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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.bcpg.attr;

import java.io.ByteArrayOutputStream;
import java.io.IOException;

import org.bouncycastle.bcpg.UserAttributeSubpacket;
import org.bouncycastle.bcpg.UserAttributeSubpacketTags;

/**
 * User-Attribute Subpacket used to encode an image, e.g. the user's avatar.
 *
 * @see 
 *     RFC4880 - Image Attribute Subpacket
 * @see 
 *     RFC9580 - Image Attribute Subpacket
 */
public class ImageAttribute 
    extends UserAttributeSubpacket
{
    public static final int JPEG = 1;

    private static final byte[] ZEROES = new byte[12];

    private int     hdrLength;
    private int     version;
    private int     encoding;
    private byte[]  imageData;

    public ImageAttribute(
        byte[]    data)
    {
        this(false, data);
    }

    public ImageAttribute(
        boolean   forceLongLength,
        byte[]    data)
    {
        super(UserAttributeSubpacketTags.IMAGE_ATTRIBUTE, forceLongLength, data);
        
        hdrLength = ((data[1] & 0xff) << 8) | (data[0] & 0xff);
        version = data[2] & 0xff;
        encoding = data[3] & 0xff;
        
        imageData = new byte[data.length - hdrLength];
        System.arraycopy(data, hdrLength, imageData, 0, imageData.length);
    }

    public ImageAttribute(
        int imageType,
        byte[] imageData)
    {
        this(toByteArray(imageType, imageData));
    }

    private static byte[] toByteArray(int imageType, byte[] imageData)
    {
        ByteArrayOutputStream bOut = new ByteArrayOutputStream();

        try
        {
            bOut.write(0x10); bOut.write(0x00); bOut.write(0x01);
            bOut.write(imageType);
            bOut.write(ZEROES);
            bOut.write(imageData);
        }
        catch (IOException e)
        {
            throw new RuntimeException("unable to encode to byte array!");
        }

        return bOut.toByteArray();
    }

    public int version()
    {
        return version;
    }
    
    public int getEncoding()
    {
        return encoding;
    }
    
    public byte[] getImageData()
    {
        return imageData;
    }
}