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Swirlds is a software platform designed to build fully-distributed applications that harness the power of the cloud without servers. Now you can develop applications with fairness in decision making, speed, trust and reliability, at a fraction of the cost of traditional server-based platforms.

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/*
 * Copyright (C) 2018-2024 Hedera Hashgraph, LLC
 *
 * 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.swirlds.common.crypto;

import java.io.IOException;
import java.io.OutputStream;
import java.security.MessageDigest;

/**
 * An OutputStream which creates a hash of all the bytes that go through it
 */
public class HashingOutputStream extends OutputStream {
    OutputStream out = null;
    MessageDigest md;

    /**
     * A constructor used to create an OutputStream that only does hashing
     *
     * @param md
     * 		the MessageDigest object that does the hashing
     */
    public HashingOutputStream(MessageDigest md) {
        super();
        this.md = md;
    }

    /**
     * A constructor used to create an OutputStream that hashes all the bytes that go though it, and also
     * writes them to the next OutputStream
     *
     * @param md
     * 		the MessageDigest object that will hash all bytes of the stream
     * @param out
     * 		the OutputStream where bytes will be sent to after being added to the hash
     */
    public HashingOutputStream(MessageDigest md, OutputStream out) {
        super();
        this.out = out;
        this.md = md;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public void write(int arg0) throws IOException {
        md.update((byte) arg0);
        if (out != null) {
            out.write(arg0);
        }
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public void write(byte[] b, int off, int len) throws IOException {
        if (b == null) {
            throw new NullPointerException();
        } else if ((off < 0) || (off > b.length) || (len < 0) || ((off + len) > b.length) || ((off + len) < 0)) {
            throw new IndexOutOfBoundsException();
        } else if (len == 0) {
            return;
        }

        md.update(b, off, len);
        if (out != null) {
            out.write(b, off, len);
        }
    }

    /**
     * Reset the digest used by the stream
     */
    public void resetDigest() {
        md.reset();
    }

    /**
     * Calculates and returns the digest of all the bytes that have been written to this stream. It also resets the
     * digest.
     *
     * @return the digest of all bytes written to the stream
     */
    public byte[] getDigest() {
        return md.digest();
    }
}