berinputstream.java

来自「《移动Agent技术》一书的所有章节源代码。」· Java 代码 · 共 160 行

package org.bouncycastle.asn1;

import java.math.BigInteger;
import java.io.*;
import java.util.*;

public class BERInputStream
    extends DERInputStream
{
	private DERObject END_OF_STREAM = new DERObject() {
										void encode(
											DEROutputStream out)
										throws IOException
										{
											throw new IOException("Eeek!");
										}

									};
    public BERInputStream(
        InputStream is)
    {
        super(is);
    }

    /**
     * read a string of bytes representing an indefinite length object.
     */
    private byte[] readIndefiniteLengthFully()
        throws IOException
    {
        ByteArrayOutputStream   bOut = new ByteArrayOutputStream();
        int                     b, b1;

        b1 = read();

        while ((b = read()) >= 0)
        {
			if (b1 == 0 && b == 0)
			{
				break;
			}

            bOut.write(b1);
            b1 = b;
        }

        return bOut.toByteArray();
    }

	private BERConstructedOctetString buildConstructedOctetString(
		DEROctetString	o1,
		DEROctetString	o2)
		throws IOException
	{
        Vector                  octs = new Vector();

		if (o1 != null)
		{
            octs.addElement(o1);
            octs.addElement(o2);
		}

		for (;;)
		{
			DERObject		o = readObject();

			if (o == END_OF_STREAM)
			{
				break;
			}

            octs.addElement(o);
		}

		return new BERConstructedOctetString(octs);
	}

    public DERObject readObject()
        throws IOException
    {
        int tag = read();
        if (tag == -1)
        {
            throw new EOFException();
        }
    
        int     length = readLength();

        if (length < 0)    // indefinite length method
        {
            byte[]  bytes;
    
            switch (tag)
            {
            case NULL:
                return null;
            case SEQUENCE | CONSTRUCTED:
                BERConstructedSequence  seq = new BERConstructedSequence();
    
				for (;;)
				{
					DERObject   obj = readObject();

					if (obj == END_OF_STREAM)
					{
						break;
					}

					seq.addObject(obj);
				}
				return seq;
            case OCTET_STRING | CONSTRUCTED:
				return buildConstructedOctetString(null, null);
            default:
                if ((tag & (TAGGED | CONSTRUCTED)) != 0)  
                {
					// with tagged object tag number is bottom 4 bits
                    BERTaggedObject tagObj = new BERTaggedObject(tag & 0x0f, readObject());
					DERObject		o = readObject();

					if (o == END_OF_STREAM)
					{
						return tagObj;
					}
					else if (o instanceof DEROctetString
							&& tagObj.getObject() instanceof DEROctetString)
					{
						//
						// it's an implicit object - mark it as so...
						//
						tagObj = new BERTaggedObject(false, tag & 0x0f, 
										buildConstructedOctetString((DEROctetString)tagObj.getObject(), (DEROctetString)o));

						return tagObj;
					}

					throw new IOException("truncated tagged object");
                }
    
            	bytes = readIndefiniteLengthFully();

                return buildObject(tag, bytes);
            }
        }
        else
        {
            if (tag == 0 && length == 0)    // end of contents marker.
            {
                return END_OF_STREAM;
            }

            byte[]  bytes = new byte[length];
    
            readFully(bytes);
    
			return buildObject(tag, bytes);
        }
    }
}