_RATIONAL from the InputStream. 
/**
     * 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.

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