/*
 * @(#)DataInputStream.java	1.47 01/11/29
 *
 * Copyright 2002 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.)
 * <p>
 * All characters in the range <code>'\u0001'</code> to
 * <code>'\u007F'</code> are represented by a single byte:
 * <center><table border="3">
 *   <tr><td><i>0</i></td>  <td>bits 0-7</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">
 *   <tr><td>1</td>  <td>1</td>  <td>0</td>  <td>bits 6-10</td></tr>
 *   <tr><td>1</td>  <td>0</td>  <td colspan=2>bits 0-5</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">
 *   <tr><td>1</td>  <td>1</td>  <td>1</td>  <td>0</td>  <td>bits 12-15</td</tr>
 *   <tr><td>1</td>  <td>0</td>  <td colspan=3>bits 6-11</td></tr>
 *   <tr><td>1</td>  <td>0</td>  <td colspan=3>bits 0-5</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 1.47, 11/29/01
 * @see     java.io.DataOutputStream
 * @since   JDK1.0
 */
public
class DataInputStream extends FilterInputStream implements DataInput {
    /**
     * Creates a <code>FilterInputStream</code>
     * and saves its  argument, the input stream
     * <code>in</code>, for later use. An internal
     *
     * @param  in   the input stream.
     */
    public DataInputStream(InputStream in) {
	super(in);
    }

    /**
     * See the general contract of the <code>read</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.
     * @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);
    }

    /**
     * See the general contract of the <code>read</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 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 {
	InputStream in = this.in;
	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 {
	InputStream in = this.in;
	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 {
	InputStream in = this.in;
	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 {
	InputStream in = this.in;
	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 {
	InputStream in = this.in;
	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 {
	InputStream in = this.in;
	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));
    }

    /**
     * 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 {
	InputStream in = this.in;
	return ((long)(readInt()) << 32) + (readInt() & 0xFFFFFFFFL);
    }

    /**
     * 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 {
	InputStream in = this.in;
	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)) {
			in = 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.
     * @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 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();
        char str[] = new char[utflen];
	int count = 0;
	int strlen = 0;
	while (count < utflen) {
	    int c = in.readUnsignedByte();
	    int char2, char3;
	    switch (c >> 4) {
	        case 0: case 1: case 2: case 3: case 4: case 5: case 6: case 7:
		    // 0xxxxxxx
		    count++;
		    str[strlen++] = (char)c;
		    break;
	        case 12: case 13:
		    // 110x xxxx   10xx xxxx
		    count += 2;
		    if (count > utflen)
			throw new UTFDataFormatException();
		    char2 = in.readUnsignedByte();
		    if ((char2 & 0xC0) != 0x80)
			throw new UTFDataFormatException();
		    str[strlen++] = (char)(((c & 0x1F) << 6) | (char2 & 0x3F));
		    break;
	        case 14:
		    // 1110 xxxx  10xx xxxx  10xx xxxx
		    count += 3;
		    if (count > utflen)
			throw new UTFDataFormatException();
		    char2 = in.readUnsignedByte();
		    char3 = in.readUnsignedByte();
		    if (((char2 & 0xC0) != 0x80) || ((char3 & 0xC0) != 0x80))
			throw new UTFDataFormatException();
		    str[strlen++] = (char)(((c & 0x0F) << 12) |
					   ((char2 & 0x3F) << 6) |
					   ((char3 & 0x3F) << 0));
		    break;
	        default:
		    // 10xx xxxx,  1111 xxxx
		    throw new UTFDataFormatException();
		}
	}
        return new String(str, 0, strlen);
    }
}