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/*
* Copyright (C) 2017 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 android.util.apk;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.security.DigestException;
/**
* {@link DataSource} which provides data from a {@link ByteBuffer}.
*/
class ByteBufferDataSource implements DataSource {
/**
* Underlying buffer. The data is stored between position 0 and the buffer's capacity.
* The buffer's position is 0 and limit is equal to capacity.
*/
private final ByteBuffer mBuf;
ByteBufferDataSource(ByteBuffer buf) {
// Defensive copy, to avoid changes to mBuf being visible in buf, and to ensure position is
// 0 and limit == capacity.
mBuf = buf.slice();
}
@Override
public long size() {
return mBuf.capacity();
}
@Override
public void feedIntoDataDigester(DataDigester md, long offset, int size)
throws IOException, DigestException {
// There's no way to tell MessageDigest to read data from ByteBuffer from a position
// other than the buffer's current position. We thus need to change the buffer's
// position to match the requested offset.
//
// In the future, it may be necessary to compute digests of multiple regions in
// parallel. Given that digest computation is a slow operation, we enable multiple
// such requests to be fulfilled by this instance. This is achieved by serially
// creating a new ByteBuffer corresponding to the requested data range and then,
// potentially concurrently, feeding these buffers into MessageDigest instances.
ByteBuffer region;
synchronized (mBuf) {
mBuf.position(0);
mBuf.limit((int) offset + size);
mBuf.position((int) offset);
region = mBuf.slice();
}
md.consume(region);
}
}
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