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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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package javax.crypto;

import java.io.*;

/**

 * A CipherInputStream is composed of an InputStream and a Cipher so

 * that read() methods return data that are read in from the

 * underlying InputStream but have been additionally processed by the

 * Cipher.  The Cipher must be fully initialized before being used by

 * a CipherInputStream.

 *

 * <p> For example, if the Cipher is initialized for decryption, the

 * CipherInputStream will attempt to read in data and decrypt them,

 * before returning the decrypted data.

 *

 * <p> This class adheres strictly to the semantics, especially the

 * failure semantics, of its ancestor classes

 * java.io.FilterInputStream and java.io.InputStream.  This class has

 * exactly those methods specified in its ancestor classes, and

 * overrides them all.  Moreover, this class catches all exceptions

 * that are not thrown by its ancestor classes.  In particular, the

 * <code>skip</code> method skips, and the <code>available</code>

 * method counts only data that have been processed by the encapsulated Cipher.

 *

 * <p> It is crucial for a programmer using this class not to use

 * methods that are not defined or overriden in this class (such as a

 * new method or constructor that is later added to one of the super

 * classes), because the design and implementation of those methods

 * are unlikely to have considered security impact with regard to

 * CipherInputStream.

 *

 * @author  Li Gong

 * @see     java.io.InputStream

 * @see     java.io.FilterInputStream

 * @see     javax.crypto.Cipher

 * @see     javax.crypto.CipherOutputStream

 *

 * @since 1.4

 */

public class CipherInputStream extends FilterInputStream {

    // the cipher engine to use to process stream data

    private Cipher cipher;

    // the underlying input stream

    private InputStream input;

    /* the buffer holding data that have been read in from the

       underlying stream, but have not been processed by the cipher

       engine. the size 512 bytes is somewhat randomly chosen */

    private byte[] ibuffer = new byte[512];

    // having reached the end of the underlying input stream

    private boolean done = false;

    /* the buffer holding data that have been processed by the cipher

       engine, but have not been read out */

    private byte[] obuffer;

    // the offset pointing to the next "new" byte

    private int ostart = 0;

    // the offset pointing to the last "new" byte

    private int ofinish = 0;

    // stream status

    private boolean closed = false;

    /**

     * private convenience function.

     *

     * Entry condition: ostart = ofinish

     *

     * Exit condition: ostart <= ofinish

     *

     * return (ofinish-ostart) (we have this many bytes for you)

     * return 0 (no data now, but could have more later)

     * return -1 (absolutely no more data)

     */

    private int getMoreData() throws IOException {

        if (done) return -1;

        int readin = input.read(ibuffer);

        if (readin == -1) {

            done = true;

            try {

                obuffer = cipher.doFinal();

            }

            catch (IllegalBlockSizeException e) {obuffer = null;}

            catch (BadPaddingException e) {obuffer = null;}

            if (obuffer == null)

                return -1;

            else {

                ostart = 0;

                ofinish = obuffer.length;

                return ofinish;

            }

        }

        try {

            obuffer = cipher.update(ibuffer, 0, readin);

        } catch (IllegalStateException e) {obuffer = null;};

        ostart = 0;

        if (obuffer == null)

            ofinish = 0;

        else ofinish = obuffer.length;

        return ofinish;

    }

    /**

     * Constructs a CipherInputStream from an InputStream and a

     * Cipher.

     * <br>Note: if the specified input stream or cipher is

     * null, a NullPointerException may be thrown later when

     * they are used.

     * @param is the to-be-processed input stream

     * @param c an initialized Cipher object

     */

    public CipherInputStream(InputStream is, Cipher c) {

        super(is);

        input = is;

        cipher = c;

    }

    /**

     * Constructs a CipherInputStream from an InputStream without

     * specifying a Cipher. This has the effect of constructing a

     * CipherInputStream using a NullCipher.

     * <br>Note: if the specified input stream is null, a

     * NullPointerException may be thrown later when it is used.

     * @param is the to-be-processed input stream

     */

    protected CipherInputStream(InputStream is) {

        super(is);

        input = is;

        cipher = new NullCipher();

    }

    /**

     * Reads the next byte of data from this input stream. The value

     * byte is returned as an <code>int</code> in the range

     * <code>0</code> to <code>255</code>. If no byte is available

     * because the end of the stream has been reached, the value

     * <code>-1</code> is returned. This method blocks until input data

     * is available, the end of the stream is detected, or an exception

     * is thrown.

     * <p>

     *

     * @return  the next byte of data, or <code>-1</code> if the end of the

     *          stream is reached.

     * @exception  IOException  if an I/O error occurs.

     */

    public int read() throws IOException {

        if (ostart >= ofinish) {

            // we loop for new data as the spec says we are blocking

            int i = 0;

            while (i == 0) i = getMoreData();

            if (i == -1) return -1;

        }

        return ((int) obuffer[ostart++] & 0xff);

    };

    /**

     * Reads up to <code>b.length</code> bytes of data from this input

     * stream into an array of bytes.

     * <p>

     * The <code>read</code> method of <code>InputStream</code> calls

     * the <code>read</code> method of three arguments with the arguments

     * <code>b</code>, <code>0</code>, and <code>b.length</code>.

     *

     * @param      b   the buffer into which the data is read.

     * @return     the total number of bytes read into the buffer, or

     *             <code>-1</code> is there is no more data because the end of

     *             the stream has been reached.

     * @exception  IOException  if an I/O error occurs.

     * @see        java.io.InputStream#read(byte[], int, int)

     */

    public int read(byte b[]) throws IOException {

        return read(b, 0, b.length);

    }

    /**

     * Reads up to <code>len</code> bytes of data from this input stream

     * into an array of bytes. This method blocks until some input is

     * available. If the first argument is <code>null,</code> up to

     * <code>len</code> bytes are read and discarded.

     *

     * @param      b     the buffer into which the data is read.

     * @param      off   the start offset in the destination array

     *                   <code>buf</code>

     * @param      len   the maximum number of bytes read.

     * @return     the total number of bytes read into the buffer, or

     *             <code>-1</code> if there is no more data because the end of

     *             the stream has been reached.

     * @exception  IOException  if an I/O error occurs.

     * @see        java.io.InputStream#read()

     */

    public int read(byte b[], int off, int len) throws IOException {

        if (ostart >= ofinish) {

            // we loop for new data as the spec says we are blocking

            int i = 0;

            while (i == 0) i = getMoreData();

            if (i == -1) return -1;

        }

        if (len <= 0) {

            return 0;

        }

        int available = ofinish - ostart;

        if (len < available) available = len;

        if (b != null) {

            System.arraycopy(obuffer, ostart, b, off, available);

        }

        ostart = ostart + available;

        return available;

    }

    /**

     * Skips <code>n</code> bytes of input from the bytes that can be read

     * from this input stream without blocking.

     *

     * <p>Fewer bytes than requested might be skipped.

     * The actual number of bytes skipped is equal to <code>n</code> or

     * the result of a call to

     * {@link #available() available},

     * whichever is smaller.

     * If <code>n</code> is less than zero, no bytes are skipped.

     *

     * <p>The actual number of bytes skipped is returned.

     *

     * @param      n the number of bytes to be skipped.

     * @return     the actual number of bytes skipped.

     * @exception  IOException  if an I/O error occurs.

     */

    public long skip(long n) throws IOException {

        int available = ofinish - ostart;

        if (n > available) {

            n = available;

        }

        if (n < 0) {

            return 0;

        }

        ostart += n;

        return n;

    }

    /**

     * Returns the number of bytes that can be read from this input

     * stream without blocking. The <code>available</code> method of

     * <code>InputStream</code> returns <code>0</code>. This method

     * <B>should</B> be overridden by subclasses.

     *

     * @return     the number of bytes that can be read from this input stream

     *             without blocking.

     * @exception  IOException  if an I/O error occurs.

     */

    public int available() throws IOException {

        return (ofinish - ostart);

    }

    /**

     * Closes this input stream and releases any system resources

     * associated with the stream.

     * <p>

     * The <code>close</code> method of <code>CipherInputStream</code>

     * calls the <code>close</code> method of its underlying input

     * stream.

     *

     * @exception  IOException  if an I/O error occurs.

     */

    public void close() throws IOException {

        if (closed) {

            return;

        }

        closed = true;

        input.close();

        try {

            // throw away the unprocessed data

            if (!done) {

                cipher.doFinal();

            }

        }

        catch (BadPaddingException | IllegalBlockSizeException ex) {

        }

        ostart = 0;

        ofinish = 0;

    }

    /**

     * Tests if this input stream supports the <code>mark</code>

     * and <code>reset</code> methods, which it does not.

     *

     * @return  <code>false</code>, since this class does not support the

     *          <code>mark</code> and <code>reset</code> methods.

     * @see     java.io.InputStream#mark(int)

     * @see     java.io.InputStream#reset()

     */

    public boolean markSupported() {

        return false;

    }

}