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/*
* Copyright (C) 2018 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.server.backup.encryption.chunking;
import android.annotation.Nullable;
import com.android.internal.util.Preconditions;
import java.io.IOException;
import java.io.OutputStream;
import java.nio.charset.Charset;
import java.util.Locale;
/**
* A {@link DiffScriptWriter} that writes an entire diff script to a single {@link OutputStream}.
*/
public class SingleStreamDiffScriptWriter implements DiffScriptWriter {
static final byte LINE_SEPARATOR = 0xA;
private static final Charset UTF_8 = Charset.forName("UTF-8");
private final int mMaxNewByteChunkSize;
private final OutputStream mOutputStream;
private final byte[] mByteBuffer;
private int mBufferSize = 0;
// Each chunk could be written immediately to the output stream. However,
// it is possible that chunks may overlap. We therefore cache the most recent
// reusable chunk and try to merge it with future chunks.
private ByteRange mReusableChunk;
public SingleStreamDiffScriptWriter(OutputStream outputStream, int maxNewByteChunkSize) {
mOutputStream = outputStream;
mMaxNewByteChunkSize = maxNewByteChunkSize;
mByteBuffer = new byte[maxNewByteChunkSize];
}
@Override
public void writeByte(byte b) throws IOException {
if (mReusableChunk != null) {
writeReusableChunk();
}
mByteBuffer[mBufferSize++] = b;
if (mBufferSize == mMaxNewByteChunkSize) {
writeByteBuffer();
}
}
@Override
public void writeChunk(long chunkStart, int chunkLength) throws IOException {
Preconditions.checkArgument(chunkStart >= 0);
Preconditions.checkArgument(chunkLength > 0);
if (mBufferSize != 0) {
writeByteBuffer();
}
if (mReusableChunk != null && mReusableChunk.getEnd() + 1 == chunkStart) {
// The new chunk overlaps the old, so combine them into a single byte range.
mReusableChunk = mReusableChunk.extend(chunkLength);
} else {
writeReusableChunk();
mReusableChunk = new ByteRange(chunkStart, chunkStart + chunkLength - 1);
}
}
@Override
public void flush() throws IOException {
Preconditions.checkState(!(mBufferSize != 0 && mReusableChunk != null));
if (mBufferSize != 0) {
writeByteBuffer();
}
if (mReusableChunk != null) {
writeReusableChunk();
}
mOutputStream.flush();
}
private void writeByteBuffer() throws IOException {
mOutputStream.write(Integer.toString(mBufferSize).getBytes(UTF_8));
mOutputStream.write(LINE_SEPARATOR);
mOutputStream.write(mByteBuffer, 0, mBufferSize);
mOutputStream.write(LINE_SEPARATOR);
mBufferSize = 0;
}
private void writeReusableChunk() throws IOException {
if (mReusableChunk != null) {
mOutputStream.write(
String.format(
Locale.US,
"%d-%d",
mReusableChunk.getStart(),
mReusableChunk.getEnd())
.getBytes(UTF_8));
mOutputStream.write(LINE_SEPARATOR);
mReusableChunk = null;
}
}
/** A factory that creates {@link SingleStreamDiffScriptWriter}s. */
public static class Factory implements DiffScriptWriter.Factory {
private final int mMaxNewByteChunkSize;
private final OutputStreamWrapper mOutputStreamWrapper;
public Factory(int maxNewByteChunkSize, @Nullable OutputStreamWrapper outputStreamWrapper) {
mMaxNewByteChunkSize = maxNewByteChunkSize;
mOutputStreamWrapper = outputStreamWrapper;
}
@Override
public SingleStreamDiffScriptWriter create(OutputStream outputStream) {
if (mOutputStreamWrapper != null) {
outputStream = mOutputStreamWrapper.wrap(outputStream);
}
return new SingleStreamDiffScriptWriter(outputStream, mMaxNewByteChunkSize);
}
}
}
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