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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;

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

import org.bouncycastle.bcpg.attr.ImageAttribute;

/**
 * reader for user attribute sub-packets
 */
public class UserAttributeSubpacketInputStream
    extends InputStream
    implements UserAttributeSubpacketTags
{
    InputStream in;

    public UserAttributeSubpacketInputStream(
        InputStream in)
    {
        this.in = in;
    }

    public int available()
        throws IOException
    {
        return in.available();
    }

    public int read()
        throws IOException
    {
        return in.read();
    }

    private void readFully(
        byte[] buf,
        int off,
        int len)
        throws IOException
    {
        if (len > 0)
        {
            int b = this.read();

            if (b < 0)
            {
                throw new EOFException();
            }

            buf[off] = (byte)b;
            off++;
            len--;
        }

        while (len > 0)
        {
            int l = in.read(buf, off, len);

            if (l < 0)
            {
                throw new EOFException();
            }

            off += l;
            len -= l;
        }
    }

    public UserAttributeSubpacket readPacket()
        throws IOException
    {
        boolean[] flags = new boolean[3];
        int bodyLen = StreamUtil.readBodyLen(this, flags);
        if (flags[StreamUtil.flag_eof])
        {
            return null;
        }
        else if (flags[StreamUtil.flag_partial])
        {
            throw new IOException("unrecognised length reading user attribute sub packet");
        }
        boolean longLength = flags[StreamUtil.flag_isLongLength];

        int tag = in.read();

        if (tag < 0)
        {
            throw new EOFException("unexpected EOF reading user attribute sub packet");
        }

        byte[] data = new byte[bodyLen - 1];

        this.readFully(data, 0, data.length);

        int type = tag;

        switch (type)
        {
        case IMAGE_ATTRIBUTE:
            return new ImageAttribute(longLength, data);
        }

        return new UserAttributeSubpacket(type, longLength, data);
    }
}