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Apache Commons Compress defines an API for working with compression and archive formats. These include bzip2, gzip, pack200, LZMA, XZ, Snappy, traditional Unix Compress, DEFLATE, DEFLATE64, LZ4, Brotli, Zstandard and ar, cpio, jar, tar, zip, dump, 7z, arj.

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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 org.apache.commons.compress.utils;

import java.io.IOException;
import java.io.InputStream;
import java.util.Objects;
import java.util.zip.Checksum;

/**
 * A stream that calculates the checksum of the data read.
 * @NotThreadSafe
 * @since 1.14
 */
public class ChecksumCalculatingInputStream extends InputStream {
    private final InputStream in;
    private final Checksum checksum;

    public ChecksumCalculatingInputStream(final Checksum checksum, final InputStream inputStream) {

        Objects.requireNonNull(checksum, "checksum");
        Objects.requireNonNull(inputStream, "inputStream");

        this.checksum = checksum;
        this.in = inputStream;
    }

    /**
     * Returns the calculated checksum.
     * @return the calculated checksum.
     */
    public long getValue() {
        return checksum.getValue();
    }

    /**
     * Reads a single byte from the stream
     * @throws IOException if the underlying stream throws or the
     * stream is exhausted and the Checksum doesn't match the expected
     * value
     */
    @Override
    public int read() throws IOException {
        final int ret = in.read();
        if (ret >= 0) {
            checksum.update(ret);
        }
        return ret;
    }

    /**
     * Reads a byte array from the stream
     * @throws IOException if the underlying stream throws or the
     * stream is exhausted and the Checksum doesn't match the expected
     * value
     */
    @Override
    public int read(final byte[] b) throws IOException {
        return read(b, 0, b.length);
    }

    /**
     * Reads from the stream into a byte array.
     * @throws IOException if the underlying stream throws or the
     * stream is exhausted and the Checksum doesn't match the expected
     * value
     */
    @Override
    public int read(final byte[] b, final int off, final int len) throws IOException {
        if (len == 0) {
            return 0;
        }
        final int ret = in.read(b, off, len);
        if (ret >= 0) {
            checksum.update(b, off, ret);
        }
        return ret;
    }

    @Override
    public long skip(final long n) throws IOException {
        // Can't really skip, we have to hash everything to verify the checksum
        if (read() >= 0) {
            return 1;
        }
        return 0;
    }

}