/*
 * @(#)DataInputStream.java	1.65 03/01/23
 *
 * Copyright 2003 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package java.io;

/**
 * A data input stream lets an application read primitive Java data
 * types from an underlying input stream in a machine-independent
 * way. An application uses a data output stream to write data that
 * can later be read by a data input stream.
 * <p>
 * Data input streams and data output streams represent Unicode
 * strings in a format that is a slight modification of UTF-8. (For
 * more information, see X/Open Company Ltd., "File System Safe
 * UCS Transformation Format (FSS_UTF)", X/Open Preliminary
 * Specification, Document Number: P316. This information also
 * appears in ISO/IEC 10646, Annex P.) Note that in the 
 * following tables, the most significant bit appears in the
 * far left-hand column.
 * <p>
 * All characters in the range <code>'\u0001'</code> to
 * <code>'\u007F'</code> are represented by a single byte:
 *
 * <center>
 *    <table border="3" summary="Bit values and bytes">
 *        <tr>
 *            <td></td>
 *            <th id="bit" colspan=2><P ALIGN="LEFT">Bit Values</P></th>
 *        </tr>
 *        <tr> 
 *            <th id="byte1">Byte 1 </th>
 *            <td headers="bit byte1"><i>0</i></td>
 *            <td>bits 6-0</td>
 *        </tr>
 *     </table>
 * </center>
 *
 * <p>
 * The null character <code>'\u0000'</code> and characters in the
 * range <code>'\u0080'</code> to <code>'\u07FF'</code> are
 * represented by a pair of bytes:
 *
 * <center>
 *     <table border="3" summary="Bit values and bytes">
 *        <tr>
 *            <td></td>
 *            <th id="bit" colspan=4><P ALIGN="LEFT">Bit Values</P></th>
 *        </tr>
 *         <tr>
 *             <th id="byte1">Byte 1 </th>
 *             <td headers="bit byte1">1</td>
 *             <td headers="bit byte1">1</td>
 *             <td headers="bit byte1">0</td>
 *             <td headers="bit byte1">bits 10-6</td>
 *         </tr>
 *         <tr>
 *             <th id="byte2">Byte 2 </th>
 *             <td headers="bit byte2">1</td>
 *             <td headers="bit byte2">0</td>
 *             <td headers="bit byte2" colspan=2>bits 5-0</td>
 *         </tr>
 *      </table>
 *  </center>
 *
 * <br>
 * Characters in the range <code>'\u0800'</code> to
 * <code>'\uFFFF'</code> are represented by three bytes:
 *
 * <center>
 *    <table border="3" summary="Bit values and bytes">
 *        <tr>
 *            <td></td>
 *            <th id="bit" colspan=5><P ALIGN="LEFT">Bit Values</P></th>
 *        </tr>
 * 
 *        <tr>
 *            <th id="byte1">Byte 1 </th>
 *            <td headers="bit byte1">1</td>
 *            <td headers="bit byte1">1</td>
 *            <td headers="bit byte1">1</td>
 *            <td headers="bit byte1">0</td>
 *            <td headers="bit byte1">bits 15-12</td>
 *        </tr>
 *        <tr>
 *            <th id="byte2">Byte 2 </th>
 *            <td headers="bit byte2">1</td>
 *            <td headers="bit byte2">0</td>
 *            <td headers="bit byte2" colspan=3>bits 11-6</td>
 *        </tr>
 *        <tr>
 *            <th id="byte3">Byte 3 </th>
 *            <td headers="bit byte3">1</td>
 *            <td headers="bit byte3">0</td>
 *            <td headers="bit byte3" colspan=3>bits 5-0</td>
 *        </tr>
 *     </table>
 *   </center>
 * <p>
 * The two differences between this format and the
 * "standard" UTF-8 format are the following:
 * <ul>
 * <li>The null byte <code>'\u0000'</code> is encoded in 2-byte format
 *     rather than 1-byte, so that the encoded strings never have
 *     embedded nulls.
 * <li>Only the 1-byte, 2-byte, and 3-byte formats are used.
 * </ul>
 *
 * @author  Arthur van Hoff
 * @version 1.65, 01/23/03
 * @see     java.io.DataOutputStream
 * @since   JDK1.0
 */
public
class DataInputStream extends FilterInputStream implements DataInput {

    /**
     * Creates a DataInputStream that uses the specified
     * underlying InputStream.
     *
     * @param  in   the specified input stream
     */
    public DataInputStream(InputStream in) {
	super(in);
    }

    /**
     * Reads some number of bytes from the contained input stream and 
     * stores them into the buffer array <code>b</code>. The number of 
     * bytes actually read is returned as an integer. This method blocks 
     * until input data is available, end of file is detected, or an 
     * exception is thrown. 
     * 
     * <p>If <code>b</code> is null, a <code>NullPointerException</code> is 
     * thrown. If the length of <code>b</code> is zero, then no bytes are 
     * read and <code>0</code> 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 <code>-1</code> is returned;
     * otherwise, at least one byte is read and stored into <code>b</code>. 
     * 
     * <p>The first byte read is stored into element <code>b[0]</code>, the 
     * next one into <code>b[1]</code>, and so on. The number of bytes read 
     * is, at most, equal to the length of <code>b</code>. Let <code>k</code> 
     * be the number of bytes actually read; these bytes will be stored in 
     * elements <code>b[0]</code> through <code>b[k-1]</code>, leaving 
     * elements <code>b[k]</code> through <code>b[b.length-1]</code> 
     * unaffected. 
     * 
     * <p>If the first byte cannot be read for any reason other than end of 
     * file, then an <code>IOException</code> is thrown. In particular, an 
     * <code>IOException</code> is thrown if the input stream has been closed. 
     * 
     * <p>The <code>read(b)</code> method has the same effect as: 
     * <blockquote><pre>
     * read(b, 0, b.length) 
     * </pre></blockquote>
     *
     * @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 the stream has been reached.
     * @exception  IOException  if an I/O error occurs.
     * @see        java.io.FilterInputStream#in
     * @see        java.io.InputStream#read(byte[], int, int)
     */
    public final int read(byte b[]) throws IOException {
	return in.read(b, 0, b.length);
    }

    /**
     * Reads up to <code>len</code> bytes of data from the contained 
     * input stream into an array of bytes.  An attempt is made to read 
     * as many as <code>len</code> bytes, but a smaller number may be read, 
     * possibly zero. The number of bytes actually read is returned as an 
     * integer.
     *
     * <p> This method blocks until input data is available, end of file is
     * detected, or an exception is thrown.
     *
     * <p> If <code>b</code> is <code>null</code>, a
     * <code>NullPointerException</code> is thrown.
     *
     * <p> If <code>off</code> is negative, or <code>len</code> is negative, or
     * <code>off+len</code> is greater than the length of the array
     * <code>b</code>, then an <code>IndexOutOfBoundsException</code> is
     * thrown.
     *
     * <p> If <code>len</code> is zero, then no bytes are read and
     * <code>0</code> 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 <code>-1</code> is returned; otherwise, at least one
     * byte is read and stored into <code>b</code>.
     *
     * <p> The first byte read is stored into element <code>b[off]</code>, the
     * next one into <code>b[off+1]</code>, and so on. The number of bytes read
     * is, at most, equal to <code>len</code>. Let <i>k</i> be the number of
     * bytes actually read; these bytes will be stored in elements
     * <code>b[off]</code> through <code>b[off+</code><i>k</i><code>-1]</code>,
     * leaving elements <code>b[off+</code><i>k</i><code>]</code> through
     * <code>b[off+len-1]</code> unaffected.
     *
     * <p> In every case, elements <code>b[0]</code> through
     * <code>b[off]</code> and elements <code>b[off+len]</code> through
     * <code>b[b.length-1]</code> are unaffected.
     *
     * <p> If the first byte cannot be read for any reason other than end of
     * file, then an <code>IOException</code> is thrown. In particular, an
     * <code>IOException</code> is thrown if the input stream has been closed.
     *
     * @param      b     the buffer into which the data is read.
     * @param      off   the start offset of the data.
     * @param      len   the maximum number of bytes read.
     * @return     the total number of bytes read into the buffer, or
     *             <code>-1</code> if there is no more data because the end
     *             of the stream has been reached.
     * @exception  IOException  if an I/O error occurs.
     * @see        java.io.FilterInputStream#in
     * @see        java.io.InputStream#read(byte[], int, int)
     */
    public final int read(byte b[], int off, int len) throws IOException {
	return in.read(b, off, len);
    }

    /**
     * See the general contract of the <code>readFully</code>
     * method of <code>DataInput</code>.
     * <p>
     * Bytes
     * for this operation are read from the contained
     * input stream.
     *
     * @param      b   the buffer into which the data is read.
     * @exception  EOFException  if this input stream reaches the end before
     *               reading all the bytes.
     * @exception  IOException   if an I/O error occurs.
     * @see        java.io.FilterInputStream#in
     */
    public final void readFully(byte b[]) throws IOException {
	readFully(b, 0, b.length);
    }

    /**
     * See the general contract of the <code>readFully</code>
     * method of <code>DataInput</code>.
     * <p>
     * Bytes
     * for this operation are read from the contained
     * input stream.
     *
     * @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 input stream reaches the end before
     *               reading all the bytes.
     * @exception  IOException   if an I/O error occurs.
     * @see        java.io.FilterInputStream#in
     */
    public final void readFully(byte b[], int off, int len) throws IOException {
	if (len < 0)
	    throw new IndexOutOfBoundsException();
	int n = 0;
	while (n < len) {
	    int count = in.read(b, off + n, len - n);
	    if (count < 0)
		throw new EOFException();
	    n += count;
	}
    }

    /**
     * See the general contract of the <code>skipBytes</code>
     * method of <code>DataInput</code>.
     * <p>
     * Bytes
     * for this operation are read from the contained
     * input stream.
     *
     * @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 final int skipBytes(int n) throws IOException {
	int total = 0;
	int cur = 0;

	while ((total<n) && ((cur = (int) in.skip(n-total)) > 0)) {
	    total += cur;
	}

	return total;
    }

    /**
     * See the general contract of the <code>readBoolean</code>
     * method of <code>DataInput</code>.
     * <p>
     * Bytes
     * for this operation are read from the contained
     * input stream.
     *
     * @return     the <code>boolean</code> value read.
     * @exception  EOFException  if this input stream has reached the end.
     * @exception  IOException   if an I/O error occurs.
     * @see        java.io.FilterInputStream#in
     */
    public final boolean readBoolean() throws IOException {
	int ch = in.read();
	if (ch < 0)
	    throw new EOFException();
	return (ch != 0);
    }

    /**
     * See the general contract of the <code>readByte</code>
     * method of <code>DataInput</code>.
     * <p>
     * Bytes
     * for this operation are read from the contained
     * input stream.
     *
     * @return     the next byte of this input stream as a signed 8-bit
     *             <code>byte</code>.
     * @exception  EOFException  if this input stream has reached the end.
     * @exception  IOException   if an I/O error occurs.
     * @see        java.io.FilterInputStream#in
     */
    public final byte readByte() throws IOException {
	int ch = in.read();
	if (ch < 0)
	    throw new EOFException();
	return (byte)(ch);
    }

    /**
     * See the general contract of the <code>readUnsignedByte</code>
     * method of <code>DataInput</code>.
     * <p>
     * Bytes
     * for this operation are read from the contained
     * input stream.
     *
     * @return     the next byte of this input stream, interpreted as an
     *             unsigned 8-bit number.
     * @exception  EOFException  if this input stream has reached the end.
     * @exception  IOException   if an I/O error occurs.
     * @see         java.io.FilterInputStream#in
     */
    public final int readUnsignedByte() throws IOException {
	int ch = in.read();
	if (ch < 0)
	    throw new EOFException();
	return ch;
    }

    /**
     * See the general contract of the <code>readShort</code>
     * method of <code>DataInput</code>.
     * <p>
     * Bytes
     * for this operation are read from the contained
     * input stream.
     *
     * @return     the next two bytes of this input stream, interpreted as a
     *             signed 16-bit number.
     * @exception  EOFException  if this input stream reaches the end before
     *               reading two bytes.
     * @exception  IOException   if an I/O error occurs.
     * @see        java.io.FilterInputStream#in
     */
    public final short readShort() throws IOException {
        int ch1 = in.read();
        int ch2 = in.read();
        if ((ch1 | ch2) < 0)
            throw new EOFException();
        return (short)((ch1 << 8) + (ch2 << 0));
    }

    /**
     * See the general contract of the <code>readUnsignedShort</code>
     * method of <code>DataInput</code>.
     * <p>
     * Bytes
     * for this operation are read from the contained
     * input stream.
     *
     * @return     the next two bytes of this input stream, interpreted as an
     *             unsigned 16-bit integer.
     * @exception  EOFException  if this input stream reaches the end before
     *               reading two bytes.
     * @exception  IOException   if an I/O error occurs.
     * @see        java.io.FilterInputStream#in
     */
    public final int readUnsignedShort() throws IOException {
        int ch1 = in.read();
        int ch2 = in.read();
        if ((ch1 | ch2) < 0)
            throw new EOFException();
        return (ch1 << 8) + (ch2 << 0);
    }

    /**
     * See the general contract of the <code>readChar</code>
     * method of <code>DataInput</code>.
     * <p>
     * Bytes
     * for this operation are read from the contained
     * input stream.
     *
     * @return     the next two bytes of this input stream as a Unicode
     *             character.
     * @exception  EOFException  if this input stream reaches the end before
     *               reading two bytes.
     * @exception  IOException   if an I/O error occurs.
     * @see        java.io.FilterInputStream#in
     */
    public final char readChar() throws IOException {
        int ch1 = in.read();
        int ch2 = in.read();
        if ((ch1 | ch2) < 0)
            throw new EOFException();
        return (char)((ch1 << 8) + (ch2 << 0));
    }

    /**
     * See the general contract of the <code>readInt</code>
     * method of <code>DataInput</code>.
     * <p>
     * Bytes
     * for this operation are read from the contained
     * input stream.
     *
     * @return     the next four bytes of this input stream, interpreted as an
     *             <code>int</code>.
     * @exception  EOFException  if this input stream reaches the end before
     *               reading four bytes.
     * @exception  IOException   if an I/O error occurs.
     * @see        java.io.FilterInputStream#in
     */
    public final int readInt() throws IOException {
        int ch1 = in.read();
        int ch2 = in.read();
        int ch3 = in.read();
        int ch4 = in.read();
        if ((ch1 | ch2 | ch3 | ch4) < 0)
            throw new EOFException();
        return ((ch1 << 24) + (ch2 << 16) + (ch3 << 8) + (ch4 << 0));
    }

    private byte readBuffer[] = new byte[8];

    /**
     * See the general contract of the <code>readLong</code>
     * method of <code>DataInput</code>.
     * <p>
     * Bytes
     * for this operation are read from the contained
     * input stream.
     *
     * @return     the next eight bytes of this input stream, interpreted as a
     *             <code>long</code>.
     * @exception  EOFException  if this input stream reaches the end before
     *               reading eight bytes.
     * @exception  IOException   if an I/O error occurs.
     * @see        java.io.FilterInputStream#in
     */
    public final long readLong() throws IOException {
        readFully(readBuffer, 0, 8);
        return (((long)readBuffer[0] << 56) +
                ((long)(readBuffer[1] & 255) << 48) +
                ((long)(readBuffer[2] & 255) << 40) +
                ((long)(readBuffer[3] & 255) << 32) +
                ((long)(readBuffer[4] & 255) << 24) +
                ((readBuffer[5] & 255) << 16) +
                ((readBuffer[6] & 255) <<  8) +
                ((readBuffer[7] & 255) <<  0));
    }

    /**
     * See the general contract of the <code>readFloat</code>
     * method of <code>DataInput</code>.
     * <p>
     * Bytes
     * for this operation are read from the contained
     * input stream.
     *
     * @return     the next four bytes of this input stream, interpreted as a
     *             <code>float</code>.
     * @exception  EOFException  if this input stream reaches the end before
     *               reading four bytes.
     * @exception  IOException   if an I/O error occurs.
     * @see        java.io.DataInputStream#readInt()
     * @see        java.lang.Float#intBitsToFloat(int)
     */
    public final float readFloat() throws IOException {
	return Float.intBitsToFloat(readInt());
    }

    /**
     * See the general contract of the <code>readDouble</code>
     * method of <code>DataInput</code>.
     * <p>
     * Bytes
     * for this operation are read from the contained
     * input stream.
     *
     * @return     the next eight bytes of this input stream, interpreted as a
     *             <code>double</code>.
     * @exception  EOFException  if this input stream reaches the end before
     *               reading eight bytes.
     * @exception  IOException   if an I/O error occurs.
     * @see        java.io.DataInputStream#readLong()
     * @see        java.lang.Double#longBitsToDouble(long)
     */
    public final double readDouble() throws IOException {
	return Double.longBitsToDouble(readLong());
    }

    private char lineBuffer[];

    /**
     * See the general contract of the <code>readLine</code>
     * method of <code>DataInput</code>.
     * <p>
     * Bytes
     * for this operation are read from the contained
     * input stream.
     *
     * @deprecated This method does not properly convert bytes to characters.
     * As of JDK 1.1, the preferred way to read lines of text is via the
     * <code>BufferedReader.readLine()</code> method.  Programs that use the
     * <code>DataInputStream</code> class to read lines can be converted to use
     * the <code>BufferedReader</code> class by replacing code of the form:
     * <blockquote><pre>
     *     DataInputStream d = new DataInputStream(in);
     * </pre></blockquote>
     * with:
     * <blockquote><pre>
     *     BufferedReader d
     *          = new BufferedReader(new InputStreamReader(in));
     * </pre></blockquote>
     *
     * @return     the next line of text from this input stream.
     * @exception  IOException  if an I/O error occurs.
     * @see        java.io.BufferedReader#readLine()
     * @see        java.io.FilterInputStream#in
     */
    public final String readLine() throws IOException {
	char buf[] = lineBuffer;

	if (buf == null) {
	    buf = lineBuffer = new char[128];
	}

	int room = buf.length;
	int offset = 0;
	int c;

loop:	while (true) {
	    switch (c = in.read()) {
	      case -1:
	      case '\n':
		break loop;

	      case '\r':
		int c2 = in.read();
		if ((c2 != '\n') && (c2 != -1)) {
		    if (!(in instanceof PushbackInputStream)) {
			this.in = new PushbackInputStream(in);
		    }
		    ((PushbackInputStream)in).unread(c2);
		}
		break loop;

	      default:
		if (--room < 0) {
		    buf = new char[offset + 128];
		    room = buf.length - offset - 1;
		    System.arraycopy(lineBuffer, 0, buf, 0, offset);
		    lineBuffer = buf;
		}
		buf[offset++] = (char) c;
		break;
	    }
	}
	if ((c == -1) && (offset == 0)) {
	    return null;
	}
	return String.copyValueOf(buf, 0, offset);
    }

    /**
     * See the general contract of the <code>readUTF</code>
     * method of <code>DataInput</code>.
     * <p>
     * Bytes
     * for this operation are read from the contained
     * input stream.
     *
     * @return     a Unicode string.
     * @exception  EOFException  if this input stream reaches the end before
     *               reading all the bytes.
     * @exception  IOException   if an I/O error occurs.
     * @exception  UTFDataFormatException if the bytes do not represent a valid UTF-8 encoding of a string.
     * @see        java.io.DataInputStream#readUTF(java.io.DataInput)
     */
    public final String readUTF() throws IOException {
        return readUTF(this);
    }

    /**
     * Reads from the
     * stream <code>in</code> a representation
     * of a Unicode  character string encoded in
     * Java modified UTF-8 format; this string
     * of characters  is then returned as a <code>String</code>.
     * The details of the modified UTF-8 representation
     * are  exactly the same as for the <code>readUTF</code>
     * method of <code>DataInput</code>.
     *
     * @param      in   a data input stream.
     * @return     a Unicode string.
     * @exception  EOFException            if the input stream reaches the end
     *               before all the bytes.
     * @exception  IOException             if an I/O error occurs.
     * @exception  UTFDataFormatException  if the bytes do not represent a
     *               valid Java modified UTF-8 encoding of a Unicode string.
     * @see        java.io.DataInputStream#readUnsignedShort()
     */
    public final static String readUTF(DataInput in) throws IOException {
        int utflen = in.readUnsignedShort();
        StringBuffer str = new StringBuffer(utflen);
        byte bytearr [] = new byte[utflen];
        int c, char2, char3;
	int count = 0;

 	in.readFully(bytearr, 0, utflen);

	while (count < utflen) {
     	    c = (int) bytearr[count] & 0xff;
	    switch (c >> 4) {
	        case 0: case 1: case 2: case 3: case 4: case 5: case 6: case 7:
		    /* 0xxxxxxx*/
		    count++;
                    str.append((char)c);
		    break;
	        case 12: case 13:
		    /* 110x xxxx   10xx xxxx*/
		    count += 2;
		    if (count > utflen)
			throw new UTFDataFormatException();
		    char2 = (int) bytearr[count-1];
		    if ((char2 & 0xC0) != 0x80)
			throw new UTFDataFormatException(); 
                    str.append((char)(((c & 0x1F) << 6) | (char2 & 0x3F)));
		    break;
	        case 14:
		    /* 1110 xxxx  10xx xxxx  10xx xxxx */
		    count += 3;
		    if (count > utflen)
			throw new UTFDataFormatException();
		    char2 = (int) bytearr[count-2];
		    char3 = (int) bytearr[count-1];
		    if (((char2 & 0xC0) != 0x80) || ((char3 & 0xC0) != 0x80))
			throw new UTFDataFormatException();	  
                    str.append((char)(((c     & 0x0F) << 12) |
                    	              ((char2 & 0x3F) << 6)  |
                    	              ((char3 & 0x3F) << 0)));
		    break;
	        default:
		    /* 10xx xxxx,  1111 xxxx */
		    throw new UTFDataFormatException();		  
		}
	}
        // The number of chars produced may be less than utflen
        return new String(str);
    }
}