1 /* 2 * Copyright (C) 2017 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 package android.util.apk; 18 19 import java.io.IOException; 20 import java.nio.ByteBuffer; 21 import java.security.DigestException; 22 23 /** 24 * {@link DataSource} which provides data from a {@link ByteBuffer}. 25 */ 26 class ByteBufferDataSource implements DataSource { 27 /** 28 * Underlying buffer. The data is stored between position 0 and the buffer's capacity. 29 * The buffer's position is 0 and limit is equal to capacity. 30 */ 31 private final ByteBuffer mBuf; 32 33 ByteBufferDataSource(ByteBuffer buf) { 34 // Defensive copy, to avoid changes to mBuf being visible in buf, and to ensure position is 35 // 0 and limit == capacity. 36 mBuf = buf.slice(); 37 } 38 39 @Override 40 public long size() { 41 return mBuf.capacity(); 42 } 43 44 @Override 45 public void feedIntoDataDigester(DataDigester md, long offset, int size) 46 throws IOException, DigestException { 47 // There's no way to tell MessageDigest to read data from ByteBuffer from a position 48 // other than the buffer's current position. We thus need to change the buffer's 49 // position to match the requested offset. 50 // 51 // In the future, it may be necessary to compute digests of multiple regions in 52 // parallel. Given that digest computation is a slow operation, we enable multiple 53 // such requests to be fulfilled by this instance. This is achieved by serially 54 // creating a new ByteBuffer corresponding to the requested data range and then, 55 // potentially concurrently, feeding these buffers into MessageDigest instances. 56 ByteBuffer region; 57 synchronized (mBuf) { 58 mBuf.position(0); 59 mBuf.limit((int) offset + size); 60 mBuf.position((int) offset); 61 region = mBuf.slice(); 62 } 63 64 md.consume(region); 65 } 66 } 67
