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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 java.util.zip;

import libcore.io.Streams;

import java.io.IOException;
import java.io.InputStream;

/**
 * The {@code CheckedInputStream} class is used to maintain a checksum at the
 * same time as the data, on which the checksum is computed, is read from a
 * stream. The purpose of this checksum is to establish data integrity,
 * comparing the computed checksum against a published checksum value.
 */
public class CheckedInputStream extends java.io.FilterInputStream {

    private final Checksum check;

    /**
     * Constructs a new {@code CheckedInputStream} on {@code InputStream}
     * {@code is}. The checksum will be calculated using the algorithm
     * implemented by {@code csum}.
     *
     * 

Warning: passing a null source creates an invalid * {@code CheckedInputStream}. All operations on such a stream will fail. * * @param is * the input stream to calculate checksum from. * @param csum * an entity implementing the checksum algorithm. */ public CheckedInputStream(InputStream is, Checksum csum) { super(is); check = csum; } /** * Reads one byte of data from the underlying input stream and updates the * checksum with the byte data. * * @return {@code -1} at the end of the stream, a single byte value * otherwise. * @throws IOException * if an {@code IOException} occurs. */ @Override public int read() throws IOException { int x = in.read(); if (x != -1) { check.update(x); } return x; } /** * Reads up to {@code byteCount} bytes of data from the underlying input stream, storing it * into {@code buffer}, starting at offset {@code byteOffset}. The checksum is * updated with the bytes read. * Returns the number of bytes actually read or {@code -1} if arrived at the * end of the filtered stream while reading the data. * * @throws IOException * if this stream is closed or some I/O error occurs. */ @Override public int read(byte[] buffer, int byteOffset, int byteCount) throws IOException { int bytesRead = in.read(buffer, byteOffset, byteCount); if (bytesRead != -1) { check.update(buffer, byteOffset, bytesRead); } return bytesRead; } /** * Returns the checksum calculated on the stream read so far. */ public Checksum getChecksum() { return check; } /** * Skip up to {@code byteCount} bytes of data on the underlying input * stream. Any skipped bytes are added to the running checksum value. * * @param byteCount the number of bytes to skip. * @throws IOException if this stream is closed or another I/O error occurs. * @return the number of bytes skipped. */ @Override public long skip(long byteCount) throws IOException { return Streams.skipByReading(this, byteCount); } }





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