/*

  * Copyright (c) 1994, 2011, Oracle and/or its affiliates. All rights reserved.

  * 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 java.io;

 /**

  * A <code>PushbackInputStream</code> adds

  * functionality to another input stream, namely

  * the  ability to "push back" or "unread"

  * one byte. This is useful in situations where

  * it is  convenient for a fragment of code

  * to read an indefinite number of data bytes

  * that  are delimited by a particular byte

  * value; after reading the terminating byte,

  * the  code fragment can "unread" it, so that

  * the next read operation on the input stream

  * will reread the byte that was pushed back.

  * For example, bytes representing the  characters

  * constituting an identifier might be terminated

  * by a byte representing an  operator character;

  * a method whose job is to read just an identifier

  * can read until it  sees the operator and

  * then push the operator back to be re-read.

  *

  * @author  David Connelly

  * @author  Jonathan Payne

  * @since   JDK1.0

  */

 public

 class PushbackInputStream extends FilterInputStream {

     /**

      * The pushback buffer.

      * @since   JDK1.1

      */

     protected byte[] buf;

     /**

      * The position within the pushback buffer from which the next byte will

      * be read.  When the buffer is empty, <code>pos</code> is equal to

      * <code>buf.length</code>; when the buffer is full, <code>pos</code> is

      * equal to zero.

      *

      * @since   JDK1.1

      */

     protected int pos;

     /**

      * Check to make sure that this stream has not been closed

      */

     private void ensureOpen() throws IOException {

         if (in == null)

             throw new IOException("Stream closed");

     }

     /**

      * Creates a <code>PushbackInputStream</code>

      * with a pushback buffer of the specified <code>size</code>,

      * and saves its  argument, the input stream

      * <code>in</code>, for later use. Initially,

      * there is no pushed-back byte  (the field

      * <code>pushBack</code> is initialized to

      * <code>-1</code>).

      *

      * @param  in    the input stream from which bytes will be read.

      * @param  size  the size of the pushback buffer.

      * @exception IllegalArgumentException if size is <= 0

      * @since  JDK1.1

      */

     public PushbackInputStream(InputStream in, int size) {

         super(in);

         if (size <= 0) {

             throw new IllegalArgumentException("size <= 0");

         }

         this.buf = new byte[size];

         this.pos = size;

     }

     /**

      * Creates a <code>PushbackInputStream</code>

      * and saves its  argument, the input stream

      * <code>in</code>, for later use. Initially,

      * there is no pushed-back byte  (the field

      * <code>pushBack</code> is initialized to

      * <code>-1</code>).

      *

      * @param   in   the input stream from which bytes will be read.

      */

     public PushbackInputStream(InputStream in) {

         this(in, 1);

     }

     /**

      * 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> This method returns the most recently pushed-back byte, if there is

      * one, and otherwise calls the <code>read</code> method of its underlying

      * input stream and returns whatever value that method returns.

      *

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

      *             stream has been reached.

      * @exception  IOException  if this input stream has been closed by

      *             invoking its {@link #close()} method,

      *             or an I/O error occurs.

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

      */

     public int read() throws IOException {

         ensureOpen();

         if (pos < buf.length) {

             return buf[pos++] & 0xff;

         }

         return super.read();

     }

     /**

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

      * an array of bytes.  This method first reads any pushed-back bytes; after

      * that, if fewer than <code>len</code> bytes have been read then it

      * reads from the underlying input stream. If <code>len</code> is not zero, the method

      * blocks until at least 1 byte of input is available; otherwise, no

      * bytes are read and <code>0</code> is returned.

      *

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

      * @param      off   the start offset in the destination array <code>b</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  NullPointerException If <code>b</code> is <code>null</code>.

      * @exception  IndexOutOfBoundsException If <code>off</code> is negative,

      * <code>len</code> is negative, or <code>len</code> is greater than

      * <code>b.length - off</code>

      * @exception  IOException  if this input stream has been closed by

      *             invoking its {@link #close()} method,

      *             or an I/O error occurs.

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

      */

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

         ensureOpen();

         if (b == null) {

             throw new NullPointerException();

         } else if (off < 0 || len < 0 || len > b.length - off) {

             throw new IndexOutOfBoundsException();

         } else if (len == 0) {

             return 0;

         }

         int avail = buf.length - pos;

         if (avail > 0) {

             if (len < avail) {

                 avail = len;

             }

             arraycopy(buf, pos, b, off, avail);

             pos += avail;

             off += avail;

             len -= avail;

         }

         if (len > 0) {

             len = super.read(b, off, len);

             if (len == -1) {

                 return avail == 0 ? -1 : avail;

             }

             return avail + len;

         }

         return avail;

     }

     /**

      * Pushes back a byte by copying it to the front of the pushback buffer.

      * After this method returns, the next byte to be read will have the value

      * <code>(byte)b</code>.

      *

      * @param      b   the <code>int</code> value whose low-order

      *                  byte is to be pushed back.

      * @exception IOException If there is not enough room in the pushback

      *            buffer for the byte, or this input stream has been closed by

      *            invoking its {@link #close()} method.

      */

     public void unread(int b) throws IOException {

         ensureOpen();

         if (pos == 0) {

             throw new IOException("Push back buffer is full");

         }

         buf[--pos] = (byte)b;

     }

     /**

      * Pushes back a portion of an array of bytes by copying it to the front

      * of the pushback buffer.  After this method returns, the next byte to be

      * read will have the value <code>b[off]</code>, the byte after that will

      * have the value <code>b[off+1]</code>, and so forth.

      *

      * @param b the byte array to push back.

      * @param off the start offset of the data.

      * @param len the number of bytes to push back.

      * @exception IOException If there is not enough room in the pushback

      *            buffer for the specified number of bytes,

      *            or this input stream has been closed by

      *            invoking its {@link #close()} method.

      * @since     JDK1.1

      */

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

         ensureOpen();

         if (len > pos) {

             throw new IOException("Push back buffer is full");

         }

         pos -= len;

         arraycopy(b, off, buf, pos, len);

     }

     /**

      * Pushes back an array of bytes by copying it to the front of the

      * pushback buffer.  After this method returns, the next byte to be read

      * will have the value <code>b[0]</code>, the byte after that will have the

      * value <code>b[1]</code>, and so forth.

      *

      * @param b the byte array to push back

      * @exception IOException If there is not enough room in the pushback

      *            buffer for the specified number of bytes,

      *            or this input stream has been closed by

      *            invoking its {@link #close()} method.

      * @since     JDK1.1

      */

     public void unread(byte[] b) throws IOException {

         unread(b, 0, b.length);

     }

     /**

      * Returns an estimate of the number of bytes that can be read (or

      * skipped over) from this input stream without blocking by the next

      * invocation of a method for this input stream. The next invocation might be

      * the same thread or another thread.  A single read or skip of this

      * many bytes will not block, but may read or skip fewer bytes.

      *

      * <p> The method returns the sum of the number of bytes that have been

      * pushed back and the value returned by {@link

      * java.io.FilterInputStream#available available}.

      *

      * @return     the number of bytes that can be read (or skipped over) from

      *             the input stream without blocking.

      * @exception  IOException  if this input stream has been closed by

      *             invoking its {@link #close()} method,

      *             or an I/O error occurs.

      * @see        java.io.FilterInputStream#in

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

      */

     public int available() throws IOException {

         ensureOpen();

         int n = buf.length - pos;

         int avail = super.available();

         return n > (Integer.MAX_VALUE - avail)

                     ? Integer.MAX_VALUE

                     : n + avail;

     }

     /**

      * Skips over and discards <code>n</code> bytes of data from this

      * input stream. The <code>skip</code> method may, for a variety of

      * reasons, end up skipping over some smaller number of bytes,

      * possibly zero.  If <code>n</code> is negative, no bytes are skipped.

      *

      * <p> The <code>skip</code> method of <code>PushbackInputStream</code>

      * first skips over the bytes in the pushback buffer, if any.  It then

      * calls the <code>skip</code> method of the underlying input stream if

      * more bytes need to be skipped.  The actual number of bytes skipped

      * is returned.

      *

      * @param      n  {@inheritDoc}

      * @return     {@inheritDoc}

      * @exception  IOException  if the stream does not support seek,

      *            or the stream has been closed by

      *            invoking its {@link #close()} method,

      *            or an I/O error occurs.

      * @see        java.io.FilterInputStream#in

      * @see        java.io.InputStream#skip(long n)

      * @since      1.2

      */

     public long skip(long n) throws IOException {

         ensureOpen();

         if (n <= 0) {

             return 0;

         }

         long pskip = buf.length - pos;

         if (pskip > 0) {

             if (n < pskip) {

                 pskip = n;

             }

             pos += pskip;

             n -= pskip;

         }

         if (n > 0) {

             pskip += super.skip(n);

         }

         return pskip;

     }

     /**

      * 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;

     }

     /**

      * Marks the current position in this input stream.

      *

      * <p> The <code>mark</code> method of <code>PushbackInputStream</code>

      * does nothing.

      *

      * @param   readlimit   the maximum limit of bytes that can be read before

      *                      the mark position becomes invalid.

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

      */

     public synchronized void mark(int readlimit) {

     }

     /**

      * Repositions this stream to the position at the time the

      * <code>mark</code> method was last called on this input stream.

      *

      * <p> The method <code>reset</code> for class

      * <code>PushbackInputStream</code> does nothing except throw an

      * <code>IOException</code>.

      *

      * @exception  IOException  if this method is invoked.

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

      * @see     java.io.IOException

      */

     public synchronized void reset() throws IOException {

         throw new IOException("mark/reset not supported");

     }

     /**

      * Closes this input stream and releases any system resources

      * associated with the stream.

      * Once the stream has been closed, further read(), unread(),

      * available(), reset(), or skip() invocations will throw an IOException.

      * Closing a previously closed stream has no effect.

      *

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

      */

     public synchronized void close() throws IOException {

         if (in == null)

             return;

         in.close();

         in = null;

         buf = null;

     }

     static void arraycopy(byte[] value, int srcBegin, byte[] dst, int dstBegin, int count) {

         while (count-- > 0) {

             dst[dstBegin++] = value[srcBegin++];

         }

     }

 }