java/io/RandomAccessFile.java

/*
 * Copyright (c) 1994, 2013, 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
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package java.io;

import java.nio.channels.FileChannel;
import sun.nio.ch.FileChannelImpl;
import sun.misc.IoTrace;
import android.system.ErrnoException;
import dalvik.system.CloseGuard;
import libcore.io.IoBridge;
import libcore.io.Libcore;
import static android.system.OsConstants.*;


/**
 * Instances of this class support both reading and writing to a
 * random access file. A random access file behaves like a large
 * array of bytes stored in the file system. There is a kind of cursor,
 * or index into the implied array, called the <em>file pointer</em>;
 * input operations read bytes starting at the file pointer and advance
 * the file pointer past the bytes read. If the random access file is
 * created in read/write mode, then output operations are also available;
 * output operations write bytes starting at the file pointer and advance
 * the file pointer past the bytes written. Output operations that write
 * past the current end of the implied array cause the array to be
 * extended. The file pointer can be read by the
 * <code>getFilePointer</code> method and set by the <code>seek</code>
 * method.
 * <p>
 * It is generally true of all the reading routines in this class that
 * if end-of-file is reached before the desired number of bytes has been
 * read, an <code>EOFException</code> (which is a kind of
 * <code>IOException</code>) is thrown. If any byte cannot be read for
 * any reason other than end-of-file, an <code>IOException</code> other
 * than <code>EOFException</code> is thrown. In particular, an
 * <code>IOException</code> may be thrown if the stream has been closed.
 *
 * @author  unascribed
 * @since   JDK1.0
 */

public class RandomAccessFile implements DataOutput, DataInput, Closeable {

    private final CloseGuard guard = CloseGuard.get();
    private final byte[] scratch = new byte[8];
    private boolean syncMetadata = false;
    private int mode;

    private FileDescriptor fd;
    private FileChannel channel = null;
    private boolean rw;

    /* The path of the referenced file */
    private final String path;

    private Object closeLock = new Object();
    private volatile boolean closed = false;

    /**
     * Creates a random access file stream to read from, and optionally
     * to write to, a file with the specified name. A new
     * {@link FileDescriptor} object is created to represent the
     * connection to the file.
     *
     * <p> The <tt>mode</tt> argument specifies the access mode with which the
     * file is to be opened.  The permitted values and their meanings are as
     * specified for the <a
     * href="#mode"><tt>RandomAccessFile(File,String)</tt></a> constructor.
     *
     * <p>
     * If there is a security manager, its <code>checkRead</code> method
     * is called with the <code>name</code> argument
     * as its argument to see if read access to the file is allowed.
     * If the mode allows writing, the security manager's
     * <code>checkWrite</code> method
     * is also called with the <code>name</code> argument
     * as its argument to see if write access to the file is allowed.
     *
     * @param      name   the system-dependent filename
     * @param      mode   the access <a href="#mode">mode</a>
     * @exception  IllegalArgumentException  if the mode argument is not equal
     *               to one of <tt>"r"</tt>, <tt>"rw"</tt>, <tt>"rws"</tt>, or
     *               <tt>"rwd"</tt>
     * @exception FileNotFoundException
     *            if the mode is <tt>"r"</tt> but the given string does not
     *            denote an existing regular file, or if the mode begins with
     *            <tt>"rw"</tt> but the given string does not denote an
     *            existing, writable regular file and a new regular file of
     *            that name cannot be created, or if some other error occurs
     *            while opening or creating the file
     * @exception  SecurityException         if a security manager exists and its
     *               <code>checkRead</code> method denies read access to the file
     *               or the mode is "rw" and the security manager's
     *               <code>checkWrite</code> method denies write access to the file
     * @see        java.lang.SecurityException
     * @see        java.lang.SecurityManager#checkRead(java.lang.String)
     * @see        java.lang.SecurityManager#checkWrite(java.lang.String)
     * @revised 1.4
     * @spec JSR-51
     */
    public RandomAccessFile(String name, String mode)
        throws FileNotFoundException
    {
        this(name != null ? new File(name) : null, mode);
    }

    /**
     * Creates a random access file stream to read from, and optionally to
     * write to, the file specified by the {@link File} argument.  A new {@link
     * FileDescriptor} object is created to represent this file connection.
     *
     * <a name="mode"><p> The <tt>mode</tt> argument specifies the access mode
     * in which the file is to be opened.  The permitted values and their
     * meanings are:
     *
     * <blockquote><table summary="Access mode permitted values and meanings">
     * <tr><th><p align="left">Value</p></th><th><p align="left">Meaning</p></th></tr>
     * <tr><td valign="top"><tt>"r"</tt></td>
     *     <td> Open for reading only.  Invoking any of the <tt>write</tt>
     *     methods of the resulting object will cause an {@link
     *     java.io.IOException} to be thrown. </td></tr>
     * <tr><td valign="top"><tt>"rw"</tt></td>
     *     <td> Open for reading and writing.  If the file does not already
     *     exist then an attempt will be made to create it. </td></tr>
     * <tr><td valign="top"><tt>"rws"</tt></td>
     *     <td> Open for reading and writing, as with <tt>"rw"</tt>, and also
     *     require that every update to the file's content or metadata be
     *     written synchronously to the underlying storage device.  </td></tr>
     * <tr><td valign="top"><tt>"rwd"&nbsp;&nbsp;</tt></td>
     *     <td> Open for reading and writing, as with <tt>"rw"</tt>, and also
     *     require that every update to the file's content be written
     *     synchronously to the underlying storage device. </td></tr>
     * </table></blockquote>
     *
     * The <tt>"rws"</tt> and <tt>"rwd"</tt> modes work much like the {@link
     * java.nio.channels.FileChannel#force(boolean) force(boolean)} method of
     * the {@link java.nio.channels.FileChannel} class, passing arguments of
     * <tt>true</tt> and <tt>false</tt>, respectively, except that they always
     * apply to every I/O operation and are therefore often more efficient.  If
     * the file resides on a local storage device then when an invocation of a
     * method of this class returns it is guaranteed that all changes made to
     * the file by that invocation will have been written to that device.  This
     * is useful for ensuring that critical information is not lost in the
     * event of a system crash.  If the file does not reside on a local device
     * then no such guarantee is made.
     *
     * <p> The <tt>"rwd"</tt> mode can be used to reduce the number of I/O
     * operations performed.  Using <tt>"rwd"</tt> only requires updates to the
     * file's content to be written to storage; using <tt>"rws"</tt> requires
     * updates to both the file's content and its metadata to be written, which
     * generally requires at least one more low-level I/O operation.
     *
     * <p> If there is a security manager, its <code>checkRead</code> method is
     * called with the pathname of the <code>file</code> argument as its
     * argument to see if read access to the file is allowed.  If the mode
     * allows writing, the security manager's <code>checkWrite</code> method is
     * also called with the path argument to see if write access to the file is
     * allowed.
     *
     * @param      file   the file object
     * @param      mode   the access mode, as described
     *                    <a href="#mode">above</a>
     * @exception  IllegalArgumentException  if the mode argument is not equal
     *               to one of <tt>"r"</tt>, <tt>"rw"</tt>, <tt>"rws"</tt>, or
     *               <tt>"rwd"</tt>
     * @exception FileNotFoundException
     *            if the mode is <tt>"r"</tt> but the given file object does
     *            not denote an existing regular file, or if the mode begins
     *            with <tt>"rw"</tt> but the given file object does not denote
     *            an existing, writable regular file and a new regular file of
     *            that name cannot be created, or if some other error occurs
     *            while opening or creating the file
     * @exception  SecurityException         if a security manager exists and its
     *               <code>checkRead</code> method denies read access to the file
     *               or the mode is "rw" and the security manager's
     *               <code>checkWrite</code> method denies write access to the file
     * @see        java.lang.SecurityManager#checkRead(java.lang.String)
     * @see        java.lang.SecurityManager#checkWrite(java.lang.String)
     * @see        java.nio.channels.FileChannel#force(boolean)
     * @revised 1.4
     * @spec JSR-51
     */
    public RandomAccessFile(File file, String mode)
        throws FileNotFoundException
    {
        String name = (file != null ? file.getPath() : null);
        this.mode = -1;
        if (mode.equals("r")) {
            this.mode = O_RDONLY;
        } else if (mode.startsWith("rw")) {
            // Android changed: Added. O_CREAT
            this.mode = O_RDWR | O_CREAT;
            rw = true;
            if (mode.length() > 2) {
                if (mode.equals("rws")) {
                    syncMetadata = true;
                } else if (mode.equals("rwd")) {
                    // Android-changeD: Should this be O_DSYNC and the above O_SYNC ?
                    this.mode |= O_SYNC;
                } else {
                    this.mode = -1;
                }
            }
        }

        if (this.mode < 0) {
            throw new IllegalArgumentException("Illegal mode \"" + mode
                                               + "\" must be one of "
                                               + "\"r\", \"rw\", \"rws\","
                                               + " or \"rwd\"");
        }

        if (name == null) {
            throw new NullPointerException("file == null");
        }

        if (file.isInvalid()) {
            throw new FileNotFoundException("Invalid file path");
        }
        this.path = name;

        // Android-changed: Use IoBridge.open() instead of open.
        fd = IoBridge.open(file.getPath(), this.mode);
        if (syncMetadata) {
            try {
                fd.sync();
            } catch (IOException e) {
                // Ignored
            }
        }
        guard.open("close");
    }

    /**
     * Returns the opaque file descriptor object associated with this
     * stream. </p>
     *
     * @return     the file descriptor object associated with this stream.
     * @exception  IOException  if an I/O error occurs.
     * @see        java.io.FileDescriptor
     */
    public final FileDescriptor getFD() throws IOException {
        if (fd != null) return fd;
        throw new IOException();
    }

    /**
     * Returns the unique {@link java.nio.channels.FileChannel FileChannel}
     * object associated with this file.
     *
     * <p> The {@link java.nio.channels.FileChannel#position()
     * </code>position<code>} of the returned channel will always be equal to
     * this object's file-pointer offset as returned by the {@link
     * #getFilePointer getFilePointer} method.  Changing this object's
     * file-pointer offset, whether explicitly or by reading or writing bytes,
     * will change the position of the channel, and vice versa.  Changing the
     * file's length via this object will change the length seen via the file
     * channel, and vice versa.
     *
     * @return  the file channel associated with this file
     *
     * @since 1.4
     * @spec JSR-51
     */
    public final FileChannel getChannel() {
        synchronized (this) {
            if (channel == null) {
                channel = FileChannelImpl.open(fd, path, true, rw, this);
                /*
                 * FileDescriptor could be shared by FileInputStream or
                 * FileOutputStream.
                 * Ensure that FD is GC'ed only when all the streams/channels
                 * are done using it.
                 * Increment fd's use count. Invoking the channel's close()
                 * method will result in decrementing the use count set for
                 * the channel.
                 */
                // fd.incrementAndGetUseCount();
            }
            return channel;
        }
    }

    /**
     * Reads a byte of data from this file. The byte is returned as an
     * integer in the range 0 to 255 (<code>0x00-0x0ff</code>). This
     * method blocks if no input is yet available.
     * <p>
     * Although <code>RandomAccessFile</code> is not a subclass of
     * <code>InputStream</code>, this method behaves in exactly the same
     * way as the {@link InputStream#read()} method of
     * <code>InputStream</code>.
     *
     * @return     the next byte of data, or <code>-1</code> if the end of the
     *             file has been reached.
     * @exception  IOException  if an I/O error occurs. Not thrown if
     *                          end-of-file has been reached.
     */
    public int read() throws IOException {
        return (read(scratch, 0, 1) != -1) ? scratch[0] & 0xff : -1;
    }

    /**
     * Reads a sub array as a sequence of bytes.
     * @param b the buffer into which the data is read.
     * @param off the start offset of the data.
     * @param len the number of bytes to read.
     * @exception IOException If an I/O error has occurred.
     */
    private int readBytes(byte b[], int off, int len) throws IOException {
        return IoBridge.read(fd, b, off, len);
    }

    /**
     * Reads up to <code>len</code> bytes of data from this file into an
     * array of bytes. This method blocks until at least one byte of input
     * is available.
     * <p>
     * Although <code>RandomAccessFile</code> is not a subclass of
     * <code>InputStream</code>, this method behaves in exactly the
     * same way as the {@link InputStream#read(byte[], int, int)} method of
     * <code>InputStream</code>.
     *
     * @param      b     the buffer into which the data is read.
     * @param      off   the start offset in array <code>b</code>
     *                   at which the data is written.
     * @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 file has been reached.
     * @exception  IOException If the first byte cannot be read for any reason
     * other than end of file, or if the random access file has been closed, or if
     * some other I/O error occurs.
     * @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>
     */
    public int read(byte b[], int off, int len) throws IOException {
        return readBytes(b, off, len);
    }

    /**
     * Reads up to <code>b.length</code> bytes of data from this file
     * into an array of bytes. This method blocks until at least one byte
     * of input is available.
     * <p>
     * Although <code>RandomAccessFile</code> is not a subclass of
     * <code>InputStream</code>, this method behaves in exactly the
     * same way as the {@link InputStream#read(byte[])} method of
     * <code>InputStream</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> if there is no more data because the end of
     *             this file has been reached.
     * @exception  IOException If the first byte cannot be read for any reason
     * other than end of file, or if the random access file has been closed, or if
     * some other I/O error occurs.
     * @exception  NullPointerException If <code>b</code> is <code>null</code>.
     */
    public int read(byte b[]) throws IOException {
        return readBytes(b, 0, b.length);
    }

    /**
     * Reads <code>b.length</code> bytes from this file into the byte
     * array, starting at the current file pointer. This method reads
     * repeatedly from the file until the requested number of bytes are
     * read. This method blocks until the requested number of bytes are
     * read, the end of the stream is detected, or an exception is thrown.
     *
     * @param      b   the buffer into which the data is read.
     * @exception  EOFException  if this file reaches the end before reading
     *               all the bytes.
     * @exception  IOException   if an I/O error occurs.
     */
    public final void readFully(byte b[]) throws IOException {
        readFully(b, 0, b.length);
    }

    /**
     * Reads exactly <code>len</code> bytes from this file into the byte
     * array, starting at the current file pointer. This method reads
     * repeatedly from the file until the requested number of bytes are
     * read. This method blocks until the requested number of bytes are
     * read, the end of the stream is detected, or an exception is thrown.
     *
     * @param      b     the buffer into which the data is read.
     * @param      off   the start offset of the data.
     * @param      len   the number of bytes to read.
     * @exception  EOFException  if this file reaches the end before reading
     *               all the bytes.
     * @exception  IOException   if an I/O error occurs.
     */
    public final void readFully(byte b[], int off, int len) throws IOException {
        int n = 0;
        do {
            int count = this.read(b, off + n, len - n);
            if (count < 0)
                throw new EOFException();
            n += count;
        } while (n < len);
    }

    /**
     * Attempts to skip over <code>n</code> bytes of input discarding the
     * skipped bytes.
     * <p>
     *
     * This method may skip over some smaller number of bytes, possibly zero.
     * This may result from any of a number of conditions; reaching end of
     * file before <code>n</code> bytes have been skipped is only one
     * possibility. This method never throws an <code>EOFException</code>.
     * The actual number of bytes skipped is returned.  If <code>n</code>
     * is negative, no bytes are skipped.
     *
     * @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 int skipBytes(int n) throws IOException {
        long pos;
        long len;
        long newpos;

        if (n <= 0) {
            return 0;
        }
        pos = getFilePointer();
        len = length();
        newpos = pos + n;
        if (newpos > len) {
            newpos = len;
        }
        seek(newpos);

        /* return the actual number of bytes skipped */
        return (int) (newpos - pos);
    }

    // 'Write' primitives

    /**
     * Writes the specified byte to this file. The write starts at
     * the current file pointer.
     *
     * @param      b   the <code>byte</code> to be written.
     * @exception  IOException  if an I/O error occurs.
     */
    public void write(int b) throws IOException {
        scratch[0] = (byte) (b & 0xff);
        write(scratch, 0, 1);
    }

    /**
     * Writes a sub array as a sequence of bytes.
     * @param b the data to be written
     * @param off the start offset in the data
     * @param len the number of bytes that are written
     * @exception IOException If an I/O error has occurred.
     */
    private void writeBytes(byte b[], int off, int len) throws IOException {
        IoBridge.write(fd, b, off, len);
        // if we are in "rws" mode, attempt to sync file+metadata
        if (syncMetadata) {
            fd.sync();
        }
    }

    /**
     * Writes <code>b.length</code> bytes from the specified byte array
     * to this file, starting at the current file pointer.
     *
     * @param      b   the data.
     * @exception  IOException  if an I/O error occurs.
     */
    public void write(byte b[]) throws IOException {
        writeBytes(b, 0, b.length);
    }

    /**
     * Writes <code>len</code> bytes from the specified byte array
     * starting at offset <code>off</code> to this file.
     *
     * @param      b     the data.
     * @param      off   the start offset in the data.
     * @param      len   the number of bytes to write.
     * @exception  IOException  if an I/O error occurs.
     */
    public void write(byte b[], int off, int len) throws IOException {
        writeBytes(b, off, len);
    }

    // 'Random access' stuff

    /**
     * Returns the current offset in this file.
     *
     * @return     the offset from the beginning of the file, in bytes,
     *             at which the next read or write occurs.
     * @exception  IOException  if an I/O error occurs.
     */
    public long getFilePointer() throws IOException {
        try {
            return Libcore.os.lseek(fd, 0L, SEEK_CUR);
        } catch (ErrnoException errnoException) {
            throw errnoException.rethrowAsIOException();
        }
    }

    /**
     * Sets the file-pointer offset, measured from the beginning of this
     * file, at which the next read or write occurs.  The offset may be
     * set beyond the end of the file. Setting the offset beyond the end
     * of the file does not change the file length.  The file length will
     * change only by writing after the offset has been set beyond the end
     * of the file.
     *
     * @param      offset   the offset position, measured in bytes from the
     *                   beginning of the file, at which to set the file
     *                   pointer.
     * @exception  IOException  if <code>pos</code> is less than
     *                          <code>0</code> or if an I/O error occurs.
     */
    public void seek(long offset) throws IOException {
        if (offset < 0) {
            throw new IOException("offset < 0: " + offset);
        }
        try {
            Libcore.os.lseek(fd, offset, SEEK_SET);
        } catch (ErrnoException errnoException) {
            throw errnoException.rethrowAsIOException();
        }
    }

    /**
     * Returns the length of this file.
     *
     * @return     the length of this file, measured in bytes.
     * @exception  IOException  if an I/O error occurs.
     */
    public long length() throws IOException {
        try {
            return Libcore.os.fstat(fd).st_size;
        } catch (ErrnoException errnoException) {
            throw errnoException.rethrowAsIOException();
        }
    }

    /**
     * Sets the length of this file.
     *
     * <p> If the present length of the file as returned by the
     * <code>length</code> method is greater than the <code>newLength</code>
     * argument then the file will be truncated.  In this case, if the file
     * offset as returned by the <code>getFilePointer</code> method is greater
     * than <code>newLength</code> then after this method returns the offset
     * will be equal to <code>newLength</code>.
     *
     * <p> If the present length of the file as returned by the
     * <code>length</code> method is smaller than the <code>newLength</code>
     * argument then the file will be extended.  In this case, the contents of
     * the extended portion of the file are not defined.
     *
     * @param      newLength    The desired length of the file
     * @exception  IOException  If an I/O error occurs
     * @since      1.2
     */
    public void setLength(long newLength) throws IOException {
        if (newLength < 0) {
            throw new IllegalArgumentException("newLength < 0");
        }
        try {
            Libcore.os.ftruncate(fd, newLength);
        } catch (ErrnoException errnoException) {
            throw errnoException.rethrowAsIOException();
        }

        long filePointer = getFilePointer();
        if (filePointer > newLength) {
            seek(newLength);
        }
        // if we are in "rws" mode, attempt to sync file+metadata
        if (syncMetadata) {
            fd.sync();
        }
    }


    /**
     * Closes this random access file stream and releases any system
     * resources associated with the stream. A closed random access
     * file cannot perform input or output operations and cannot be
     * reopened.
     *
     * <p> If this file has an associated channel then the channel is closed
     * as well.
     *
     * @exception  IOException  if an I/O error occurs.
     *
     * @revised 1.4
     * @spec JSR-51
     */
    public void close() throws IOException {
        guard.close();
        synchronized (closeLock) {
            if (closed) {
                return;
            }
            closed = true;
        }

        if (channel != null && channel.isOpen()) {
            channel.close();
            channel = null;
        }
        IoBridge.closeAndSignalBlockedThreads(fd);
    }

    //
    //  Some "reading/writing Java data types" methods stolen from
    //  DataInputStream and DataOutputStream.
    //

    /**
     * Reads a <code>boolean</code> from this file. This method reads a
     * single byte from the file, starting at the current file pointer.
     * A value of <code>0</code> represents
     * <code>false</code>. Any other value represents <code>true</code>.
     * This method blocks until the byte is read, the end of the stream
     * is detected, or an exception is thrown.
     *
     * @return     the <code>boolean</code> value read.
     * @exception  EOFException  if this file has reached the end.
     * @exception  IOException   if an I/O error occurs.
     */
    public final boolean readBoolean() throws IOException {
        int ch = this.read();
        if (ch < 0)
            throw new EOFException();
        return (ch != 0);
    }

    /**
     * Reads a signed eight-bit value from this file. This method reads a
     * byte from the file, starting from the current file pointer.
     * If the byte read is <code>b</code>, where
     * <code>0&nbsp;&lt;=&nbsp;b&nbsp;&lt;=&nbsp;255</code>,
     * then the result is:
     * <blockquote><pre>
     *     (byte)(b)
     * </pre></blockquote>
     * <p>
     * This method blocks until the byte is read, the end of the stream
     * is detected, or an exception is thrown.
     *
     * @return     the next byte of this file as a signed eight-bit
     *             <code>byte</code>.
     * @exception  EOFException  if this file has reached the end.
     * @exception  IOException   if an I/O error occurs.
     */
    public final byte readByte() throws IOException {
        int ch = this.read();
        if (ch < 0)
            throw new EOFException();
        return (byte)(ch);
    }

    /**
     * Reads an unsigned eight-bit number from this file. This method reads
     * a byte from this file, starting at the current file pointer,
     * and returns that byte.
     * <p>
     * This method blocks until the byte is read, the end of the stream
     * is detected, or an exception is thrown.
     *
     * @return     the next byte of this file, interpreted as an unsigned
     *             eight-bit number.
     * @exception  EOFException  if this file has reached the end.
     * @exception  IOException   if an I/O error occurs.
     */
    public final int readUnsignedByte() throws IOException {
        int ch = this.read();
        if (ch < 0)
            throw new EOFException();
        return ch;
    }

    /**
     * Reads a signed 16-bit number from this file. The method reads two
     * bytes from this file, starting at the current file pointer.
     * If the two bytes read, in order, are
     * <code>b1</code> and <code>b2</code>, where each of the two values is
     * between <code>0</code> and <code>255</code>, inclusive, then the
     * result is equal to:
     * <blockquote><pre>
     *     (short)((b1 &lt;&lt; 8) | b2)
     * </pre></blockquote>
     * <p>
     * This method blocks until the two bytes are read, the end of the
     * stream is detected, or an exception is thrown.
     *
     * @return     the next two bytes of this file, interpreted as a signed
     *             16-bit number.
     * @exception  EOFException  if this file reaches the end before reading
     *               two bytes.
     * @exception  IOException   if an I/O error occurs.
     */
    public final short readShort() throws IOException {
        int ch1 = this.read();
        int ch2 = this.read();
        if ((ch1 | ch2) < 0)
            throw new EOFException();
        return (short)((ch1 << 8) + (ch2 << 0));
    }

    /**
     * Reads an unsigned 16-bit number from this file. This method reads
     * two bytes from the file, starting at the current file pointer.
     * If the bytes read, in order, are
     * <code>b1</code> and <code>b2</code>, where
     * <code>0&nbsp;&lt;=&nbsp;b1, b2&nbsp;&lt;=&nbsp;255</code>,
     * then the result is equal to:
     * <blockquote><pre>
     *     (b1 &lt;&lt; 8) | b2
     * </pre></blockquote>
     * <p>
     * This method blocks until the two bytes are read, the end of the
     * stream is detected, or an exception is thrown.
     *
     * @return     the next two bytes of this file, interpreted as an unsigned
     *             16-bit integer.
     * @exception  EOFException  if this file reaches the end before reading
     *               two bytes.
     * @exception  IOException   if an I/O error occurs.
     */
    public final int readUnsignedShort() throws IOException {
        int ch1 = this.read();
        int ch2 = this.read();
        if ((ch1 | ch2) < 0)
            throw new EOFException();
        return (ch1 << 8) + (ch2 << 0);
    }

    /**
     * Reads a character from this file. This method reads two
     * bytes from the file, starting at the current file pointer.
     * If the bytes read, in order, are
     * <code>b1</code> and <code>b2</code>, where
     * <code>0&nbsp;&lt;=&nbsp;b1,&nbsp;b2&nbsp;&lt;=&nbsp;255</code>,
     * then the result is equal to:
     * <blockquote><pre>
     *     (char)((b1 &lt;&lt; 8) | b2)
     * </pre></blockquote>
     * <p>
     * This method blocks until the two bytes are read, the end of the
     * stream is detected, or an exception is thrown.
     *
     * @return     the next two bytes of this file, interpreted as a
     *                  <code>char</code>.
     * @exception  EOFException  if this file reaches the end before reading
     *               two bytes.
     * @exception  IOException   if an I/O error occurs.
     */
    public final char readChar() throws IOException {
        int ch1 = this.read();
        int ch2 = this.read();
        if ((ch1 | ch2) < 0)
            throw new EOFException();
        return (char)((ch1 << 8) + (ch2 << 0));
    }

    /**
     * Reads a signed 32-bit integer from this file. This method reads 4
     * bytes from the file, starting at the current file pointer.
     * If the bytes read, in order, are <code>b1</code>,
     * <code>b2</code>, <code>b3</code>, and <code>b4</code>, where
     * <code>0&nbsp;&lt;=&nbsp;b1, b2, b3, b4&nbsp;&lt;=&nbsp;255</code>,
     * then the result is equal to:
     * <blockquote><pre>
     *     (b1 &lt;&lt; 24) | (b2 &lt;&lt; 16) + (b3 &lt;&lt; 8) + b4
     * </pre></blockquote>
     * <p>
     * This method blocks until the four bytes are read, the end of the
     * stream is detected, or an exception is thrown.
     *
     * @return     the next four bytes of this file, interpreted as an
     *             <code>int</code>.
     * @exception  EOFException  if this file reaches the end before reading
     *               four bytes.
     * @exception  IOException   if an I/O error occurs.
     */
    public final int readInt() throws IOException {
        int ch1 = this.read();
        int ch2 = this.read();
        int ch3 = this.read();
        int ch4 = this.read();
        if ((ch1 | ch2 | ch3 | ch4) < 0)
            throw new EOFException();
        return ((ch1 << 24) + (ch2 << 16) + (ch3 << 8) + (ch4 << 0));
    }

    /**
     * Reads a signed 64-bit integer from this file. This method reads eight
     * bytes from the file, starting at the current file pointer.
     * If the bytes read, in order, are
     * <code>b1</code>, <code>b2</code>, <code>b3</code>,
     * <code>b4</code>, <code>b5</code>, <code>b6</code>,
     * <code>b7</code>, and <code>b8,</code> where:
     * <blockquote><pre>
     *     0 &lt;= b1, b2, b3, b4, b5, b6, b7, b8 &lt;=255,
     * </pre></blockquote>
     * <p>
     * then the result is equal to:
     * <p><blockquote><pre>
     *     ((long)b1 &lt;&lt; 56) + ((long)b2 &lt;&lt; 48)
     *     + ((long)b3 &lt;&lt; 40) + ((long)b4 &lt;&lt; 32)
     *     + ((long)b5 &lt;&lt; 24) + ((long)b6 &lt;&lt; 16)
     *     + ((long)b7 &lt;&lt; 8) + b8
     * </pre></blockquote>
     * <p>
     * This method blocks until the eight bytes are read, the end of the
     * stream is detected, or an exception is thrown.
     *
     * @return     the next eight bytes of this file, interpreted as a
     *             <code>long</code>.
     * @exception  EOFException  if this file reaches the end before reading
     *               eight bytes.
     * @exception  IOException   if an I/O error occurs.
     */
    public final long readLong() throws IOException {
        return ((long)(readInt()) << 32) + (readInt() & 0xFFFFFFFFL);
    }

    /**
     * Reads a <code>float</code> from this file. This method reads an
     * <code>int</code> value, starting at the current file pointer,
     * as if by the <code>readInt</code> method
     * and then converts that <code>int</code> to a <code>float</code>
     * using the <code>intBitsToFloat</code> method in class
     * <code>Float</code>.
     * <p>
     * This method blocks until the four bytes are read, the end of the
     * stream is detected, or an exception is thrown.
     *
     * @return     the next four bytes of this file, interpreted as a
     *             <code>float</code>.
     * @exception  EOFException  if this file reaches the end before reading
     *             four bytes.
     * @exception  IOException   if an I/O error occurs.
     * @see        java.io.RandomAccessFile#readInt()
     * @see        java.lang.Float#intBitsToFloat(int)
     */
    public final float readFloat() throws IOException {
        return Float.intBitsToFloat(readInt());
    }

    /**
     * Reads a <code>double</code> from this file. This method reads a
     * <code>long</code> value, starting at the current file pointer,
     * as if by the <code>readLong</code> method
     * and then converts that <code>long</code> to a <code>double</code>
     * using the <code>longBitsToDouble</code> method in
     * class <code>Double</code>.
     * <p>
     * This method blocks until the eight bytes are read, the end of the
     * stream is detected, or an exception is thrown.
     *
     * @return     the next eight bytes of this file, interpreted as a
     *             <code>double</code>.
     * @exception  EOFException  if this file reaches the end before reading
     *             eight bytes.
     * @exception  IOException   if an I/O error occurs.
     * @see        java.io.RandomAccessFile#readLong()
     * @see        java.lang.Double#longBitsToDouble(long)
     */
    public final double readDouble() throws IOException {
        return Double.longBitsToDouble(readLong());
    }

    /**
     * Reads the next line of text from this file.  This method successively
     * reads bytes from the file, starting at the current file pointer,
     * until it reaches a line terminator or the end
     * of the file.  Each byte is converted into a character by taking the
     * byte's value for the lower eight bits of the character and setting the
     * high eight bits of the character to zero.  This method does not,
     * therefore, support the full Unicode character set.
     *
     * <p> A line of text is terminated by a carriage-return character
     * (<code>'&#92;r'</code>), a newline character (<code>'&#92;n'</code>), a
     * carriage-return character immediately followed by a newline character,
     * or the end of the file.  Line-terminating characters are discarded and
     * are not included as part of the string returned.
     *
     * <p> This method blocks until a newline character is read, a carriage
     * return and the byte following it are read (to see if it is a newline),
     * the end of the file is reached, or an exception is thrown.
     *
     * @return     the next line of text from this file, or null if end
     *             of file is encountered before even one byte is read.
     * @exception  IOException  if an I/O error occurs.
     */

    public final String readLine() throws IOException {
        StringBuffer input = new StringBuffer();
        int c = -1;
        boolean eol = false;

        while (!eol) {
            switch (c = read()) {
            case -1:
            case '\n':
                eol = true;
                break;
            case '\r':
                eol = true;
                long cur = getFilePointer();
                if ((read()) != '\n') {
                    seek(cur);
                }
                break;
            default:
                input.append((char)c);
                break;
            }
        }

        if ((c == -1) && (input.length() == 0)) {
            return null;
        }
        return input.toString();
    }

    /**
     * Reads in a string from this file. The string has been encoded
     * using a
     * <a href="DataInput.html#modified-utf-8">modified UTF-8</a>
     * format.
     * <p>
     * The first two bytes are read, starting from the current file
     * pointer, as if by
     * <code>readUnsignedShort</code>. This value gives the number of
     * following bytes that are in the encoded string, not
     * the length of the resulting string. The following bytes are then
     * interpreted as bytes encoding characters in the modified UTF-8 format
     * and are converted into characters.
     * <p>
     * This method blocks until all the bytes are read, the end of the
     * stream is detected, or an exception is thrown.
     *
     * @return     a Unicode string.
     * @exception  EOFException            if this file reaches the end before
     *               reading all the bytes.
     * @exception  IOException             if an I/O error occurs.
     * @exception  UTFDataFormatException  if the bytes do not represent
     *               valid modified UTF-8 encoding of a Unicode string.
     * @see        java.io.RandomAccessFile#readUnsignedShort()
     */
    public final String readUTF() throws IOException {
        return DataInputStream.readUTF(this);
    }

    /**
     * Writes a <code>boolean</code> to the file as a one-byte value. The
     * value <code>true</code> is written out as the value
     * <code>(byte)1</code>; the value <code>false</code> is written out
     * as the value <code>(byte)0</code>. The write starts at
     * the current position of the file pointer.
     *
     * @param      v   a <code>boolean</code> value to be written.
     * @exception  IOException  if an I/O error occurs.
     */
    public final void writeBoolean(boolean v) throws IOException {
        write(v ? 1 : 0);
        //written++;
    }

    /**
     * Writes a <code>byte</code> to the file as a one-byte value. The
     * write starts at the current position of the file pointer.
     *
     * @param      v   a <code>byte</code> value to be written.
     * @exception  IOException  if an I/O error occurs.
     */
    public final void writeByte(int v) throws IOException {
        write(v);
        //written++;
    }

    /**
     * Writes a <code>short</code> to the file as two bytes, high byte first.
     * The write starts at the current position of the file pointer.
     *
     * @param      v   a <code>short</code> to be written.
     * @exception  IOException  if an I/O error occurs.
     */
    public final void writeShort(int v) throws IOException {
        write((v >>> 8) & 0xFF);
        write((v >>> 0) & 0xFF);
        //written += 2;
    }

    /**
     * Writes a <code>char</code> to the file as a two-byte value, high
     * byte first. The write starts at the current position of the
     * file pointer.
     *
     * @param      v   a <code>char</code> value to be written.
     * @exception  IOException  if an I/O error occurs.
     */
    public final void writeChar(int v) throws IOException {
        write((v >>> 8) & 0xFF);
        write((v >>> 0) & 0xFF);
        //written += 2;
    }

    /**
     * Writes an <code>int</code> to the file as four bytes, high byte first.
     * The write starts at the current position of the file pointer.
     *
     * @param      v   an <code>int</code> to be written.
     * @exception  IOException  if an I/O error occurs.
     */
    public final void writeInt(int v) throws IOException {
        write((v >>> 24) & 0xFF);
        write((v >>> 16) & 0xFF);
        write((v >>>  8) & 0xFF);
        write((v >>>  0) & 0xFF);
        //written += 4;
    }

    /**
     * Writes a <code>long</code> to the file as eight bytes, high byte first.
     * The write starts at the current position of the file pointer.
     *
     * @param      v   a <code>long</code> to be written.
     * @exception  IOException  if an I/O error occurs.
     */
    public final void writeLong(long v) throws IOException {
        write((int)(v >>> 56) & 0xFF);
        write((int)(v >>> 48) & 0xFF);
        write((int)(v >>> 40) & 0xFF);
        write((int)(v >>> 32) & 0xFF);
        write((int)(v >>> 24) & 0xFF);
        write((int)(v >>> 16) & 0xFF);
        write((int)(v >>>  8) & 0xFF);
        write((int)(v >>>  0) & 0xFF);
        //written += 8;
    }

    /**
     * Converts the float argument to an <code>int</code> using the
     * <code>floatToIntBits</code> method in class <code>Float</code>,
     * and then writes that <code>int</code> value to the file as a
     * four-byte quantity, high byte first. The write starts at the
     * current position of the file pointer.
     *
     * @param      v   a <code>float</code> value to be written.
     * @exception  IOException  if an I/O error occurs.
     * @see        java.lang.Float#floatToIntBits(float)
     */
    public final void writeFloat(float v) throws IOException {
        writeInt(Float.floatToIntBits(v));
    }

    /**
     * Converts the double argument to a <code>long</code> using the
     * <code>doubleToLongBits</code> method in class <code>Double</code>,
     * and then writes that <code>long</code> value to the file as an
     * eight-byte quantity, high byte first. The write starts at the current
     * position of the file pointer.
     *
     * @param      v   a <code>double</code> value to be written.
     * @exception  IOException  if an I/O error occurs.
     * @see        java.lang.Double#doubleToLongBits(double)
     */
    public final void writeDouble(double v) throws IOException {
        writeLong(Double.doubleToLongBits(v));
    }

    /**
     * Writes the string to the file as a sequence of bytes. Each
     * character in the string is written out, in sequence, by discarding
     * its high eight bits. The write starts at the current position of
     * the file pointer.
     *
     * @param      s   a string of bytes to be written.
     * @exception  IOException  if an I/O error occurs.
     */
    public final void writeBytes(String s) throws IOException {
        int len = s.length();
        byte[] b = new byte[len];
        s.getBytes(0, len, b, 0);
        writeBytes(b, 0, len);
    }

    /**
     * Writes a string to the file as a sequence of characters. Each
     * character is written to the data output stream as if by the
     * <code>writeChar</code> method. The write starts at the current
     * position of the file pointer.
     *
     * @param      s   a <code>String</code> value to be written.
     * @exception  IOException  if an I/O error occurs.
     * @see        java.io.RandomAccessFile#writeChar(int)
     */
    public final void writeChars(String s) throws IOException {
        int clen = s.length();
        int blen = 2*clen;
        byte[] b = new byte[blen];
        char[] c = new char[clen];
        s.getChars(0, clen, c, 0);
        for (int i = 0, j = 0; i < clen; i++) {
            b[j++] = (byte)(c[i] >>> 8);
            b[j++] = (byte)(c[i] >>> 0);
        }
        writeBytes(b, 0, blen);
    }

    /**
     * Writes a string to the file using
     * <a href="DataInput.html#modified-utf-8">modified UTF-8</a>
     * encoding in a machine-independent manner.
     * <p>
     * First, two bytes are written to the file, starting at the
     * current file pointer, as if by the
     * <code>writeShort</code> method giving the number of bytes to
     * follow. This value is the number of bytes actually written out,
     * not the length of the string. Following the length, each character
     * of the string is output, in sequence, using the modified UTF-8 encoding
     * for each character.
     *
     * @param      str   a string to be written.
     * @exception  IOException  if an I/O error occurs.
     */
    public final void writeUTF(String str) throws IOException {
        DataOutputStream.writeUTF(str, this);
    }

    @Override protected void finalize() throws Throwable {
        try {
            if (guard != null) {
                guard.warnIfOpen();
            }
            close();
        } finally {
            super.finalize();
        }
    }
}