/*
* Copyright (C) 2016 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.apksig.util;
import java.io.IOException;
import java.nio.ByteBuffer;
/**
* Abstract representation of a source of data.
*
* <p>This abstraction serves three purposes:
* <ul>
* <li>Transparent handling of different types of sources, such as {@code byte[]},
* {@link java.nio.ByteBuffer}, {@link java.io.RandomAccessFile}, memory-mapped file.</li>
* <li>Support sources larger than 2 GB. If all sources were smaller than 2 GB, {@code ByteBuffer}
* may have worked as the unifying abstraction.</li>
* <li>Support sources which do not fit into logical memory as a contiguous region.</li>
* </ul>
*
* <p>There are following ways to obtain a chunk of data from the data source:
* <ul>
* <li>Stream the chunk's data into a {@link DataSink} using
* {@link #feed(long, long, DataSink) feed}. This is best suited for scenarios where there is no
* need to have the chunk's data accessible at the same time, for example, when computing the
* digest of the chunk. If you need to keep the chunk's data around after {@code feed}
* completes, you must create a copy during {@code feed}. However, in that case the following
* methods of obtaining the chunk's data may be more appropriate.</li>
* <li>Obtain a {@link ByteBuffer} containing the chunk's data using
* {@link #getByteBuffer(long, int) getByteBuffer}. Depending on the data source, the chunk's
* data may or may not be copied by this operation. This is best suited for scenarios where
* you need to access the chunk's data in arbitrary order, but don't need to modify the data and
* thus don't require a copy of the data.</li>
* <li>Copy the chunk's data to a {@link ByteBuffer} using
* {@link #copyTo(long, int, ByteBuffer) copyTo}. This is best suited for scenarios where
* you require a copy of the chunk's data, such as to when you need to modify the data.
* </li>
* </ul>
*/
public interface DataSource {
/**
* Returns the amount of data (in bytes) contained in this data source.
*/
long size();
/**
* Feeds the specified chunk from this data source into the provided sink.
*
* @param offset index (in bytes) at which the chunk starts inside data source
* @param size size (in bytes) of the chunk
*
* @throws IndexOutOfBoundsException if {@code offset} or {@code size} is negative, or if
* {@code offset + size} is greater than {@link #size()}.
*/
void feed(long offset, long size, DataSink sink) throws IOException;
/**
* Returns a buffer holding the contents of the specified chunk of data from this data source.
* Changes to the data source are not guaranteed to be reflected in the returned buffer.
* Similarly, changes in the buffer are not guaranteed to be reflected in the data source.
*
* <p>The returned buffer's position is {@code 0}, and the buffer's limit and capacity is
* {@code size}.
*
* @param offset index (in bytes) at which the chunk starts inside data source
* @param size size (in bytes) of the chunk
*
* @throws IndexOutOfBoundsException if {@code offset} or {@code size} is negative, or if
* {@code offset + size} is greater than {@link #size()}.
*/
ByteBuffer getByteBuffer(long offset, int size) throws IOException;
/**
* Copies the specified chunk from this data source into the provided destination buffer,
* advancing the destination buffer's position by {@code size}.
*
* @param offset index (in bytes) at which the chunk starts inside data source
* @param size size (in bytes) of the chunk
*
* @throws IndexOutOfBoundsException if {@code offset} or {@code size} is negative, or if
* {@code offset + size} is greater than {@link #size()}.
*/
void copyTo(long offset, int size, ByteBuffer dest) throws IOException;
/**
* Returns a data source representing the specified region of data of this data source. Changes
* to data represented by this data source will also be visible in the returned data source.
*
* @param offset index (in bytes) at which the region starts inside data source
* @param size size (in bytes) of the region
*
* @throws IndexOutOfBoundsException if {@code offset} or {@code size} is negative, or if
* {@code offset + size} is greater than {@link #size()}.
*/
DataSource slice(long offset, long size);
}