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ASN1InputStream.java：源码内容
							package org.bouncycastle.asn1;
import java.math.BigInteger;
import java.io.*;
import java.util.*;
/**
 * a general purpose ASN.1 decoder - note: this class differs from the
 * others in that it returns null after it has read the last object in
 * the stream. If an ASN.1 NULL is encountered a DER/BER Null object is
 * returned.
 */
public class ASN1InputStream
    extends DERInputStream
{
	private DERObject END_OF_STREAM = new DERObject() {
										void encode(
											DEROutputStream out)
										throws IOException
										{
											throw new IOException("Eeek!");
										}
									};
    boolean eofFound = false;
    public ASN1InputStream(
        InputStream is)
    {
        super(is);
    }
    protected int readLength()
        throws IOException
    {
        int length = read();
        if (length < 0)
        {
            throw new IOException("EOF found when length expected");
        }
        if (length == 0x80)
        {
            return -1;      // indefinite-length encoding
        }
        if (length > 127)
        {
            int size = length & 0x7f;
            length = 0;
            for (int i = 0; i < size; i++)
            {
                int next = read();
                if (next < 0)
                {
                    throw new IOException("EOF found reading length");
                }
                length = (length << 8) + next;
            }
        }
        return length;
    }
    protected void readFully(
        byte[]  bytes)
        throws IOException
    {
        int     left = bytes.length;
        int     len;
        if (left == 0)
        {
            return;
        }
        while ((len = read(bytes, bytes.length - left, left)) > 0)
        {
            if ((left -= len) == 0)
            {
                return;
            }
        }
        if (left != 0)
        {
            return;
            //throw new IOException("EOF encountered in middle of object");
        }
    }
	/**
	 * build an object given its tag and a byte stream to construct it
	 * from.
	 */
    protected DERObject buildObject(
		int	    tag,
		byte[]	bytes)
		throws IOException
	{
		switch (tag)
        {
        case NULL:
            return new DERNull();   
        case SEQUENCE | CONSTRUCTED:
            ByteArrayInputStream    bIn = new ByteArrayInputStream(bytes);
            ASN1InputStream         aIn = new ASN1InputStream(bIn);
            ASN1EncodableVector     v = new ASN1EncodableVector();
            DERObject   obj = aIn.readObject();
            while (obj != null)
            {
                v.add(obj);
                obj = aIn.readObject();
            }
            return new DERSequence(v);
        case SET | CONSTRUCTED:
            bIn = new ByteArrayInputStream(bytes);
            aIn = new ASN1InputStream(bIn);
            v = new ASN1EncodableVector();
            obj = aIn.readObject();
            while (obj != null)
            {
                v.add(obj);
                obj = aIn.readObject();
            }
            return new DERSet(v);
        case BOOLEAN:
            return new DERBoolean(bytes);
        case INTEGER:
            return new DERInteger(bytes);
        case ENUMERATED:
            return new DEREnumerated(bytes);
        case OBJECT_IDENTIFIER:
            return new DERObjectIdentifier(bytes);
        case BIT_STRING:
            int     padBits = bytes[0];
            byte[]  data = new byte[bytes.length - 1];
            System.arraycopy(bytes, 1, data, 0, bytes.length - 1);
            return new DERBitString(data, padBits);
        case UTF8_STRING:
            return new DERUTF8String(bytes);
        case PRINTABLE_STRING:
            return new DERPrintableString(bytes);
        case IA5_STRING:
            return new DERIA5String(bytes);
        case T61_STRING:
            return new DERT61String(bytes);
        case VISIBLE_STRING:
            return new DERVisibleString(bytes);
        case UNIVERSAL_STRING:
            return new DERUniversalString(bytes);
        case BMP_STRING:
            return new DERBMPString(bytes);
        case OCTET_STRING:
            return new DEROctetString(bytes);
        case UTC_TIME:
            return new DERUTCTime(bytes);
        case GENERALIZED_TIME:
            return new DERGeneralizedTime(bytes);
        default:
            //
            // with tagged object tag number is bottom 5 bits
            //
            if ((tag & TAGGED) != 0)  
            {
                int tagNo = tag & 0x1f;
                if (tagNo == 0x1f)
                {
                    int idx = 0;
                    tagNo = 0;
                    while ((bytes[idx] & 0x80) != 0)
                    {
                        tagNo |= (bytes[idx++] & 0x7f);
                        tagNo <<= 7;
                    }
                    tagNo |= (bytes[idx] & 0x7f);
                    byte[]  tmp = bytes;
                    bytes = new byte[tmp.length - (idx + 1)];
                    System.arraycopy(tmp, idx + 1, bytes, 0, bytes.length);
                }
                if (bytes.length == 0)        // empty tag!
                {
                    return new DERTaggedObject(tagNo);
                }
                //
                // simple type - implicit... return an octet string
                //
                if ((tag & CONSTRUCTED) == 0)
                {
                    return new DERTaggedObject(false, tagNo, new DEROctetString(bytes));
                }
                bIn = new ByteArrayInputStream(bytes);
                aIn = new ASN1InputStream(bIn);
                DEREncodable dObj = aIn.readObject();
                //
                // explicitly tagged (probably!) - if it isn't we'd have to
                // tell from the context
                //
                if (aIn.available() == 0)
                {
                    return new DERTaggedObject(tagNo, dObj);
                }
                //
                // another implicit object, we'll create a sequence...
                //
                v = new ASN1EncodableVector();
                while (dObj != null)
                {
                    v.add(dObj);
                    dObj = aIn.readObject();
                }
                return new DERTaggedObject(false, tagNo, new DERSequence(v));
            }
            return new DERUnknownTag(tag, bytes);
        }
	}
    /**
     * 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()
		throws IOException
	{
        Vector                  octs = new Vector();
		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)
        {
            if (eofFound)
            {
                throw new EOFException("attempt to read past end of file.");
            }
            eofFound = true;
            return null;
        }
    
        int     length = readLength();
        if (length < 0)    // indefinite length method
        {
            switch (tag)
            {
            case NULL:
                return new BERNull();
            case SEQUENCE | CONSTRUCTED:
                ASN1EncodableVector  v = new ASN1EncodableVector();
    
				for (;;)
				{
					DERObject   obj = readObject();
					if (obj == END_OF_STREAM)
					{
						break;
					}
					v.add(obj);
				}
				return new BERSequence(v);
            case SET | CONSTRUCTED:
                v = new ASN1EncodableVector();
    
				for (;;)
				{
					DERObject   obj = readObject();
					if (obj == END_OF_STREAM)
					{
						break;
					}
					v.add(obj);
				}
				return new BERSet(v);
            case OCTET_STRING | CONSTRUCTED:
				return buildConstructedOctetString();
            default:
                //
                // with tagged object tag number is bottom 5 bits
                //
                if ((tag & TAGGED) != 0)  
                {
                    int tagNo = tag & 0x1f;
                    if (tagNo == 0x1f)
                    {
                        int b = read();
                        tagNo = 0;
                        while ((b >= 0) && ((b & 0x80) != 0))
                        {
                            tagNo |= (b & 0x7f);
                            tagNo <<= 7;
                            b = read();
                        }
                        tagNo |= (b & 0x7f);
                    }
                    //
                    // simple type - implicit... return an octet string
                    //
                    if ((tag & CONSTRUCTED) == 0)
                    {
                        byte[]  bytes = readIndefiniteLengthFully();
                        return new BERTaggedObject(false, tagNo, new DEROctetString(bytes));
                    }
                    //
                    // either constructed or explicitly tagged
                    //
					DERObject		dObj = readObject();
					if (dObj == END_OF_STREAM)     // empty tag!
                    {
                        return new DERTaggedObject(tagNo);
                    }
                    DERObject       next = readObject();
                    //
                    // explicitly tagged (probably!) - if it isn't we'd have to
                    // tell from the context
                    //
                    if (next == END_OF_STREAM)
                    {
                        return new BERTaggedObject(tagNo, dObj);
                    }
                    //
                    // another implicit object, we'll create a sequence...
                    //
                    v = new ASN1EncodableVector();
                    v.add(dObj);
                    do
                    {
                        v.add(next);
                        next = readObject();
                    }
                    while (next != END_OF_STREAM);
                    return new BERTaggedObject(false, tagNo, new BERSequence(v));
                }
                throw new IOException("unknown BER object encountered");
            }
        }
        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);
        }
    }
}

						