apache-poi/src/java/org/apache/poi/poifs/filesystem/DocumentInputStream.java

/* ====================================================================
 * The Apache Software License, Version 1.1
 *
 * Copyright (c) 2003 The Apache Software Foundation.  All rights
 * reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
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 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. The end-user documentation included with the redistribution,
 *    if any, must include the following acknowledgment:
 *       "This product includes software developed by the
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowledgment may appear in the software itself,
 *    if and wherever such third-party acknowledgments normally appear.
 *
 * 4. The names "Apache" and "Apache Software Foundation" and
 *    "Apache POI" must not be used to endorse or promote products
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 *
 * 5. Products derived from this software may not be called "Apache",
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 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 */

package org.apache.poi.poifs.filesystem;

import java.io.*;

/**
 * This class provides methods to read a DocumentEntry managed by a
 * Filesystem instance.
 *
 * @author Marc Johnson (mjohnson at apache dot org)
 */

public class DocumentInputStream
    extends InputStream
{

    // current offset into the Document
    private int              _current_offset;

    // current marked offset into the Document (used by mark and
    // reset)
    private int              _marked_offset;

    // the Document's size
    private int              _document_size;

    // have we been closed?
    private boolean          _closed;

    // the actual Document
    private POIFSDocument    _document;

    // buffer used to read one byte at a time
    private byte[]           _tiny_buffer;

    // returned by read operations if we're at end of document
    static private final int EOD = -1;

    /**
     * Create an InputStream from the specified DocumentEntry
     *
     * @param document the DocumentEntry to be read
     *
     * @exception IOException if the DocumentEntry cannot be opened
     *            (like, maybe it has been deleted?)
     */

    public DocumentInputStream(final DocumentEntry document)
        throws IOException
    {
        _current_offset = 0;
        _marked_offset  = 0;
        _document_size  = document.getSize();
        _closed         = false;
        _tiny_buffer    = null;
        if (document instanceof DocumentNode)
        {
            _document = (( DocumentNode ) document).getDocument();
        }
        else
        {
            throw new IOException("Cannot open internal document storage");
        }
    }

    /**
     * Create an InputStream from the specified Document
     *
     * @param document the Document to be read
     *
     * @exception IOException if the DocumentEntry cannot be opened
     *            (like, maybe it has been deleted?)
     */

    public DocumentInputStream(final POIFSDocument document)
        throws IOException
    {
        _current_offset = 0;
        _marked_offset  = 0;
        _document_size  = document.getSize();
        _closed         = false;
        _tiny_buffer    = null;
        _document       = document;
    }

    /**
     * Returns the number of bytes that can be read (or skipped over)
     * from this input stream without blocking by the next caller of a
     * method for this input stream. The next caller might be the same
     * thread or or another thread.
     *
     * @return the number of bytes that can be read from this input
     *         stream without blocking.
     *
     * @exception IOException on error (such as the stream has been
     *            closed)
     */

    public int available()
        throws IOException
    {
        dieIfClosed();
        return _document_size - _current_offset;
    }

    /**
     * Closes this input stream and releases any system resources
     * associated with the stream.
     *
     * @exception IOException
     */

    public void close()
        throws IOException
    {
        _closed = true;
    }

    /**
     * Marks the current position in this input stream. A subsequent
     * call to the reset method repositions this stream at the last
     * marked position so that subsequent reads re-read the same
     * bytes.
     * <p>
     * The readlimit arguments tells this input stream to allow that
     * many bytes to be read before the mark position gets
     * invalidated. This implementation, however, does not care.
     * <p>
     * The general contract of mark is that, if the method
     * markSupported returns true, the stream somehow remembers all
     * the bytes read after the call to mark and stands ready to
     * supply those same bytes again if and whenever the method reset
     * is called. However, the stream is not required to remember any
     * data at all if more than readlimit bytes are read from the
     * stream before reset is called. But this stream will.
     *
     * @param ignoredReadlimit the maximum limit of bytes that can be
     *                         read before the mark position becomes
     *                         invalid. Ignored by this
     *                         implementation.
     */

    public void mark(int ignoredReadlimit)
    {
        _marked_offset = _current_offset;
    }

    /**
     * Tests if this input stream supports the mark and reset methods.
     *
     * @return true
     */

    public boolean markSupported()
    {
        return true;
    }

    /**
     * Reads the next byte of data from the input stream. The value
     * byte is returned as an int in the range 0 to 255. If no byte is
     * available because the end of the stream has been reached, the
     * value -1 is returned. The definition of this method in
     * java.io.InputStream allows this method to block, but it won't.
     *
     * @return the next byte of data, or -1 if the end of the stream
     *         is reached.
     *
     * @exception IOException
     */

    public int read()
        throws IOException
    {
        dieIfClosed();
        if (atEOD())
        {
            return EOD;
        }
        if (_tiny_buffer == null)
        {
            _tiny_buffer = new byte[ 1 ];
        }
        _document.read(_tiny_buffer, _current_offset++);
        return ((int)_tiny_buffer[ 0 ]) & 0x000000FF;
    }

    /**
     * Reads some number of bytes from the input stream and stores
     * them into the buffer array b. The number of bytes actually read
     * is returned as an integer. The definition of this method in
     * java.io.InputStream allows this method to block, but it won't.
     * <p>
     * If b is null, a NullPointerException is thrown. If the length
     * of b is zero, then no bytes are read and 0 is returned;
     * otherwise, there is an attempt to read at least one byte. If no
     * byte is available because the stream is at end of file, the
     * value -1 is returned; otherwise, at least one byte is read and
     * stored into b.
     * <p>
     * The first byte read is stored into element b[0], the next one
     * into b[1], and so on. The number of bytes read is, at most,
     * equal to the length of b. Let k be the number of bytes actually
     * read; these bytes will be stored in elements b[0] through
     * b[k-1], leaving elements b[k] through b[b.length-1] unaffected.
     * <p>
     * If the first byte cannot be read for any reason other than end
     * of file, then an IOException is thrown. In particular, an
     * IOException is thrown if the input stream has been closed.
     * <p>
     * The read(b) method for class InputStream has the same effect as:
     * <p>
     * <code>read(b, 0, b.length)</code>
     *
     * @param b the buffer into which the data is read.
     *
     * @return the total number of bytes read into the buffer, or -1
     *         if there is no more data because the end of the stream
     *         has been reached.
     *
     * @exception IOException
     * @exception NullPointerException
     */

    public int read(final byte [] b)
        throws IOException, NullPointerException
    {
        return read(b, 0, b.length);
    }

    /**
     * Reads up to len bytes of data from the input stream into an
     * array of bytes. An attempt is made to read as many as len
     * bytes, but a smaller number may be read, possibly zero. The
     * number of bytes actually read is returned as an integer.
     * <p>
     * The definition of this method in java.io.InputStream allows it
     * to block, but it won't.
     * <p>
     * If b is null, a NullPointerException is thrown.
     * <p>
     * If off is negative, or len is negative, or off+len is greater
     * than the length of the array b, then an
     * IndexOutOfBoundsException is thrown.
     * <p>
     * If len is zero, then no bytes are read and 0 is returned;
     * otherwise, there is an attempt to read at least one byte. If no
     * byte is available because the stream is at end of file, the
     * value -1 is returned; otherwise, at least one byte is read and
     * stored into b.
     * <p>
     * The first byte read is stored into element b[off], the next one
     * into b[off+1], and so on. The number of bytes read is, at most,
     * equal to len. Let k be the number of bytes actually read; these
     * bytes will be stored in elements b[off] through b[off+k-1],
     * leaving elements b[off+k] through b[off+len-1] unaffected.
     * <p>
     * In every case, elements b[0] through b[off] and elements
     * b[off+len] through b[b.length-1] are unaffected.
     * <p>
     * If the first byte cannot be read for any reason other than end
     * of file, then an IOException is thrown. In particular, an
     * IOException is thrown if the input stream has been closed.
     *
     * @param b the buffer into which the data is read.
     * @param off the start offset in array b at which the data is
     *            written.
     * @param len the maximum number of bytes to read.
     *
     * @return the total number of bytes read into the buffer, or -1
     *         if there is no more data because the end of the stream
     *         has been reached.
     *
     * @exception IOException
     * @exception NullPointerException
     * @exception IndexOutOfBoundsException
     */

    public int read(final byte [] b, final int off, final int len)
        throws IOException, NullPointerException, IndexOutOfBoundsException
    {
        dieIfClosed();
        if (b == null)
        {
            throw new NullPointerException("buffer is null");
        }
        if ((off < 0) || (len < 0) || (b.length < (off + len)))
        {
            throw new IndexOutOfBoundsException(
                "can't read past buffer boundaries");
        }
        if (len == 0)
        {
            return 0;
        }
        if (atEOD())
        {
            return EOD;
        }
        int limit = Math.min(available(), len);

        if ((off == 0) && (limit == b.length))
        {
            _document.read(b, _current_offset);
        }
        else
        {
            byte[] buffer = new byte[ limit ];

            _document.read(buffer, _current_offset);
            System.arraycopy(buffer, 0, b, off, limit);
        }
        _current_offset += limit;
        return limit;
    }

    /**
     * Repositions this stream to the position at the time the mark
     * method was last called on this input stream.
     * <p>
     * The general contract of reset is:
     * <p>
     * <ul>
     *    <li>
     *        If the method markSupported returns true, then:
     *        <ul>
     *            <li>
     *                If the method mark has not been called since the
     *                stream was created, or the number of bytes read
     *                from the stream since mark was last called is
     *                larger than the argument to mark at that last
     *                call, then an IOException might be thrown.
     *            </li>
     *            <li>
     *                If such an IOException is not thrown, then the
     *                stream is reset to a state such that all the
     *                bytes read since the most recent call to mark
     *                (or since the start of the file, if mark has not
     *                been called) will be resupplied to subsequent
     *                callers of the read method, followed by any
     *                bytes that otherwise would have been the next
     *                input data as of the time of the call to reset.
     *             </li>
     *         </ul>
     *     </li>
     *     <li>
     *         If the method markSupported returns false, then:
     *         <ul>
     *             <li>
     *                 The call to reset may throw an IOException.
     *             </li>
     *             <li>
     *                 If an IOException is not thrown, then the
     *                 stream is reset to a fixed state that depends
     *                 on the particular type of the input and how it
     *                 was created. The bytes that will be supplied to
     *                 subsequent callers of the read method depend on
     *                 the particular type of the input stream.
     *             </li>
     *         </ul>
     *     </li>
     * </ul>
     * <p>
     * All well and good ... this class's markSupported method returns
     * true and this method does not care whether you've called mark
     * at all, or whether you've exceeded the number of bytes
     * specified in the last call to mark. We're basically walking a
     * byte array ... mark and reset to your heart's content.
     */

    public void reset()
    {
        _current_offset = _marked_offset;
    }

    /**
     * Skips over and discards n bytes of data from this input
     * stream. The skip method may, for a variety of reasons, end up
     * skipping over some smaller number of bytes, possibly 0. This
     * may result from any of a number of conditions; reaching end of
     * file before n bytes have been skipped is only one
     * possibility. The actual number of bytes skipped is returned. If
     * n is negative, no bytes are skipped.
     *
     * @param n the number of bytes to be skipped.
     *
     * @return the actual number of bytes skipped.
     *
     * @exception IOException
     */

    public long skip(final long n)
        throws IOException
    {
        dieIfClosed();
        if (n < 0)
        {
            return 0;
        }
        int new_offset = _current_offset + ( int ) n;

        if (new_offset < _current_offset)
        {

            // wrap around in converting a VERY large long to an int
            new_offset = _document_size;
        }
        else if (new_offset > _document_size)
        {
            new_offset = _document_size;
        }
        long rval = new_offset - _current_offset;

        _current_offset = new_offset;
        return rval;
    }

    private void dieIfClosed()
        throws IOException
    {
        if (_closed)
        {
            throw new IOException(
                "cannot perform requested operation on a closed stream");
        }
    }

    private boolean atEOD()
    {
        return _current_offset == _document_size;
    }
}   // end public class DocumentInputStream