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The Bouncy Castle Java APIs for CMS, PKCS, EAC, TSP, CMP, CRMF, OCSP, and certificate generation. This jar contains APIs for JDK 1.5 to JDK 1.8. The APIs can be used in conjunction with a JCE/JCA provider such as the one provided with the Bouncy Castle Cryptography APIs.

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package org.bouncycastle.cms;

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

import org.bouncycastle.util.Arrays;

public final class InputStreamWithMAC
    extends InputStream
{
    private final InputStream base;
    private MACProvider macProvider;
    private byte[] mac;
    private boolean baseFinished;
    private int index;

    InputStreamWithMAC(InputStream base, MACProvider macProvider)
    {
        this.base = base;
        this.macProvider = macProvider;

        baseFinished = false;
        index = 0;
    }

    public InputStreamWithMAC(InputStream base, byte[] mac)
    {
        this.base = base;
        this.mac = mac;
        baseFinished = false;
        index = 0;
    }

    @Override
    public int read()
        throws IOException
    {
        int ch;
        if (!baseFinished)
        {
            ch = base.read();
            if (ch < 0)
            {
                baseFinished = true;
                if (macProvider != null)
                {
                    macProvider.init();
                    mac = macProvider.getMAC();
                }
                return mac[index++] & 0xFF;
            }
        }
        else
        {
            if (index >= mac.length)
            {
                return -1;
            }
            return mac[index++] & 0xFF;
        }
        return ch;
    }

    public byte[] getMAC()
    {
        if (!baseFinished)
        {
            throw new IllegalStateException("input stream not fully processed");
        }
        return Arrays.clone(mac);
    }

    @Override
    public int read(byte[] b, int off, int len)
        throws IOException
    {
        if (b == null)
        {
            throw new NullPointerException("input array is null");
        }
        if (off < 0 || b.length < off + len)
        {
            throw new IndexOutOfBoundsException("invalid off(" + off + ") and len(" + len + ")");
        }
        int ch;
        if (!baseFinished)
        {
            ch = base.read(b, off, len);
            if (ch < 0)
            {
                baseFinished = true;
                if (macProvider != null)
                {
                    macProvider.init();
                    mac = macProvider.getMAC();
                }
                if (len >= mac.length)
                {
                    System.arraycopy(mac, 0, b, off, mac.length);
                    index = mac.length;
                    return mac.length;
                }
                else
                {
                    System.arraycopy(mac, 0, b, off, len);
                    index += len;
                    return len;
                }
            }
            return ch;
        }
        else if (index < mac.length)
        {
            if (len >= mac.length - index)
            {
                System.arraycopy(mac, index, b, off, mac.length - index);
                int tmp = mac.length - index;
                index = mac.length;
                return tmp;
            }
            else
            {
                System.arraycopy(mac, index, b, off, len);
                index += len;
                return len;
            }
        }
        return -1;
    }
}