com.drew.lang.RandomAccessStreamReader Maven / Gradle / Ivy
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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.lang;
import com.drew.lang.annotations.NotNull;
import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
/**
* @author Drew Noakes https://drewnoakes.com
*/
public class RandomAccessStreamReader extends RandomAccessReader
{
public final static int DEFAULT_CHUNK_LENGTH = 2 * 1024;
@NotNull
private final InputStream _stream;
private final int _chunkLength;
private final ArrayList _chunks = new ArrayList();
private boolean _isStreamFinished;
private long _streamLength;
public RandomAccessStreamReader(@NotNull InputStream stream)
{
this(stream, DEFAULT_CHUNK_LENGTH, -1);
}
public RandomAccessStreamReader(@NotNull InputStream stream, int chunkLength)
{
this(stream, chunkLength, -1);
}
public RandomAccessStreamReader(@NotNull InputStream stream, int chunkLength, long streamLength)
{
if (stream == null)
throw new NullPointerException();
if (chunkLength <= 0)
throw new IllegalArgumentException("chunkLength must be greater than zero");
_chunkLength = chunkLength;
_stream = stream;
_streamLength = streamLength;
}
/**
* Reads to the end of the stream, in order to determine the total number of bytes.
* In general, this is not a good idea for this implementation of {@link RandomAccessReader}.
*
* @return the length of the data source, in bytes.
*/
@Override
public long getLength() throws IOException
{
if (_streamLength != -1) {
return _streamLength;
}
isValidIndex(Integer.MAX_VALUE, 1);
assert(_isStreamFinished);
return _streamLength;
}
/**
* Ensures that the buffered bytes extend to cover the specified index. If not, an attempt is made
* to read to that point.
*
* If the stream ends before the point is reached, a {@link BufferBoundsException} is raised.
*
* @param index the index from which the required bytes start
* @param bytesRequested the number of bytes which are required
* @throws BufferBoundsException if the stream ends before the required number of bytes are acquired
*/
@Override
protected void validateIndex(int index, int bytesRequested) throws IOException
{
if (index < 0) {
throw new BufferBoundsException(String.format("Attempt to read from buffer using a negative index (%d)", index));
} else if (bytesRequested < 0) {
throw new BufferBoundsException("Number of requested bytes must be zero or greater");
} else if ((long)index + bytesRequested - 1 > Integer.MAX_VALUE) {
throw new BufferBoundsException(String.format("Number of requested bytes summed with starting index exceed maximum range of signed 32 bit integers (requested index: %d, requested count: %d)", index, bytesRequested));
}
if (!isValidIndex(index, bytesRequested)) {
assert(_isStreamFinished);
// TODO test that can continue using an instance of this type after this exception
throw new BufferBoundsException(index, bytesRequested, _streamLength);
}
}
@Override
protected boolean isValidIndex(int index, int bytesRequested) throws IOException
{
if (index < 0 || bytesRequested < 0) {
return false;
}
long endIndexLong = (long)index + bytesRequested - 1;
if (endIndexLong > Integer.MAX_VALUE) {
return false;
}
int endIndex = (int)endIndexLong;
if (_isStreamFinished) {
return endIndex < _streamLength;
}
int chunkIndex = endIndex / _chunkLength;
// TODO test loading several chunks for a single request
while (chunkIndex >= _chunks.size()) {
assert (!_isStreamFinished);
byte[] chunk = new byte[_chunkLength];
int totalBytesRead = 0;
while (!_isStreamFinished && totalBytesRead != _chunkLength) {
int bytesRead = _stream.read(chunk, totalBytesRead, _chunkLength - totalBytesRead);
if (bytesRead == -1) {
// the stream has ended, which may be ok
_isStreamFinished = true;
int observedStreamLength = _chunks.size() * _chunkLength + totalBytesRead;
if (_streamLength == -1) {
_streamLength = observedStreamLength;
} else if (_streamLength != observedStreamLength) {
assert(false);
}
// check we have enough bytes for the requested index
if (endIndex >= _streamLength) {
_chunks.add(chunk);
return false;
}
} else {
totalBytesRead += bytesRead;
}
}
_chunks.add(chunk);
}
return true;
}
@Override
public int toUnshiftedOffset(int localOffset)
{
return localOffset;
}
@Override
public byte getByte(int index) throws IOException
{
assert(index >= 0);
final int chunkIndex = index / _chunkLength;
final int innerIndex = index % _chunkLength;
final byte[] chunk = _chunks.get(chunkIndex);
return chunk[innerIndex];
}
@NotNull
@Override
public byte[] getBytes(int index, int count) throws IOException
{
validateIndex(index, count);
byte[] bytes = new byte[count];
int remaining = count;
int fromIndex = index;
int toIndex = 0;
while (remaining != 0) {
int fromChunkIndex = fromIndex / _chunkLength;
int fromInnerIndex = fromIndex % _chunkLength;
int length = Math.min(remaining, _chunkLength - fromInnerIndex);
byte[] chunk = _chunks.get(fromChunkIndex);
System.arraycopy(chunk, fromInnerIndex, bytes, toIndex, length);
remaining -= length;
fromIndex += length;
toIndex += length;
}
return bytes;
}
}