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/*
* Copyright 2002-2017 Drew Noakes
*
* 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.
*
* More information about this project is available at:
*
* https://drewnoakes.com/code/exif/
* https://github.com/drewnoakes/metadata-extractor
*/
package com.drew.imaging.jpeg;
import com.drew.lang.SequentialReader;
import com.drew.lang.StreamReader;
import com.drew.lang.annotations.NotNull;
import com.drew.lang.annotations.Nullable;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.util.HashSet;
import java.util.Set;
/**
* Performs read functions of JPEG files, returning specific file segments.
* <p>
* JPEG files are composed of a sequence of consecutive JPEG 'segments'. Each is identified by one of a set of byte
* values, modelled in the {@link JpegSegmentType} enumeration. Use <code>readSegments</code> to read out the some
* or all segments into a {@link JpegSegmentData} object, from which the raw JPEG segment byte arrays may be accessed.
*
* @author Drew Noakes https://drewnoakes.com
*/
public class JpegSegmentReader
{
/**
* The 0xFF byte that signals the start of a segment.
*/
private static final byte SEGMENT_IDENTIFIER = (byte) 0xFF;
/**
* Private, because this segment crashes my algorithm, and searching for it doesn't work (yet).
*/
private static final byte SEGMENT_SOS = (byte) 0xDA;
/**
* Private, because one wouldn't search for it.
*/
private static final byte MARKER_EOI = (byte) 0xD9;
/**
* Processes the provided JPEG data, and extracts the specified JPEG segments into a {@link JpegSegmentData} object.
* <p>
* Will not return SOS (start of scan) or EOI (end of image) segments.
*
* @param file a {@link File} from which the JPEG data will be read.
* @param segmentTypes the set of JPEG segments types that are to be returned. If this argument is <code>null</code>
* then all found segment types are returned.
*/
@NotNull
public static JpegSegmentData readSegments(@NotNull File file, @Nullable Iterable<JpegSegmentType> segmentTypes) throws JpegProcessingException, IOException
{
FileInputStream stream = null;
try {
stream = new FileInputStream(file);
return readSegments(new StreamReader(stream), segmentTypes);
} finally {
if (stream != null) {
stream.close();
}
}
}
/**
* Processes the provided JPEG data, and extracts the specified JPEG segments into a {@link JpegSegmentData} object.
* <p>
* Will not return SOS (start of scan) or EOI (end of image) segments.
*
* @param reader a {@link SequentialReader} from which the JPEG data will be read. It must be positioned at the
* beginning of the JPEG data stream.
* @param segmentTypes the set of JPEG segments types that are to be returned. If this argument is <code>null</code>
* then all found segment types are returned.
*/
@NotNull
public static JpegSegmentData readSegments(@NotNull final SequentialReader reader, @Nullable Iterable<JpegSegmentType> segmentTypes) throws JpegProcessingException, IOException
{
// Must be big-endian
assert (reader.isMotorolaByteOrder());
// first two bytes should be JPEG magic number
final int magicNumber = reader.getUInt16();
if (magicNumber != 0xFFD8) {
throw new JpegProcessingException("JPEG data is expected to begin with 0xFFD8 (ÿØ) not 0x" + Integer.toHexString(magicNumber));
}
Set<Byte> segmentTypeBytes = null;
if (segmentTypes != null) {
segmentTypeBytes = new HashSet<Byte>();
for (JpegSegmentType segmentType : segmentTypes) {
segmentTypeBytes.add(segmentType.byteValue);
}
}
JpegSegmentData segmentData = new JpegSegmentData();
do {
// Find the segment marker. Markers are zero or more 0xFF bytes, followed
// by a 0xFF and then a byte not equal to 0x00 or 0xFF.
byte segmentIdentifier = reader.getInt8();
byte segmentType = reader.getInt8();
// Read until we have a 0xFF byte followed by a byte that is not 0xFF or 0x00
while (segmentIdentifier != SEGMENT_IDENTIFIER || segmentType == SEGMENT_IDENTIFIER || segmentType == 0) {
segmentIdentifier = segmentType;
segmentType = reader.getInt8();
}
if (segmentType == SEGMENT_SOS) {
// The 'Start-Of-Scan' segment's length doesn't include the image data, instead would
// have to search for the two bytes: 0xFF 0xD9 (EOI).
// It comes last so simply return at this point
return segmentData;
}
if (segmentType == MARKER_EOI) {
// the 'End-Of-Image' segment -- this should never be found in this fashion
return segmentData;
}
// next 2-bytes are <segment-size>: [high-byte] [low-byte]
int segmentLength = reader.getUInt16();
// segment length includes size bytes, so subtract two
segmentLength -= 2;
if (segmentLength < 0)
throw new JpegProcessingException("JPEG segment size would be less than zero");
// Check whether we are interested in this segment
if (segmentTypeBytes == null || segmentTypeBytes.contains(segmentType)) {
byte[] segmentBytes = reader.getBytes(segmentLength);
assert (segmentLength == segmentBytes.length);
segmentData.addSegment(segmentType, segmentBytes);
} else {
// Some if the JPEG is truncated, just return what data we've already gathered
if (!reader.trySkip(segmentLength)) {
return segmentData;
}
}
} while (true);
}
private JpegSegmentReader() throws Exception
{
throw new Exception("Not intended for instantiation.");
}
}
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