/* DataInputStream.java -- FilteredInputStream that implements DataInput
   Copyright (C) 1998, 1999, 2000, 2001, 2003, 2005  Free Software Foundation

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.
 
GNU Classpath 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 for more details.

You should have received a copy of the GNU General Public License
along with GNU Classpath; see the file COPYING.  If not, write to the
Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
02110-1301 USA.

Linking this library statically or dynamically with other modules is
making a combined work based on this library.  Thus, the terms and
conditions of the GNU General Public License cover the whole
combination.

As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
executable, regardless of the license terms of these independent
modules, and to copy and distribute the resulting executable under
terms of your choice, provided that you also meet, for each linked
independent module, the terms and conditions of the license of that
module.  An independent module is a module which is not derived from
or based on this library.  If you modify this library, you may extend
this exception to your version of the library, but you are not
obligated to do so.  If you do not wish to do so, delete this
exception statement from your version. */
 
package java.io;

/* Written using "Java Class Libraries", 2nd edition, ISBN 0-201-31002-3
 * "The Java Language Specification", ISBN 0-201-63451-1
 * plus online API docs for JDK 1.2 beta from http://www.javasoft.com.
 * Status:  Believed complete and correct.
 */
 
/**
 * This subclass of <code>FilteredInputStream</code> implements the
 * <code>DataInput</code> interface that provides method for reading primitive
 * Java data types from a stream.
 *
 * @see DataInput
 *
 * @author Warren Levy (warrenl@cygnus.com)
 * @author Aaron M. Renn (arenn@urbanophile.com)
 * @date October 20, 1998.  
 */
public class DataInputStream extends InputStream implements DataInput
{
    // Byte buffer, used to make primitive read calls more efficient.
    private byte[] buf = new byte [8];
  
    /**
     * The embedded InputStream object 
     */
    protected InputStream in;
  
    /**
     * This constructor initializes a new <code>DataInputStream</code>
     * to read from the specified subordinate stream.
     *
     * @param in The subordinate <code>InputStream</code> to read from
     */
    public DataInputStream(InputStream in)
    {
        this.in = in;
    }

    /**
     * This method reads a byte from the underlying stream
     * @return An int holding the byte read from the stream
     * @throws IOException If an error occurs.
     */

    public int read() throws IOException
    {
        return in.read();
    }

    /**
     * This method reads bytes from the underlying stream into the specified
     * byte array buffer.  It will attempt to fill the buffer completely, but
     * may return a short count if there is insufficient data remaining to be
     * read to fill the buffer.
     *
     * @param b The buffer into which bytes will be read.
     * 
     * @return The actual number of bytes read, or -1 if end of stream reached 
     * before reading any bytes.
     *
     * @throws IOException If an error occurs.
     */
    public final int read(byte[] b) throws IOException
    {
        return in.read(b, 0, b.length);
    }

    /**
     * This method reads bytes from the underlying stream into the specified
     * byte array buffer.  It will attempt to read <code>len</code> bytes and
     * will start storing them at position <code>off</code> into the buffer.
     * This method can return a short count if there is insufficient data
     * remaining to be read to complete the desired read length.
     *
     * @param b The buffer into which bytes will be read.
     * @param off The offset into the buffer to start storing bytes.
     * @param len The requested number of bytes to read.
     *
     * @return The actual number of bytes read, or -1 if end of stream reached
     * before reading any bytes.
     *
     * @throws IOException If an error occurs.
     */
    public final int read(byte[] b, int off, int len) throws IOException
    {
        return in.read (b, off, len);
    }

    /**
     * This method reads raw bytes into the passed array until the array is
     * full.  Note that this method blocks until the data is available and
     * throws an exception if there is not enough data left in the stream to
     * fill the buffer.  Note also that zero length buffers are permitted.
     * In this case, the method will return immediately without reading any
     * bytes from the stream.
     *
     * @param b The buffer into which to read the data
     *
     * @throws EOFException If end of file is reached before filling the
     * buffer
     * @throws IOException If any other error occurs
     */
    public final void readFully(byte[] b) throws EOFException, IOException
    {
        readFully (b, 0, b.length);
    }

    /**
     * This method reads raw bytes into the passed array <code>buf</code>
     * starting
     * <code>offset</code> bytes into the buffer.  The number of bytes read
     * will be
     * exactly <code>len</code>.  Note that this method blocks until the data is
     * available and throws an exception if there is not enough data left in
     * the stream to read <code>len</code> bytes.  Note also that zero length
     * buffers are permitted.  In this case, the method will return immediately
     * without reading any bytes from the stream.
     *
     * @param buf The buffer into which to read the data
     * @param offset The offset into the buffer to start storing data
     * @param len The number of bytes to read into the buffer
     *
     * @throws EOFException If end of file is reached before filling the
     * buffer
     * @throws IOException If any other error occurs
     */
    public final void readFully(byte[] buf, int offset, int len)
        throws EOFException, IOException
    {
        if (len < 0)
            throw new IndexOutOfBoundsException("Negative length: " + len);
    
        while (len > 0)
        {
            // in.read will block until some data is available.
            int numread = in.read (buf, offset, len);
            
            if (numread < 0)
                throw new EOFException();
            
            len -= numread;
            offset += numread;
        }
    }

    /**
     * This method attempts to skip and discard the specified number of bytes 
     * in the input stream.  It may actually skip fewer bytes than requested. 
     * This method will not skip any bytes if passed a negative number of bytes 
     * to skip. 
     *
     * @param n The requested number of bytes to skip.
     *
     * @return The requested number of bytes to skip.
     *
     * @throws IOException If an error occurs.
     */
    public int skipBytes(int n) throws IOException
    {
        if (n <= 0)
            return 0;    
    
        try
        {
            return (int) in.skip(n);
        }
        catch (EOFException x)
        {
            // do nothing.
        }         
    
        return n;
    }

    /**
     * This method reads a Java boolean value from an input stream.  It does
     * so by reading a single byte of data.  If that byte is zero, then the
     * value returned is <code>false</code>.  If the byte is non-zero, then
     * the value returned is <code>true</code>.
     * <p>
     * This method can read a <code>boolean</code> written by an object
     * implementing the <code>writeBoolean()</code> method in the
     * <code>DataOutput</code> interface. 
     *
     * @return The <code>boolean</code> value read
     *
     * @throws EOFException If end of file is reached before reading
     * the boolean
     * @throws IOException If any other error occurs
     *
     * @see DataOutput#writeBoolean
     */
    public final boolean readBoolean() throws IOException
    {
        return convertToBoolean(in.read());
    }

    /**
     * This method reads a Java byte value from an input stream.  The value
     * is in the range of -128 to 127.
     * <p>
     * This method can read a <code>byte</code> written by an object
     * implementing the <code>writeByte()</code> method in the
     * <code>DataOutput</code> interface.
     *
     * @return The <code>byte</code> value read
     *
     * @throws EOFException If end of file is reached before reading the byte
     * @throws IOException If any other error occurs
     *
     * @see DataOutput#writeByte
     */
    public final byte readByte() throws IOException
    {
        return convertToByte(in.read());
    }

    /**
     * This method reads 8 unsigned bits into a Java <code>int</code>
     * value from the stream. The value returned is in the range of 0 to
     * 255.
     * <p>
     * This method can read an unsigned byte written by an object
     * implementing the <code>writeUnsignedByte()</code> method in the
     * <code>DataOutput</code> interface.
     *
     * @return The unsigned bytes value read as a Java <code>int</code>.
     *
     * @throws EOFException If end of file is reached before reading the value
     * @throws IOException If any other error occurs
     *
     * @see DataOutput#writeByte
     */
    public final int readUnsignedByte() throws IOException
    {
        return convertToUnsignedByte(in.read());
    }

    /**
     * This method reads a signed 16-bit value into a Java in from the
     * stream.  It operates by reading two bytes from the stream and
     * converting them to a single 16-bit Java <code>short</code>.  The
     * two bytes are stored most significant byte first (i.e., "big
     * endian") regardless of the native host byte ordering.
     * <p>
     * As an example, if <code>byte1</code> and <code>byte2</code>
     * represent the first and second byte read from the stream
     * respectively, they will be transformed to a <code>short</code>. in
     * the following manner:
     * <p>
     * <code>(short)(((byte1 &amp; 0xFF) &lt;&lt; 8) | (byte2 &amp; 0xFF))</code>
     * <p>
     * The value returned is in the range of -32768 to 32767.
     * <p>
     * This method can read a <code>short</code> written by an object
     * implementing the <code>writeShort()</code> method in the
     * <code>DataOutput</code> interface.
     *
     * @return The <code>short</code> value read
     *
     * @throws EOFException If end of file is reached before reading the value
     * @throws IOException If any other error occurs
     *
     * @see DataOutput#writeShort
     */
    public final short readShort() throws IOException
    {
        readFully(buf, 0, 2);
    
        return convertToShort(buf);
    }

    /**
     * This method reads 16 unsigned bits into a Java int value from the stream.
     * It operates by reading two bytes from the stream and converting them to 
     * a single Java <code>int</code>  The two bytes are stored most
     * significant byte first (i.e., "big endian") regardless of the native
     * host byte ordering. 
     * <p>
     * As an example, if <code>byte1</code> and <code>byte2</code>
     * represent the first and second byte read from the stream
     * respectively, they will be transformed to an <code>int</code> in
     * the following manner:
     * <p>
     * <code>(int)(((byte1 &amp; 0xFF) &lt;&lt; 8) + (byte2 &amp; 0xFF))</code>
     * <p>
     * The value returned is in the range of 0 to 65535.
     * <p>
     * This method can read an unsigned short written by an object
     * implementing the <code>writeUnsignedShort()</code> method in the
     * <code>DataOutput</code> interface.
     *
     * @return The unsigned short value read as a Java <code>int</code>
     *
     * @throws EOFException If end of file is reached before reading the value
     * @throws IOException If any other error occurs
     *
     * @see DataOutput#writeShort
     */
    public final int readUnsignedShort() throws IOException
    {
        readFully(buf, 0, 2);
    
        return convertToUnsignedShort(buf);
    }

    /**
     * This method reads a Java <code>char</code> value from an input stream.  
     * It operates by reading two bytes from the stream and converting them to 
     * a single 16-bit Java <code>char</code>.  The two bytes are stored most
     * significant byte first (i.e., "big endian") regardless of the native
     * host byte ordering. 
     * <p>
     * As an example, if <code>byte1</code> and <code>byte2</code>
     * represent the first and second byte read from the stream
     * respectively, they will be transformed to a <code>char</code> in
     * the following manner: 
     * <p>
     * <code>(char)(((byte1 &amp; 0xFF) &lt;&lt; 8) | (byte2 &amp; 0xFF)</code>
     * <p>
     * This method can read a <code>char</code> written by an object
     * implementing the <code>writeChar()</code> method in the
     * <code>DataOutput</code> interface. 
     *
     * @return The <code>char</code> value read 
     *
     * @throws EOFException If end of file is reached before reading the char
     * @throws IOException If any other error occurs
     *
     * @see DataOutput#writeChar
     */
    public final char readChar() throws IOException
    {
        readFully(buf, 0, 2);

        return convertToChar(buf);
    }

    /**
     * This method reads a Java <code>int</code> value from an input stream
     * It operates by reading four bytes from the stream and converting them to
     * a single Java <code>int</code>.  The bytes are stored most
     * significant byte first (i.e., "big endian") regardless of the native
     * host byte ordering.
     * <p>
     * As an example, if <code>byte1</code> through <code>byte4</code> represent
     * the first four bytes read from the stream, they will be
     * transformed to an <code>int</code> in the following manner:
     * <p>
     * <code>(int)(((byte1 &amp; 0xFF) &lt;&lt; 24) + ((byte2 &amp; 0xFF) &lt;&lt; 16) +
     * ((byte3 &amp; 0xFF)&lt;&lt; 8) + (byte4 &amp; 0xFF)))</code>
     * <p>
     * The value returned is in the range of -2147483648 to 2147483647.
     * <p>
     * This method can read an <code>int</code> written by an object
     * implementing the <code>writeInt()</code> method in the
     * <code>DataOutput</code> interface.
     *
     * @return The <code>int</code> value read
     *
     * @throws EOFException If end of file is reached before reading the int
     * @throws IOException If any other error occurs
     *
     * @see DataOutput#writeInt
     */
    public final int readInt() throws IOException
    {
        readFully(buf, 0, 4);
    
        return convertToInt(buf);
    }

    /**
     * This method reads a Java <code>long</code> value from an input stream
     * It operates by reading eight bytes from the stream and converting them to
     * a single Java <code>long</code>.  The bytes are stored most
     * significant byte first (i.e., "big endian") regardless of the native
     * host byte ordering.
     * <p>
     * As an example, if <code>byte1</code> through <code>byte8</code> represent
     * the first eight bytes read from the stream, they will be
     * transformed to an <code>long</code> in the following manner:
     * <p>
     * <code>(long)(((byte1 &amp; 0xFF) &lt;&lt; 56) + ((byte2 &amp; 0xFF) &lt;&lt; 48) +
     * ((byte3 &amp; 0xFF) &lt;&lt; 40) + ((byte4 &amp; 0xFF) &lt;&lt; 32) +
     * ((byte5 &amp; 0xFF) &lt;&lt; 24) + ((byte6 &amp; 0xFF) &lt;&lt; 16) +
     * ((byte7 &amp; 0xFF) &lt;&lt; 8) + (byte8 &amp; 0xFF)))
     * </code>
     * <p>
     * The value returned is in the range of -9223372036854775808 to
     * 9223372036854775807.
     * <p>
     * This method can read an <code>long</code> written by an object
     * implementing the <code>writeLong()</code> method in the
     * <code>DataOutput</code> interface.
     *
     * @return The <code>long</code> value read
     *
     * @throws EOFException If end of file is reached before reading the long
     * @throws IOException If any other error occurs
     *
     * @see DataOutput#writeLong
     */
    public final long readLong() throws IOException
    {
        readFully(buf, 0, 8);
    
        return convertToLong(buf);
    }

    /**
     * This method reads a Java float value from an input stream.  It
     * operates by first reading an <code>int</code> value from the
     * stream by calling the <code>readInt()</code> method in this
     * interface, then converts that <code>int</code> to a
     * <code>float</code> using the <code>intBitsToFloat</code> method
     * in the class <code>java.lang.Float</code>
     * <p>
     * This method can read a <code>float</code> written by an object
     * implementing the <code>writeFloat()</code> method in the
     * <code>DataOutput</code> interface.
     *
     * @return The <code>float</code> value read
     *
     * @throws EOFException If end of file is reached before reading the float
     * @throws IOException If any other error occurs
     *
     * @see DataOutput#writeFloat 
     * @see java.lang.Float#intBitsToFloat
     */
    public final float readFloat() throws IOException
    {
        return Float.intBitsToFloat(readInt());
    }

    /**
     * This method reads a Java double value from an input stream.  It operates
     * by first reading a <code>long</code> value from the stream by calling the
     * <code>readLong()</code> method in this interface, then converts
     * that <code>long</code> to a <code>double</code> using the
     * <code>longBitsToDouble</code> method in the class
     * <code>java.lang.Double</code> 
     * <p>
     * This method can read a <code>double</code> written by an object
     * implementing the <code>writeDouble()</code> method in the
     * <code>DataOutput</code> interface.
     *
     * @return The <code>double</code> value read
     *
     * @throws EOFException If end of file is reached before reading
     * the double
     * @throws IOException If any other error occurs
     *
     * @see DataOutput#writeDouble
     * @see java.lang.Double#longBitsToDouble
     */
    public final double readDouble () throws IOException
    {
        return Double.longBitsToDouble (readLong ());
    }

    /**
     * This method reads a <code>String</code> from an input stream that
     * is encoded in a modified UTF-8 format.  This format has a leading
     * two byte sequence that contains the remaining number of bytes to
     * read.  This two byte sequence is read using the
     * <code>readUnsignedShort()</code> method of this interface.
     * <p>
     * After the number of remaining bytes have been determined, these
     * bytes are read an transformed into <code>char</code> values.
     * These <code>char</code> values are encoded in the stream using
     * either a one, two, or three byte format.  The particular format
     * in use can be determined by examining the first byte read.
     * <p>
     * If the first byte has a high order bit of 0, then that character
     * consists on only one byte.  This character value consists of
     * seven bits that are at positions 0 through 6 of the byte.  As an
     * example, if <code>byte1</code> is the byte read from the stream,
     * it would be converted to a <code>char</code> like so:
     * <p>
     * <code>(char)byte1</code>
     * <p>
     * If the first byte has 110 as its high order bits, then the 
     * character consists of two bytes.  The bits that make up the character
     * value are in positions 0 through 4 of the first byte and bit positions
     * 0 through 5 of the second byte.  (The second byte should have 
     * 10 as its high order bits).  These values are in most significant
     * byte first (i.e., "big endian") order.
     * <p>
     * As an example, if <code>byte1</code> and <code>byte2</code> are
     * the first two bytes read respectively, and the high order bits of
     * them match the patterns which indicate a two byte character
     * encoding, then they would be converted to a Java
     * <code>char</code> like so:
     * <p>
     * <code>(char)(((byte1 & 0x1F) << 6) | (byte2 & 0x3F))</code>
     * <p>
     * If the first byte has a 1110 as its high order bits, then the
     * character consists of three bytes.  The bits that make up the character
     * value are in positions 0 through 3 of the first byte and bit positions
     * 0 through 5 of the other two bytes.  (The second and third bytes should
     * have 10 as their high order bits).  These values are in most
     * significant byte first (i.e., "big endian") order.
     * <p>
     * As an example, if <code>byte1</code> <code>byte2</code> and
     * <code>byte3</code> are the three bytes read, and the high order
     * bits of them match the patterns which indicate a three byte
     * character encoding, then they would be converted to a Java
     * <code>char</code> like so:
     * <p>
     * <code>(char)(((byte1 & 0x0F) << 12) | ((byte2 & 0x3F) << 6) | 
     * (byte3 & 0x3F))</code>
     * <p>
     * Note that all characters are encoded in the method that requires
     * the fewest number of bytes with the exception of the character
     * with the value of <code>&#92;u0000</code> which is encoded as two
     * bytes.  This is a modification of the UTF standard used to
     * prevent C language style <code>NUL</code> values from appearing
     * in the byte stream.
     * <p>
     * This method can read data that was written by an object implementing the
     * <code>writeUTF()</code> method in <code>DataOutput</code>
     * 
     * @return The <code>String</code> read
     *
     * @throws EOFException If end of file is reached before reading
     * the String
     * @throws UTFDataFormatException If the data is not in UTF-8 format
     * @throws IOException If any other error occurs
     *
     * @see DataOutput#writeUTF
     */
    public final String readUTF() throws IOException
    {
        return readUTF(this);
    }

    /**
     * This method reads a String encoded in UTF-8 format from the 
     * specified <code>DataInput</code> source.
     *
     * @param in The <code>DataInput</code> source to read from
     *
     * @return The String read from the source
     *
     * @throws IOException If an error occurs
     *
     * @see DataInput#readUTF
     */
    public static final String readUTF(DataInput in) throws IOException
    {
        final int UTFlen = in.readUnsignedShort ();
    
        byte[] buf = new byte [UTFlen];

        // This blocks until the entire string is available rather than
        // doing partial processing on the bytes that are available and then
        // blocking.  An advantage of the latter is that Exceptions
        // could be thrown earlier.  The former is a bit cleaner.
        in.readFully (buf, 0, UTFlen);

        return convertFromUTF (buf);
    }
    
    /**
     * Skips n bytes in the input stream
     * @param n The bytes to be skipped
     * @return The actual number of bytes skipped
     * @throws IOException If any I/O error occurs
     */
    
    public long skip(long n) throws IOException
    {
        return in.skip(n);
    }
    
    /**
     * Returns the number of available bytes which may be read w/o blocking
     * @return The number of available bytes
     * @throws IOException if any I/O error occurs
     */

    public int available() throws IOException
    {
        return in.available();
    }

    /**
     * Closes the input stream
     * @throws IOException if any I/O error occurs
     */
    
    public void close() throws IOException
    {
        in.close();
    }

    /**
     * Marks the current position in the input stream
     * @param limit The number of bytes which may be read before the mark
     * becomes invalid
     */

    public synchronized void mark(int limit)
    {
        in.mark(limit);
    }

    /**
     * Resets the starting position in the input stream to the last marked one
     * @throws IOException If any I/O error occurs
     */

    public synchronized void reset() throws IOException
    {
        in.reset();
    }
    
    /**
     * Returns true if this stream supports the mark() and reset() methods
     */
    
    public boolean markSupported()
    {
        return in.markSupported();
    }

    private static byte convertToByte(int i) throws IOException
    {
        if (i < 0)
            throw new IOException();
    
        return (byte) i;
    }

    private static boolean convertToBoolean(int b) throws IOException
    {
        if (b < 0)
            throw new IOException ();
    
        return (b != 0);
    }

    private static int convertToUnsignedByte(int i) throws IOException
    {
        if (i < 0)
            throw new IOException();
    
        return (i & 0xFF);
    }

    private static short convertToShort(byte[] buf)
    {
        return (short) ((buf [0] << 8) | (buf [1] & 0xff));  
    }  

    private static int convertToUnsignedShort(byte[] buf)
    {
        return (((buf [0] & 0xff) << 8) | (buf [1] & 0xff));  
    }

    private static char convertToChar(byte[] buf)
    {
        return (char) ((buf [0] << 8) | (buf [1] & 0xff));  
    }  

    private static int convertToInt(byte[] buf)
    {
        return (((buf [0] & 0xff) << 24)
            | ((buf [1] & 0xff) << 16)
            | ((buf [2] & 0xff) << 8)
            | (buf [3] & 0xff));  
    }

    private static long convertToLong(byte[] buf)
    {
        return (((long)(buf [0] & 0xff) << 56) |
            ((long)(buf [1] & 0xff) << 48) |
            ((long)(buf [2] & 0xff) << 40) |
            ((long)(buf [3] & 0xff) << 32) |
            ((long)(buf [4] & 0xff) << 24) |
            ((long)(buf [5] & 0xff) << 16) |
            ((long)(buf [6] & 0xff) <<  8) |
            ((long)(buf [7] & 0xff)));  
    }

    // FIXME: This method should be re-thought.  I suspect we have multiple
    // UTF-8 decoders floating around.  We should use the standard charset
    // converters, maybe and adding a direct call into one of the new
    // NIO converters for a super-fast UTF8 decode.
    private static String convertFromUTF(byte[] buf)
        throws EOFException, UTFDataFormatException
    {
        // Give StringBuffer an initial estimated size to avoid 
        // enlarge buffer frequently
        StringBuffer strbuf = new StringBuffer (buf.length / 2 + 2);

        for (int i = 0; i < buf.length; )
        {
             if ((buf [i] & 0x80) == 0) // bit pattern 0xxxxxxx
                 strbuf.append ((char) (buf [i++] & 0xFF));
             else if ((buf [i] & 0xE0) == 0xC0) // bit pattern 110xxxxx
             {
                 if (i + 1 >= buf.length || (buf [i + 1] & 0xC0) != 0x80)
                     throw new UTFDataFormatException ();

                 strbuf.append((char) (((buf [i++] & 0x1F) << 6)
                    | (buf [i++] & 0x3F)));
             }
             else if ((buf [i] & 0xF0) == 0xE0) // bit pattern 1110xxxx
             {
                 if (i + 2 >= buf.length
                    || (buf [i + 1] & 0xC0) != 0x80
                    || (buf [i + 2] & 0xC0) != 0x80)
                 {
                    throw new UTFDataFormatException ();
                 }

                 strbuf.append((char) (((buf [i++] & 0x0F) << 12)
                    | ((buf [i++] & 0x3F) << 6)
                    | (buf [i++] & 0x3F)));
             }
             else
             {
                 // must be ((buf [i] & 0xF0) == 0xF0 || (buf [i] & 0xC0) == 0x80)
                 // bit patterns 1111xxxx or 10xxxxxx
                 throw new UTFDataFormatException ();
             }
        }

        return strbuf.toString();
    }
}
