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The Bouncy Castle Java APIs for the OpenPGP Protocol. The APIs are designed primarily to be used in conjunction with the BC LTS provider but may also be used with other providers providing cryptographic services.

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package org.bouncycastle.gpg.keybox;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.nio.ByteBuffer;

/**
 * Wraps an existing ByteArrayBuffer with support for unsigned int reads.
 * Method names in the nomenclature of the spec.
 */
class KeyBoxByteBuffer
{
    private final ByteBuffer buffer;

    public KeyBoxByteBuffer(ByteBuffer buffer)
    {
        this.buffer = buffer;
    }

    static KeyBoxByteBuffer wrap(Object src)
        throws IOException
    {

        if (src == null)
        {
            return null;
        }
        else if (src instanceof KeyBoxByteBuffer) // Same type.
        {
            return (KeyBoxByteBuffer)src;
        }
        else if (src instanceof ByteBuffer) // ByteBuffer
        {
            return new KeyBoxByteBuffer((ByteBuffer)src);
        }
        else if (src instanceof byte[]) // ByteArray
        {
            return wrap(ByteBuffer.wrap((byte[])src));
        }
        else if (src instanceof ByteArrayOutputStream) // ByteArrayInputStream specifically.
        {
            return wrap(((ByteArrayOutputStream)src).toByteArray());
        }
        else if (src instanceof InputStream) // InputStream
        {
            ByteArrayOutputStream bos = new ByteArrayOutputStream();

            byte[] buf = new byte[4096];
            int i;

            while ((i = ((InputStream)src).read(buf)) >= 0)
            {
                bos.write(buf, 0, i);
            }

            bos.flush();
            bos.close();

            return wrap(bos);
        }

        throw new IllegalStateException("Could not convert " + src.getClass().getCanonicalName() + " to KeyBoxByteBuffer");
    }

    public int size()
    {
        return this.buffer.limit() - 20;
    }

    public byte[] rangeOf(int start, int end)
    {
        if (end - start < 0 || start < 0)
        {
            throw new IllegalArgumentException("invalid range " + start + ":" + end);
        }

        if (end > buffer.limit())
        {
            throw new IllegalArgumentException("range exceeds buffer remaining");
        }

        int p = buffer.position();
        ((java.nio.Buffer)buffer).position(start);
        byte[] data = new byte[end - start];
        buffer.get(data);
        ((java.nio.Buffer)buffer).position(p);
        return data;
    }

    public boolean hasRemaining()
    {
        return buffer.hasRemaining();
    }

    public int remaining()
    {
        return buffer.remaining();
    }

    public int position()
    {
        return buffer.position();
    }

    public void position(int p)
    {
        ((java.nio.Buffer)buffer).position(p);
    }

    public int u16()
    {
        return (u8() << 8) | u8();
    }

    public long u32()
    {
        return ((u8() << 24) | (u8() << 16) | (u8() << 8) | u8());
    }

    public int u8()
    {
        return ((int)buffer.get() & 0xFF);
    }


    public void consume(int size)
    {
        if (size > remaining())
        {
            throw new IllegalArgumentException("size exceeds buffer remaining");
        }

        while (--size >= 0)
        {
            buffer.get();
        }
    }

    public byte[] bN(int size)
    {
        if (size < 0)
        {
            throw new IllegalArgumentException("size less than 0");
        }

        if (size > remaining())
        {
            throw new IllegalArgumentException("size exceeds buffer remaining");
        }

        byte[] b = new byte[size];
        buffer.get(b);
        return b;
    }

    public ByteBuffer getBuffer()
    {
        return buffer;
    }
}