content: /*
   * 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);
  }
  